The extraperitoneal perivisceral fat pad. II. Roentgen interpretation of pathological alterations.

Abstract

THE PURPOSE of this paper is to describe the roentgen manifestations of alterations of the normal anatomy of the extraperitoneal perivisceral fat pad and to emphasize that both intra- and extraperitoneal pathologic processes can affect the e. p. f. p. Intraperitoneal Disease A. Fluid: Intraperitoneal fluid in the upper abdomen frequently manifests itself radiologically by collecting adjacent to the properitoneal fat line as a linear density, displacing the colon medially and thinning the properitoneal fat. This shadow has been called the “flank stripe” (5). In addition, the medial margin of the “hepatic angle” may be lost (Fig. 1). What is the explanation for the loss of the hepatic angle by intraperitoneal fluid if the shadow of the hepatic angle is cast by the liver's contrasting with extraperitoneal Iat?3 The great pliability of the e. p. f. p. explains this finding. The intraperitoneal fluid fills the peritoneal recess about the posterior inferior portions of the liver, widening and blunting it. The fluid also displaces the liver medially and anteriorly. The pliable e. p. f. p. which encases this medial portion of the hepatic angle is thinned and flattened (similarly to the properitoneal fat line) by the combined fluid and liver in the peritoneal recess. The resultant anterior-posterior soft-tissue-fat interface disappears, rendering the hepatic angle invisible to the roentgen ray (Figure 2). A similar explanation applies to the loss of the splenic angle with intraperitoneal fluid. B. Mass: Intraperitoneal masses which significantly indent the e. p. f. p. may be visualized on plain supine films. These masses are located posteriorly in the peritoneum (Fig. 3). Anteriorly situated intraperitoneal masses are notoriously difficult to visualize except as they displace gas-containing portions of the gastrointestinal tract. The difficulty in demonstrating hydrops of the gallbladder on plain films is an example of this. Extraperitoneal Disease A. Fluid: Extraperitoneal fluid infiltrates the e. p. f. p. and by increasing the fat's density negates its contrast, causing loss of the normal shadows. The obliteration of the psoas and renal shadows by extraperitoneal fluid are well known radiological signs. Less well known manifestations of extraperitoneal fluid should, however, be emphasized. Extraperitoneal fluid in the posterior right upper quadrant may dissect superiorly and laterally. It can obliterate the hepatic angle by infiltrating the properitoneal fat laterally and, medially, the e. p. f. p. which juxtaposes the medial inferior border of the liver angle (Fig. 4). In addition, when the fluid is loculated in the perirenal space medial to the lateroconal fascia and without extension into the pararenal space, the hepatic angle can be lost, even though the properitoneal fat line is intact.