Microvascular architecture of the human urinary bladder wall: A corrosion casting study

The vascular system of the urinary bladder wall effectively performs its fu nction in spite of considerable spatial changes due to the filling/voiding cycle. However, only a few studies have dealt with the microvascular archit ecture of the bladder wall and only two, using old-fashioned techniques, we re devoted to the human bladder. This study presents the microvasculature o f the human bladder wall visualized by scanning electron microscopy of vasc ular corrosion casts. Postoperative bladder specimens obtained. from patients with advanced bladd er tumors were filled with small amount (80 ml) of saline and perfused via at least four largest arteries with anticoagulant-containing saline followe d by paraformaldehyde/glutaraldehyde fixative and Mercer resin. After polym erization of the resin, the vascular casts were macerated with potassium hy droxide, cleaned with formic acid and water and freeze dried. Only regions of the bladder wall distant to the tumor were examined in light and scannin g electron microscopes. The almost empty state of the bladder was manifested by extensive folding o f the mucosa and tortuosity of almost all vessels other than capillaries. T he branches of main arteries and veins formed an adventitial/ serosal plexu s which directly supplied/drained the capillary network of the muscularis a nd sent long perpendicular vessels to the mucosal plexus. These vessels had straight or coiled course depending on whether they terminated at the top or at the base of the mucosal folds. The rich mucosal plexus followed the f olds parallel to their surface and gave off short, straight, mostly perpend icular twigs communicating with the subepithelial capillary network. Apart from very few vascular interconnections between the mucosal plexus and the muscularis, the submucosa was generally avascular. The subepithelial capill ary network showed extreme density and uneven contours of the capillaries, only in less folded areas of trigone and urethral orifice the network was l ooser and capillaries thinner. The capillary system of the muscularis was p oorly developed. Due to its architecture, tortuosity, and coiling/uncoiling capabilities, th e microvasculature of the human urinary bladder wall seems to efficiently a ccommodate changes associated with cyclic contraction and stretching. Distu rbances in blood flow induced by overdistension of the bladder reported in several studies maybe due to pressure of the urine affecting the patency of the vessels rather than to the spatial insufficiency of the vascular syste m. Anat Rec 254:375-381, 1999. (C) 1999 Wiley-Liss, Inc.