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Disorders Techniques in Investigation and Diagnosis - part 9

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Nail u ác tính khối u ác tính của bộ máy móng tay phổ biến nhất bắt nguồn từ ma trận, ít hơn nhiều từ nền móng hoặc hyponychium. Matrix khối u ác tính thường gây ra theo chiều dọc melanonychia (xem Chương 5). Cho dù tăng sản melanocytic không điển hình đã được subungual ở u ác tính tại chỗ là không hoàn toàn rõ ràng. | Histopathology of common nail conditions 277 Nail melanoma Melanoma of the nail apparatus most commonly derives from the matrix much less frequently from the nail bed or hyponychium. Matrix melanoma usually causes longitudinal melanonychia see Chapter 5 . Whether atypical melanocytic hyperplasia is already subungual in situ melanoma is not entirely clear. Large atypical melanocytes in all layers of the matrix and nail bed epithelium pycnotic melanocytes in the nail plate mirroring the pagetoid spread in the epithelium and mitoses are seen as proof of a malignant melanoma. Sometimes nail clippings reveal single intraungual pycnotic melanoma cells which retain their protein S-100 positivity. Most subungual melanomas are of acrolentiginous type however those in the nail bed tend instead to be nodular melanomas. Even long-standing melanomas are often still very superficial. Invasive melanomas have therefore usually a decade-long history. Epidermoid carcinoma The term epidermoid carcinoma denotes both ungual Bowen s disease and squamous cell carcinoma. Commonly originating from the lateral sulcus Bowen s disease slowly spreads under and around the nail. Histologically all changes typical of Bowen s disease of the skin are seen loss of orderly architecture and polarity of basal cells atypical nuclei pathological mitoses some giant cells dyskeratoses often vacuolization and even clear cells. After decades the lesion develops into invasive squamous cell carcinoma which however may also develop without prior bowenoid changes. Malignant onycholemmal cyst is probably a particular form of Bowen s disease as was seen in a case in which the cyst after incomplete removal rapidly showed the features of typical squamous cell carcinoma author s unpublished observation . FURTHER READING Alessi E Zorzi F Gianotti R Parafiori A 1994 Malignant proliferating onycholemmal cyst J Cut Pathol 21 183-188. Baran R Goettmann S 1998 Distal digital keratoacanthoma a report of 12 cases and review