Idiopathic myointimal hyperplasia of mesenteric veins: radiological evaluation using CT angiography

Abstract

A 44-year-old man presented with a chief complaint of constipation. Initial contrast-enhanced CT showed extensive bowel wall thickening, mainly in the left colon, with a thin cord-like inferior mesenteric vein (IMV), in contrast to ectatic mesenteric venous branches, suggesting bowel ischaemia owing to venous stasis. One month later, at the time of symptom exacerbation, CT angiography showed a cord-like IMV and ectatic mesenteric venous branches with early enhancement, suggesting the presence of an arteriovenous fistula (AVF). Owing to the progression of bowel ischaemia and necrosis with peritonitis, emergency surgery was performed. Surgical specimens showed focal myointimal hyperplasia of the proximal mesenteric veins in both ischaemic and non-ischaemic lesions of the resected colon, thus leading to the diagnosis of idiopathic myointimal hyperplasia of mesenteric veins (IMHMV) when combined with the clinical and imaging findings. IMHMV is a bowel ischaemic disease caused by non-thrombotic venous obstruction that requires bowel resection and has been suggested to be associated with AVF. Cord-like IMV and AVF in the mesentery are important CT findings that characterize IMHMV. CT angiography is useful in diagnosing IMHMV.

Clinical presentation

A 44-year-old man with a chief complaint of constipation for several weeks without abdominal pain and fever was referred to our hospital for further evaluation. On physical examination, a hard palpable mass was observed in the lower left to mid-abdomen with local warmth. White blood cell (WBC) count and C-reactive protein (CRP) were 6500/μL and 2.7 mg/dL, respectively. Colonoscopy performed at another hospital revealed significant oedema of the sigmoid colon mucosa and narrowing of the lumen, which made it difficult to pass the scope through the colon. The patient had similar symptoms 10 years prior and had undergone colonoscopy; however, no abnormal findings were noted. The past medical history included medications for hypertension. There was no other medical or medication history, including herbal medications, significant dietary history, or surgical history.

Investigations/imaging findings

Initial contrast-enhanced CT showed an oedematous thickening of the bowel wall from the splenic flexure to the rectum. The CT also showed a thin cord-like inferior mesenteric vein (IMV) in contrast to the ectatic mesenteric venous branches, whereas the inferior mesenteric artery (IMA) was patent, suggesting that venous stasis owing to venous occlusion was associated with bowel ischaemia (Figure 1). There were no apparent thrombi in either the arteries or veins, arteriosclerotic changes, or calcifications along the veins and colonic walls.

Clinically, inflammatory bowel disease (IBD) and eosinophilic enteritis were suspected as differential diagnoses owing to the presence of ascites. However, the endoscopic biopsy specimen showed only a mildly inflamed mucosa without significant eosinophilic infiltration, which was incompatible with IBD or eosinophilic enteritis.

The patient was managed with careful observation because he had bowel movements, no abdominal pain, and showed only mild inflammation.

One month later, the patient complained of lower abdominal pain for 1 week and was taking non-steroidal anti-inflammatory drugs for self-medication. Physical examination revealed tenderness and guarding of the lower left abdomen. The body temperature was elevated to 38.0°C. WBC count and CRP were elevated to 18600/μL and 20.5 mg/dL, respectively.

CT angiography was performed because vascular abnormalities, such as cord-like IMV and ectatic mesenteric venous branches, were suspected to be associated with the observed pathophysiology changes in the previous CT. Contrast-enhanced CT revealed oedematous bowel wall thickening extending into the mid-transverse colon. Poor mural enhancement is observed in the sigmoid colon, suggesting bowel necrosis. Peritoneal thickening was also observed. In the arterial phase of CT, marked enhancement was observed in the ectatic mesenteric venous branches, suggesting the presence of an arteriovenous fistula (AVF) (Figures 2 and 3).

Differential diagnosis

The differential diagnosis of venous non-thrombotic bowel ischaemia in our case included the following:

• mesenteric inflammatory veno-occlusive disease (MIVOD)

• early stage of phlebosclerotic colitis (PC)

• idiopathic myointimal hyperplasia of mesenteric veins (IMHMV)

Treatment

Owing to the progression of bowel ischaemia and necrosis with peritonitis, emergency left hemicolectomy and proctectomy with transverse colostomy were performed. In the surgical specimen, almost the entire resected colon was oedematous, with focal mural necrosis (Figure 4). In both ischaemic and non-ischaemic lesions of the resected colon, at least focal muscular thickening of the intima was observed in the submucosal, subserosal, and mesenteric veins, which was considered to be the cause of bowel ischaemia (Figure 5). Although venous wall fibrosis was partly detected, phlebitis or venous wall calcification was not observed. Microscopically, chronic thrombi and recanalization were found only in the ischaemic lesions of the resected colon and were considered secondary changes.

Outcome and follow-up

Based on the clinical manifestations and course, radiological findings, including cord-like IMV and AVF in the mesentery on CT angiography, and characteristic mesenteric vein pathology, IMHMV was the final multidisciplinary diagnosis. The patient was discharged on postoperative day 11 without complications, and there was no evidence of recurrence 1 year after surgery.

Discussion

The 2 main causes of bowel ischaemia are arterial and venous. Arterial thrombotic disease is the most common cause of bowel ischaemia. Venous caused bowel ischaemia is less common and is typically thrombotic. Non-thrombotic causes are rare and include systemic vasculitis, such as systemic lupus erythematosus and Behçet’s disease, localized phlebitis called MIVOD, and non-inflammatory causes, such as PC and IMHMV. In particular, MIVOD and IMHMV require bowel resection. Therefore, it is important to distinguish MIVOD and IMHMV from other bowel ischaemias that can be treated conservatively.

IMHMV is an extremely rare disease, first described by Genta and Haggit in 1991,¹ who reported striking intimal thickening involving the small mesenteric veins and their intramural branches. This report suggested that intimal thickening was caused by the proliferation of smooth muscle cells in a proteoglycan matrix and that elastic staining was required to differentiate thickened veins from arteries.¹ In general, IMHMV has the following features: (1) young, previously healthy male patient; (2) segmental rectosigmoid colon involvement; (3) relatively protracted clinical course; (4) endoscopic and clinical impression of IBD; (5) endoscopic biopsy findings not compatible with IBD; (6) clinical complications necessitating segmental resection; (7) typical mesenteric vein pathology; and (8) uneventful follow-up with no recurrence.² The present case fulfilled all of these criteria. The aetiology of IMHMV remains unknown. It has been hypothesized that intermittent torsion and stretching of the highly mobile sigmoid colon may have been contributed to it.²

Two characteristic imaging findings have been reported in IMHMV.^3–6 First, a cord-like IMV has been reported as a feature of IMHMV.³ Although the affected area of the colon in IMHMV is compatible with ischaemic colitis, the cord-like IMV suggests that IMHMV is not just ischaemic colitis. In the present case, cord-like IMV was initially assumed to have developed after the thrombus disappearance; however, the hypercoagulable workup showed no abnormalities. Therefore, cord-like IMV is considered the cause of bowel ischaemia. The report referred to aneurysmal changes in the pericolic veins,³ which were also observed in the splenic flexure in this case on the initial CT. Aneurysmal changes in the pericolic veins may reflect venous stasis owing to the cord-like IMV and hepatofugal blood flow in the mesenteric venous branches (Figure 6). Secondly, an arteriovenous connection has been reported angiographically in IMHMV.⁴ The presence of AVF in the mesentery has been suggested since the first case report of IMHMV,¹ but it has been difficult to prove it pathologically. A previous histological study has suggested that arterial pressure is required for the formation of myointimal hyperplasia.⁷ There are several other case reports that include imaging evaluations with angiography; however, in many of these reports, AVF remained undetected.^5,6 Using angiographic evaluation, ectatic mesenteric vein branches may be recognized as arteries owing to hepatofugal blood flow in the early phase. It should also be noted that the IMV in patients with IMHMV may not be visible on angiography because of its thin, cord-like form, lack of early venous drainage, and lack of delayed contrast filling. In the present case, CT angiography was chosen instead of angiography to evaluate vascular abnormalities. Compared with angiography, CT angiography is more useful in the diagnosis of IMHMV because it is less invasive and can show the anatomic course of the IMA and IMV, abnormal enhancement of the mesenteric venous branches in the arterial phase, and cord-like IMV in the equilibrium phase without visible enhancement. Most previously reported IMHMV cases ultimately result in surgery,⁸ in contrast to ischaemic colitis, which is often treated conservatively. Patients with IMHMV should be evaluated at an early stage with CT angiography to minimize the need for surgical resection.

In the present case, MIVOD and PC were considered in the differential diagnosis of venous non-thrombotic bowel ischaemia because there were no other symptoms suggestive of systemic vasculitis. Due to no pathological evidence of phlebitis, MIVOD was excluded. In 2 previously reported MIVOD cases, a striking paucity of larger draining veins with a diminutive/irregular appearance of the IMV have been shown,⁹ which is similar to the cord-like IMV in IMHMV. AVF in the mesentery has also been reported in one MIVOD case.¹⁰ These 3 reported MIVOD cases demonstrated pathological myointimal hyperplasia. It has also been suggested that IMHMV is the presentation of a more advanced stage of MIVOD and that there is an overlap between the 2, although they are considered separate entities depending on whether vasculitis is present.⁹ Therefore, we believe that cord-like IMV and AVF in the mesentery are characteristic of IMHMV. PC is characterized by a predilection for the right side of the colon, calcification along the venous wall, and association with herbal medications (especially Sanshishi), which were not evident in this case. Although there is one report of PC, including a left-sided case with only slight calcification of the submucosal veins,¹¹ no other PC cases have been reported to be left-sided, and the present case presented with no calcification both radiologically and pathologically. Therefore, IMHMV was considered to be the most appropriate diagnosis in this case.

Conclusions

IMHMV is a bowel ischaemia due to non-thrombotic venous obstruction, the treatment of which mostly requires bowel resection. Radiologists should be aware of the characteristic findings of IMHMV. Cord-like IMV and AVF in the mesentery with bowel ischaemia are findings suggestive of IMHMV, and contrast-enhanced CT with CT angiography is necessary for detection.

Learning points

• IMHMV causes non-thrombotic venous bowel ischaemia, which mostly requires bowel resection.

• IMHMV is characterized by striking intimal thickening involving the small mesenteric veins and their intramural branches, mostly affecting the left side of the colon. Elastic staining is required to differentiate between thickened veins and arteries.

• The characteristic imaging findings of IMHMV are cord-like IMV and AVF in the mesentery with bowel ischaemia. Because cord-like IMV cannot be depicted by angiography, CT angiography, which enables the simultaneous evaluation of cord-like IMV and AVF in the mesentery, is necessary for the diagnosis of IMHMV.

• If thickening of the bowel wall of the left-sided colon, such as in ischaemic colitis, is observed on CT, it is important to search for cord-like IMV and, if present, to add CT angiography for the evaluation of AVF in the mesentery.

Acknowledgements

We appreciate Nobuyuki Nagasawa from the Radiological Center, National Defense Medical College Hospital for providing the volume rendering reformatted image.

We would like to thank Editage (www.editage.jp) for English language editing.

Funding

None declared.

Conflicts of interest

None declared.

Consent

Written informed consent was obtained from the patient for this case report, including accompanying images.

References