EP2029 - Gut Instincts Gone Awry: Unmasking Idiopathic Myointimal Hyperplasia of the Mesenteric Veins

Purpose/Background: Idiopathic Myointimal Hyperplasia of the Mesenteric Veins (IMHMV) is a rare, non-inflammatory vascular condition affecting the mesenteric veins which can lead to severe pain and life-threatening bleeding. The histopathological findings of IMHMV was first described by Genta and Haggit in 1991 and it is known to pose a diagnostic challenge due to its mimicry of inflammatory bowel disease (IBD) and ischemic colitis. Key histopathological findings include smooth muscle proliferation within the venous intima and thickening of mesenteric veins, contributing to obstructive vascular lesions. This case series aims to highlight the clinical diversity, diagnostic challenges and potential management of IMHMV.

Methods/Interventions: We reviewed three cases of histologically confirmed IMHMV. Clinical data, imaging findings, operative reports, and pathology results were analyzed. Each patient underwent surgical resection due to persistent or life-threatening gastrointestinal bleeding refractory to conservative management. Histopathologic analysis of resected specimens confirmed venous myointimal proliferation without evidence of thrombosis or inflammation. Literature review was performed to contextualize findings and explore mechanistic associations.

Results/Outcomes: All three patients were male, aged 36-76 years, presenting with abdominal pain and hematochezia.

Case 1: A 76-year-old male presented with massive hematochezia and hemodynamic instability. Imaging revealed mesenteric vascular dilation without intervenable lesions. Surgical resection demonstrated IMHMV with histologic features suggestive of a concurrent AVM, raising the possibility of a venous hypertension-driven pathogenesis.

Case 2: A 36-year-old male presented with rectal pain and was found to have a pseudoaneurysm and AVF involving the inferior mesenteric circulation. Following low anterior resection, pathology confirmed IMHMV with mural ischemic changes and venous intimal thickening, supporting a potential link between arteriovenous shunting and myointimal proliferation.

Case 3: A 47-year-old male with presumed ulcerative colitis failed immunosuppressive therapy and developed massive lower GI bleeding. Abdominoperineal resection revealed IMHMV without inflammatory infiltrate or arterial thrombosis.

All patients recovered well postoperatively, with resolution of symptoms and no recurrence on follow-up. Surgical resection served both diagnostic and curative roles in all cases.

Conclusion/Discussion: The diagnosis and treatment of IMHMV are challenging due to its rarity, frequent mimicry of other conditions, atypical presentations, and the fact that definitive diagnosis relies solely on histopathological confirmation of the surgical specimen. It's uncommoness as well as similarity to other diseases can delay diagnosis and definitive treatment, thus underscoring the need for heightened clinical suspicion.

We present 3 cases of IMHMV for patients presenting with a combination of bleeding and pain. Diagnostic uncertainty can lead to delayed treatment. Surgical resection remains the primary treatment and is associated with positive outcomes both in the literature and in our observed cases. Further research into its pathogenesis, especially any associations with AVMs or venous hemodynamic alterations, could improve diagnostic accuracy and understanding of this underrecognized condition.