Inferior mesenteric arteriovenous fistula: Three case reports

Abstract

BACKGROUND

Inferior mesenteric arteriovenous fistula (IMAVF) is an extremely rare condition characterized by abnormal communication between the inferior mesenteric artery and vein. IMAVF often mimics ischemic bowel disease and ulcerative colitis (UC), leading to diagnostic challenges and treatment failures.

CASE SUMMARY

Three consecutive cases presented with non-specific symptoms including perianal pain and bloody diarrhea were reported. Initial diagnosis included acute severe UC and ischemic colitis. Pathology suggested ischemic changes, and with further contrast-enhanced computed tomography together with digital subtraction angiography which confirmed the diagnosis of IMAVF. All three cases were treated by vascular embolization, and symptoms improved rapidly following treatment.

CONCLUSION

We presented the largest single center IMAVF series with detailed clinical characteristics, facilitating early diagnosis for similar cases in the future.

Key Words: Inferior mesenteric arteriovenous fistula; Diagnosis; Treatment; Ulcerative colitis; Ischemic bowel disease; Case report

Core Tip: Inferior mesenteric arteriovenous fistula (IMAVF) is a rare condition characterized by abnormal communication between the inferior mesenteric artery and vein. Presentations of IMAVF are usually non-specific and therefore poses diagnostic challenge and delay. We reported three consecutive cases of IMAVF that mimics ulcerative colitis and ischemic bowel disease, and provided a brief literature review, aiming to facilitate rapid recognition and timely treatment in clinical practice.

INTRODUCTION

Inferior mesenteric arteriovenous fistula (IMAVF) is a rare condition involving abnormal communication between the inferior mesenteric artery and vein. It’s a rare clinical condition with limited case report[1]. IMAVF may result in various non-specific clinical manifestations, including abdominal pain, diarrhea, abdominal mass, ischemic bowel disease, portal hypertension, and even heart failure[2]. When presenting with abdominal pain, diarrhea, and bloody stool, IMAVF is frequently misdiagnosed as ischemic bowel disease or inflammatory bowel disease (IBD), such as ulcerative colitis (UC). We reported three consecutive cases of IMAVF, constituting the largest single-center case series to date. A literature review was also conducted to summarize the clinical characteristics, diagnostic approaches, and treatment strategies for this rare condition.

CASE PRESENTATION

Chief complaints

Case 1: A 48-year-old male was referred to our hospital in March 2024 due to persistent severe pain in the perianal region and lower abdomen, accompanied by mucopurulent bloody stool for one month.

Case 2: A 72-year-old male was referred to our hospital in April 2024 with recurrent abdominal pain and diarrhea for three months.

Case 3: A 40-year-old male was referred to our hospital in June 2024 due to severe perianal pain and diarrhea lasting for five days.

History of present illness

Case 1: He developed recurrent abdominal pain and diarrhea for three months. Colonoscopy performed at a local hospital revealed diffuse rectal erosion with ulceration, leading to a suspected diagnosis of acute severe UC. Based on this diagnosis, the patient was treated with steroids and subsequently with infliximab, both of which were ineffective. He continued to experience severe pain requiring multiple analgesics, and the bloody diarrhea persisted. Due to the lack of treatment response, a second colonoscopy was performed, revealing diffuse ulcers extending from the rectum to 15 cm proximal to the sigmoid colon (Figure 1A). Histopathology indicated ischemic changes and vascular lesions (Figure 1B).

Figure 1 Endoscopies, pathology and imaging of the three cases. A: Endoscopy from case 1 showed diffuse ulceration in the rectum; B: Pathology of the rectum showed epithelial damage and exfoliation, crypt distortion, stromal hemorrhage with local hyaline degeneration, capillary dilation in the stroma, and local thickening of the vascular wall; C: Contrast-enhanced abdominal computed tomography (CT) revealed circumferential wall thickening of the rectum; D: Abdominal CT angiography (CTA) demonstrated an arteriovenous fistula in the inferior mesenteric vessels; E: Endoscopic image of case 2 illustrated diffuse swelling of the rectosigmoid mucosa; F: Epithelial damage and exfoliation, crypt distortion, stromal hemorrhage with local hyaline degeneration, capillary dilation in the stroma, and local thickening of the vascular wall; G: Contrast-enhanced abdominal CT depicted edematous thickening of the rectosigmoid wall with surrounding exudates; H: Abdominal CTA revealed an arteriovenous fistula in the inferior mesenteric vessels; I: Endoscopic image of case 3 displayed diffuse mucosal roughness, congestion, and ulceration from the colonic anastomosis to the anal verge; J: Epithelial damage and exfoliation, crypt distortion, stromal hemorrhage with local hyaline degeneration, capillary dilation in the stroma, and local thickening of the vascular wall; K: Contrast-enhanced abdominal CT indicated swelling of the colorectal wall distal to the anastomosis with surrounding blurry exudation; L: Abdominal CTA showed an arteriovenous fistula in the inferior mesenteric vessels.

Case 2: He had a maximum of over ten times diarrhea per day and suffered from persistent dull pain at the left lower quadrant. Colonoscopy showed diffuse swelling of the rectosigmoid mucosa, more pronounced toward the anal side (Figure 1E). Histopathology indicated ischemic changes of the colonic mucosa (Figure 2F).

Figure 2 Pre-embolization and post-embolization endoscopy. A-C: Pre-treatment endoscopic images of the patient show diffuse ulceration of the rectal mucosa; D-F: Post-embolization endoscopic review indicates significant improvement of the mucosal lesions.

Case 3: He presented with persistent and severe perianal pain, which responded poorly to non-steroidal anti-inflammatory drugs and antispasmodic medications. Colonoscopy showed diffuse hyperemia of the mucosa distal to the anastomosis (Figure 1I), and histopathology suggested acute ischemic changes (Figure 2J).

History of past illness

Case 1: The patient had a history of appendectomy 30 years ago.

Case 2: The patient had no prior history of abdominal surgery or trauma.

Case 3: Six months ago, he was diagnosed with descending colon cancer and underwent laparoscopic left hemicolectomy, with preservation of the rectum and sigmoid colon, together with mesenteric lymph node dissection and pelvic adhesion lysis.

Personal and family history

No significant findings for all three cases.

Physical examination

Case 1: Physical examination revealed tenderness in the mid-lower and left lower abdomen.

Case 2 and case 3: Physical examination revealed tenderness in the left lower abdomen.

Laboratory examinations

Case 1: Laboratory tests showed a white blood cell (WBC) count of 19.7 × 10⁹/L and a high-sensitivity C-reactive protein level of 21.4 mg/L. Stool test for occult blood and WBC were all negative. Other laboratory findings were unremarkable.

Case 2: Stool test for occult blood was positive.

Case 3: Stool test for occult blood as well as WBC were all positive.

Imaging examinations

Case 1: Contrast-enhanced computed tomography (CT) of the abdomen showed a thickened rectal wall surrounded by tortuous and dilated small vessels (Figure 1C). These findings excluded IBD and raised suspicion of a vascular etiology. CT angiography (CTA) reconstruction confirmed the presence of IMAVF (Figure 1D).

Case 2: Abdominal CTA revealed cavernous transformation of the portal vein, narrowing of the splenic and superior mesenteric veins, multiple small varices around the stomach and mesentery, and edema with thickening of the rectosigmoid wall accompanied by exudation (Figure 1G and H). Digital subtraction angiography (DSA) demonstrated increased and disorganized vascular branches of the sigmoid colon with extensive varices, confirming the diagnosis of IMAVF (Figure 3A and B).

Figure 3 Digital subtraction angiography imaging during inferior mesenteric artery angiography and embolization in case 2 and case 3. A: Angiography from case 2, showing dilation of the inferior mesenteric artery, early visualization and significant dilation of the inferior mesenteric vein, along with a disordered vasculature; B: Post-embolization imaging from case 2, showing the disappearance of the local disordered vasculature and the visualization of the inferior mesenteric vein; C: Angiography from case 3, showing dilation of the inferior mesenteric artery, early visualization and significant dilation of the inferior mesenteric vein, along with a disordered vascular network; D: Post-embolization review from case 3, showing the disappearance of the local disordered vasculature and the visualization of the inferior mesenteric vein.

Case 3: Abdominal CTA revealed swelling of the colonic wall distal to the anastomosis, surrounded by blurry exudates, and identified an IMAVF (Figure 1K and L). DSA further confirmed the diagnosis by demonstrating increased and disorganized vascular branches of the sigmoid colon with multiple varices.

FINAL DIAGNOSIS

Case 1

Idiopathic IMAVF.

Case 2

IMAVF with secondary portal hypertension.

Case 3

IMAVF secondary to left hemicolectomy.

TREATMENT

Case 1

The patient underwent vascular embolization at another hospital (imaging not retrieved), resulting in rapid improvement of both pain and bloody diarrhea.

Case 2

The patient underwent vascular embolization, resulting in symptom improvement.

Case 3

Similar to the first two cases, the patient underwent vascular embolization (Figure 3C and D), which led to rapid resolution of perianal pain and diarrhea.

OUTCOME AND FOLLOW-UP

Case 1

Follow-up colonoscopy for this patient one month later showed significant ulcer healing (Figure 2).

Case 2

Follow-up colonoscopy three months later showed resolution of mucosal ischemia, and abdominal CT indicated remission of colonic edema.

Case 3

Follow-up abdominal CT two months later showed marked improvement in colonic wall edema and exudation.

DISCUSSION

IMAVF[3] is an extremely rare condition, with no more than fifty cases from previous literature[4-8]. IMAVF that can be classified as congenital, secondary, or idiopathic when no apparent cause is identified. Congenital arteriovenous malformations arise from undifferentiated embryonic vessels that fail to differentiate into arteries and veins, resulting in abnormal vascular connections. Secondary IMAVF typically results from trauma, such as blunt or penetrating abdominal injury, or from iatrogenic causes, including arterial catheterization, cholangiography, splenoportography, or surgical procedures such as left colectomy or sigmoidectomy[1]. Previous reports have also implicated specific drugs, such as bevacizumab, in the development of IMAVF[9]. We summarized all cases of IMAVF from the previous literature and summarized the epidemiological characteristics of the disease[3] as follows: (1) The age of onset ranged from 22 years to 81 years, with a mean age of 56 years and a median age of 61 years; (2) The male-to-female ratio is approximately 3.7:1; and (3) Secondary IMAVF accounts for about 38% of reported cases[4-8].

The pathophysiological features of IMAVF are generally associated with reduced perfusion to the affected tissues and increased venous pressure distal to the fistula. In the current case report, the first and second cases were considered idiopathic, while the third was attributed to iatrogenic causes following abdominal surgery. The steal phenomenon among intestinal arteries caused by the fistula leads to ischemic mucosal necrosis, while diversion of arterial blood from the inferior mesenteric artery into the portal circulation may result in portal hypertension, manifesting as variceal bleeding, ascites, and splenomegaly. Increased portal blood flow can induce a compensatory rise in hepatic vascular resistance[10]. Approximately 50% of patients with visceral arteriovenous fistulas develop portal hypertension. Fabre et al[11] reported that increased venous return may also contribute to heart failure in some cases, and that embolization of the fistula can improve cardiac function and increase ejection fraction. IMAVF can present with various nonspecific clinical manifestations, including abdominal pain, diarrhea, abdominal mass, portal hypertension, and even heart failure[2]. When presenting with abdominal pain, diarrhea, and hematochezia, IMAVF can be misdiagnosed as ischemic bowel disease or UC.

All three patients in our series presented with clinical manifestations of mucosal ischemic necrosis, with the second case additionally complicated by portal hypertension. IMAVF-related bowel disease is particularly challenging to distinguish from ischemic bowel disease and UC, often resulting in misdiagnosis and delayed treatment. The key characteristics derived from our cases are summarized as follows. First, the disease typically has a short course, with either acute or subacute onset. Second, pain is a prominent feature, especially severe pain located at the perianal area, as well as dull pain at lower abdomen, which often required multiple analgesics with limited relief. Third, abdominal trauma and surgery consists high risk factors for secondary IMAVF, such as the case of the third IMAVF in the current report. Forth, endoscopic findings closely mimic those of ischemic bowel disease and UC. Notably, IMAVF often involves the rectum, which may aid in distinguishing it from ischemic bowel disease, while pathological findings of ischemic changes can help differentiate it from UC. Fifth, radiological findings may be subtle and easily overlooked on initial review. Characteristic imaging features include early enhancement of the inferior mesenteric vein and its branches during the arterial phase of CTA, accompanied by dilated, disorganized local vasculature.

Treatment options for IMAVF include surgery, arterial embolization, and medical therapy. According to our review of the existing literature[3-7], approximately 20 (43%) patients underwent surgical treatment, 19 (40%) patients received embolization therapy, 5 (11%) patients were treated with a combination approach, and 3 (6%) patients were managed conservatively[8].

Arterial embolization is minimally invasive and repeatable, but may result in extensive thrombosis, ischemic necrosis, or incomplete embolization[9]. It is not recommended for fistulas larger than 8–9 mm due to the risk of ectopic embolism[12]. Five cases of post-embolization complications have been reported, including incomplete embolization and bowel necrosis or perforation, which required surgical resection. Surgical resection of the fistula and affected bowel segment remains a viable option, depending on the extent and severity of ischemia[13]. A total of 20 surgically treated cases have been documented. Medical management is appropriate only for asymptomatic patients with mild ischemic changes and no portal hypertension. In one report, a patient managed conservatively showed gradual improvement over one month, with abdominal CTA revealing collateral vein formation, reduced venous congestion, and resolution of left colonic wall edema, which was confirmed by colonoscopy[1]. All three patients in our series were treated with embolization, resulting in significant symptom improvement without recurrence or complications during follow-up. Although the three cases provided by our center currently represent the largest single-center series reported in the literature, the sample size remains too small to fully represent all the clinical manifestations and treatment outcomes of IMAVF. The generalizability of the conclusions drawn in this study regarding the disease characteristics of IMAVF is limited. More cases are needed in the future to validate the clinical, endoscopic, imaging, and pathological features, as well as the treatment efficacy of IMAVF primarily presenting with lower gastrointestinal symptoms.

CONCLUSION

We reported three consecutive cases of IMAVF presenting with abdominal pain, diarrhea, and bloody stools, constituting the largest single-center case series to date. We further summarized the key clinical, endoscopic, pathological, and radiological features of IMAVF and outlined important considerations for differentiating IMAVF from other conditions such as ischemic bowel disease and UC. These insights may facilitate earlier recognition and timely intervention in future clinical practice.