The diagnosis of cutaneous adnexal neoplasms, a heterogeneous group of entities, is often perceived by practising pathologists as challenging. A systematic approach to diagnosis is necessary for classification of these lesions, which establishes the tumour differentiation (follicular, sebaceous, sweat gland or apocrine) and evaluates histological features differentiating between benign and malignant entities. Consideration of clinical history is a necessary adjunct in evaluation of the adnexal neoplasm, as characteristic anatomical sites are described for many adnexal lesions. In some instances, immunohistochemical studies may also be employed to aid the diagnosis. The differential diagnosis between primary cutaneous adnexal neoplasms and cutaneous metastases from visceral tumours may also be difficult. Clinical, radiological, histological and immunohistochemical characteristics will be further discussed, considering that the correct diagnosis has a significant impact on the patient's management and prognosis.
The differential diagnosis of heavily pigmented melanocytic neoplasms includes melanoma (especially animal type), melanosis of partially or completely regressed melanoma, blue naevus (BN), pigmented Spitzoid lesions, recurrent naevus, combined naevus, pigmented spindle cell naevus, epithelioid blue naevus of the Carney complex/pigmented epithelioid melanocytoma, deep penetrating naevus, hyperpigmented scar after surgery of melanoma in which there are also melanophages and hyperpigmentation due to the minocycline, a tattoo or a hyperpigmented scar. Pathologists face challenges when evaluating a pigmented lesion, especially in a small superficial biopsy, because it is difficult to access important histopathological features to differentiate benign versus malignant melanocytic lesions. The histological features that favour a diagnosis of melanoma include dimension (>6 mm), asymmetry, poor circumscription, irregular confluent nests, confluent lentiginous junctional melanocytic proliferation, lack of maturation with descent in the dermis, suprabasal pagetoid melanocytes, asymmetrical distribution of melanin pigment, cytological atypia, dermal mitotic figures, asymmetrical dermal lymphocytic infiltrate and necrosis.
We report a case of cutaneous Stenotrophomonas maltophilia infection which presented with clinical and histopathological findings that mimicked a gamma/delta (γδ) T-cell lymphoma. In this case, tissue culture of the biopsy specimen was key to determining the diagnosis and allowing appropriate treatment with oral trimethoprim-sulfamethoxazole and topical silvadene. A prompt complete resolution of lesions was observed following antibiotic treatment, with no recurrence of disease over the last 5 years, supporting an infectious rather than malignant etiology. In our patient, radiation therapy was indicated based on the misdiagnosis of γδ T-cell lymphoma, which was supported both clinically and histopathologically. However, tissue culture in this case avoided unnecessary radiation exposure and highlights the role of tissue culture in the evaluation of the biopsy of an undiagnosed cutaneous lesion.
Anaplastic thyroid carcinoma is a highly aggressive cancer accounting for 1-2% of thyroid malignancies. Cutaneous metastases from anaplastic thyroid carcinoma are exceedingly rare. We report a 65-year-old woman with anaplastic thyroid carcinoma (BRAF V600E mutation) who had lymph node metastases (pT4 N1b) treated by total thyroidectomy, postoperative radiotherapy, adjuvant chemotherapy (paclitaxel and pazopanib) and targeted therapy (vemurafenib). Nine months after initial diagnosis, radiographic studies revealed multiple pulmonary metastases. A dermatologic examination showed a solitary 1.2-cm chest nodule. Skin biopsy from this nodule revealed infiltrative dermal spindle cells arranged in poorly formed fascicles. Immunohistochemical studies demonstrated the tumor cells to be PAX-8 (+), pancytokeratin (+, focally), TTF-1 (-) and SOX-10 (-). Comparison with the patient's primary anaplastic thyroid carcinoma revealed focal areas of poorly differentiated spindle cells morphologically similar to the malignant spindle cells in the skin biopsy. Together, these findings confirmed the diagnosis of anaplastic thyroid carcinoma metastatic to skin. Cutaneous metastasis of anaplastic thyroid carcinoma composed exclusively of spindle cells broadens the histologic differential diagnosis of cutaneous spindle cell malignancies and presents further diagnostic challenges. PAX-8 may be useful in discerning the spindle cell component of anaplastic thyroid carcinoma from other spindle cell malignancies in the skin.
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