Diffuse Extraperitoneal

Radiologic localization of diffuse extraperitoneal gas to a specific compartment is greatly advanced by anatomic knowledge gained from careful study of body sections, postmortem injections, and retroperitoneal pneumog-raphy.9 Fascial boundaries and tissue planes direct the spread and localization of extraperitoneal gas, depending on its source.

In presacral pneumography, if the needle is inserted in the midline behind the rectum, the gas ordinarily rises symmetrically up both sides.13 While the kidneys and adrenal glands are shown with striking clarity, much of the extraperitoneal gas is outside the perirenal space. A considerable part undoubtedly enters this compartment through its inferior communication with the iliac fossa, but there is also significant distribution into the posterior pararenal space in particular, outlining the contours of the liver, spleen, upper poles of the kidneys, medial crura of the diaphragm, and subphrenic extraperitoneal tissues (Fig. 8-210). Furthermore, because of the fusion of the renal fascial layers with the diaphragm superiorly, perirenal gas alone does not lead to pneumomedias-tinum and cervical emphysema, whereas gas in the posterior pararenal compartment frequently does.

Flank Stripe

Fig. 8—208. Posterior pararenal lymphatic extravasation in a child presenting with a cystic flank mass.

(a) Lymphangiogram. Extravasated droplets of contrast material extend laterally toward flank mass. At this site, flank-stripe fat is discretely lost and is maintained only in segments bordering the lymphocyst (arrows). The posterior collection also causes loss of visualization of the hepatic angle.

(b) Lateral projection documents the extreme posterior extravasation (arrows).

(c) Later film shows that with further extravasation into the enlarged mass all of the flank fat is effaced. (Reproduced from Meyers et al.12)

Fig. 8—208. Posterior pararenal lymphatic extravasation in a child presenting with a cystic flank mass.

(a) Lymphangiogram. Extravasated droplets of contrast material extend laterally toward flank mass. At this site, flank-stripe fat is discretely lost and is maintained only in segments bordering the lymphocyst (arrows). The posterior collection also causes loss of visualization of the hepatic angle.

(b) Lateral projection documents the extreme posterior extravasation (arrows).

(c) Later film shows that with further extravasation into the enlarged mass all of the flank fat is effaced. (Reproduced from Meyers et al.12)

It is also apparent that extraperitoneal gas is not truly fixed in position but retains some mobility through the tissues. This is demonstrable clinically by the changeable distribution between supine and erect films (Figs. 8-211 and 8-212).

The general extraperitoneal region can be thought of as Y-shaped in the frontal and lateral planes of the body. In an anteroposterior plane, continuity from the pelvis extends to both sides. It appears that extraperitoneal gaseous extravasation originating from disease processes in the pelvis or at the level of the iliac fossa does not typically enter the perirenal space; rather, it extends into the anterior and posterior pararenal spaces, presumably because the inferior apex of the cone of renal fascia is rapidly sealed off by associated inflammatory adhesions. Figure 8-213 illustrates an example of lateral leak from acute rectal perforation leading to extraperitoneal gas identifiable in each of the three spaces.

These considerations provide a rationale for the observation that bilateral spread of gas through the extra-peritoneal tissue planes originates most often in the pelvic region. Extraperitoneal gas arising in the upper abdomen does not generally descend enough to cross over the midline to the opposite side at the level of the lumbosacral junction. An exception to unilateral confinement in the upper abdomen has been seen in gas-producing pancreatitis, presumably by virtue of the digestive enzymes involved. Extraperitoneal gas originating in and confined to the left upper quadrant is rare but may follow a perforated carcinoma or diverticulitis of the proximal descending colon or an abscess of the tail of the pancreas. If both intraperitoneal and extra-

Fig. 8-209. Posterior pararenal development of reticulum cell sarcoma.

(a) Excretory urogram, oblique projection. Large circumscribed mass displaces the right ureter and the lower pole of the right kidney anteriorly. Obstructive hydronephrosis is present.

(b) Nephrotomogram. The sarcomatous mass (M) results in loss of visualization of the lower psoas segment and lateral displacement of the lower renal pole. The perirenal fat and upper psoas segment are intact. These changes localize the lymphoma to the posterior pararenal space.

Fig. 8-209. Posterior pararenal development of reticulum cell sarcoma.

(a) Excretory urogram, oblique projection. Large circumscribed mass displaces the right ureter and the lower pole of the right kidney anteriorly. Obstructive hydronephrosis is present.

(b) Nephrotomogram. The sarcomatous mass (M) results in loss of visualization of the lower psoas segment and lateral displacement of the lower renal pole. The perirenal fat and upper psoas segment are intact. These changes localize the lymphoma to the posterior pararenal space.

Fig. 8-210. Posterior pararenal fat (PeF).

This provides contrast to the medial crus (small arrows) and inferior margin (large arrow) of the diaphragm, and to the postero-medial border of the spleen (Sp) S = stomach; L = liver; Ao = aorta.

Medial Border The SpleenPosition Diaphragm When Erect

Fig. 8—211. Rectal perforation.

Supine and erect films demonstrate extraperitoneal gas paralleling the lateral borders of the psoas muscles (arrows). Cephalad extension on the left outlines the upper pole of the kidney, the adrenal gland, the medial border of the spleen, the medial crus of the diaphragm, and the immediate subphrenic tissues (crossed arrows). These findings localize the gas to the posterior pararenal compartments. The suprarenal and subphrenic gas collection increases in the erect position. (Reproduced from Meyers.9)

Fig. 8—211. Rectal perforation.

Supine and erect films demonstrate extraperitoneal gas paralleling the lateral borders of the psoas muscles (arrows). Cephalad extension on the left outlines the upper pole of the kidney, the adrenal gland, the medial border of the spleen, the medial crus of the diaphragm, and the immediate subphrenic tissues (crossed arrows). These findings localize the gas to the posterior pararenal compartments. The suprarenal and subphrenic gas collection increases in the erect position. (Reproduced from Meyers.9)

peritoneal gas are present, it can be confidently assumed that the source is a perforation of an extraperitoneal structure that has broken through the posterior parietal peritoneum268 (Fig. 8-213b,c).

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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