Segmental arterial mediolysis and fibromuscular dysplasia: what comes first, the chicken or the egg?

Segmental arterial mediolysis (SAM) is a rare vasculopathy characterized by lysis of the outer media in splanchnic arteries and formation of dissecting pseudoaneurysms that may spontaneously rupture, leading to massive and often fatal intraabdominal hemorrhage. The pathogenesis of SAM is poorly understood. Healed SAM lesions closely resemble fibromuscular dysplasia (FMD), leading some authors to postulate that SAM represents a precursor to FMD despite distinct clinical differences between these two disorders. Herein, we present a 61-year-old woman with fatal SAM who showed histologic features in her aorta suggesting the opposite pathogenetic relationship, with an unclassified "FMD-like" arteriopathy preceding development of SAM.