Idiopathic myointimal hyperplasia of mesenteric veins.

Nonthrombotic occlusion or stenosis of the mesenteric veins is a rare cause of intestinal ischemia that usually occurs in association with systemic vasculitis. The current report includes four male patients with segmental ischemic colitis caused by idiopathic myointimal hyperplasia in the small mesenteric veins and their intramural branches; neither vasculitis nor arterial involvement were present. Three of the four patients were less than or equal to 38 years of age; the fourth was 67. All four patients were previously healthy and had no history of drug use of any kind. Clinical findings included abdominal pain, diarrhea, bloody stools, and colonic strictures discovered by barium enema. The intima of the mesenteric and intestinal mural veins was focally thickened by a marked increase in cells and matrix between the endothelium and internal elastic lamina, whereas the vessel walls external to the thickened intima appeared normal. Histochemistry and immunoreactivity with antibodies to muscle-specific actins (HHF-35) disclosed that the intimal thickening was caused by proliferation of smooth muscle cells in a proteoglycan matrix. All patients recovered completely after segmental resection of the ischemic portion of the colon and had no recurrence of intestinal symptoms on follow-up of up to 7 years. These unusual venous lesions do not appear to have been previously described; their etiology and pathogenesis remain unknown.