The patient was submitted to a resection of the brain lesion; histology confirmed it to be metastatic lung cancer. The case is a good example of how to approach a ring-enhancing cerebral mass and the difficulties that sometimes occur when trying to differentiate between high-grade glioma and metastasis.

MICROSCOPIC DESCRIPTION: Paraffin sections show discrete islands of a densely hypercellular tumor within brain parenchyma. These are composed of epithelioid cells in which a prominent peripheral basaloid type cell layer differentiates centrally into squamous epithelial cells. Foci of keratinization are discernible as well as intercellular bridges. Frequent mitotic figures are identified. All tumor islands show extensive central necrosis imparting a pseudo-cystic appearance. The features are of metastatic poorly differentiated squamous cell carcinoma and are most consistent with an origin from lung.

DIAGNOSIS: "Left frontal brain lesion": Metastatic poorly differentiated squamous cell carcinoma with features most consistent with an origin from lung.