Technique
Barium Enema
Contrary to the opinion of some computed tomography (CT) and magnetic resonance imaging (MRI) enthusiasts, a double-contrast barium enema continues to be a viable option in a setting of suspected colitis, colorectal cancer screening and detection, and follow-up after therapy. Similarly, it is a sad reflection on medical practice that occasionally a statement still appears in print that barium sulfate is toxic to the colon (1).
One of the present indications for a barium enema is failed colonoscopy, although in some centers CT colonography is gaining ground and magnetic resonance (MR) virtual colono- scopy is on the horizon. An obvious concern in performing any enema shortly after failed colonoscopy is risk of perforation. Contrary to the experience of some investigators, the author has found barium enemas performed on the same day as colonoscopy to be mostly unsatis- factory; invariably the patient is “tired out” from the colonoscopy, has difficulty cooperating, excessive colonic spasm is often encountered, and residual fluid interferes with mucosal coating. A formal air contrast barium enema, performed a week or so later, tends to be of superior quality.
Proctography
Evacuation proctography, a dynamic imaging modality, evaluates functional and morphologic abnormalities of the anorectal region. This examination, also called dynamic proctography or defecography, requires specially adopted fluoroscopic equipment, including rapid filming, that is not available in many radiology departments. It has a role in evaluating unex- plained constipation, incontinence, rectal pro- lapse, and rectal pain. It evaluates the presence or absence of a sigmoidocele, rectocele, rectal prolapse, puborectalis muscle contraction, anal canal opening, changes in anorectal angle, and rectal emptying. Resultant findings appear to be independent of contrast agent viscosity used.
Pre- and postproctography questionnaires by referring clinicians revealed that clinicians found this study of major benefit in 40% and of moderate benefit in 40% (2); the primary diag- nosis was changed in 18% of patients, intended surgical management became nonsurgical in 14%, intended nonsurgical therapy became sur- gical in 4%, and type of surgery contemplated changed in 10%.
Although detailed and precise anatomic measurements are possible with this study, their clinical relevance is still not clear. In particular, the borderland between normal and abnormal is poorly defined. Lack of confidence in some
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of the findings becomes evident after patient symptoms persist following surgical correction of an alleged abnormality.
Computed tomographic proctography is fea- sible, but rarely performed. The study is per- formed with the patient seated; coronal images aid in outlining perineal floor muscles. Sagittal reconstruction allows comparison with conven- tional proctography.
An open configuration MR system allows image acquisition with the patient in a vertical position. Anorectal angle changes, anal canal function, puborectalis muscle configuration, and pelvic floor dynamics are evaluated at rest and during straining (3). Even if an open MR unit is not available, conventional procto- graphy is gradually being replaced by pelvic floor MRI using an endoanal coil. Suspected fistulas, sphincter lacerations, rectoceles, tumor invasion by low rectal carcinomas, and other pelvic floor disorders are imaged in detail with this technique. Currently this is considered to be the most accurate imaging test of distal perirectal structures, especially the external sphincter.
Two approaches are possible for MR rectal studies: either rectal distention with fluid and use of a surface coil or no distention and use of a rectal MR coil. More studies have addressed the latter technique, but advances in hardware and software design make it difficult to predict which path will be superior. One technique con- sists of opacifying the rectum with 200 mL of an ultrasonography (US) gel and obtaining a single sagittal T2-weighted gradient echo sequence through the rectum (4); with a 1.5-T MR unit, a temporal resolution of 1.1 second is obtained, allowing imaging at rest and during straining and evacuation.
Using a surface coil in the anal canal, endorectal MRI appears superior to endorec- tal US in visualizing the external sphincter, although internal sphincter lesions are better evaluated with endorectal US (5).
Colonoscopy
Conventional
The prevalence of incomplete colonoscopy varies considerably among endoscopists and institutions, ranging from several percent up to one third of studies. A majority of incomplete
colonoscopies are in women. A prior abdominal hysterectomy is associated with a higher rate of incomplete colonoscopy.
Complete colonoscopy consists in visualiz- ing cecal landmarks, an elusive task in some patients. Attempts to provide photographs of cecal landmarks have met with limited success.
Experienced endoscopists display consider- able disparity in deciding whether complete colonoscopy had been performed when review- ing photographs of cecal landmarks (6).
The polyp miss rate of colonoscopy was esti- mated by performing two consecutive back-to- back colonoscopies on the same day (7); overall polyp miss rate was 24%, being 27% for polyps
£5 mm, 13% for lesions 6 to 9 mm, and 6% for those ≥1 cm. The miss rates for small polyps occurred among essentially all endoscopists.
Polyp size is routinely estimated by endo- scopists. Because of endoscopic lens system limitations, apparent measurements tend to be smaller than actual. Lesions in the periphery of the field of view are smaller than in the center.
Likewise, size varies with depth of view. Com- paring magnified radiographic polyp measure- ments (which are magnified due to inherent focus-object-film geometry) with the minified endoscopic appearance results in considerable discrepancy.
Laser fluorescence spectroscopy performed during colonoscopy has detected colonic dys- plasia with a claimed sensitivity and specificity of over 90% (8).
Computed Tomographic Colonography
The introduction of multidetector CT opened possibilities for complex three-dimensional (3D) colon studies, allowing the entire abdomen and pelvis to be covered with a slice thickness of <3 mm in under 30 seconds, allowing single breath-hold scanning. An effective slice thick- ness approaching 1 mm should, in theory, detect all relevant polyps. Once lumen distention is introduced, one is well on the road toward CT detection of colon neoplasms. Yet although multiple publications have established the fea- sibility of screening CT colonography, its role remains undefined.
The terms CT colonography, CT colonoscopy,
and virtual colonoscopy have often been used
interchangeably to describe a global examina-
tion designed to detect colonic tumors regard-
less of specific images obtained. Computed
tomographic colonography appears to better
describe this procedure, but virtual colonoscopy is ingrained in the literature, although a trend has developed to use CT colonography for a global examination consisting of narrow colli- mation data reconstructed to various combina- tions of 2D multiplanar reformatting and 3D images and to limit the term virtual colonoscopy to specific colonoscopy-like images. Hydro-CT is a less often used term to describe colonic dis- tention with fluid during a CT study.
Currently CT colonography is a viable alter- nate after failed or incomplete conventional colonoscopy. Residual colonic distention is ade- quate in many patients when CT is performed shortly after incomplete colonoscopy, but addi- tional air insufflation is often helpful. Indica- tions for CT colonography have expanded considerably and in some centers it has mostly replaced conventional colonoscopy for polyp detection, leaving the latter modality for therapy of detected polyps.
Technique
Although CT colonography is generally regarded as a technically easy study, interpreta- tion requires a steep learning curve. Data eval- uation time and number of false positive findings decrease with experience. Similar to a barium enema, a colon-cleansing regimen is required with most current CT colonography techniques. Numerous false positives ensue if residual stool is present, thus emphasizing the importance of a colon-cleansing regimen, a difficult task in most practices. One study achieved ideal bowel preparation in only 19% of 200 patients (9). The two bowel preparations commonly employed are a polyethylene glycol electrolyte (“wet”) solution or a phospho-soda (“dry”) preparation, both given the day prior to CT colonography. Polyethylene glycol elec- trolyte solution results in considerably more bowel residual fluid.
Current limitations of CT colonography include fluid retention and inadequate luminal distention due to spasm. Similar to a barium enema, polyps tend to be missed if the lumen is not distended. Spasm is minimized by judicious use of an antispasmodic agent. Problems inher- ent with fluid retention are partly overcome by performing the study with the patient both prone and supine, at the expense of doubling the radiation dose. Nevertheless, acquisition and
review of supine and prone images significantly increase polyp detection sensitivity (10), and the trend is to use both positions.
Ingestion of oral contrast agents is generally considered inadequate preparation for CT cancer detection. In practice, colonic lavage combined with oral barium contrast for stool tagging and oral iodinated contrast for elec- tronic fluid marking are useful techniques. A viable option consists of oral contrast combined with laxatives in frail, elderly patients who do not tolerate more vigorous CT colonography or a barium enema, realizing that this technique detects only more bulky tumors.
Air is commonly used to distend the lumen.
Carbon dioxide is an alternative agent but the relative merits of one over the other are arguable. Adequacy of distention is evaluated with a CT scout image. With newer CT scanners, if a study is being performed for suspected colitis, especially ischemic colitis, some authors find little advantage for intraluminal contrast.
As an aside, a tap-water enema is often administered if colon visualization is desired during abdominal CT examination. Comparing water, methylcellulose, and ultrasound gel as multislice CT rectal contrast agents, methylcel- lulose was significantly superior to ultrasound gel in differentiating normal from diseased bowel (11); although better rectal distention was achieved with methylcellulose and ultra- sound gel, superior more proximal colon dis- tention was obtained with water. Of these three agents, the authors recommend rectal methylcellulose.
Computed tomographic colonography with multidetector CT results in significantly better colonic distention and yields fewer respi- ratory artifacts compared to single-detector CT.
Computed tomographic colonography is a viable alternate after failed or incomplete con- ventional colonoscopy. A prospective study of patients performed within 2 hours of incom- plete colonoscopy found that although residual colonic distention was adequate in most patients, additional air insufflation significantly increased colon distention (12).
Once patient scanning is completed, the data are transferred to a workstation for analysis.
These are complex examinations, and hundreds
of images are generated in transverse, multi-
planar reformatted, and 3D endoluminal
modes. The relative advantages of axial, coronal,
2D, and 3D display techniques are still evolving;
in some patients several techniques are neces- sary to adequately visualize the entire colonic wall. A typical practice is to use primarily 2D multiplanar reformatted imaging for analysis and reserve 3D imaging for specific problems;
endoluminal views appear necessary to differ- entiate polyps from folds. Several commercial 3D endoluminal volume rendering and naviga- tional systems are available and further improvements are to be expected. Adding color (translucency rendering) to 3D aids in ruling out false polyps (13). Interpretation of 2D images is faster; on the other hand, navigation with 3D endoluminal imaging mimics the con- ventional colonoscopic appearance (Fig. 5.1). A panoramic view perpendicular to the centerline is also feasible, with sequential panoramic video views scanning the colon surface.
Results
Polyp detection sensitivity varies depending on scanning and image reconstruction parameters employed and on polyp size. No consensus exists on preferred viewing modes. For larger polyps a panoramic display results in greater sensitivity than a virtual endoluminal display and 3D displays are more sensitive than 2D dis-
plays. Experienced abdominal radiologists achieve similar polyp detection rates using 2D multiplanar reformation and 3D display tech- niques (14). Computed tomography colonogra- phy using axial 2D data and a cine mode and 3D
“fly-through” with surface-rendered and multi- planar reformatted images identified the same number of polyps with both techniques (15). A metaanalysis of reported accuracy of CT colonography found a pooled per-patient sensi- tivity for polyps >10 mm to be 88%, for polyps 6–9 mm 84% and for polyps 5 mm or smaller 65% (16); per-polyp sensitivity for polyps
>10 mm was 81%.
CT colonoscopy perforation rates are low and should be similar to those with a barium enema.
Rectal perforation is a potential complication with blind air insufflation in a setting of more proximal rectosigmoid obstruction.
Future Studies
Attempts to circumvent a colon cleansing regimen are theoretically feasible by tagging colonic content with ingested barium sulfate, with subsequent digital subtraction of this material. In patients with suspected or known colonic polyps, sensitivity for identifying
Figure 5.1. A,B: Two views of three-dimensional (3D) computed tomography (CT) double-contrast virtual colonoscopy. Images can be analyzed from any perspective in space. (Courtesy of Wolfgang Luboldt, M.D., Johann Wolfgang Goethe University, Frankfurt-am- Main.)A B
patients with polyps 1 cm or larger was 80% to 100% if these patients ingested multiple dilute contrast doses over a prior 48 hours (17).
Using signal processing of CT colonography data to identify tumors protruding into bowel lumen, an automated polyp detection algorithm achieved a 64% sensitivity for detecting polyps 10 mm or greater (18). Another approach is to use tumor contrast enhancement superimposed on a virtual double contrast and endoscopic display (19) (Fig. 5.2). Shape-based polyp detec- tion and polyp edge enhancement are helpful in identifying polyps.
Teleradiology of CT colonography using wavelet compression to 1 : 1, 10 : 1, and 20 : 1 ratios detected all lesions >10 mm for all com- pression ratios, but sensitivities for smaller lesions fell off with increasing compression ratios (20).
A claimed advantage of CT colonography is that extracolonic abnormalities are also detected. Among consecutive patients undergo- ing CT colonography, important extracolonic findings in 11% led to further imaging studies, and as a result several patients underwent surgery (21). Nevertheless, being designed for optimal colonic imaging, CT colonography is limited in evaluating solid organs (compared to a fine-tuned CT study of a specific organ or abnormality in question).
Magnetic Resonance Colonography
Similar to CT colonography, MR colonography is feasible, with relative advantages of CT versus MR colonography still evolving. Two broad approaches are possible:
1. Bright lumen MR colonography relies on colon filling with a paramagnetic contrast- water enema and T1-weighted gradient- recalled echo (GRE) single breath-hold acquisition, which results in a hyperintense luminal image, with other tissues being hypointense. Multiplanar reformatted 3D images and virtual colonoscopic images are then obtained.
2. Dark lumen MR colonography obtained by colon filling with a tap-water enema, which is hypointense on T1-weighted GRE imaging and an intravenous paramagnetic contrast agent to produce a hyperintense colonic wall. A variant technique is to use gas or air to distend the lumen; gas has no signal.
Another technique consists of colonic disten- tion with fluid and use of T2-weighted spin echo (SE) imaging. The colon is studied both in cross section and using a virtual intraluminal outline.
Often a coronal plane is useful.
Figure 5.2. Computer-aided polyp detection. A,B: Focal increased tumor perfusion after IV contrast can be automated to “detect”
potential neoplasms (arrow). (Courtesy of Wolfgang Luboldt, M.D., Johann Wolfgang Goethe University, Frankfurt-am-Main.) B
A
The disadvantages of the bright lumen tech- nique include retained air bubbles, which mimic polyps. Therefore, both prone and supine views are necessary. Surface-rendered MR virtual colonoscopic views, orthogonal sections and water-sensitive single-shot fast spin echo (FSE) MR images in patients (post–gadolinium-water enema) achieved a 93% sensitivity and 99%
specificity in detecting tumors >10 mm (22). To illustrate the complexity of these studies, they often require instillation of a gadolinium-water enema, prone and supine positioning, breath- hold 3D spoiled gradient recalled echo (SGRE) sequences and also 2D images pre– and post–intravenous contrast, and, wherever neces- sary, virtual intraluminal images.
Comparing manganese chloride, iron glyc- erophosphate, and gadolinium-based enemas for use in T1 shortening 3D GRE MR colonog- raphy, the contrast-to-noise ratios for the iron enema were highest (23); the authors suggest replacing gadolinium with iron due to cost considerations.
Using a gadopentetate-water enema and breath-hold 3D SGE sequences, a virtual double-contrast display is achieved by calculat- ing signal intensity differences between adja- cent voxels and making adjacent voxels with similar intensities lucent while adjacent voxels with different intensities are made opaque (24);
the resultant colonic display can be magnified
and rotated around its axis for detailed study from different planes (Fig. 5.3).
Some authors use the term hydro-MRI when a water, saline, or some other contrast enema is administered prior to MRI. Such an approach is helpful when the study is performed primarily for suspected colonic disease, and it is a step toward formal MR colonography. Confusing the issue is that hydro-MRI is also used by some authors if oral water or contrast is ingested prior to a MR small bowel study. Thus the type of con- trast (including water and air) and route of administration need to be specified. The term
double-contrast MR imaging is used by somewhen both an MR contrast enema and an MR intravenous (IV) contrast agent are employed.
Due to its ambiguity, it is probably best avoided.
A typical technique for colon neoplasms consists of breath-hold T2-weighted half- Fourier acquisition single-shot turbo spin echo (HASTE) and gadolinium-enhanced breath- hold fat-suppressed T1-weighted SGE images (25); inflammatory changes appear best on the gadolinium-enhanced breath-hold fat- suppressed T1-weighted SGE images.
Air bubbles with the dark lumen technique are hypointense and blend into the surrounding hypointense water; thus only one patient posi- tion is necessary, resulting in a shorter scan time. Likewise, polyps enhance with IV contrast and stool does not. Potentially, the dark lumen
Figure 5.3. A,B: Two 3D double-contrast MR virtual colonoscopy images. Visualization is similar to that obtained with CT (see Fig.5.1). (Courtesy of Wolfgang Luboldt, M.D., Johann Wolfgang Goethe University, Frankfurt-am-Main.)
A B
technique is also useful to evaluate colitis because of bowel wall enhancement.
Using lumen distention with CO
2, breath-hold single-shot FSE MRI performed during a CO
2enema in seven patients with known colon car- cinoma detected cancers in all and correctly identified tumor extension through muscularis propria in four (26).
Colon cleansing is required with most of the above methods. Similar to CT colonography, use of an oral paramagnetic contrast agents to label stool (called fecal tagging) in an unprepared colon results in stool being hyperintense and thus blending in with a bright lumen. Or, concentrated oral barium sulfate, which is hypointense and thus useful with a dark lumen technique, is combined with IV gadolinium to enhance the colonic wall and any associated tumors (27). These MR stool-tagging techniques are still in their infancy.
Ultrasonography
Compared to other intraabdominal sites, colon US is rather limited. In some centers it has found a niche in following patients with colonic Crohn’s disease but appears less useful with ulcerative colitis and diverticulitis. Its role in pediatric intussusception reduction is well established, less so in adult tumor detection and staging. Ultrasonography findings are not disease-specific. Also, in general, a negative US examination does not exclude disease.
Colon US performed after a water enema is called hydrocolonic sonography (occasionally a methylcellulose-water mixture is used). Hydro- colonic US does detect larger polyps but it is very operator dependent and has been over- shadowed by CT colonography.
Doppler US evaluates colonic blood flow.
Thus viability of an obstructed bowel segment is suspected if Doppler US detects no blood flow. Similarly, in inflammatory bowel disease and in acute appendicitis Doppler flow through a thickened bowel segment can suggest an acute or ongoing inflammation.
The published terminology is somewhat inconsistent for US performed with rectal probes: Endoscopic and endoluminal US include either a rectal or vaginal probe, whereas the terms transrectal and endorectal US are used interchangeably. Anorectal echo-endoscopy and similar terms are also in use.
Endovaginal US evaluates the rectum and adjacent structures, including puborectalis muscle thickness, sphincter thickness, and sphincter defects. Distending the rectum with a water enema better delineates perirectal tissue planes.
Endorectal US defines surrounding struc- tures. Urogenital structures and perirectal spaces are readily imaged. Both proctography and endorectal US evaluate internal and external rectal sphincters. Three-dimensional endorectal US appears to provide more accurate control of a biopsy needle toward a perirectal lesion than is available with other modalities, although the data for this are sparse. The current primary use of endorectal US is in a setting of rectal cancer and in the workup of evacuation disorders.
Available US miniprobes fit through the working channel of an endoscope. Similar to upper gastrointestinal endoscopic US, the role of flexible colonoscopic US in detecting and staging neoplasms is not yet clear.
Scintigraphy
A gamma camera scintigraphic technique estimates colonic transit, an infrequently used study in clinical practice.
The application of scintigraphy in inflamma- tory bowel disease and in the bleeding patient is covered in each respective section later in this chapter. Abdominal positron emission tomo- graphy (PET) scanning is discussed in more detail in Chapter 14.
Congenital Abnormalities
Malposition
Midgut malrotation is discussed in Chapter 4.
The interposition of small or large bowel into
the right subphrenic space, first described by
Chilaiditi in 1910, is rarely symptomatic and
should be considered a normal variant. Bilateral
bowel interposition is rare (28). Some authors
use the term Chilaiditi’s syndrome to describe
all such bowel interposition; others limit the
term only to the symptomatic patient. Preva-
lence of such bowel hepatodiaphragmatic inter-
position appears to depend on patient position
and is identified more often with the patient
supine.
Detection of bowel interposition is generally straightforward with conventional radiography and barium studies. The appearance is confus- ing with US, where interposed bowel loops mimic an abnormal mass. Computed tomo- graphy detects ascending colon interposition between kidney and psoas muscle (pararenal space) in about 1% (29). Retropsoas interposi- tion is slightly more common with the ascend- ing colon (3%) and descending colon (2%) (30);
little retroperitoneal fat favors interposition. A colon interposed posterior to the pancreas, between the spleen and left hemidiaphragm, is rare.
Duplication
Gastrointestinal duplications are associated with both vertebral and genitourinary tract abnormalities. They occur roughly in one out of 4000 births. Least common are hindgut duplica- tions. Most are detected in the young.
Colonic duplications have either a spherical or tubular appearance, with some long duplica- tions mimicking a second colon lumen. Most of these duplications do not communicate with the lumen and occur along the mesenteric border. Occasionally a duplication contains noncolonic mucosa, such as heterotopic gastric mucosa, small bowel, pancreatic, and even respiratory epithelium. The mucosa of some duplications continues secreting and a noncom- municating duplication thus increases in size with time. Imaging identifies an abdominal cystic tumor.
A rare duplication intussuscepts; it acts as a source of cecal volvulus, or is an incidental palpable mass at initial presentation. An occa- sional one develops a fistula to an adjacent structure. Magnetic resonance imaging is useful with the rare rectal duplication in a neonate to show no posterior extension, thus excluding a meningocele.
Obstruction
Common distal ileal obstructions in neonates are due to meconium ileus and ileal atresia; in the colon obstructions include imperforate anus, meconium plug syndrome, and Hirschsprung’s disease. From a practical view- point, distal ileal and colonic obstructions in the
neonate are lumped together as low intestinal obstructions.
A microcolon in a neonate is a descriptive term of a contrast enema finding rather than a specific disorder and usually suggests distal small bowel obstruction. Colonic disorders associated with a small caliber of the entire colon include total colonic aganglionosis of Hirschsprung’s disease and a microcolon seen with prematurity. Conventional radiography usually differentiates between a high and a low intestinal obstruction. A contrast enema is nec- essary to define the obstruction further.
Atresia
In rectal atresia the anus is normal, with the atretic segment located more proximal. No bowel fistula is identified. Atresia proximal to the rectum is uncommon, although it can occur anywhere in the colon. Colonic stenosis is rare.
A contrast enema reveals a small caliber colon distal to the obstructed, atretic segment.
Imperforate Anus
The most common neonatal colonic obstruction is an imperforate anus. Although the term
imperforate anus implies a single and simpledefect, in reality this is a complex deformity often also involving genitourinary tract struc- tures and other anomalies. Cryptorchidism is common; in general, a more superior level of anorectal malformation increases the risk of cryptorchidism.
Rectal atresia differs from an imperforate anus. With an imperforate anus the hindgut does not descend and communicate with the anus, but either ends blindly or forms a fistula in an abnormal location (ectopic anus). An imperforate anus is classified as being high or low using the puborectalis sling as a dividing line. The differentiation between a high and low lesion is often made clinically, and imaging plays a limited direct role. The presence of a perineal dimple or passage of meconium from the genitourinary tract is a useful guide. In some boys conventional radiography reveals gas in the bladder.
The puborectalis muscle tends to be
hypoplastic with a high obstruction.With a high
lesion, the rectum can end blindly, although
more often in boys it terminates in the posterior
urethra, and less often in the bladder or anterior urethra. In girls the rectum tends to terminate in the vagina. Prior to definitive surgery, most high lesions are treated with a bypass colostomy. The underlying anatomy is then studied through the distal colostomy limb (mucous fistula) or, if needed, by cystography and urethrography.
A low lesion is usually associated with a per- ineal dimple, and no communication exists with the genitourinary tract. A variant of a low lesion is a congenital triad consisting of an anorectal malformation, sacral abnormality, and a pre- sacral tumor, first described by Currarino et al.
(31) in 1981 (Table 5.1). Magnetic resonance imaging is useful in this triad to detect a tethered cord.
Imaging aids in detecting any associated renal or sacral abnormalities. Magnetic reso- nance imaging outlines the hindgut, bony and muscular pelvic anomalies, including the puborectalis muscle and external sphincter, and other surrounding anatomy. T1-weighted images establish whether the puborectalis muscle is hypoplastic. Magnetic resonance imaging tends not to identify small fistulous tracts, however, and a contrast study is useful to define them.
Some boys have a mix of meconium and urine and the meconium calcifies; these calcifi- cations are intraluminal in location, thus distin- guishing them from meconium peritonitis. Such a mix of meconium and urine does not occur in girls with anal atresia; calcified intraluminal content in a girl should suggest a cloacal
malformation consisting of communication between the urethra and rectum, generally through a single perineal channel.
After surgical correction of an anorectal mal- formation—such as rectal pull-through(peri- neoplasty) or posterior sagittal reconstruction (anorectoplasty)—MRI is helpful in detecting complications and to evaluate muscle integrity.
Residual internal and external sphincter dis- ruptions are identified.
Megacystis-Microcolon-Intestinal Hypoperistalsis Syndrome
In the megacystis-microcolon-intestinal hypo- peristalsis syndrome the bladder is markedly distended and a contrast enema shows what ini- tially looks like a small-caliber colon. Although the initial appearance suggests an obstruction, no mechanical obstruction is found. A short- ened small bowel, at times malrotated, reveals poor or absent peristalsis. Hydronephrosis is common. Hydrometrocolpos and segmental colonic dilation also occur. Etiology of this rare autosomal-recessive disorder is unknown. Neu- ronal dysplasia is identified in some. This syn- drome also occurs without megacystis; with such a presentation it blends into the general category of functional intestinal obstruction in neonates.
The diagnosis should be considered in a newborn with a markedly distended bladder and suspected intestinal obstruction.
Meconium Plug Syndrome
Meconium plug syndrome and small left colon syndrome are probably the same entity. Dia- betes in the mother is common. These full-term neonates have colonic obstruction due to inspis- sated intestinal contents. The colonic lumen is narrowed distally and distended proximally.
An abrupt transition between dilated and nondilated bowel is evident in some.
Hirschsprung’s disease is in the differential diagnosis.
Hirschsprung’s Disease Pediatric
Hirschsprung’s disease is caused by incomplete caudal migration of neural cells, with bowel
Table 5.1. Currarino triad: anorectal malformation, sacralabnormality and presacral mass findings in 11 patients
Abnormality Number
Anorectal malformation
Low imperforate anus 3
Anorectal stenosis 8
Presacral tumor
Teratoma 7
Meningocele 2
Dermoid cyst 1
Enteric/dermoid cyst 1
Sacral and other
Deformed sacrum 11
Tethered cord 2
Source: Date from Lee et al. (32).
distal to the point of migration arrest constitut- ing an aganglionotic segment. By definition, the aganglionotic segment is continuous and extends to the anus; still, rare patients have seg- mental skip regions. Most often aganglionosis involves the rectum, but occasionally this segment extends more proximally, including the right colon, and the neonate presents with a microcolon. Also uncommon is for agangliono- sis to be limited to the internal sphincter region only. To give an example of the varied involve- ment, in one Central European hospital among 142 children treated for Hirschsprung’s disease, 52% had typical rectal involvement, 30% a long colonic segment, in 13% only a very short rectal segment was involved, and 4% suffered from total colonic aganglionosis (33).
For unknown reasons Hirschsprung’s disease is uncommon in prematures. The prevalence in boys is several times greater than in girls.
An association exists between multiple endocrine neoplasia (MEN) type IIA and Hirschsprung’s disease. Mutations in the RET proto-oncogene are found in both entities (patients with MEN type IIB also have colonic abnormalities, including chronic constipation, but any relationship with aganglionosis is not clear). Hirschsprung’s disease is more common in patients with Down syndrome. Patients with Ondine’s curse (congenital hypoventilation syndrome) and congenital neuroblastoma also develop Hirschsprung’s disease; they tend toward total colonic aganglionosis. Both Hirschsprung’s disease and ganglioneuroblas- tomas manifest aberrations of neural crest cell growth and development.
Radiologists generally perform a barium enema when suspecting Hirschsprung’s disease.
A low-osmolality water-soluble contrast enema has also been used. Although a contrast enema tends to be diagnostic in most, in neonates a transition zone is not well defined during the first several weeks of life, and a normal exami- nation does not exclude the diagnosis (Fig. 5.4).
At times uncoordinated contractions are detected in the aganglionic segment.
In total colonic aganglionosis a contrast enema reveals a microcolon or a transition zone in the small bowel, or, rarely, it is even normal.
A definitive diagnosis is made by rectal biopsy. In some infants a full-thickness biopsy is necessary. At times biopsy reveals ganglion cells in the face of an abnormal barium enema, and
in such a setting an allergic colitis should be considered in the differential diagnosis.
The usual therapy for established Hirschsprung’s disease is an initial colostomy, followed by endorectal pull-through (Soave procedure).
Adult
Occasionally a mild form of what appears to be Hirschsprung’s disease is detected in adults.
This acquired intestinal aganglionosis is often labeled adult Hirschsprung’s disease, but this term is tenuous at best. Biopsy often reveals a ganglionitis and loss of neurons. In some patients, with time, the involved segment becomes more extensive. Whether such acquired intestinal aganglionosis is indeed a variant of Hirschsprung’s disease, an allergic manifestation, or some other as yet undefined condition, is speculation.
Presentation in adults is generally similar but milder to that seen in children. It is diag- nosed with a barium enema, anorectal manom- etry, and tissue biopsy. Occasionally adult Hirschsprung’s disease mimics rectal Crohn’s
Figure 5.4. Hirschsprung’s disease. Barium enema identifies a narrowed rectum (arrows) and a dilated colon more proximally.(Courtesy of Luann Teschmacher, M.D., University of Rochester.)
disease; manometry helps distinguish between these two.
Allergic Colitis in Infancy
Allergic colitis, such as an allergy to cow milk proteins, tends to mimic the barium enema appearance of Hirschsprung’s disease. A barium enema reveals an irregular rectal narrowing and a transition zone (34); rectal biopsies identify ganglion cells and a lamina propria inflam- matory infiltrate. Symptoms resolve after diet change.
Cystic Fibrosis
Cystic fibrosis is discussed in more detail in Chapter 4. Mentioned here are findings perti- nent to the large bowel. Some authors use the term fibrosing colonopathy or severe indetermi-
nate colitis to describe colonic changes.A child with cystic fibrosis developed ascend- ing colon diverticulitis (35).
Patients with cystic fibrosis receiving large doses of pancreatic enzymes develop colonic strictures. Histologically, these strictures consist of chronic inflammation, extensive collagen deposition, submucosa fibrosis, and ulcerations.
These strictures are probably different from those seen in Crohn’s disease. Confusing the issue is that several of these patients have devel- oped an inflammatory bowel disease. Whether this indeed represents classic inflammatory bowel disease or is a sequela of cystic fibrosis and thus a separate entity is conjecture.
Abnormal barium enema findings are common in children with severe cystic fibrosis and suspected distal bowel obstruction unre- sponsive to medical management and consist of strictures, loss of haustra, and longitudinal foreshortening. Computed tomography shows bowel wall thickening, mesenteric infiltration, increased pericolonic fat, and mural striation, findings more prominent in the proximal colon.
Patients with cystic fibrosis developing
Clostridium difficile colitis do not developwatery diarrhea. Therapy for impaction and related conditions is unsatisfactory, and CT detection of a pancolitis in such a clinical setting should suggest antibiotic-associated (C.
difficile) colitis (36).
Short Colon Syndrome
In the congenital short colon syndrome the colon is either entirely or partially replaced by a dilated pouch. In the partial type some normal-appearing colon is evident between the ileum and a dilated pouch; in the complete variety the ileum inserts directly into a pouch.
Some of these infants have associated anorectal malformations and colourinary fistulas. This condition appears to be more common in northern India than in other regions.
Trauma
Perforation
Most colon perforations manifest as a pneu- moperitoneum and are readily detected. A retroperitoneal perforation, on the other hand, is more difficult to detect; at times no perfora- tion is evident initially, but an abscess or hematoma develop later.
Penetrating injuries to the colon are usually managed by a diverting colostomy, although the trend is toward primary repair.
Obstetrical Trauma
Endorectal and transvaginal US are useful to evaluate sphincter injury after childbirth trauma, although endorectal MRI appears supe- rior in establishing the site and extent of a tear;
MRI also evaluates the integrity of individual anal sphincter muscles.
Wall Thickening
An uncommon cause of colonic wall thickening, generally involving mostly right colon in other- wise asymptomatic cirrhotic patients, is conges- tion secondary to portal hypertension.
Inflammation/Infection
Detection of Colitis
Focal or diffuse colonic wall thickening is the
primary CT finding of colitis. Although such
thickening is abnormal, it is nonspecific and
occurs not only with various colitides but also
with some tumors and other infiltrative condi- tions. Similarly, the target sign (discussed in Chapter 4) is abnormal but nonspecific; it is, however, a marker for colitis and some infiltra- tive conditions but is not found with neoplasms.
The term target sign is also used by ultrasono- graphers when describing an intussusception.
Differentiating patients by clinical presentation, some investigators use the term colitis synony- mously with inflammatory bowel disease, although in a broader sense these are not the same entities.
Using criteria of mucosal thickness >1.5 mm, bowel wall thickness >4 mm, mucosal irregu- larity, absence of haustra, and terminal ileal thickness >4 mm, hydrocolonic US in ulcerative colitis and Crohn’s patients achieved 100%
sensitivity in detecting active inflammatory bowel disease and 87% in identifying disease extension (37).
Technetium-99m (Tc-99m)–hexamethyl- propyleneamine oxime (HMPAO) leukocyte scintigraphy is a noninvasive test requiring no bowel preparation and is readily performed even in ill patients. It is a sensitive test for inflammation, being positive even in a setting of normal barium studies in patients later shown to have Crohn’s disease or ulcerative colitis. In patients with acute inflammatory and infectious colitis, Tc-99m-HMPAO leukocyte scintigraphy achieves sensitivities and specificities >80% in detecting involved seg- ments. Tc-99m–2,3-dimercaptosuccinic acid (DMSA) scintigraphy reaches an overall sensi- tivity and specificity of >90% in detecting bowel inflammation (38).
18F-fluoro-deoxy-D-glucose (FDG) PET is primarily a neoplasm imaging agent, yet increased uptake is also evident in other hyper- metabolic states such as acute enterocolitis.
Inflammatory Bowel Disease General Findings
The term inflammatory bowel disease is reserved by most authors for Crohn’s disease and ulcerative colitis. The term is also used by some authors to describe a similar-appearing colitis when a specific underlying disorder is in doubt, at times prefacing the term with
nonspecific or indeterminate.Some of the infective, drug-related and ischemic colitides mimic inflammatory bowel disease in their appearance; they are classified separately once a specific etiology is established.
In particular, an etiology other than Crohn’s disease or ulcerative colitis should be sought if a previous colitis resolves. Occasionally described is a nongranulomatous ulcerative enterocolitis manifesting with severe chronic diarrhea; even after an extensive investigation, no specific diagnosis is made.
Most patients with inflammatory bowel disease have a chronic, indolent presentation.
An occasional patient, however, is first seen with an acute massive bleed or acute episode of severe colitis. Even toxic megacolon has mani- fested during an initial presentation.
A number of indices measure disease activity, but most have had limited clinical adoption. An interesting one involves use of the water-soluble radiographic contrast agent iohexol. Urinary excretion of ingested iohexol is significantly higher in patients with active inflammatory bowel disease than in those with quiescent disease or in controls (39).
Several studies have documented a lower seroprevalence of Helicobacter pylori infection in patients with Crohn’s disease and ulcerative colitis than in controls.
Inflammatory bowel disease is not limited to the bowel, but also involves hepatobiliary, mus- culoskeletal, ocular, dermatologic, and other organ systems. A possible association with glycogen storage disease type IB exists. An asso- ciation exists between inflammatory bowel disease and sclerosing cholangitis and cholan- giocarcinoma, although a relationship between colonic and bile duct disease activity is not straightforward; after liver transplantation for sclerosing cholangitis, inflammatory bowel disease can be reactivated despite maintenance immunosuppression. Likewise, colon carcinoma has developed after liver transplantation. Thus serial colon cancer screening is necessary after liver transplantation.
Pathologic Findings
The presence of crypt abnormalities, basal
plasmacytosis with chronic inflammation, and
distal Paneth cell metaplasia point toward
inflammatory bowel disease rather than other
colitides. Thr histology of a colorectal biopsy
suggests Crohn’s disease if epithelial granulo- mas, microgranulomas, or isolated giant cells are detected; these findings, however, are often lacking from biopsies of patients with obvious Crohn’s disease. In some patients a diagnosis of indeterminate colitis is appropriate.
Biopsy in ulcerative colitis reveals an irregu- lar or villous surface, a decrease in mucous content, and crypt atrophy. Initially diffuse small ulcers develop surrounded by inflamma- tion and hyperemia. With disease progression the bowel wall thickens and lumen narrows. The muscularis mucosa thickens markedly and fore- shortens, leading to shortening of colonic length. In distinction to Crohn’s disease, a vas- culitis is uncommon in ulcerative colitis. A transmural lymphocytic phlebitis, however, is detected in some patients.
Postinflammatory polyps, also called pseudopolyps, are a common finding in ulcera- tive colitis, although they also develop in a number of other colitides, including some infec- tions. With partial healing the overlying mucosa becomes hyperplastic. In some patients these polyps become sufficiently large and extensive to obstruct bowel lumen. These polyps can cause a protein-losing enteropathy.
Differential Diagnosis Clinical
Although in most patients differentiation between Crohn’s disease and ulcerative colitis is straightforward, in a small subset radiologic studies, colonoscopy, and biopsy do not differ- entiate with any degree of certainty between these two entities. An attempt at differentiation using serologic testing has had rather limited success. Intestinal mucosal lymphocytes iso- lated mostly from lamina propria contain higher levels of CD19, transferrin receptor, T- cell receptors alpha/beta, and T-cell receptors gamma/delta in ulcerative colitis patients than in Crohn’s patients (40); the clinical significance of these findings is not clear.
In a vast majority of patients ulcerative colitis extends from the rectum proximally for varying lengths, with a pancolitis found in a minority.
Skip areas are not found, and in a setting of a right-sided colitis with rectal sparing ulcerative colitis should not be in the differential diagno-
sis. Nevertheless, it is difficult to place some patients in the proper perspective. For instance, a clinical, radiographic, endoscopic, and histo- logic follow-up in a patient with right-sided colitis consisting of multiple shallow ulcers, erosion, and stenoses and sparing of the rectum and left colon appeared to exclude Crohn’s disease, tuberculosis, yersiniosis, Behçet’s disease, and ischemic colitis (41); the authors concluded that the patient was indeed suffering from right-sided ulcerative colitis.
Toxic megacolon is generally associated with ulcerative colitis, on rare occasions even being an initial manifestation of this disease.
One should keep in mind, however, that toxic megacolon is also encountered in severe acute Crohn’s disease and some infectious colitides.
Imaging
The role of double-contrast barium enema and colonoscopy in diagnosing both Crohn’s disease and ulcerative colitis is well established. A number of studies have concluded that the double-contrast barium enema and colono- scopy are complementary imaging modalities for optimal detection of all mucosal and struc- tural colonic lesions, with the exception of those that do not distort the mucosa.
The terminal ileum is often involved in Crohn’s disease but is spared in ulcerative colitis (with the exception of backwash ileitis). The barium enema appearances of terminal ileal Crohn’s disease and backwash ileitis are quite different, and radiologists readily differentiate these entities.
In Crohn’s disease CT identifies thickening of diseased bowel in most patients, and in the acute phase such thickening is universal. The bowel wall has a homogeneous appearance in Crohn’s disease, but in ulcerative colitis it ranges from homogeneous to a target sign (discussed in Chapter 4). The outer colonic contour tends to be smooth in severe ulcerative colitis; in Crohn’s disease it can be either smooth or irregular.
Rectal involvement results in presacral space
widening and is found both with Crohn’s proc-
titis and ulcerative colitis. Computed tomogra-
phy shows this widening to be mostly secondary
to infiltration by fat-containing linear and
nodular soft tissue densities.
In young adults with chronic abdominal pain and bowel dysfunction, some authors establish an arbitrary upper normal US bowel wall thick- ness, with inflammatory bowel disease sug- gested if this thickness is exceeded. Thus in consecutive outpatients, use of a 7-mm upper normal bowel wall thickness achieved a sensi- tivity of 74% and specificity of 98% in suggest- ing inflammatory bowel disease (42); these findings could be further subdivided into an 84% sensitivity and 98% specificity for Crohn’s disease and 38% and 98%, respectively, for ulcerative colitis.
After distending the large bowel with water (hydrocolonic US), US normally differentiates five wall layers having different echogenicities.
The colonic wall is hypoechoic and thickened, and these five colonic wall layers cannot be visu- alized in most Crohn’s disease patients, but they tend to be preserved in ulcerative colitis; loss of this layer stratification is due to fibrosis and implies an irreversible change.
Postcontrast MR in colonic Crohn’s disease reveals transmural bowel wall enhancement, a finding distinct from typical ulcerative colitis where enhancement is limited to the mucosa and MRI identifies less bowel wall thickening.
Thus after lumen distention with oral and rectal fluid, pre– and post–gadolinium (Gd)–diethyl- enetriamine pentaacetic acid (DTPA) HASTE and dynamic fast low-angle shot (FLASH) axial and coronal images allowed differentiation of Crohn’s disease and ulcerative colitis in 81% of 27 patients with inflammatory bowel disease (43). Low-field MRI (0.1 T) tends to overestimate and underestimate disease extension both in Crohn’s patients and in ulcerative colitis patients.
Although Tc-99m-HMPAO–white blood cell scintigraphy is very sensitive and specific in detecting colonic inflammation (44), it has a limited role in differentiating active colonic Crohn’s disease from ulcerative colitis. Discon- tinuous uptake suggests Crohn’s disease, but some children with ulcerative colitis also have discontinuous uptake.
Crohn’s Disease Clinical
Crohn’s disease is discussed in more detail in Chapter 4. Covered here are those aspects related to the colon (Crohn’s colitis). Although
Crohn’s disease is most often found in the distal small bowel, disease confined to the colon and rectum is not uncommon. A later age of disease onset appears related to an increased prevalence of colorectal rather than small bowel involvement.
In a retrospective cohort study of patients with colorectal Crohn’s disease, distribution was segmental in 40%, total in 31%, and left-sided in 26% (45); perianal or rectal fistulas developed in 37%. In those patients attaining clinical remis- sion, the 5-year cumulative relapse rate was 67%. Half of these patients underwent a resec- tion within the first 10 years, and half of these ultimately required an ileostomy. Analysis of the cause of death of patients with Crohn’s disease during 1973 to 1980 in Rochester, New York, found that Crohn’s disease was the causative factor in 44% of deaths, but during 1981 to 1989 deaths due to Crohn’s disease decreased to 6%
(46).
Imaging
Early colonic manifestations of Crohn’s disease consist of lymph follicle prominence and pres- ence of aphthae. These are readily detected with a double-contrast barium enema but are not visualized with CT. The presence of aphthae implies active colitis but is not pathognomonic of Crohn’s disease (Fig. 5.5); lymphoid hyper-
Figure 5.5. Cecal Behçet’s disease. Aphthae are scattered throughout. Crohn’s disease has a similar appearance.
plasia, on the other hand, exists without disease activity.
Progression of inflammation leads to filiform polyposis and diffuse intramural thickening (Fig. 5.6). With established disease, the presence of homogeneously thickened bowel wall during an arterial phase CT study generally implies the presence of fibrosis.
Magnetic resonance imaging is very accurate in detecting active Crohn’s colitis (Fig. 5.7).After oral bowel opacification with a 2.5% mannitol solution, axial and coronal breath-hold MRI using contrast-enhanced T-1 weighted FLASH and T2-weighted HASTE sequences identified more diseased segments than comparable barium studies (47). Current evidence suggests that a hydro-MRI study is very reliable in both
detecting and evaluating the extent of Crohn’s disease.
Some authors suggest that specific imaging findings can suggest whether a particular stage of Crohn’s disease is reversible or not. Thus presence of a target sign suggests that fibrosis has not yet developed and the underlying abnormalities are reversible with appropriate therapy. Whether this is indeed so remains to be proven.
Complications
The earlier literature rarely mentioned cancer developing in a setting of Crohn’s disease. Some of these publications should be held suspect because a number of these patients were misdi- agnosed. More recent publications document an increased incidence of cancer in bowel involved by Crohn’s disease. Typically the interval from initial Crohn’s diagnosis until cancer is detected is up to 20 years. Some cancers are multiple.
They have developed in a defunctionalized rectal stump. An occasional one involves a Crohn’s-induced anorectal sinus tract or fistula.
Patients with inflammatory bowel disease (both Crohn’s disease and ulcerative colitis) tend to develop a diffusely infiltrating and metastasizing carcinoma, called linitis plastica of the colon. Most of these are adenocarcino- mas. Radiologically, these cancers tend to mimic a benign stricture, and at times even a biopsy is nondiagnostic.
Anal fissures and low anal fistulas are common in Crohn’s disease and tend to be asso- ciated with an adjacent phlegmon or abscess.
Most sinus tracts and fistulas in a setting of Crohn’s colitis end blindly or are enteroenteric;
an occasional fistula extends to an unusual
Figure 5.6. Crohn’s disease. Extensive filiform polyposis ispresent. (Courtesy of Arunas Gasparaitis, M.D., University of Chicago.)
Figure 5.7. Comparison of MR HASTE sequences (A) and contrast-enhanced GRE sequences (B) of bowel segment involved with Crohn’s disease. (Courtesy of Wolfgang Luboldt, M.D., Johann Wolfgang Goethe University, Frankfurt-am-Main.)
A B
