This chapter discusses the peritoneum, the intra- and extra-peritoneal soft tissues, pelvic structures, diaphragm, and the anterior abdom- inal wall. The extraperitoneal abdominal struc- tures are in continuity with the diaphragm superiorly, pelvic structures inferiorly, and the abdominal wall along both flanks. Some authors prefer the term extraperitoneal rather than
retroperitoneal because it more accuratelyreflects the location, especially for pelvic struc- tures, but both terms are in use synonymously.
The intra- and extraperitoneal portions of the gastrointestinal and genitourinary tracts and other major organs are discussed in their respective chapters.
Technique
Computed Tomography
Multislice computed tomography (CT), espe- cially coronal and three-dimensional (3D) reconstructions, are very useful in defining extraperitoneal tumor spread and tissue planes.
Computed tomography fluoroscopy is useful for guiding abdominal interventional proce- dures which cannot be managed with ultra- sonography (US). Intermittent CT fluoroscopy using real-time fluoroscopic reconstruction at six frames per second confirms the needle posi- tion. Patient and operator radiation doses can be decreased with CT fluoroscopy compared to conventional CT guidance by limiting CT flu-
oroscopy to needle tip scanning rather than the entire needle.
Computed tomography peritoneography is occasionally useful in otherwise inapparent hernias or suspected peritoneal leaks in patients on peritoneal dialysis.
Ultrasonography
The primary limitations of abdominal US are the inherent physical limitations of this technique and, less well appreciated among clinicians, its considerable dependence on the operator. Proficiency in US, especially use of newer techniques and contrast agents, requires considerable training. Unskilled use of US is an invitation to disaster.
New US techniques and addition of contrast agents are changing this field. In the abdomen, tissue harmonic US using pulse-inversion tech- niques improves image quality and organ struc- ture resolution compared to conventional US. A further improvement in overall image quality consists of combining tissue harmonic US with real-time spatial compound US (1). Yet the type of technique used may need to be tailored to study indication; thus what is optimal for detecting stone disease differs from is ideal in tumor detection.
Similar to intraperitoneal structures, US is useful for extraperitoneal lymph node biopsy. It is efficacious for deep nodes as small as 1 cm in diameter.
Peritoneum, Mesentery, and Extraperitoneal Soft Tissues
865
Endoscopic US detects enlarged lymph node and tumors. Aspiration biopsy can also be per- formed using endoscopic US as a guide.
Probes for performing laparoscopic US allow the surgeon to increase visualization of sur- rounding structures. Such laparoscopic US has a high sensitivity in detecting liver and other metastases. Overall, it improves tumor staging, but additional trocar sites are necessary for the US probe and laparoscopy is prolonged.At some sites the insufflated carbon dioxide makes probe contact with an organ in question more difficult;
at times instilling saline into the peritoneal cavity is helpful.
Magnetic Resonance Imaging
Echo planar imaging is a fast imaging technique with images obtained in 50 to 150 msec. Breath- ing and peristaltic artifacts cause little image degradation with such fast scanning and rela- tively high-resolution images are obtained with a single breath hold.
Magnetic resonance imaging (MRI) is use- ful in differentiating extraperitoneal from intraperitoneal tumors. The superior magnetic resonance (MR) soft tissue contrast resolution (compared to CT) makes it more suitable for identifying tumor margins and tumor infiltra- tion of adjacent structures. Similar to CT, a fast MRI technique, together with intraperitoneally instilled saline, visualizes the peritoneal sur- faces, omentum, and adjacent mesentery; saline also aids intraperitoneal tumor visualization.
Various intraperitoneal recesses are identified.
In distinction to CT, retained barium in the bowel does not create artifacts on MRI.
Any fibrosis is accentuated against back- ground fat on T1-weighted spoiled gradient echo (SGE) images. Tumors, abscesses, and other inflammation are best evaluated on intra- venous (IV) contrast-enhanced images.
No uniform definition of MR lymphography exists. Whether a conventional MR study focus- ing on lymph nodes should be called MR lym- phography is a matter of definition. Often a more appropriate study consists of heavily T2- weighted images processed using maximum intensity projection accentuating stationary or very slowly flowing fluid, similar to magnetic resonance cholangiopancreatography (MRCP);
a limitation of such a study of retroperitoneal structures is incomplete suppression of signals from veins.
Ultrasmall superparamagnetic iron oxide (SPIO) particles are of potential use in MR lym- phography (these agents are discussed in more detail in Chapter 7). Using SPIO as an endolym- phatic contrast agent results in contrast uptake by normal lymph nodes but not by those replaced by tumor. Potentially, nodal uptake occurs even after IV injection if the iron oxide particles are sufficiently small. Magnetic reso- nance imaging is typically performed 24 to 36 hours after IV infusion of these contrast agents.
The use of IV SPIO in patients with suspected lymph node metastases results in additional diseased nodes being detected than with pre- contrast scans. Normal lymph nodes decrease in signal intensity on enhanced T2-weighted and T2*-weighted gradient-echo images, indi- cating uptake of this contrast agent, but nodes infiltrated by tumor have no appreciable con- trast uptake and thus reveal no signal change on pre- and postcontrast images (2). Also, postcon- trast, T1-weighted signal intensity increases in metastatic nodes, probably due to altered node capillary permeability. These findings are not absolute, and nodes involved by benign disease also tend not to take up contrast.
Scintigraphy
Radionuclide agents used to image inflamma- tion and abscesses are gallium 67, indium- 111–labeled leukocytes and technetium-99m (Tc-99m)–labeled leukocytes. Imaging with Ga 67 is performed 48 to 72 hours after injecting the radionuclide; because one of its excretion pathways is via the colon, residual colonic activ- ity interferes with abscess detection, although to a large degree single photon emission computed tomography (SPECT) imaging overcomes this limitation. Indium 111 is cyclotron produced and is not as readily available as the other agents. It is distributed primarily in the liver, spleen, and bone marrow, and bowel activity is less of a concern than with the other two agents.
Labeled leukocyte scintigraphy requires in vitro labeling of a sample of the patient’s blood with either In 111 or Tc-99m–hexamethylpropyle- neamine oxime (HMPAO), a somewhat involved procedure. Most of the nucleotide is labeled to neutrophils, and thus this procedure is most useful for neutrophil-involved inflammatory conditions.
Indium-111–satumomab pendetide (Onco-
Scint) is the first murine origin monoclonal
antibody approved by the Food and Drug Administration for tumor imaging, a technique termed immunoscintigraphy. This specific antibody attaches to a colorectal or ovarian cancer–associated antigen and the attached radionuclide allows cancer detection. Either a diagnostic or therapeutic procedure is possible depending on the radionuclide selected. Its primary use is with suspected intraabdominal metastases, including carcinomatosis. False- positive tests do occur with satumomab pende- tide. In an occasional patient increased upper abdominal uptake persists for days in regions of chronic inflammation. Isotope uptake in a non- functional adrenal adenoma has resulted in false-positive results.
Lymphoscintigraphy assesses the lymphatic system and, for the most part, has replaced direct lymphography. It is a useful study to investigate chyluria, chyloperitoneum, and chylothorax. Multiple views are obtained for several hours after intradermal injection of Tc- 99m–sulfur colloid. Both lymphatic channels and nodes can be evaluated, and the study is used to detect lymphatic obstruction and fistulas. More lymphatic channels and more lymph nodes are visualized using smaller filtra- tion, thus increasing diagnostic certainty in detecting diseased lymph nodes.
The current primary clinical application of positron emission tomography (PET) is to detect cancer using the positron-emitting com- pound 2-[18F]-fluoro-deoxy-D-glucose (FDG).
Transported across cell membranes of metabol- ically active tumors, the deoxy component of FDG prevents further metabolization, leading to intracellular accumulation and an increase in tumor-to-background of fluorine 18. The amount of FDG accumulating within a tumor is proportional, within broad limits, to the degree of malignancy. Thus in a setting of a tumor of unknown significance detected by another imaging modality, PET suggests whether the tumor is benign or malignant, depending on its metabolic activity. In the abdomen, PET is most useful for lymphoma, colon cancer, and metas- tases from melanomas and lung and breast carcinoma. It has a role in tumor staging and appears to be of prognostic significance. In general, increased tumor metabolic activity signifies a worse prognosis. Positron emission tomography is also useful after cancer therapy.
Its ability to detect recurrent or residual meta- bolically active tumor is independent of under-
lying distortion due to fibrosis, and such tumor detection is superior to what is currently available with CT or MRI. Combining PET and CT images improves tumor localization significantly compared with each modality alone.
Test results are degraded by urinary and colon retention of FDG. These artifacts can be minimized by a colon cleansing regimen, patient hydration after FDG injection, adminis- tration of furosemide and bladder drainage and instillation of normal saline into the bladder prior to pelvic scanning. Use of oral Gastro- grafin to outline the intestines during a com- bined PET-CT study does not degrade FDG images. A limitation of FDG-PET in detecting small tumors is its minimal spatial resolution of about 5 mm. Also, inflammation does lead to false-positive PET results, influencing detection specificity. Recurrent or residual tumor detec- tion is thus best studied after postoperative inflammation has subsided.
Positron emission tomography using oxygen- 15–labeled water provides information on tissue perfusion; it is mostly a research tool with limited current clinical use.
Lymphography
Performed more often prior to the introduction of CT, MR, and lymphoscintigraphy, the current indications for lymphography have decreased considerably. It is a relatively prolonged, det- ailed procedure liked by few radiologists and even fewer radiology residents.
Although CT will detect an enlarged node, differentiation between most benign and malig- nant is not possible. Lymphography, on the other hand, can identify internal derangement even in a normal-sized node infiltrated by tumor.
The older literature reported rare but var- ied complications with lymphography, mostly related to contrast overinjection (3), including embolization to brain; a right-to-left cardiac shunt is responsible for some of these complications.
Peritoneography
Direct peritoneography using either a contrast
agent or its scintigraphic counterpart has
limited indications and is rarely performed. One
use is in a setting of peritoneal carcinomatosis prior to chemotherapy through a catheter implanted in the abdominal wall to evaluate drug distribution.
Biopsy
Either a conventional large core needle or a fine- needle aspiration technique is used for percuta- neous biopsy of suspicious tumors; fine-needle aspiration is often preferred, but especially with benign lesions it achieves a low success rate. On average, core needle biopsies obtain a specific diagnosis in over 90% of biopsies, while fine- needle aspirations average only about 50%; the complication rate, chiefly bleeding, is grossly similar with both techniques.
Either CT or US (and occasionally fluo- roscopy) is used for biopsy localization and other percutaneous interventional procedures.
In general, in most hospitals US equipment is more readily accessible, the study is quicker, and it results in faster patient throughput.
Special interventional equipment designed to be used with MR guidance is available. Little used at present, MR interventional radiology is undergoing rapid expansion with tissue biop- sies, fluid drainages, and guidance of other per- cutaneous therapeutic procedures. An open magnet provides ready patient access.
Endoscopic US-guided fine-needle aspiration biopsy is useful for diagnosis and staging of malignancies. Diagnostic sensitivities and specificities of about 90% are achieved with both extraluminal tumors and lymph nodes.
Nerve Block
Celiac plexus and splanchnic nerve block pro- vides pain palliation for patients with unre- sectable upper abdominal malignancies. This technique was initially designed to be per- formed using fluoroscopic guidance, although CT provides more accurate guidance. An alcohol-contrast agent combination provides localization.
Congenital Abnormalities
Situs
Situs refers to orientation of certain organs to the midline. In general, the bilobed lung, left
atrium, descending aorta, spleen, and stomach are all located on one side of the body. When these structures are normally placed on the left side the condition is called situs solitus. Situs
inversus is a mirror image and results whenthese structures are on the right side and the trilobed lung, right atrium, inferior vena cava, gallbladder, and liver are on the left (Fig. 14.1).
The prevalence of situs inversus is about 1 in 10,000. These patients are at an increased risk for nasal polyposis, chronic sinusitis, and bronchiectasis (Kartagener’s syndrome) and a higher than normal risk for congenital heart disease.
Situs inversus can be associated with multi- ple spleens and other defects. Often a conven- tional radiograph is a good starting point in evaluating these anomalies.
Heterotaxy Syndrome
The term heterotaxy, or situs ambiguous, describes complex congenital abnormalities dif- fering from situs solitus or situs inversus. Some authors use the terms asplenia and polysplenia to subdivide heterotaxy into specific categories, but these classifications are incomplete and at times confusing. Others use the terms left and
right isomerism.Figure 14.1. Situs inversus in an 85–year-old woman. Polysple- nia is present on the right (arrows). The stomach is also on the right.
Complex familial inheritance patterns exist for heterotaxy. An X-linked recessive inheritance appears to account for a male preponderance.
These patients usually have complex congen- ital cardiac abnormalities that tend to over- shadow abdominal findings. Complex bowel rotation anomalies are encountered with both right and left isomerism. Aortic and gastric positions are variable. Right-sided isomerism results in asplenia. The liver extends across both upper quadrants of the abdomen. Some of these patients have a left-sided inferior vena cava.
Gallbladder duplications occur in right-sided isomerism.
Heterotaxy with left abdominal isomerism results in polysplenia. Cardiac anomalies tend to be less severe than in asplenia. Most patients have azygous continuation with interruption of the inferior vena cava. The spleen(s) is (are) on the same side as the stomach. An absent gallbladder is more common in left-sided isomerism. An association exists between poly- splenia and biliary atresia. Midgut malrotation is a common associated finding, and midgut volvulus develops in some of these infants.
Traditionally, heterotaxy has been evaluated with angiocardiography. While both CT and pulse and color Doppler US are helpful in out- lining some anomalies, MRI is evolving as the preferred modality.
Liver/spleen scintigraphy detects splenic tissue in suspected heterotaxy; in some infants with negative planar imaging, the presence of splenic tissue is shown by SPECT.
Abdominal Wall Defects
Bladder exstrophy is discussed in Chapter 11.
Cloacal malformations are discussed in Chapter 12.
Omphalocele
Failure of the abdominal wall to close normally results in several defects.A defect cephalic to the umbilicus results in a supraumbilical ventral hernia, anterior diaphragmatic defects, and related conditions. Additional failure of lateral wall fusion results in an omphalocele. The degree of visceral herniation depends on the size of the defect. Peritoneum covers the viscera,
and the defect is obvious. Associated bowel malrotation is common.
Prognosis in these neonates is often limited by other associated abnormalities, at times major. The abdominal organs tend to be malpo- sitioned, leading to unusual imaging findings.
Gastroschisis
Defects in gastroschisis involve the lateral abdominal wall. The gross appearance is similar to that of an omphalocele, but with gastroschi- sis the umbilicus is in its normal position.
Among infants with gastroschisis, about two thirds have a simple defect, and in one third complex defects are identified, ranging from bowel atresia, stenosis, and perforation, to volvulus (4); survival of those with a simple defect was 100%, but those with a complex defect had a mortality rate of 28%.
Neonates with gastroschisis are often pre- mature. Small bowel dysmotility and a pro- longed transit time are common. Conventional radiography often reveals bowel wall thickening and lumen dilation. Delayed barium transit sug- gests obstruction, although actual small bowel obstruction is uncommon. Bowel atresia, if present, does result in a high mortality.
After surgical repair of gastroschisis these infants are at increased risk for necrotizing enterocolitis, although even then overall sur- vival rate is quite high.
Prune Belly Syndrome (Eagle-Barrett Syndrome)
The prune belly syndrome, named after the lax, wrinkled abdominal wall seen in this condition, consists of abdominal wall hypoplasia, geni- tourinary anomalies—including bilateral cryp- torchidism in males—and other, at times major, systemic abnormalities. Occurring mostly in males, the more severely affected neonates die shortly after birth. An incomplete expression of this syndrome exists, and some neonates have only mild manifestations. Unilateral abdominal wall hypoplasia also occurs. An association between congenital cytomegaloviral infection and prune belly syndrome has been raised, but the precise etiology is unknown.
A minority of these neonates have a ure- thral obstruction such as atresia or valves;
most, however, have functional bladder outlet
obstruction. A voiding cystourethrogram rev- eals a hypertrophied bladder wall. The presence of a urachal remnant is also common.
The prostatic urethra is dilated, and a dilated prostatic utricle is often seen. Vesicoureteric reflux is common into dilated, aperistaltic ureters. Renal dysplasia is identified in some patients.
Diaphragmatic Abnormalities
Diaphragmatic development is complex, with the ventral portion evolving from the septum transversum and the dorsal portion originat- ing from the pleuroperitoneal membrane. A Morgagni hernia anteriorly or a Bochdalek hernia posteriorly is a result of incomplete for- mation of these two diaphragmatic segments. A Bochdalek hernia is more common, usually is on the left, and can be massive to the point that respiratory distress is evident.
Diaphragmatic agenesis is occasionally detected in an asymptomatic adult. Imaging reveals associated herniation of colon, small bowel, and even kidney into the chest, together with a hypoplastic underlying lung.
Inadequate striated muscle development leads to diaphragmatic eventration. Eventration can be complete or partial. When extensive, imaging findings mimic a diaphragmatic her- nia. Minor diaphragmatic eventration is of little significance and tends to resolve with age. A partial eventration is difficult to detect in neonates.
Conventional radiography detects most diaphragmatic hernias, although US is useful not only for diagnosis but also for follow-up. A peroral contrast study is generally diagnostic.
Noonan’s Syndrome
Noonan’s syndrome is a mostly autosomal- dominant condition with facial dysmorphism, a number of congenital cardiac defects, and short stature. It is linked to the cardiofaciocutaneous syndrome, and both probably represent a vari- able expression of the same genetic defect. An association also exists between neurofibromato- sis type 1 and Noonan’s syndrome. The reason for including this syndrome in a book on abdominal disorders is that some of these indi-
viduals have abdominal lymphangiectasia, at times involving the gastrointestinal tract. About two thirds of children with Noonan’s syndrome have poor feeding and gastrointestinal dysfunc- tion—findings suggesting delayed gastrointesti- nal motor development—and require tube feedings. Also, a number of these patients suffer from various bleeding disorders. In some, lymphangiectasia is associated with pleural effusions, lymphedema, or a protein-losing ent- eropathy and a resultant hypoproteinemia.
Lymphangiectasia can be identified in these individuals by lymphangiography, or, curren- tly more often by lymphoscintigraphy, which reveals dilated and tortuous abdominal and pelvic lymphatic channels and abnormal lym- phatic flow.
Computed tomography after bipedal lym- phangiography in a 21-year-old man with Noonan’s syndrome and protein-losing enteropathy confirmed intestinal lymphangiec- tasia (5). After cardiac catheterization, a 15- year-old girl with this syndrome developed cutaneous lymphatic fluid oozing from a groin site (6).
Trauma
Unstable Patient
A hemodynamically unstable trauma patient requires immediate resuscitation. Exploration is considered in a patient with clinically evident abdominal trauma who is unresponsive to resuscitation. Imaging simply delays therapy in such a setting. A possible exception is a limited US study for intraperitoneal fluid while the patient is being resuscitated, but keep in mind the limitations of such a study.
Computed tomography of children in shock reveals dilated, fluid-filled bowel; intense enhancement of bowel wall, mesentery, pan- creas, kidneys, and adrenal glands; and enhancement of a smaller than normal aorta and inferior vena cava (7). Similar but less pronounced changes are found in adults.
Stable Patient
A pneumoperitoneum in a trauma patient,
regardless of whether detected with conven-
tional radiography or CT, generally is an indica- tion for exploration. Other findings, such as organ damage, peritoneal fluid, or a hematoma, in a stable patient are more judgmental. In some, whether to proceed with exploration in an otherwise stable patient with imaging-evident peritoneal fluid or organ damage is not clear, and a policy of observation is adopted; a repeat of appropriate imaging studies is often in order for these patients.
Currently most minor liver and splenic trauma is managed conservatively, although a trend is evident toward nonoperative mana- gement of hemodynamically stable patients even with more severe injury. Thus stable patients even with a moderate amount of hemo- peritoneum have been managed conservatively, with no differences found between nonopera- tive and operative groups in resultant abdomi- nal complications and hospital length of stay (8).
Penetrating Injury
The vast majority of gunshot wounds involving the peritoneal cavity require surgical repair. The diagnostic dilemma is determining which of these injuries penetrate the peritoneum. Several diagnostic peritoneal lavage studies in gunshot wound patients achieved a sensitivity of and specificity of over 95% in determining peri- toneal penetration. To a large degree CT has supplanted lavage in patients with penetrating trauma, also achieving sensitivities and speci- ficities of over 95% (9).
Most traumatic visceral artery aneurysms (pseudoaneurysm) are due to penetrating injury. A not uncommon scenario is a patient who has surgery shortly after trauma, under- goes arterial ligation, and then presents with a gastrointestinal bleed several weeks later from an aneurysm.
A reasonable approach in stable patients with abdominal stab wounds is to obtain initial CT or US, and in the absence of evidence for imme- diate surgery to follow them with serial imaging.
Diagnostic Peritoneal Lavage
In the 1980s diagnostic peritoneal lavage was generally considered superior to CT, although
its use has decreased markedly over the last decade, having been supplanted by CT and US.
Nevertheless, an occasional clinician still rec- ommends that lavage be performed first in a setting of blunt trauma if no contraindications exist.
Diagnostic peritoneal lavage relies on detect- ing blood in the peritoneal cavity. Generally an arbitrary threshold for a positive test, such as 10,000 red blood cells per cubic millimeter, is assumed. A higher threshold increases the missed injury rate and a lower one increases the false positive rate. The advantages of diagnostic peritoneal lavage include its simplicity and its relatively high sensitivity in detecting intra- peritoneal blood. It does not evaluate the sever- ity of injury, and thus is limited in predicting a need for surgery. It is insensitive for retroperi- toneal injuries. Even with intraperitoneal injuries, it may miss blood in patients with previous abdominal surgery and extensive adhesions.
A comparison of diagnostic peritoneal lavage and CT in patients with blunt trauma is difficult because each study evaluates different findings.
Peritoneal Fluid
Although a number of investigators believe that US readily detects intraperitoneal fluid, less often discussed is how much fluid is necessary for detection with US. In a blinded prospective study of 100 patients undergoing diagnostic peritoneal lavage, continuous US scanning of Morison’s pouch revealed that the mean volume of infused fluid first detected was 619 mL and that detection sensitivity after infusing 1 L was 97% (10). Even keeping in mind that intraperi- toneal fluid appears to be twice as common in the pouch of Douglas than in Morison’s pouch, statements in the literature about small, moder- ate, and large amounts of fluid detected with US should be viewed with a jaundiced eye.
Multiple US scans are necessary to detect
abnormal fluid; a single view, such as only of
Morison’s pouch, misses intraperitoneal fluid in
a number of patients. In general, in patients with
acute trauma evaluated with US, the sensitivity
for detecting free fluid is about 65% to 80% and
the specificity about 95%, with free fluid in the
pelvis being the most common reason for a
false-negative finding. Most peritoneal fluid
detected after trauma represents blood; less common is urine, bile, or intestinal content. Pus and chyle develop if presentation is delayed.
The presence of intraperitoneal fluid corre- lates with injury but does not predict whether surgery will be necessary. Surgical teaching often mandates laparotomy after blunt trauma if isolated intraperitoneal fluid is detected by imaging, yet this is a complex and controversial topic. In general, blunt trauma patients eventu- ally requiring laparotomy have more intraperi- toneal fluid than those managed conservatively;
an association also exists between the amount of mesenteric fluid and mesenteric laceration.
General Imaging Considerations
Multiorgan damage is common in major trauma; thus a finding of an abnormal collec- tion of intra- or extraperitoneal fluid is not nec- essarily due to a visible liver or splenic injury, but could also represent a synchronous mesen- teric or bowel injury. A US study of over 1000 women of reproductive age with blunt trauma concluded that fluid isolated to the cul-de-sac is likely physiologic, but those with free intraperi- toneal fluid usually have clinically important abdominal injuries (11).
If one has the luxury of time, chest and abdominal radiography are reasonable studies, although if CT is available, a strong argument can be made for using it initially. The ready availability of diagnostic CT and its ability to detect other conditions continue to expand the indications for CT in patients with abdominal trauma, and in many centers CT is the first imaging examination performed in a hemo- dynamically stable patient with a suspected intraabdominal injury. Exceptions include the hemodynamically unstable patient, one with an immediate life-threatening condition, or the patient who is to undergo emergent surgery for nonabdominal trauma.
In spite of an occasional admonition by emer- gency physicians, radiologists in the United States administer both IV and oral contrast prior to CT to most trauma patients. Very few complications due to contrast are reported. An extensive literature exists on IV contrast reac- tions, and this topic is beyond the scope of this book. Most radiologists believe that oral con- trast aids in study interpretation, and that the advantages of contrast use outweigh any possi-
ble disadvantages. Gastroesophageal reflux and aspiration is uncommon even in obtunded or uncooperative patients, and oral contrast is often administered through a nasogastric tube.
Lung contrast results if contrast is instilled through a tube placed into a bronchus. The oral iodinated contrast agents used in CT are hypo- osmolar and should not be compared to hyper- osmolar full-strength contrast agents employed for other examinations.
A pneumoperitoneum can develop after chest trauma. Some of these patients also have an associated pneumothorax, pneumomedi- astinum, or a retropneumoperitoneum. The pneumoperitoneum can generally be identified with conventional radiography, although occa- sionally it is detected only with CT.
The vital signs of trauma patients are gener- ally being monitored, and an imaging study should not be relied on to detect hypotension.
Nevertheless, on a contrast-CT study the pres- ence of a prolonged nephrogram without excre- tion into collecting systems should suggest hypotension. A collapsed inferior vena cava should suggest hypovolemia, with or without hypotension. Likewise, the spleen may become smaller than normal. Small bowel ischemia, manifesting as diffuse bowel wall thickening, may develop.
Computed tomography evaluates both the presence of fluid and organ injury. At times a CT study is equivocal. If surgical exploration is not contemplated, repeat CT is often help- ful in monitoring the progression of any abnormalities.
In some institutions, especially outside the
United States, US rather than CT has replaced
diagnostic peritoneal lavage and is often used as
a screening modality for suspected abdominal
trauma. Use of US in trauma patients has
generated strong opinions. Statements such as
CT “. . . is costly, time-consuming, requires
sedation, and may be associated with complica-
tions in young children . . .” while US “. . . is
quick, noninvasive, repeatable, and cost-
effective . . .” have appeared in the trauma liter-
ature (12). Numerous studies extol the virtues of
US in trauma patients, yet operator experience
is difficult to place in perspective. Pediatric sur-
geons in particular advocate US as a triage tool
in pediatric trauma patients and believe that it
alone is sufficient to evaluate children after
blunt abdominal trauma. Some believe that only
those with abnormal US should be further studied with CT, a conclusion of dubious validity.
Advocates of US in a setting of trauma rely primarily on detecting intraperitoneal fluid, yet such reliance as a sole indicator of visceral injury does not appear warranted. Although a minority, some patients with later proven vis- ceral injuries develop little or no hemoperi- toneum. Nevertheless, screening US studies in patients with blunt abdominal trauma have published sensitivities of 85% to 95% for detect- ing injuries severe enough to require laparo- tomy. Abdominal US is considered positive if either intra- or retroperitoneal fluid is detected.
False negative studies include retroperitoneal injury, bowel injury and intraperitoneal solid organ injury without presence of a hemoperi- toneum. Yet critical analyses of US point to a study of limited value. Major organ damage is missed and active hemorrhage is not iden- tified. The bowel and pancreas are poorly visualized. In a trauma setting, the superiority of CT over US has been established by a number of studies. In one study, CT revealed fluid, organ injury, or both in 33% of consecutive chil- dren with blunt abdominal trauma (13); the sen- sitivity and specificity of US for fluid detection only was 47% to 59% and 79%, respectively (for two observers), and the sensitivity and specificity of US when fluid and organ injury were considered was 65% to 71% and 71% to 79%, respectively; the authors concluded that the low US sensitivity suggests that “a normal screening sonography alone in the setting of blunt abdominal trauma fails to confidently exclude . . . intraabdominal injury” (13). Ultra- sonography can probably be justified, however, in those institutions lacking the ready availabil- ity of CT.
At times CT is used in patients with minimal trauma to decide whether to discharge a patient or not. Ultrasonography is generally considered not adequate to answer this question and many trauma US studies rely on keeping a patient under observation for some time.
Currently MR is not considered appropriate for screening trauma patients.
Diagnostic/therapeutic laparoscopy has been performed in patients with suspected abdomi- nal trauma, with conversion to open exploration as needed. The role for such laparoscopy is yet to be established.
Bowel Injury/Perforation
In a trauma setting, CT detection of peritoneal fluid, in the absence of any visible solid organ injury, suggests bowel injury. About half of these patients have small bowel or diaphragmatic injury, although isolated intraperitoneal fluid can be associated with unsuspected injury from bowel and mesenteric injuries, to solid organ trauma.
Complicating the issue is that some patients with subsequently detected major bowel injury have no hemoperitoneum on admission CT and US, but bowel and mesenteric injury is detected only hours later; even then, bowel and mesen- teric injury can be difficult to diagnose. Cur- rently such injury is probably best studied with CT. Both IV and oral contrast are helpful. A prospective CT study achieved a sensitivity of only 64% but a specificity of 97% in detecting bowel injury in patients with blunt abdominal trauma (14); findings used to detect bowel injury included mesenteric infiltration, bowel wall thickening, extravasation either of vascular or enteric contrast, and the presence of pneu- moperitoneum. Bowel wall thickening, in par- ticular, is difficult to put in proper perspective as a finding of major bowel injury. If associated with a mesenteric hematoma, sufficiently severe mesenteric or bowel injury is generally pre- sumed to warrant considering surgery. On the other hand, a focal mesenteric hematoma without adjacent bowel wall thickening occurs both in those patients requiring surgery and those who do not. Computed tomography has a high specificity in detecting a mesenteric hematoma. Nevertheless, the true accuracy of CT in establishing major bowel or mesenteric injury is difficult to judge, and published con- clusions vary.
With a perforation, imaging rarely identifies bowel wall discontinuity. Intraperitoneal spill of oral or rectal contrast identified by CT is usually assumed to represent a bowel perforation, but although diagnostic, it is rarely detected. Spill of instilled contrast from a urinary tract perfora- tion is in the differential diagnosis.
In pediatrics the role of CT in detecting bowel
perforation appears even more limited than in
adults, and CT identifies small bowel injury only
in a minority. Clinicians should be aware of this
CT limitation and not be lulled into a false sense
of security, leading to a delay in surgery.
Mesenteric stranding, often in association with adjacent blood, suggests mesenteric injury, although laceration of an adjacent loop of bowel results in similar findings.
With rare exceptions, the presence of extra- luminal gas (either pneumoperitoneum or extraperitoneal gas) is diagnostic of bowel per- foration. Extraluminal gas is readily detected with both conventional radiography and CT.
The inability to reliably and consistently detect a pneumoperitoneum is a limitation of US.
The small bowel normally contains little gas, and a number of bowel perforations manifest later as an intraabdominal abscess rather than as an immediate pneumoperitoneum. Colo- nic perforation, on the other hand, commonly results in a pneumoperitoneum, which is readily detected. Other indirect signs for perforation include intraperitoneal fluid, bowel wall thick- ening, bowel wall contrast enhancement, and bowel lumen dilation. None of the latter signs is specific for a perforation.
Bleeding
Bleeding leads to mesenteric or bowel hematomas, identified by CT as hazy streaking in mesenteric fat, or results in peritoneal or extraperitoneal fluid. Computed tomography scans of direct extravasation of IV contrast is evidence of active bleeding, and such bleeding in a setting of trauma is assumed to represent an injury to the involved viscera. Diffuse extravasation is implied by detecting extravasated contrast material, keeping in mind that extravasated contrast usually has a lower attenuation than the aorta. Not all intra- or extraperitoneal bleeding is due to trauma;
a ruptured aneurysm, a vessel weakened by tumor, anticoagulation therapy, or even venous obstruction and superimposed ischemia lead to bleeding and hematoma formation. Other rare causes of hemorrhage include severe pancreati- tis or even an intraabdominal pregnancy.
Intraperitoneal blood pools in dependent spaces. Thus with upper abdominal bleeding a common site is Morison’s pouch and subphrenic spaces. More inferior locations include para- colic gutters and pouch of Douglas.
Computed tomography attenuation of intraperitoneal blood varies with age; initially it is isodense to intravascular blood. Hemoglo- bin concentration when blood clots, occurring
within several hours, raises the attenuation to over 50 Hounsfield units (HU). Subsequent clot lysis, in a matter of days, gradually leads to an attenuation decrease, and in several weeks may approach the attenuation of water. Lower CT attenuation values are found in patients with preexisting anemia or if blood mixes with ascites or other fluid; thus fluid having a low attenuation does not exclude acute bleeding.
A hematoma often is not homogeneous in appearance. The rate of clot lysis in a hematoma varies, and a lower attenuation may be present at the periphery. Likewise, intermittent bleeding leads to simultaneous clotting and lysis and results in regions containing different attenua- tion values. If contrast-enhanced CT is per- formed during active arterial bleeding, the extravasating blood is isodense to adjacent arte- rial blood. Invariably an associated hematoma is present. A recent bleed can be denser than the rest of a hematoma, and such a sentinel clot tends to be located close to the site of bleeding.
At times nonhemorrhagic ascites also enhances with CT IV contrast.
The MR appearance of a hematoma (and intraperitoneal blood) also varies depending on clot age. Within a day or so of bleeding a hematoma is hypointense on both T1- and T2- weighted images. Then within several days it gradually becomes isointense to hyperintense on T1- but remains hypointense on T2-weighted images. This prominent hypointensity on T2- weighted images allows differentiation of blood from ascites, which is very hyperintense on T2- weighted images. A pneumoperitoneum is also hypointense on T2-weighted images, but other MR sequences and the relative location of gas versus fluid in the peritoneal cavity allow dif- ferentiation. Within a week or so a hematoma becomes hyperintense on both T1- and T2- weighted images, but while evolving to this stage some hematomas reveal a hyperintense rim sur- rounding a hypointense central portion on T1- weighted images. Eventually, if fibrosis develops around a prior hematoma, a hypointense rim on both T1- and T2-weighted images encloses this region.
Diaphragmatic Injury
Diaphragmatic injury is one cause of visceral
herniation into the chest. A majority of hemidi-
aphragmatic ruptures occur on the left side.
The most common site for rupture is at the diaphragmatic dome, and the least common is at the rib muscular insertions (15). A number of these posttraumatic diaphragmatic ruptures are not initially apparent; herniation increases in size with time, and thus delayed imaging is nec-
essary. Some of these hernias are detected only months later. Intubation appears to hinder the detection of diaphragmatic rupture. Thus an initial chest radiograph or CT detects only about half of diaphragmatic ruptures (Fig. 14.2).
These hernias became clinically symptomatic from days to years after trauma, and either con- ventional chest radiographs or upper gastroin- testinal studies are diagnostic (Fig. 14.3).
Strangulation of intestinal content has devel- oped, including delayed gastric perforation into the pleural cavity.
A rare cause of diaphragmatic rupture is car- diopulmonary resuscitation.
Computed tomography detection sensitivi- ties for diaphragmatic rupture are disappoint- ing, especially for right hemidiaphragmatic rupture, and are of limited use; keep in mind that detection rates vary with time after trauma.
Diaphragmatic crura are not thickened in patients with an injured diaphragm (16);
coronal and sagittal reconstructions are also of limited value in detecting subtle diaphragmatic injury. Computed tomography usually does not reveal diaphragmatic discontinuity even with thin sectioning (except in the rare diaphrag- matic avulsion); rather, intestinal content not confined by the diaphragm but spilling into the thorax is diagnostic of a hernia, and in the appropriate clinical setting provides indirect
Figure 14.2. Traumatic rupture of left hemidiaphragm. A scoutview localizer prior to computed tomography (CT) reveals medi- astinal shift to the right, partial left lung atelectasis and an ele- vated stomach. (Courtesy of Patrick Fultz, M.D., University of Rochester.)
Figure 14.3. Traumatic left hemidiaphragm rupture.A: Chest radiograph reveals gas and fluid at the left lung base.B: A barium study performed through a nasogastric tube identifies part of the stomach in the chest.This study was performed several hours after that in part A, and now considerably more abdominal content has herniated into the chest.
A B
evidence for diaphragmatic rupture. A waist- like intestinal constriction at the site of hernia- tion is occasionally detected if rupture is limited in scope. These traumatic hernias need to be distinguished from congenital diaphragmatic hernias and from hernias through the esophageal hiatus.
Ultrasonography findings in patients with diaphragmatic rupture due to blunt trauma range from diaphragmatic disruption to a non- visualized diaphragm. Occasionally detected is a diaphragm surrounded by fluid or abdominal content herniating through a diaphragmatic defect.
Preliminary reports suggest that MRI is reli- able in detecting diaphragmatic injury; coronal and sagittal MRI reveal the site of a diaphrag- matic tear and detect abdominal visceral herni- ating into the thorax, but keep in mind the limitation on early detection, as discussed previously.
Scintigraphy using intraperitoneally instil- led Tc-99m–macroaggregated albumin (MAA) detects a diaphragmatic rupture but is rarely necessary.
Arecdotal reports describe spontaneous diaphragmatic rupture.
Barotrauma
A pneumoperitoneum is a rare complication of mechanical ventilation. Detection of free gas in these generally rather sick patients leads to a diagnostic dilemma—Is the pneumoperi- toneum secondary to an unsuspected bowel perforation? A number of these patients undergo surgical exploration.
Acute Abdomen
The causes of an acute abdomen are legion, including infection, bowel perforation, inflam- mation, obstruction, ischemia, volvulus of various structures, gynecologic abnormalities, and tumor infiltration; these conditions are dis- cussed in their respective chapters. At times the first evidence of a serious underlying disease is an acute abdomen, such as Crohn’s disease manifesting as bowel perforation. Colonic epi- ploic appendagitis, a condition diagnosable by imaging, is an example of an acute abdomen not
requiring surgical intervention. Less common etiologies for an acute abdomen include lym- phoma infiltrating the bowel and resulting in perforation, a perforating primary small bowel neoplasm, and a perforated bowel duplication cyst with spill of the contents into the peritoneal cavity.
In pediatrics, perforation is more common in neonates than in older children. Among neonates with gastrointestinal perforation, most common etiologies are necrotizing enterocoli- tis, isolated ileal perforations, a combination and sequella of malrotation/volvulus. Etiologic factors in children are trauma, Meckel’s diverticula complications, intussusception, pseudomembranous colitis, and post-operative complications.
In children, screening US detects an abdomi- nal abnormality in about half of those with acute or subacute abdominal pain.
Past teaching has been to study an acute abdomen with conventional radiographs, an approach supplanted by CT, generally without IV contrast. At times images with and without IV contrast are useful (Fig. 14.4). Computed tomography has had a major impact in the diag-
Figure 14.4. Acute abdomen secondary to jejunal perforation.
Oral and intravenous (IV) contrast-enhanced CT reveals ascites and pneumoperitoneum. Higher density material is present within this fluid adjacent the liver (arrow) and also in the left upper quadroon (curved arrow). Although angiography revealed patent vessels, surgery suggested emboli and ischemia for the patient’s perforation. (Courtesy of Patrick Fultz, M.D., Uni- versity of Rochester.)
nosis and subsequent management of patients presenting with an acute abdomen. Some studies suggest that CT is superior to clinical evaluation in diagnosing a cause for an acute abdomen. Such an approach appears to hold up regardless of the duration of signs and symp- toms and in patients with no prior disease. Nev- ertheless, rather than use CT in a shotgun approach for all patients presenting with an acute abdomen, a more selective choice of imaging studies often establishes a diagnosis more quickly. For instance, with suspected cholecystitis, US should be the initial imaging modality; suspected acute uncomplicated pan- creatitis generally requires little or no imaging, except possibly endoscopic retrograde cholan- giopancreatography (ERCP), while pancreatic necrosis calls for contrast-enhanced CT or MR.
Ultrasonography is more commonly employed in pediatric patients. CT is especially useful in obese patients, nondiagnostic US, or with sus- pected bowel obstruction.
In some centers US is used liberally for the initial study of patients with an acute abdomen.
It is readily performed and detects a number of acute conditions. One limitation is the presence of dilated bowel. Also, while in experienced hands such diagnoses as appendicitis are readily made, a normal US examination does not ex- clude appendicitis, pyelonephritis, and other disorders. Likewise, early pancreatitis and bowel ischemia do not have specific US findings.
Laparoscopy is still preferred by some as a diagnostic and therapeutic modality in patients presenting with an acute abdomen. Even if con- version to an open laparotomy is necessary, laparoscopic findings are useful as a guide for the subsequent incision.
Infection/Inflammation
Abscess
Intraperitoneal Clinical
Some abscesses develop spontaneously, although most are secondary to postoperative complications or spread from a source in an adjacent structure, such as diverticular disease, appendicitis, cholecystitis, and so on. Fluid col- lections communicating with bowel can become
huge, and patients have few symptoms due to the internal drainage (Fig. 14.5). At times an abscess and peritonitis coexist, and the initial inciting event is difficult to identify.
A gallstone falling into the peritoneal cavity during laparoscopic cholecystectomy may not be readily retrievable. Although many of these intraperitoneal gallstones are innocuous, they do serve as a potential nidus for abscess forma- tion, with some of these abscesses manifesting years later. An occasional dropped appen- dicolith, occurring mostly during laparoscopic appendectomy, results in a similar finding. At times the specific etiology for such an abscess is suggested by CT or US.
Imaging
Computed tomography, US, MRI, or scintigra- phy should detect and localize most intraab- dominal abscesses, and most can then be drained percutaneously, generally under US guidance. Numerous comparison studies have shown CT and US accuracies of over 90% in detecting intraabdominal abscesses. Whether the greater resolution of CT or the greater portability of US determine the modality used, clinically the availability is the deciding factor.
Figure 14.5. Postoperative abscess extending from the left hemidiaphragm inferiorly into left lower quadrant (arrows), communicating with the stomach. Barium sulfate was the con- trast material used; it does not affect abscess healing.
A note about subphrenic abscesses. It is almost unheard of to have a subphrenic abscess without an associated pleural effusion. Even a chest radiograph should detect such an effu- sion, and the absence of effusion essentially excludes a subphrenic abscess. If imaging iden- tifies a suspicious abscess beneath the right hemidiaphragm but no pleural effusion is detected, an intrahepatic rather than a sub- phrenic abscess is more likely.
Gas in a fluid collection generally implies an abscess, but gas bubbles are also seen in retained surgical sponges even without an abscess. Large amounts of gas suggest bowel communication, a finding seen with other benign and malignant conditions (Fig. 14.6).
Computed tomography of a typical abscess shows a fluid-filled structure surrounded by a contrast-enhancing rim. Such a finding is not limited to abscesses and is also seen with some necrotic tumors and other benign conditions such as a hematoma and various cystic struc- tures. Also, not all abscesses have this appear- ance. Differentiation of an abscess and a benign fluid collection is difficult, especially if the wall is thick. Loculated fluid after abdominal surgery tends to develop primarily in the abdomen and
after pelvic surgery loculated fluid is mostly in the pelvis, but this is of limited use in differen- tiating benign fluid from an abscess.
Abscesses are hypointense on T1- and hyper- intense on T2-weighted MR images; about half are homogeneous in appearance. Gadoli- nium-enhanced T1-weighted fat-suppressed images identify abscesses as fluid collections surrounded by a contrast-enhancing rim. Gas within an abscess appears as a signal void on both T1- and T2-weighted images. Coronal and sagittal reconstruction aids in differentiating an abscess from bowel. Fluid layering occurs in some abscesses, with hypointense material, pre- sumably representing protein, being dependent on T2-weighted images, and such a finding in the peritoneal cavity is strong presumptive evi- dence of an abscess. Overall, MR sensitivity in detecting abscesses is close to 100%.
Scintigraphy detects most abdominal abs- cesses. Useful radiopharmaceuticals include gallium-67 citrate, indium-111 leukocytes, and Tc-99m leukocytes. A major limitation of Ga-67 citrate scintigraphy is the prolonged time required to perform the study.
Therapy
Percutaneous abdominal abscess drainage is an established technique, and almost all well- defined unilocular abscesses can be successfully drained. A majority of abscesses are cured with initial drainage. Recurrent abscesses can be drained percutaneously in most patients and surgery avoided in about half (17). Complex abscesses consisting of loculated, poorly confined, or multiple abscesses or those associ- ated with a fistula have a lower success rate and often require several drains. A single abscess is often drained using US guidance, but multiple abscesses are easier to drain with CT guidance.
Distinguishing an abscess from necrotic tissue can be difficult. At times aspirate cytology is helpful. Similar to surgical drainage, attempts to drain infected necrotic tumors percutaneously are rarely successful. Conversion to surgical drainage (and often associated resection) is required with the presence of unhealing abscesses or fistulas and bowel or pancreatic necrosis. Catheter-induced bleeding is an occasional complication requiring surgical correction.
Figure 14.6. Left subphrenic abscess secondary to a perforated gastric fundal adenocarcinoma. The entire fundus is amputated by tumor and abscess (arrows). The study was performed pri- marily for unexplained weight loss.
Crohn’s disease abscesses can be drained per- cutaneously using image guidance, and the patient is thus stabilized. These abscesses tend not to resolve completely, especially if they involve an enteric fistula.
Some left subphrenic abscesses cannot be readily drained using a transabdominal approach, and a transpleural approach is neces- sary. At times a drainage catheter is inserted through the pleura. Regardless of catheter posi- tion, most abscesses are successfully drained, although a transpleural approach risks a pneu- mothorax, requiring its own therapy.
Abscess drainage using a transrectal or transvaginal approach with a combination of endoluminal US and fluoroscopy for needle advancement, tract dilation, and catheter inser- tion, combined with appropriate antibiotics, is effective therapy for most pelvic abscesses.
Patients undergoing transrectal aspiration or drainage have less procedure-related pain and catheter pain than those with a transvaginal approach (18). A viable option for some pelvic abscesses is US-guided transperineal catheter drainage.
Pelvic abscesses are readily drained in chil- dren and adolescents. The average hospital stay for children after image-guided transrec- tal drainage of pelvic abscesses tends to be shorter than after open surgical drainage.
Surgical drainage is associated with more com- plications than percutaneous drainage, but comparison studies often have a built-in bias against surgery—patients undergoing surgical drainage tend to be sicker.
Computed tomography–guided transgluteal percutaneous drainage of deep pelvic abscesses through the greater sciatic foramen is an option in both adults and children (19).
A majority of vancomycin-resistant entero- coccal abscesses can be drained percutaneously, although the rate of successful therapy is lower than with more conventional abscesses (20); at times drainage provides a first clue to the pres- ence of vancomycin-resistant enterococci.
Abdominal Wall Abscess
Occasionally diverticulitis or cholecystitis evolves into an abdominal wall abscess. Like- wise, an occasional biliary or other neoplasm leads to an abdominal wall abscess. Imaging
readily differentiates those abscesses involving the rectus abdominis muscle from intraabdom- inal conditions.
Psoas Muscle Abscess
An abnormal fluid collection in the psoas muscle region most often is an abscess, and less often a hematoma. In a setting of pancreatitis, a pseudocyst is also in the differential. A primary iliopsoas abscess is not common; a number of these occur in IV drug users and those posi- tive for human immunodeficiency virus. More often these abscesses develop from a gastroin- testinal, genitourinary, or spinal source. Some retroperitoneal abscesses involve not only the psoas muscles but also spread along soft tissue planes into adjacent compartments. Psoas abscesses develop in Crohn’s patients with disease.
Gram stain and a culture of the abscess con- tents should establish the responsible organism.
Blood cultures are less often helpful. Both gram- positive and gram-negative organisms are involved. In some parts of the world a tubercu- lous psoas abscess is more common than a pyo- genic abscess; a tuberculous abscess tends to involve the adjacent vertebrae. Tuberculous psoas abscesses can be successfully drained per- cutaneously, although abscess recurrence often requires repeat drainage.
The clinical triad of fever, flank or thigh pain, and limitation of hip movement is found only in about half or fewer patients with a psoas abscess. Sepsis is common.
Computed tomography readily detects psoas abscesses; however, differentiation from a tumor purely on CT criteria is problematic (Fig.
14.7). A hematoma is also often in the differen- tial. Image-guided needle aspiration should be diagnostic and percutaneous catheter drainage therapeutic.
Magnetic resonance imaging is very useful in evaluating psoas muscles. Normal psoas muscle is hypointense on T2-weighted images, while abscesses and the occasional psoas muscle tumor are hyperintense. Contrast-enhanced MR of a psoas abscess reveals a signal void sur- rounded by intense enhancement.
Conventional therapy of these abscesses
is surgical drainage, although percutaneous
drainage using CT or US guidance is becoming
more common. In distinction to intraabdominal abscesses, surgical psoas abscess drainage appears to result in a shorter patient hospital- ization than with percutaneous drainage. On the other hand, serious complications are more common after surgical drainage than after percutaneous drainage (21). Imaging confirms abscess resolution.
Peritonitis
Peritonitis either is primary or develops sec- ondary to an infected adjacent structure. It ranges from localized to diffuse. In the elderly, peritonitis tends to manifest initially in a more advanced or severe form than in a younger patient. At times both peritonitis and ascites coexist. Conditions presenting primarily with ascites are discussed in a later section.
Gastrointestinal perforation is a common cause of acute peritonitis and occurs both in the very young and very old. Peritonitis can develop after inadvertent gallbladder puncture during a liver biopsy or percutaneous nephrostomy.
Occasionally encountered is aseptic peritoni- tis, usually in association with a peritoneal malignancy.
Primary peritonitis is rare in children, but more common in girls. Some of these
children are clinically suspected to have appendicitis, and the diagnosis is made only during surgery.
Imaging has a limited role in detecting acute peritonitis. Some degree of ascites is common.
Contrast-enhanced CT and MR reveal increased peritoneal enhancement.
Infectious Peritonitis
Discussed here are only some of the more unusual organisms associated with infectious peritonitis.
Patients undergoing peritoneal dialysis are at increased risk of cryptococcal peritonitis.
Cryptococcal peritonitis also occurs in patients with cirrhosis and end-stage renal disease.
Listeria is a rare cause of spontaneous bacte- rial peritonitis. About two thirds of reported patients have chronic liver disease or an under- lying malignancy, or the patient was undergoing peritoneal dialysis.
Actinomycosis is a chronic infection by an anaerobic gram-positive commensal bacterium present in body orifices. Typically involved are the genitourinary tract and occasionally bowel.
Rarely, it involves the peritoneum or greater omentum. Needle biopsies do not always provide a diagnosis; at times only inflammatory tissue is obtained and only an open biopsy provides the organisms.
Fitz-Hugh–Curtis syndrome, or venereal per- ihepatitis, is a complication of genital gonococ- cal or chlamydial infection. In Europe and the United States infection by Chlamydia trachoma-
tis is more frequent. A majority of patients arewomen. Clinically, acute right upper quadrant symptoms mimic those of biliary disease, but liver function tests are normal. Likewise, US of the gallbladder and bile ducts is normal yet gall- bladder wall thickening develops in some and multislice CT can detect transient liver attenua- tion abnormalities (22). Pathologically, perihep- atitis consists of adhesions and peritoneal inflammation. Perihepatic fluid is often present.
A biopsy should be diagnostic. The diagnosis is confirmed by finding Neisseria gonorrhoeae or
C. trachomatis organisms in perihepatic tissues.Some of these patients have undergone laparoscopy before the true diagnosis is suspected.
A rare cause of peritonitis is acute ascaris peritonitis due to bowel perforation. This con-
Figure 14.7. Psoas abscess. Transverse CT image reveals anenlarged, mostly hypodense right psoas muscle (arrow) displac- ing kidney anterior. (Source: Paley M, Sidhu PS, Evans RA, Karani JB. Retroperitoneal collections—aetiology and radiological implications. Clin Radiol 1997;52:290–294, with permission from the Royal Collage of Radiologists.)
