Cutaneous Scalp Metastasis Unveiling an Occult Lung Adenocarcinoma: A Case Report

Cutaneous metastasis from internal malignancies is an uncommon clinical occurrence, with skin involvement as the initial manifestation of visceral malignancy being particularly rare. We report the case of an 84-year-old male who presented with a hyperpigmented proliferative lesion on the left parietal scalp, clinically suspected to be a primary skin malignancy. Wide local excision was performed, and histopathological examination surprisingly revealed metastatic adenocarcinoma. Immunohistochemistry (IHC) of the tissue showed positivity for Cytokeratin (CK) 7, CK 20 and Thyroid Transcription Factor (TTF1), indicative of a pulmonary origin. Subsequent Fluorodeoxyglucose Positron Emission Tomography (FDG PET)-Computed Tomography (CT) imaging identified a metabolically active mass in the right lower lobe of the lung, along with right paratracheal lymphadenopathy and skeletal metastases. This case highlights the critical role of histopathology and IHC in identifying metastatic skin lesions and determining their origin. Lung adenocarcinoma is known to metastasise to the skin, although scalp involvement as the initial presentation is extremely rare. This case underscores the importance of considering metastatic disease in atypical skin lesions, particularly in elderly patients, and illustrates the need for a multidisciplinary approach to diagnosis and management.