Vascular dilatation in the pelvis: identification with CT and MR imaging.

Focal or diffuse dilatation of pelvic vessels is observed occasionally on computed tomographic or magnetic resonance images. Two major mechanisms may account for dilatation. The first mechanism is development of collateral channels as a result of venous obstruction or stenosis. Symptoms associated with vessel dilatation vary according to the level of obstruction. Portal hypertension also may result in the formation of numerous collateral vessels. In addition, left renal venous compression between the aorta and the superior mesenteric artery, which results in blood flow from the left renal vein toward the left gonadal vein, causes a variety of symptoms. The second major mechanism for dilatation is increased blood flow through collateral vessels associated with a neoplasm or vascular lesion. Hypervascular pelvic tumors such as uterine leiomyomas, gestational trophoblastic neoplasms, ovarian solid tumors, and mesenteric tumors may be associated with a marked increase in the number of draining vessels. The assessment of such vessels can assist in identification of tumor origins. Visual recognition of abnormal pelvic vasculature and abnormal hemodynamics is clinically important because it helps to improve diagnosis of a wide variety of pelvic and systemic diseases. Moreover, recognition of abnormal hemodynamics facilitates understanding of the physiology of such conditions. Recognition of the pattern of collateral channels also assists in identification of the level of narrowing even when the level is not readily apparent and is dependent on postural position.