Idiopathic Myointimal Hyperplasia of the Mesenteric Veins as a Differential Diagnosis in Patients With Colitis of Unknown Etiology

Introduction: Idiopathic myointimal hyperplasia of the mesenteric veins is an exceedingly rare cause of ischemic colitis. It classically involves the rectosigmoid colon of middle-aged men. The clinical and endoscopic similarities with inflammatory bowel disease make a definitive diagnosis without surgery a challenge. Here we describe a case of idiopathic myointimal hyperplasia of mesenteric veins diagnosed after left colectomy for ischemic colitis. Case Description/Methods: A 49-year-old man with a month-long history of abdominal pain and diarrhea was evaluated extensively with 2 flexible sigmoidoscopies consistent with colitis of unknown etiology which was unsuccessfully treated with antibiotics and chronic steroids. The patient was hospitalized with COVID-19 and subsequently developed a saddle pulmonary embolism. After thrombectomy and heparinization, he reported worsening abdominal symptoms with intractable pain, cramping, and diarrhea. Repeat flexible sigmoidoscopy demonstrated ischemic nonbleeding mucosa. After a detailed discussion, resection was recommended. Biopsy following left colectomy showed intimal smooth muscle hyperplasia of medium-sized mesenteric veins with luminal obliteration in the mesentery and bowel wall. Based on the biopsy findings, a diagnosis of idiopathic myointimal hyperplasia of mesenteric veins was made, for which resection is curative (Figure 1). Discussion: Idiopathic myointimal hyperplasia of mesenteric veins (IMHMV) is an uncommon but important diagnosis affecting the colon. It is important to raise awareness for its consideration in cases of colitis of unknown origin after ruling out inflammatory bowel disease and before proceeding to surgery. Detection requires detailed endoscopic and radiologic images as well as extensive biopsies with careful interpretation by experienced pathologists. Early diagnosis and intervention can prevent prolonged symptoms and unnecessary medical treatment.Figure 1.: Intimal smooth muscle hyperplasia of medium-sized mesenteric veins (blue arrow) with luminal obliteration. The artery (star) is unremarkable.