The Retroperitoneal Space
The kidneys have been described in Chap. 9.
Abdominal Aorta
Abdominal aortic analysis should be routine in any critical situation. The examination should be done gently, in order to avoid any uncontrolled pressure. Bowel gas can be a source of failure. How- ever, a left translumbar approach can bypass the anterior gas obstacles.
Basic signs of abdominal aortic aneurysm are a loss of parallelism of the aorta walls with a fusiform or sometimes sacciform shape (Fig. 10.1).
If local conditions are favorable, ultrasound will provide, like CT, a global overview of the lumen, thrombosis, wall thickness (increased in the case of inflammation) and collateral vessels. In the case of leakage, a collection will be found in the left retroperitoneal space (Fig. 10.2). In one rare case, it was possible to observe a precise area of whirling in rhythm with heart frequency, within the hemat- ic effusion. This dynamic pattern obviously indi- cated the location of the leakage. This observation was serendipitous, and indicated extremely urgent surgery.
Fortuitous discovery of incipient aneurysm is frequent in the medical ICU and should prompt further investigations. An atherosclerotic aorta with irregular borders is a sign indicating that the patient may have diffuse potential arterial damage.
A dissection of the abdominal aorta yields enlarged lumen with an intimal flap separating two channels.When the aorta can be followed to its bifurcation, the progressive disappearance of one channel can be noted (Fig. 10.3).
CHAPTER 10
Fig. 10.1. a Transverse scan of the epigastric area. The aorta is recognized by its location anterior to the rachis (R), at the left of the inferior vena cava (V). A substantial enlargement of its caliper is immediately noted. There is a large thrombosis within the aneurysm, with a tissue- like peripheral layer and quasi-normal caliper of the lumen. A simple aortography would obviously unde- restimate this aneurysm. b Longitudinal scan, specify- ing the extension of the aneurysm
a
b
Other Information Available from Abdominal Aorta Study
For maximal use of the full potential of noninva- sive ultrasound, it may be of interest to investigate the aortic caliper in patients in shock.
One hypothesis is that this caliper diminishes when there is vasoconstriction. We know that in case of vasoparalysis, only arteriolar resistances
can be altered. However, early findings indicate that the large-vessel caliper can also be variable (Fig. 10.4). The aorta should be supple, not athero- matous. The measurement is taken at a precise and therefore reproducible level. We propose crossing with the left renal vein.
Retroperitoneal Hematoma and Other Disorders
Ultrasound finds a generally voluminous mass, heterogeneous, with often a dependent zone that is rather echoic, corresponding to blood clots, and a nondependent area that is rather poorly echoic, corresponding to the serum. This area can be rich in septations due to fibrin deposits (Fig. 10.2). It is possible to follow this hematoma up to the inser- tion of the psoas muscle. However, we must admit that subtle signs are rarely required in often plethoric patients. Peritoneal blood effusion can be associated with contiguity and should not be misleading.
A posterior translumbar approach is logical, but an extensive hematoma generally comes in contact with the anterior abdominal wall (clinically detectable). The differential diagnosis with a pari- etal hematoma, whose treatment is different, will be resolved by studying the linking angles.
When a superinfection is suspected, an ex- ploratory, ultrasound-guided tap is possible.
Pneumoretroperitoneum should theoretically yield a characteristic image, since air stops the ultrasound beam.
Retroperitoneal Hematoma and Other Disorders 63
Fig. 10.2. Patient in shock with abdominal pain. Huge echoic heterogeneous roughly rounded mass with an- terior contact (transversal scan, left flank approach).
Acute retroperitoneal hematoma, with early clotting
Fig. 10.3. Epigastric transversal view in a patient in shock with thoracoabdominal pain. Throughout the liver and at the left of the inferior vena cava (V), the abdominal aorta is clearly visible. It is possible to detect a flap (arrow, which was positioned at the level of the true channel) separating the aortic lumen into two parts. When the probe moves downward, the superior channel (false channel) progressively vanishes
Fig. 10.4. The caliper of the abdominal aorta in this young female in shock appears extremely low (9 mm). It may correspond to major vasoconstriction or hypovolemia.
Epigastric transverse scan. V, inferior vena cava; R, rachis
Inferior Vena Cava
The inferior vena cava is studied in Chap. 13.
Pancreas
Precisely localized using the vascular landmarks (see Fig.4.6,p 21),the pancreas can be hard to detect since there is a frequent reflex ileus [1]. However, gas collections can be mobilized, and the stomach
can be filled with liquid in order to create an acoustic window. In favorable cases, the study is contributive, and the main pancreatic duct and all the bile ducts can be studied (Fig. 10.5). Maximal dimensions of a normal pancreas are 35 mm at the head, 25 mm at the isthmus and 30 mm at the body [2].
Acute pancreatitis is a familiar field in radiolo- gy [3]. The organ has increased in size, with a hypoechoic heterogeneous pattern. Necrotic roads can be observed in the pancreatic space (Fig. 10.6) but are also very remote. In some instances, the pancreas can have a normal pattern [4].
CT is usually indicated in first-line investiga- tions for the positive diagnosis of acute pancre- atitis, since gases are not a hindrance, and a regional and remote analysis is easy to do. Ultra- sound is used for monitoring after an initial CT.
Iterative ultrasound scans detect the appearance of fluid within the pancreas, surrounding it, or from a distance. Venous thrombosis (splenic or superior mesenteric veins) is accessible (see p 38, Chap. 6). The constitution of false aneurysms (mainly the superior mesenteric artery) can be monitored.
The appearance of a collection (whose echo- genicity can be variable) can be caused by simple necrosis or infectious abscess (Fig. 10.7). Ultra- sound can answer the question by tapping the collection, provided there is no bowel or vascular interposition. One disorder must be ruled out before any tap: false aneurysm. Doppler is usually able to answer this question, but if two-dimension- al ultrasound identifies dynamic changes within 64 Chapter 10 The Retroperitoneal Space
Fig. 10.5. In this transverse epigastric scan, the pancre- atic parenchyma is perfectly identified, homogeneous, with a well-defined main pancreatic duct (arrows), end of the common bile duct (M) and confluence of the portal and mesenteric superior veins (V). Normal pan- creas
Fig. 10.6. Hemorrhagic necrotizing acute pancreatitis.
The head and body of the pancreas are enlarged (ar- rows) and heterogeneous. A hypoechoic image can be distinguished within the head (M), and a collection sur- rounding the pancreatic space, anterior to the body (asterisk). A, aorta; a, superior mesenteric artery; V, inferior vena cava, v, splenic vein. Transverse scan
Fig. 10.7. Hemorrhagic necrotizing acute pancreatitis, transverse scan. The pancreas can be identified only using the vascular landmarks. Numerous hypoechoic collections along the head (m) and the body (M)
the collection, it can also answer the question:
slow, nonsystematized particle movements can be safely tapped. Whirling systolic movements, when visible, clearly indicate false aneurysm. An exploratory tap with thin material is easy and dis- tinguishes abscess from necrosis. An evacuation procedure requires large, invasive material since the collection can contain large debris. Some authors recommend surgery for central collec- tions, and percutaneous procedures for peripheral ones [5].
A pancreatic pseudocyst produces a well- defined, anechoic image with a thin regular wall.
The size is often substantial. Dependent echoes suggest superinfection.
Vertebral Disks
The rachis, which is the posterior limit of the retroperitoneum, stops the ultrasound beam.
However, ultrasound can go through interverte- bral disks. It is then possible to analyze unusual structures such as the content of the spinal canal (Fig. 10.8).We have not given this analysis a partic- ular relevance (should meningitis yield a particu- lar pattern?), but Fig. 10.8 is a striking example of the still untapped features of ultrasound.
References
1. Silverstein W, Isckoff MB, Hill MC, Barkin J (1981) Diagnostic imaging of acute pancreatitis: prospec- tive study using computed tomography and sonogra- phy. Am J Roentgenol 137:497
2. Weill FS (1985) Pathologie pancréatique. In: Weill FS (ed) L’ultrasonographie en pathologie digestive.
Vigot, Paris, pp 345–375
3. Freeny P, Lawson TL (1982) Imaging of the pancreas.
Springer Verlag, Berlin Heidelberg New York 4. Lawson TL (1978) Sensitivity of pancreatic ultraso-
nography in the detection of pancreatic disease.
Radiology 128:733
5. Lee MJ, Rattner DW, Legemate DA, Saini S, Dawson SL, Hahn PF, Warshaw AL, Mueller PR (1992) Acute complicated pancreatitis: redefining the role of inter- ventional radiology. Radiology 183:171–174
References 65
Fig. 10.8. This ghostly apparition seemingly observing the viewer, here intended to relax the reader, shows how well ultrasound can perform. In this transverse scan passing through an intervertebral disk, the spinal canal and the intervertebral foramen are well defined, form- ing the nose and eyes of the creature. Depending on one’s imagination, a gorilla in the mist or one of the main characters from the »Star Wars« movies may be- come visible
