Arteriovenous malformation of the bladder presenting as gross hematuria.

Arteriovenous malformation, in which direct communication is present between arterioles and venules, are reflected histologically by abrupt changes in the thickness of the medial and elastin layers of the vessels. Another result of the lack of the interposed capillary bed is abnormal dilation and, often, advanced small vessel disease, which is due to the increased intravascular pressures as well as to the basic defects in the blood vessel walls. The diversion of arterial flow and small vessel disease may lead to ischemia, which is postulated to stimulate proliferation of the vascular channels in these lesions. Hence, they tend to grow slowly with time. The ischemia, increased pressure, and small vessel disease predispose to ulceration and hemorrhage, which is a common mode of presentation for these lesions. Common sites for arteriovenous malformations are the intestine, central nervous system, lungs, and extremities. The lesion has not been reported in the urinary bladder. The present case of massive hematuria was found at autopsy to be due to an arteriovenous malformation of the bladder neck.