What are the clinical manifestations and management of an Arteriovenous Malformation (AVM) in the inferior mesenteric area?

Clinical Manifestations of Inferior Mesenteric Artery AVM

An arteriovenous malformation in the inferior mesenteric area typically presents with ischemic colitis manifesting as abdominal pain, distension, and chronic diarrhea, with imaging revealing abnormal direct connections between the inferior mesenteric artery and vein, often accompanied by massive left-sided congestive colitis. 1, 2

Clinical Presentation

Inferior mesenteric AVMs are exceedingly rare, with only approximately 30 cases reported in the literature 3. The clinical picture differs dramatically from intracranial AVMs:

Primary Symptoms

• Chronic gastrointestinal symptoms: Months of diarrhea, nausea, and vomiting are common presenting features 2
• Acute abdominal pain and distension: Typically lasting 48-72 hours when patients seek emergency care 1
• Ischemic colitis: The dominant clinical manifestation, resulting from venous congestion and arterial steal phenomenon 1, 2
• Nonpulsatile abdominal mass: May be palpable on physical examination as a hard, minimally mobile mass 3
• Chronic anemia: Can develop from occult gastrointestinal bleeding 4

Pathophysiology

The AVM creates abnormal direct connections between the inferior mesenteric artery and vein, bypassing the normal capillary bed 1. This high-flow shunt causes:

• Venous congestion leading to bowel wall edema
• Arterial steal phenomenon causing intestinal ischemia
• Massive left-sided congestive colitis 1

Diagnostic Imaging Characteristics

CT Angiography (Gold Standard for Diagnosis)

CT angiography is the critical diagnostic tool, showing no definite boundary between the inferior mesenteric artery and vein, with early venous filling and dilated tortuous vessels 3. Key findings include:

• Loss of normal arteriovenous boundaries: The IMA and IMV appear confluent without clear separation 3
• Dilated, tortuous feeding vessels: Prominent arterial feeders and draining veins 2
• Massive bowel wall thickening: Particularly affecting the left colon 1
• Mucosal enhancement patterns: Indicating venous congestion 2

Colonoscopy Findings

• Diffuse mucosal vascular congestion: Nonspecific appearance that can mimic inflammatory bowel disease 2
• No discrete mass lesions: Despite symptoms suggesting space-occupying pathology 3
• Normal mucosa on histopathology: Biopsy typically shows nonspecific changes, making diagnosis challenging 2

MR Angiography

• Demonstrates the AVM nidus and feeding vessels 2
• Shows flow voids on T1 and T2 sequences 2
• Useful for treatment planning but less specific than CT angiography 2

Critical Diagnostic Pitfalls

Invasive procedures like fine needle aspiration are absolutely contraindicated and can be fatal, causing catastrophic hemorrhage requiring emergency laparotomy 5. This represents a critical difference from other abdominal masses.

Why Diagnosis is Challenging

• Clinical masquerading: Symptoms mimic inflammatory bowel disease, infectious colitis, or malignancy 2
• Nonspecific endoscopic findings: Colonoscopy shows only mucosal congestion without diagnostic features 2, 3
• Rarity creates low clinical suspicion: Even experienced radiologists and surgeons may not initially recognize the entity 5, 2
• Histopathology is nondiagnostic: Biopsy specimens show only secondary changes from ischemia 2

Etiology Classification

Idiopathic/Congenital (Primary)

• No history of trauma or prior surgery 1, 5
• Represents the minority of cases 1

Acquired (Secondary)

• Post-surgical: Most commonly follows colon surgery 1
• Post-traumatic: Can develop after abdominal trauma 1
• Iatrogenic: May result from prior interventions 1

Management Approach

The definitive treatment requires surgical resection of the affected bowel segment with complete removal of the AVM nidus, typically preceded by preoperative embolization to reduce intraoperative bleeding risk 1, 3.

Two-Stage Treatment Protocol

1. First stage - Preoperative embolization: Coil and liquid embolization of dominant feeding vessels to decrease blood flow 1, 2
2. Second stage - Surgical resection: Resection of affected colon segment with the AVM nidus, followed by primary anastomosis 1, 3

When to Choose Surgery Over Embolization Alone

• Complex fistulas with multiple feeding vessels 3
• Presence of ischemic colitis symptoms 3
• Failed embolization or recurrence 3

Intraoperative Considerations

• Have operating room ready before any diagnostic procedure: Given the catastrophic bleeding risk 5
• Ligate inflow vessels first: Before resecting the affected segment 4
• Consider ICG angiography: For precise intraoperative identification of the AVM extent (though this is more established for duodenal AVMs) 4

Prognosis and Follow-up

Successful treatment results in complete symptom resolution with weight gain and normalization of bowel function 3. Follow-up colonoscopy at 2-6 months should demonstrate:

• Normal anastomotic site 3
• Normal colonic mucosa without congestion 3
• No recurrence of symptoms 3, 4