PATHOLOGY TEACH AND TELL: INTRAVASCULAR ENDOTHELIAL HYPERPLASIA FORMING COLONIC POLYPS

A12-year-oldmale childwasbrought to the emergency roomwith fresh rectalbleeding for the preceeding 24 h.There was a similar episode 6 months earlier that had subsided spontaneously. On examination, the child was pale, restless, and the peripheral pulses were thready. His blood pressure was 60=40 mmHg in the right upper limb; hemoglobin was 6.6 mmol=l, platelet count and coagulation pro¢le were normal.The child was resuscitated with fresh whole blood and explored.The entire colon up to the ileocecal junctionwas ¢lled with fresh blood. On careful palpation of the colon, a nodular circumscribed ¢rmmass,0.5 cm in diameter, was felt arising in the transverse colon near the splenic £exure. The segment of the colon containing the mass was resected and colon continuity was restored by end-to-end anastomosis. Gross examination of the colon showed small sessile polypoidal projections ranging in size from 0.3 to 0.6 cm in diameter. Few of the polyps were hemorrhagic. On microscopy, the vessels in the mucosa and submucosa revealed a variety of lesions. Many vessels showed an exhuberant solid intravascular endothelial proliferation forming tumor nodules within the vessels with total occlusion of their lumina (F|gure1).These intravascular nodules projected into the lumenof thebowel as polyps. The proliferating cells were plump endothelial cells with small lumina that did not showanyatypia ormitosis (F|gure 2).The endothelial nature of the cells was con¢rmed by a strong positive immunostaining for factor VIII^ related antigen. Some of the vessels were lined by large prominent endothelial cells only and few revealed multilayering with slight luminal compromise (F|gure 3). Few of the polyps containing vessels with intravascular endothelial proliferation revealed ulceration with active bleeding (F|gure 4). Only an occasional vessel showed endothelial proliferation admixed with ¢brin (F|gure 4).