Sections show ulcerated skin and deep soft tissue with extensive architecture disruption by a dual necrotizing and suppurative process. The dermis and subcutis exhibit prominent lymphoid aggregates, panniculitis, and extensive sheets of neutrophils mixed with fibrin and karyorrhectic debris, forming acute abscess cavities. Confluent fragments of amorphous, non-viable necrotic slough are present. Distinct zones of caseating granulomatous inflammation are identified, featuring central areas of acellular, eosinophilic granular debris rimmed by palisading epithelioid histiocytes, lymphocytes, and Langhans multinucleated giant cells. The periphery shows an active healing response with a thick wall of exuberant granulation tissue containing proliferating capillaries, reactive fibroblasts, lipid vacuoles from necrotic adipocytes, and hemosiderin-laden macrophages. There is no cytological atypia or evidence of malignancy.
Mid thigh abscess.
Multiple soft tissue pieces partially covered by skin measuring in aggregate 8 x 7 x 1 cm; the largest measured 2.5 x 1.5 x 1 cm.
Skin and soft tissue, mid-thigh, debridement:
Comment:
The differential diagnosis for caseating granulomatous and suppurative inflammation includes mycobacterial infection (e.g., Mycobacterium tuberculosis, atypical mycobacteria) and deep fungal infection. Special stains (AFB, Fite, GMS, PAS) and correlation with microbiological cultures are recommended.