A 78 year-old woman presented with a 3 X 2 cm dermal nodule on the scalp. The clinical differential diagnosis was cylindroma plexiform neurofibroma vs angiofibroma. A punch biopsy in the middle of the lesion was performed.
The following diagnosis was rendered: "Epithelial tumor with eccrine differentiation in deep dermis, extending to specimen margins, see note. Note: The lesion is positive for keratin and negative for SMA consistent with an appendageal tumor, most suggestive of nodular hidradenoma. No necrosis, significant cytologic atypia or mitoses are seen, however the lateral circumscription, infiltrative nature or potential behavior cannot be determined on this incisional biopsy.” A complete excision was recommended which was performed.
Cutaneous sweat gland tumors can present diagnostic challenges because they are uncommon and can have a variety of histologic appearances that define different subtypes (which have many different names). The most important decision is benign vs. malignant.
Well-circumscribed, lobular growth
Two cell layers to ducts
Clear cell change, squamoid areas, papillary apocrine features
Fibrous stroma, thick capsule
Small dark nuclei, minimal pleomorphism
Rare mitoses, no necrosis
Tumor invades capsule
Large, pleomorphic nuclei
Recurrence after incomplete excision