Segmental arterial mediolysis

Segmental arterial mediolysis (SAM) is a rare, non-inflammatory, non-atherosclerotic vascular disorder that affects medium-sized and large muscular arteries. It is characterized by lysis (breakdown) and degeneration of the outer media (the middle layer of the arterial wall), which can lead to arterial dissection, aneurysm formation, stenosis, and potentially life-threatening hemorrhage. SAM most commonly involves the abdominal visceral arteries, including the celiac, superior mesenteric, hepatic, splenic, and renal arteries, though other arterial beds may also be affected. Patients may present acutely with sudden abdominal or flank pain due to arterial dissection or rupture, intra-abdominal hemorrhage, or organ ischemia. Some cases are discovered incidentally on imaging performed for other reasons. The condition predominantly affects middle-aged to older adults, though cases have been reported across a range of ages. The exact cause of SAM remains unknown, though it is thought to involve a vasospastic mechanism or abnormal smooth muscle cell response rather than an inherited genetic defect. Treatment depends on the clinical presentation and severity. Acute hemorrhage or organ ischemia may require urgent endovascular intervention (such as embolization or stenting) or surgical repair. In stable patients with incidental findings, conservative management with close imaging surveillance may be appropriate. There is no specific medical therapy for the underlying arterial wall abnormality. Prognosis varies; some patients experience a self-limited course, while others may develop recurrent or progressive arterial lesions requiring ongoing monitoring.

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