Segmental arterial mediolysis (SAM) is a rare vasculopathy of unknown etiology characterized by disruption of the arterial medial layer, with resultant susceptibility to vessel dissection, hemorrhage, and ischemia. Since the first case of SAM described by Slavin and Gonzalez-Vitale in 1976 (1), approximately 50 cases have been reported in the literature (2). Although the abdominal visceral arteries are most frequently affected in SAM (3), any vessel may be involved, including the retroperitoneal (4), intracranial (2, 5, 6) and coronary arteries (7–9). The histopathologic changes begin with vacuolar degeneration of smooth muscle cells in the arterial media, followed by fibrin deposition at the medial-adventitial junction (7). This in turn predisposes to dissecting aneurysms (3, 10). The angiographic appearance of SAM is variable, ranging from arterial dilation to aneurysm formation (single or multiple) to stenoses or occlusion, frequently with dissection (3, 11). Correspondingly, symptoms arise both from stenoses and occlusions (e.g., postprandial pain from intestinal ischemia) and from dissections and aneurysms (e.g., sudden and catastrophic intraperitoneal bleeding). In contrast to true vasculitis, inflammatory cells in SAM are present inconsistently and, when present, are thought to be secondary rather than primary to the pathogenesis of the disease (1). The differential diagnosis of SAM includes atherosclerosis, fibromuscular dysplasia, infection (e.g., mycotic aneurysm and endocarditis), connective tissue diseases (e.g., Bechet’s disease and polyarteritis nodosa), neurofibromatosis, and inherited defects in vessel wall structural proteins (e.g., type IV Ehlers Danlos and Marfan’s syndrome) (Table 1). Herein, we describe two cases of SAM seen at our instituation over the past 20 years and review the salient clinical presentation and treatment of SAM. We report characteristics that may be helpful in distinguishing cases of SAM from other entities in the differential diagnosis. Table 1 Clinical and laboratory features distinguishing Segmental Arterial Mediolysis (SAM) from its mimics*. Case 1 The patient was a 25-year-old female who was admitted to the hospital with an eleven-month history of intermittent episodes of anorexia, abdominal pain, and diarrhea. Symptoms had persisted despite discontinuation of oral contraception and initiation of low-dose aspirin therapy. Her past medical history was unremarkable. Family history was unremarkable except for benign hypermobility syndrome in the patient’s mother. On physical examination, the patient was normotensive and had normal height and arm span. She had no carotid, subclavian, abdominal, or femoral bruits. Skin, chest, abdominal, and neurologic examinations were normal. Joint exam was remarkable only for hyperextensibility of the knees, reducible flexion contractures of the fingers, and hammertoe deformities of the feet. Complete blood count revealed anemia with hemoglobin of 11 g/dl. Serum creatinine, liver enzymes, amylase, and lipase were normal, and urine pregnancy test was negative. Antinuclear antibody assay (ANA) was positive to a low titer of (1:80). The erythrocyte sedimentation rate was 20 mm/hr. The remainder of the serologic, metabolic, immunologic, and hematologic evaluations were within normal limits, including negative hepatitis serologies, negative double-stranded DNA, anti-Smith, and anti-ribonucleoprotein (RNP) antibodies, and normal complement C3 and C4 levels. Computed tomography (CT) of the abdomen showed thickening of the colonic wall with mucosal enhancement and fat stranding surrounding the splenic flexure. Colonoscopy revealed ischemic colitis of the splenic flexure. Biopsies of the ischemic areas were not obtained due to risk of possible perforation. Biopsies of the non-ischemic areas were normal, as was magnetic resonance angiography (MRA) of the abdomen. Conventional mesenteric angiography revealed focal stenoses of the right and left hepatic arteries, occlusion of the left colic artery near the splenic flexure with collateral vessel formation, and hyperemia of multiple branches of the splenic artery (Figure 1). Figure 1 Angiographic and histologic features of segmental arterial mediolysis in Case 1. (a) Focal stenoses of the right and left hepatic arteries (arrows). (b) Hyperemic blush in the left colonic flexure, suggesting formation of small collateral vessels from ... Because of persistent ischemic colitis, the patient underwent a partial colectomy of the splenic flexure. Vascular pathology of the colonic arteries showed patchy, isolated destruction of the arterial media involving both the internal and external elastic laminae (Figure 1). In a few sections the media was absent, with direct juxtaposition of the intima and the adventitia. In areas of medial destruction, there was intimal proliferation with marked luminal narrowing. All of the lesions were of a similar age. There was no evidence of inflammation, and giant cells, neutrophils, and cholesterol deposits were absent. After two years of followup, the patient remains asymptomatic.
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Open Access
Jul 15, 2022
Hyo-Jin Kang 
