Extraperitoneal Gas of Supradiaphragmatic Origin

Gas arising above the diaphragm may pass down the mediastinum through the diaphragmatic hiati and directly into the posterior pararenal space. If the gas gains entrance to structures of the chest wall, its extension to the extraperitoneal tissues of the abdomen may pursue a characteristic course. The endothoracic fascia of the chest is continuous with the transversalis fascia of

Rectal Perforation

Fig. 8—213. Extraperitoneal gas in all three spaces secondary to rectal perforation from colonoscopic polypectomy.

(a) CT scan shows gas in the perirectal and presacral space following rectal perforation (arrows). R = rectum.

(b) Extraperitoneal gas is noted in the retrocecal area (arrows) and around the right iliac vessels (arrowheads). P = pneumoperitoneum, most likely secondary to perforation of the posterior parietal peritoneum.

(c) Gas is evident in the perirenal space outlining the right kidney (RK) and ureter (arrow) and in the posterior pararenal space. There is dissection of the properitoneal fat with subcutaneous emphysema developing in the region of the superior lumbar triangle (arrowhead). P = pneumoperitoneum.

(d) Scan through the liver shows anterior pararenal space gas outlining the superior coronary ligament (arrow), bare area of the liver (arrowheads), and inferior vena cava (JVC). Retrocrural gas spreads to the mediastinum.

(Reproduced from Nguyen and Beckman.267)

Fig. 8—213. Extraperitoneal gas in all three spaces secondary to rectal perforation from colonoscopic polypectomy.

(a) CT scan shows gas in the perirectal and presacral space following rectal perforation (arrows). R = rectum.

(b) Extraperitoneal gas is noted in the retrocecal area (arrows) and around the right iliac vessels (arrowheads). P = pneumoperitoneum, most likely secondary to perforation of the posterior parietal peritoneum.

(c) Gas is evident in the perirenal space outlining the right kidney (RK) and ureter (arrow) and in the posterior pararenal space. There is dissection of the properitoneal fat with subcutaneous emphysema developing in the region of the superior lumbar triangle (arrowhead). P = pneumoperitoneum.

(d) Scan through the liver shows anterior pararenal space gas outlining the superior coronary ligament (arrow), bare area of the liver (arrowheads), and inferior vena cava (JVC). Retrocrural gas spreads to the mediastinum.

(Reproduced from Nguyen and Beckman.267)

Fig. 8-214. Rectal perforation.

Bilateral gas in the posterior pararenal compartments outlines the complete lateral borders of the psoas muscles (arrows) and the upper poles of the kidneys and immediate subphrenic tissues.

Anterior Left Subphrenic

Fig. 8-215. Relationships and structures of the three extraperitoneal spaces on the left.

The sigmoid colon is in continuity with the posterior and anterior pararenal compartments. L = liver; P = pancreas; K = kidney; C = colon. (Reproduced from Meyers.8)

Fig. 8-214. Rectal perforation.

Bilateral gas in the posterior pararenal compartments outlines the complete lateral borders of the psoas muscles (arrows) and the upper poles of the kidneys and immediate subphrenic tissues.

Fig. 8-215. Relationships and structures of the three extraperitoneal spaces on the left.

The sigmoid colon is in continuity with the posterior and anterior pararenal compartments. L = liver; P = pancreas; K = kidney; C = colon. (Reproduced from Meyers.8)

Fig. 8-216. Perforated sigmoid diverticulitis.

CT displays gas in the posterior and anterior pararenal spaces on the left, enveloping the cone of the renal fascia.

Sigmoid Mesocolon Cat

Fig. 8—217. Sigmoid perforation into mesocolon.

CT scans, imaged with wide window settings, demonstrate in the pelvis (a) that gas has dissected between the leaves of the sigmoid mesocolon (arrows) and at the level of the kidneys (b) the gas has arisen bilaterally in the anterior pararenal spaces (arrows), outlining the aorta (A) and inferior vena cava (C).

(Courtesy of Michiel Feldberg, M.D., University of Utrecht, The Netherlands.)

Fig. 8—217. Sigmoid perforation into mesocolon.

CT scans, imaged with wide window settings, demonstrate in the pelvis (a) that gas has dissected between the leaves of the sigmoid mesocolon (arrows) and at the level of the kidneys (b) the gas has arisen bilaterally in the anterior pararenal spaces (arrows), outlining the aorta (A) and inferior vena cava (C).

(Courtesy of Michiel Feldberg, M.D., University of Utrecht, The Netherlands.)

the abdomen. Gas originating in the chest or even in the neck may pass deep to the endothoracic fascia, external to the parietal pleura, and continue directly into

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the abdominal wall. The lucencies may then extend preferentially within the flank fat (Fig. 8-218), although some gas may be seen in the deeper portions of the posterior pararenal compartment. Rarely, gas has been noted to dissect inferiorly as scrotal subcutaneous emphysema.273

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