A 12-year-old child presents with annular, skin-colored papules over the dorsal surfaces of both hands that have persisted for 3 months. Dermoscopic examination and biopsy are performed. The histological section shows a characteristic ring-like arrangement of inflammatory cells surrounding a central zone of degenerated collagen and mucin. The structure marked **A** in the diagram represents the inflammatory cells forming this distinctive palisade pattern. Which of the following best describes the cell type and its role in the pathogenesis of this lesion?

Explanation

## Why option 1 is correct The structure marked **A** (palisading histiocytes) is the defining histological hallmark of granuloma annulare. These activated macrophages arrange themselves in a palisade pattern around a central zone of degenerated collagen and mucin deposition, creating the characteristic granulomatous response. This benign, self-limited condition is most common in children and young adults, presenting as annular (ring-shaped) lesions on the dorsa of hands, feet, and fingers. According to Robbins 10e Ch 25, the palisading histiocytes are the key inflammatory component that distinguishes granuloma annulare histologically and defines its granulomatous nature. ## Why each distractor is wrong - **Option 2**: Langerhans cells are antigen-presenting cells seen in contact dermatitis and other hypersensitivity reactions. Granuloma annulare is not a hypersensitivity reaction to a known exogenous antigen, and Langerhans cells do not form the palisading pattern seen in this condition. - **Option 3**: Epithelioid cells and multinucleated giant cells are seen in caseating granulomas (tuberculosis, leprosy) and non-caseating granulomas (sarcoidosis). Granuloma annulare does not form true epithelioid granulomas with giant cells; it is characterized by palisading histiocytes without caseation. - **Option 4**: Diffuse plasma cell and lymphocyte infiltration is typical of systemic autoimmune conditions and chronic inflammatory dermatoses. Granuloma annulare is a benign, localized condition with a specific palisading histiocytic pattern, not diffuse lymphoplasmacytic infiltration. **High-Yield:** Granuloma annulare = palisading histiocytes around degenerated collagen + mucin; benign, self-resolving in children; distinguish from tinea corporis (KOH positive, scale) and sarcoidosis (systemic features, diffuse granulomas). [cite: Robbins 10e Ch 25]