シリコーン肉芽腫におけるFite染色：これまで報告されていなかった診断上の落とし穴と潜在的な診断補助

Silicone granulomas can have histologic features that mimic xanthogranulomatous inflammation, particularly in small samples or when the diagnosis is unsuspected. Histochemical stains for microorganisms may be performed to assess for infection in such cases. After observing diffuse Fite staining in a specimen exhibiting histologic features of silicone granuloma, the frequency of Fite staining in a series of confirmed silicone granulomas was assessed. Modified acid-fast (Fite) staining was performed in 20 silicone granuloma cases. In a subset (n=5), Ziehl-Neelsen (Z-N), Grocott's methenamine silver (GMS), and Brown & Brenn (B&B) stains, as well as mycobacterial immunohistochemistry were also performed. All 20 cases (100%) demonstrated Fite staining, ranging from patchy (45%) to diffuse (55%). Finely vacuolated histiocytes exhibited reticular to granular Fite staining, some morphologically resembling bacteria, whereas larger vacuolar spaces showed globular to crescent-like staining at their peripheral edges. Focal Z-N staining in a pattern similar to Fite staining was observed in 4 of the 5 cases examined. GMS, B&B, and mycobacterial IHC were negative. Silicone granulomas consistently show Fite staining. While the reason for this is uncertain, it is postulated that the hydrophobicity of silicone polymers may simulate the hydrophobic barrier of mycolic acids, preventing entry of decolorizer and removal of the primary stain. Recognition of this phenomenon is important to avoid misinterpretation of silicone granulomas as infectious. Fite staining may also serve as a potential diagnostic aid in cases with histologic features of silicone granuloma in which a history of silicone injection or silicone implant use is not established.