Intraperitoneal fluid consistently seeks the pouch of Douglas, the most caudal and posterior part of the peritoneal cavity, and then the lateral paravesical recesses (Fig. 4-106). The lower extension of the peritoneal reflections, comprising the pouch of Douglas, projects generally at the level of the lower second to upper fourth sacral segment (Fig. 4-107). This variability is determined by the developmental fixation of the peritoneum to Denonvillier's fascia (rectovaginal or rectovesical septum) and the degree to which the urinary bladder and rectum are distended.99 It is a particularly useful land-
mark, demarcating the junction between the rectum and sigmoid colon. Thus, it is apparent that the ventral surface of the rectosigmoid junction faces the pouch of Douglas.
Seeding at this site is most common. On barium enema study, this results in a characteristic pattern of fixed parallel folds or a nodular indentation on the anterior aspect of the rectosigmoid junction3,100 (Figs. 4-108
Fig. 4-108. Different cases of metastatic seeding in the pouch of Douglas.
Associated desmoplastic response characteristically results in (a) fixed transverse parallel folds, (b) nodular mass, or (c) mass with mucosal tethering along the ventral aspect of the rectosigmoid junction. The primary tumors were (a) carcinoma of the ovary, (b) carcinoma of the pancreas, and (c) carcinoma of the stomach.
(Reproduced from Meyers and McSweeney.1)
through 4-110). These changes reflect the coalescence of deposits with a dense fibrous reaction. This may be clinically palpable as the classic Blumer's shelf.99,101 It is thought that the factor essential to the development of a rectal shelf tumor is pathologic fixation of the uppermost part of Denonvillier's fascia.99 Sectional imaging readily demonstrates seeding as this site (Figs. 4-111 and 4-112). The nodular impression on the ventral aspect of the rectosigmoid junction from seeding in the pouch of Douglas may be duplicated by endometriosis, peri-proctitis, tumors, inflammation of the seminal vesicles, 99,100 or postirradiation changes. The presence of as-cites, however, indicates these findings as part of peritoneal carcinomatosis.
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