Pulse Granuloma-Like Lesion of the Portal Vein in a Liver Explant: A Case Supporting the Endogenous Theory

Pulse granuloma (PG) is a rare histopathological finding characterized by eosinophilic hyaline material aggregates and granulomatous inflammation. The pathogenesis of PG remains controversial, with two main theories: the exogenous theory attributing PG to plant-based foreign bodies and the endogenous theory suggesting vascular wall degeneration as the origin. We report a case of PG-like histological features in the portal vein of a patient with autoimmune hepatitis and a history of azathioprine (AZA) treatment, supporting the endogenous theory. The patient was a 49-year-old female with over 10 years of AZA therapy history, who had discontinued AZA treatment four years prior due to cholestatic hepatitis. Histopathological examination of the resected liver revealed portal vein intimal thickening and granulomatous inflammation with eosinophilic hyaline material aggregates and multinucleated giant cells within the intima. These findings resembled PG, but no vegetable matter was identified. This case supports the endogenous theory of PG pathogenesis, suggesting that some lesions traditionally attributed to vegetable matter may instead result from vascular damage and subsequent collagen degeneration.