Idiopathic Myointimal Hyperplasia of Mesenteric Veins

Idiopathic myointimal hyperplasia of mesenteric veins (IMHMV) is an uncommon and poorly understood disease that classically occurs in the rectosigmoid colon of relatively young, otherwise healthy males. The clinical presentation of IMHMV mimics that of inflammatory bowel disease, and colon resection has been invariably required in these patients after a prolonged course of failed medical therapy. The etiology of IMHMV is unknown, and this condition has been diagnosed only after histopathologic review of the resected colon.¹

IMHMV was first reported in 1991 by Genta and Haggitt, and fewer than a dozen case reports have subsequently been published in the literature.² The clinical course of this disease is usually characterized by protracted abdominal pain, weight loss, and bloody diarrhea in young, previously healthy men, although IMHMV has more recently been reported in older patients, including women.^3-6 Segmental involvement of the rectosigmoid colon is most commonly reported, although involvement of the ileum has also been described.⁵ IMHMV is routinely mistaken for inflammatory bowel disease because of the similarity in age distribution, symptoms, and endoscopic findings. Friable, edematous, and erythematous colonic mucosa is commonly observed early in the disease course, followed later by patchy ulcerations and inflammatory exudate.^1,7

An important clue when differentiating inflammatory bowel disease from IMHMV comes from the evaluation of biopsies, as the typical endoscopic features of ulcerative colitis or Crohn’s disease are notably absent in patients with IMHMV. Although specific criteria for the diagnosis of IMHMV based on mucosal biopsies have been reported, biopsy findings are usually nonspecific or suggest an ischemic etiology.^1,3,8 The key point for the clinician is that the biopsies do not support the presumptive diagnosis of inflammatory bowel disease. Fortunately, surgery appears to be curative, as disease recurrence after resection has not been described to our knowledge.

It is quite difficult to determine the true incidence of IMHMV, as this condition has only been diagnosed to date in patients who experience a complication that requires colon resection. It is possible that there are milder forms of IMHMV that do not have the virulent nature of the cases reported in the literature, as the diagnosis of this condition has routinely been established only after histopathologic review of the colectomy specimen. Endo-scopic biopsy findings of IMHMV are subtle and consist of congestion, ischemic change, and regenerative mucosal changes; however, there is no sign of chronicity to suggest inflammatory bowel disease. High-power magnification reveals numerous prominent dilated vessels that are diffusely distributed throughout the lamina propria. As opposed to the dramatic and “spectacular” findings noted in the veins of the surgical specimen, the mucosal changes are relatively nonspecific.¹

The pathognomonic findings in the resected specimen consist of nonthrombotic, noninflammatory occlusion of the mesenteric veins secondary to intimal smooth muscle hyperplasia. In other settings when venous occlusion leads to ischemic bowel, there is mesenteric vein thrombosis.⁹ On routine hematoxylin and eosin stains, the characteristic venous occlusion/hyperplasia can be mistaken for the more common findings of arterial occlusion even when actin staining is used for smooth muscle identification, potentially creating diagnostic confusion.⁷ Therefore, in cases of suspected IMHMV, elastin stains are particularly valuable for differentiating arterial from venous blood vessels.¹⁰

Nonthrombotic mesenteric vein occlusion has been shown to occur in forms of systemic vasculitis, such as Behçet disease, systemic lupus erythematosus, and enterocolic lymphocytic phlebitis.^2,8 These disorders, which are known as mesenteric inflammatory veno-occlusive diseases, have unique patient demographics, unique distribution of disease, and a characteristic lymphocytic infiltrate on histology that is not present in IMHMV samples.^11,12 Mesenteric inflammatory veno-occlusive diseases are rare conditions that occur without gender preference, across a wide age distribution, and involve different segments of the small and large intestines; there is no known relationship between this inflammatory phlebitis and the noninflammatory changes of IMHMV.

Abu-Alfa and associates initially hypothesized that IMHMV is caused by acquired segmental arteriovenous fistulization secondary to trauma because mesenteric veins in patients with this disease closely resemble arterialized vessels from saphenous vein bypass grafts or dialysis fistulae.^8,13,14 Focal myointimal hyperplasia has been shown to occur more often in bowel patients who have undergone trauma prior to resection such as previous surgery, incarceration, or intussusception.⁷ A retrospective angiographic review of a patient with IMHMV revealed a tortuous, enlarged marginal artery in the region of the rectosigmoid colon, but there was no obvious sign of early venous filling.¹⁵

Korenblit and colleagues presented a case report of a 62-year-old man with IMHMV.⁶ As is usual in this condition, the signs, symptoms, and endoscopic findings were strongly suggestive of inflammatory bowel disease. The patient’s presentation of crampy abdominal pain and bloody stools, endoscopic findings consistent with inflammatory bowel disease, and prolonged unsuccessful treatment with 5-aminosalicylic acid, steroids, and biologic agents are all routine for patients who are ultimately diagnosed with IMHMV. The figures in this case report show inflammatory pseudopolyps and cobblestoning of the mucosa, which certainly resemble endoscopic findings of inflammatory bowel disease. The finding of chronic active colitis on biopsies taken 8 months prior to presentation makes this case challenging, as mucosal changes in IMHMV patients do not typically appear to support the diagnosis of inflammatory bowel disease and have been a “red flag” in previous reports.

Of note in this case report, the final colectomy specimen did not demonstrate mucosal findings suggestive of inflammatory bowel disease. There was no architectural distortion of the crypts or Paneth cell metaplasia. Whether the initial biopsies were misinterpreted or the findings were confounded by Clostridium difficile infection or another concomitant process is unclear, particularly since this patient had pancolitis rather than the more usual segmental disease. Figure 5 nicely exemplifies the myointimal hyperplasia causing obliteration of the lumen of the veins. An elastin stain confirmed that the changes were confined to the venous outflow.

In summary, IMHMV should be suspected in young men presenting with proctosigmoiditis when biopsies are not consistent with inflammatory bowel disease. With increasing awareness, clinicians may be able to identify IMHMV prior to complications that necessitate surgery. Having said that, there is no known medical cure for IMHMV, as the few cases reported to date have not responded to the usual medical regimens for treatment of inflammatory bowel disease. As this disease becomes more widely recognized and reported, the pathogenesis, distribution of disease, natural history, and best treatment will hopefully become known. Fortunately, IMHMV patients who have been resected appear to be cured, with no recurrence of disease-related activity or symptoms.