Introduction

Inferior mesenteric artery and vein (IMA-V) arteriovenous fistula (AVF) is a rare abnormal high flow communication with only 40 primary and secondary cases reported in literature (Tables 1 and 2). It is characterized from nonspecific clinical signs and symptoms such as abdominal pain, gastrointestinal bleeding, ischemic colitis, portal hypertension, and heart failure. Primary or congenital AVFs occur from undifferentiated embryonic vessels that fail to differentiate into arteries and veins. Secondary IMA-V AVFs can occur following penetrating abdominal injuries, arterial catheterization, or surgery [1].

Table 1 Congenital cases of inferior mesenteric arteriovenous fistula
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Table 2 Traumatic–iatrogenic cases of inferior mesenteric arteriovenous fistula
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Symptom intensities are flow-dependent and can range from minimal abdominal symptoms to severe heart failure due to left to right shunt. Furthermore shunting of arterial flow through the IMV to the portal system can cause portal hypertension that is usually associated with the diagnosis of AVF. According to its infrequency and great variability of symptoms, a radiological or intraoperative examination is often necessary to reach the diagnosis of IMA-V AVFs. Similarly, as regards treatment, it should be adapted to clinicopathological characteristics associated with this rare pathologic process.

Herein we present a rare case of transitory colonic ischemia caused by a congenital IMA-V AVF. At our knowledge, this is the 4th case reported in literature that was managed conservatively. We also review the literature and discuss the characteristics and treatments of this rare pathologic process.

Case report

A 72-year-old man without past history of abdominal surgery or trauma was referred to our department for a 2-month history of abdominal pain and intermittent diarrhea, without bloody stools. The physical examination of the abdomen was unremarkable and the patient had no signs or symptoms of portal hypertension. Full laboratory tests were also unremarkable. The colonoscopy showed an edematous and fragile mucosa with mild subepithelial hemorrhages. These findings were consistent with a diagnosis of ischemic colitis extended from the rectosigmoid junction to the splenic flexure. Biopsies taken at these levels showed submucosal hemorrhage and edema with few areas of fibrosis and were consistent with the diagnosis of ischemic colitis. A computed tomography (CT) of the abdomen confirmed a bowel wall thickening with congestion and decreased enhancement in the same segments associated to dilation of the vascular branches of the IMA-V plexus (Fig. 1a–b). A multidetector CT angiography of the IMA was performed and demonstrated an AVF involving the left colic artery and the inferior mesenteric vein. The IMV appeared dilated and varicose with a caliber of 18 mm and with a fast wash-out in portal system. (Fig. 2a–b). Colonic ischemia was the result of the arterial flow shunting through the inferior mesenteric vein and portal system with a venous stasis caused by the AVF.

Fig. 1
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Abdominal CT scan showing a bowel wall thickening with congestion and decreased enhancement extended from the rectosigmoid junction to the splenic flexure. a Coronal and b axial view

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Fig. 2
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a, b Main findings of multidetector CT angiography. The inferior mesenteric vein appeared dilated (red arrow) and supplied by inferior mesenteric artery (red star)

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Initially, we considered embolization of the feeding artery with possible subsequent colic resection; however, in the following month, the patient reported a progressive and spontaneous improvement of symptoms. An angio CT scan with color subtraction imaging permitted to optimize the vascular study and confirmed the reduction of venous vascular engorgement due to venous collateral circles development with significant regression of parietal thickening of the left and sigmoid colon (Figs. 3 a–b, 4 a–b). Although of considerable interest for the completeness of the clinical case, these findings made it possible to avoid the execution of a control angiographic examination. Resolution of colonic ischemia confirmed endoscopically and the complete symptoms remission, verified at 1-year follow-up, permitted a non-operative management.

Fig. 3
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Control CT scan showing the reduction of venous vascular engorgement with significant regression of parietal thickening of the left and sigmoid colon. a Coronal and b axial view

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Fig. 4
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Angio CT scan with color subtraction imaging showing a reduction of venous vascular engorgement (a coronal view) and a significant regression of parietal thickening of the sigmoid colon (b axial view)

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Discussion

Different etiopathogenesis have been identified for the development of IMA-V AVFs. Congenital AVFs occur from undifferentiated embryonic vessels that fail to differentiate into arteries and veins.

Secondary or iatrogenic IMA-V AVFs can occur following blunt or penetrating abdominal injuries, arterial catheterization, cholangiography, splenoportography or various surgical procedures such as a left hemicolectomy or sigmoidectomy [1]. In literature, it is also reported that the rupture of a congenital arterial aneurysm very close to a vein can also result in the formation of an AVF [2]. Our patient had no medical history of abdominal surgery or trauma; therefore, was possible to assume that the fistula originated from idiopathic etiology. An AVF is usually associated with decreased arterial blood flow to the tissue beyond the fistula and increased venous pressure distal to the fistula.

Colonic ischemia, commonly associated with this type of arteriovenous malformation, is the result of a steal phenomenon of the arterial flow through the inferior mesenteric vein and portal system. As reported by Slutski S. et al., this vascular engorgement of the bowel mucosa can be also responsible of lower GI bleeding [3]. Portal hypertension with esophageal or duodenal varices can be instead responsible of upper GI bleeding which is often associated with ascites, hepatic encephalopathy, and splenomegaly [4]. The left to right shunt caused by these IMA-V AVFs is the real responsible of the pathophysiologic alteration of bowel function and of the variety of nonspecific clinical signs and symptoms related. High flow comunication through an AVF, due to left to right shunt, can lead to cardiac failure that is another important symptom of these arteriovenous malformations. As reported by Fabre et al. the embolization of the AVF can also result in improvement of cardiac function and an increased ejection fraction [5]. Two major clinical manifestations of IMA-V AVF are portal hypertension and ischemic bowel disease. The only presence of abdominal mass, also reported in literature, is rare and usually leads to missed diagnosis and suboptimal intervention [6]. To prevent misdiagnosis, a high clinical suspicion is requested but for a diagnostic certainty a clinical sign of an ischemic colon combined to the angiographic proof of the fistula’s presence is mandatory. Concerning AVF treatment, our literature search found 18 cases of IMA-V AVF that received surgery, 14 embolization, 5 combination therapy, and 3 non-operative management. Two patients of the non-operative management group, who refused intervention, remained paucisymptomatic and were therefore enrolled in a follow-up program (4, 7,8,9,10). According to this great variability of symptoms, the treatment of IMA-V AVF remains case specific and can range from non-operative management, percutaneous endovascular embolization of the feeding artery or surgical correction of the AVF with or without bowel resection. A non-operative management for this type of rare pathologic process seems to be feasible only for paucisymptomatic patients when there is no development of portal hypertension and in presence of mild colonic ischemia. Dual arterial and venous embolization with or without subsequent bowel resection may be needed to manage severe portal hypertension secondary to this rare pathologic process. We reported an extremely rare case of IMA-V AVF that was managed conservatively without any intervention. In our case, we observed progressive and spontaneous improvement of symptoms which, due to venous collateral circles development, was associated to reduction of venous vascular engorgement and significant regression of colic parietal thickening.

IMA-V AVF, bypassing the capillary bed of the colon, can be a rare cause of ischemic colitis. If necessary, an appropriate treatment based on high clinical suspicion can reduce the risk of complications related to a missed diagnosis.