June 2022 – Gastroenterology Pathology

Idiopathic myointimal hyperplasia of the mesenteric veins.

Idiopathic myointimal hyperplasia of the mesenteric veins (IMHMV) is a rare noninflammatory type of chronic ischemic colitis of unknown etiology. Some have speculated the myointimal hyperplasia is a consequence of mechanical stress from a mesenteric arteriovenous malformation or arteriovenous shunting.^1,2

IMHMV predominately affects adult males with nonspecific symptoms including abdominal pain, hematochezia, and diarrhea. IMHMV has a predilection for the left colon and rectosigmoid with features of ulceration, erythema, edema, and possibly strictures seen on colonoscopy.^3,4

Microscopically, the pathognomonic feature of IMHMV in resection specimens is myointimal smooth muscle hyperplasia of the mural veins leading to stenosis or even complete occlusion, while the arteries are unaffected (Figure 2). An elastin stain such as Verhoff Van Gieson can be used to distinguish the mural veins from arteries (Figure 3). No lymphocytic phlebitis or lymphocytic cuff is identified in and around the mural veins. The overlying mucosa shows histologic changes consistent with ischemia including focal lamina propria hemorrhage, withered crypts, crypt architectural distortion, ulceration/erosion, and hyalinized lamina propria (Figure 1). Additionally, mucosal capillaries frequently display “arterialization,” subendothelial fibrin, and perivascular hyalinization likely due to venous hypertension (Figure 1). One study by Yantiss et al. mentions the mucosal capillary changes are sensitive and specific to assist in the diagnosis of IMHMV on mucosal biopsy.^1,5

In many cases, patients with IMHMV are misdiagnosed with inflammatory bowel disease such as Crohn’s disease because of the similarities in presentation, endoscopy, and histology. IMHMV patients will fail medical therapy for inflammatory bowel disease and often undergo partial colectomy, which is curative. Recognizing histologic features of IMHMV is very important to prevent patients with IMHMV from being misdiagnosed with inflammatory bowel disease and receive unnecessary immunosuppressive treatment. The mucosal capillary changes can be a helpful finding on mucosal biopsy to make this distinction. In a resection specimen, the absence of transmural inflammation with the characteristic mural vein myointimal hyperplasia is pathognomonic of IMHMV. Thickening of the colonic wall on imaging also raises the clinical concern for neoplasia, which can be excluded with histologic evaluation. Another entity in the differential diagnosis with IMHMV is enterocolic lymphocytic phlebitis, which demonstrates lymphocytic phlebitis and/or a lymphocytic cuff, which are features not seen in IMHMV. Finally, radiation colitis can also enter the differential with IMHMV, but the absence of thin walled ectatic vessels and radiation induced stromal atypia can exclude this entity.⁵

References

1. Yantiss RK, Cui I, Panarelli NC, Jessurun J. Idiopathic myointimal hyperplasia of mesenteric veins: An uncommon cause of ischemic colitis with distinct mucosal features. Am J Surg Pathol. 2017;41(12):1657-1665.
2. Genta RM, Haggitt RC. Idiopathic myointimal hyperplasia of mesenteric veins. Gastroenterology. 1991;101(2):533-539.
3. Anderson B, Smyrk TC, Graham RP, Lightner A, Sweetser S. Idiopathic myointimal hyperplasia is a distinct cause of chronic colon ischaemia. Colorectal Dis. 2019;21(9):1073-1078.
4. Kelly Wu W, Tombazzi CR, Howe CF, et al. Idiopathic myointimal hyperplasia of the mesenteric veins: a rare imitator of inflammatory bowel disease. Am Surg. 2020:3134820973390.
5. Zhang L, Chandan V, Wu TT, et al. Surgical pathology of non-neoplastic gastrointestinal diseases. Springer. 2019