Acute and chronic hepatic allograft rejection: pathology and classification.

Hepatic allograft rejection has been divided into humoral (or hyperacute), acute (or cellular), and chronic (or ductopenic) forms. Humoral rejection is extremely uncommon in the liver and is not graded. Acute rejection will occur in approximately 50% of liver allografts, is more common in the first few weeks posttransplantation, and is defined by Snover's triad of portal hepatitis, endothelialitis (or endotheliitis), and lymphocytic cholangitis. This form of rejection is generally reversible, either spontaneously or with additional immunosuppressive therapy, and can be reliably graded using a system with categories of mild, moderate, and severe rejection, associated with 37%, 48%, and 75% unfavorable shortterm and 1%, 12%, and 14% unfavorable long-term outcomes, respectively. Chronic rejection is characterized histologically by progressive duct loss and a lipid-rich vasculopathy that can be difficult to diagnose in early phases. Chronic rejection typically occurs several months to a year posttransplantation, although exceptions exist.