Fig. 4

a Gross feature of surgical excision specimen. Deep longitudinal ulcers with fusion tendency were scattered in the large intestine. The yellow line indicates the site where the following tissue examination was performed. b Histopathology showed only minor changes in the mucosalstructure, but many veins in submucosal layer demonstrated prominent myointimal hyperplasia with narrowed lumens. Hematoxylin-eosin staining. c Arteries of submucosal layer were essentially normal (*). Venous thrombi of varying age were identified (arrow heads). d Small mesenteric vein and its intramural tributaries showed partly organized thrombi. Hematoxylin-eosin staining