Early pseudoaneurysm degeneration in biologic extracellular matrix patch for carotid repair.

A newly-approved carotid patch, derived from porcine small intestinal submucosa (SIS), is thought to allow functional tissue regeneration by acting as a biologic scaffold of extracellular matrix. We report three cases of asymptomatic pseudoaneurysm after SIS patch closure. At exploration there were intact suture lines, no growth from cultures, and central patch herniation. Histopathologic examination showed postendarterectomy neointima in the artery and disorganized collagen in the pseudoaneurysm. SIS patch remnants adjacent to macrophage infiltration and neovascularization indicated ongoing processes of degradation and synthesis. Imbalances between degradation and host tissue synthesis are problems that may unpredictably affect SIS patch integrity.