Diagnosis and treatment of malignant-appearing arteriovenous malformation

Abstract

Arteriovenous malformations (AVM) are most commonly found in the gastrointestinal tract, and presentation can range from asymptomatic to massive gastrointestinal hemorrhage. This case highlights a unique presentation of AVMs. During a screening colonoscopy, a 5-cm mass was discovered in the transverse colon encompassing 25% to 50% of the circumference of the lumen. Biopsies showed polypoid AVM with overlying inflammatory polyps without evidence of malignancy or dysplasia. There are many treatment options for AVM removal. In this case, since suspicion for malignancy was high, the patient underwent surgery and will be closely monitored.

Arteriovenous malformations (AVMs) may present in a variety of ways and are usually discovered incidentally. In this case, a large AVM was found on screening colonoscopy and raised concerns for malignancy.

CASE DESCRIPTION

A 58-year-old man was referred for a screening colonoscopy. He had been feeling well and denied any recent constipation, diarrhea, hematochezia, melena, or weight loss. His father had colon cancer at the age of 76, and a brother had colon polyps at the age of 55. During this first screening colonoscopy, two polyps (5-9 mm, sessile) were found in the ascending colon and sigmoid colon and were removed by cold snare. A mass measuring approximately 5 cm was discovered in the transverse colon encompassing 25% to 50% of the circumference of the lumen. It was malignant appearing and easily traversed (Figure 1). Colonoscopy was otherwise normal. Pathology results for the smaller polyp showed tubular adenoma with low-grade dysplasia, and the 5 cm mass showed polypoid AVM with overlying inflammation. No malignancy or adenomatous dysplasia was identified. However, despite the lack of evidence for malignancy, clinical suspicion for a malignant process was high and the patient was referred to colorectal surgery. Computed tomography of the abdomen and pelvis showed no evidence of metastatic disease. Approximately 2 weeks after tissue examination, laparoscopic colectomy with anastomosis was performed. Pathology from the resection showed a 6.1 cm polypoid AVM with overlying inflammatory polyps, as well as three tubular adenomas ranging from 0.3 to 0.8 cm with low-grade dysplasia and multiple benign mesocolic lymph nodes. The patient tolerated the operation well and continued to heal well at all follow-up appointments.

Figure 1.

A 5 cm transverse colon mass encompassing 25% to 50% of the circumference of the lumen.

DISCUSSION

AVMs are an abnormal joining between arteries and veins that bypass the capillary system. They are most commonly found in the gastrointestinal tract, and presentation can range from asymptomatic to massive gastrointestinal hemorrhage.¹ AVMs fall within the taxonomy of vascular anomalies and are synonymously referred to as angiodysplasias, angiectasias, and vascular ectasias.

AVMs often present with painless bleeding and are most often found during evaluation of chronic iron deficiency anemia, where they are usually in the right colon. They can occasionally cause hypotension due to large volume blood loss; however, this is uncommon and they cannot definitively be named the cause of gastrointestinal bleeding unless bleeding is observed during endoscopy.²

It has been suggested that AVMs develop due to chronic sporadic obstruction of the submucosal veins by increased contractility in the muscularis propria or intraluminal pressure resulting in increased bowel wall tension and compression of submucosal venules.^3,4 As a result, capillary congestion and arteriovenous collaterals develop. This theory is somewhat supported by the increased incidence in older patients and the high probability of AVMs being located in the ascending colon and cecum (locations in the bowel with larger diameter and thinner walls).

The intermittent ischemia caused by contraction of the muscularis propria causes hypoxia, which is known to increase expression of proangiogenic factors. Vascular endothelial growth factor (VEGF) is one such growth factor that has been found in higher quantities in hypoxic environments.⁵ VEGF inhibitors have been studied in the treatment of AVMs; however, due to their extensive side effect profile, they are not commonly used for long-term treatment.⁶ Other therapies commonly employed in treatment of AVMs include endoscopic ligation and surgical intervention, as well as argon plasma coagulation. In argon plasma coagulation, an electrical current is combined with argon gas. The gas is ionized and allows a high-frequency electric current to be conducted to the tissue without direct contact. This method decreases tissue depth injury, especially when used in conjunction with a prior submucosal saline injection to the target area to form a cushion.^7,8 Pharmacological therapy with octreotide is also commonly used. One study showed that administration of octreotide long-acting release for 6 months resulted in a significant reduction in bleeding episodes and transfusion requirements in patients who had mostly failed argon plasma coagulation therapy.⁹

Advances in diagnostic and therapeutic options have reduced the need for surgical intervention.¹⁰ Surgery is curative, but care must be taken to ensure that the offending bleeding lesion is removed to prevent recurrence of bleeding at a different location. Conservative management with oral or intravenous iron supplementation should be considered, as most patients with AVMs present with iron deficiency anemia. In elderly patients or patients unable to tolerate the aforementioned therapies, iron replacement may be the most appropriate method of treatment.¹¹