Describe the microscopic features of nodular vasculitis.

Nodular vasculitis presents as a lobular panniculitis with a mixed infiltrate that may be granulomatous. Vasculitis of a medium-sized artery or vein is present deep in the fat. Caseous necrosis is present in up to 50% of cases. Although necrosis can occur in cases not associated with tuberculosis, it may be more common in lesions that are positive for Mycobacterium tuberculosis–complex DNA.

Boonchai W, Suthipinittharm P, Mahaisavariya P: Panniculitis in tuberculosis: a clinicopathologic study of nodular panniculitis associated with tuberculosis, Int J Dermatol 37:361–363, 1998.