What is the primary cause of allograft failure?

• A. Acute Rejection
• B. Neointimal Hyperplasia or Restenosis
• C. Infection
• D. Chronic Rejection

Answer: (B)

The main idea here is that a vascular allograft fails most often because the vessel lumen narrows due to neointimal hyperplasia, leading to restenosis. After a graft is placed, injury to the vessel wall triggers smooth muscle cells to migrate into the intima and proliferate, with extracellular matrix piling up. This thickens the inner layer, constricting the lumen and reducing or blocking blood flow through the graft. That direct loss of patency is the primary mechanism driving allograft failure in many vascular cases.

Acute rejection is an immune attack that tends to cause early problems but isn’t the typical long-term driver of graft failure. Infection can complicate healing and graft viability, but again it’s not the usual primary cause of chronic failure. Chronic rejection involves progressive immune-mediated damage and fibrosis over time, contributing to dysfunction, but the specific process that most directly reduces graft patency is the neointimal hyperplasia that causes restenosis.