Occult very small lung carcinoma with a solitary brain metastasis that is clinically diagnosed as cavernous hemangioma: a case report

The author reports herein a case of occult very small lung carcinoma with a solitary brain metastasis that is clinically diagnosed as cavernous hemangioma, with an emphasis on pathologic findings. A 48-year-old Japanese man was admitted to our hospital complaining of mild paresis of left leg. Brain CT and MRI showed a solitary tumor (2 cm) with features of cavernous hemangioma in the right temporal lobe. Tumorectomy was performed, and it was pathologically undifferentiated carcinoma. An immunohistochemical analysis reveled that the carcinoma cells were positive for four types of pancytokeratin, cytokeratin (CK) 5/6, CK7, CK18, CK19, p63, and Ki-67 (78%). They were negative for high molecular weight CK, CK14, CK20, TTF-1, PE-10, melanosome, S100 protein, EMA, vimentin, CD34, myoglobin, CEA, p53, desmin, alpha-smooth muscle actin, chromogranin, synaptophysin, CD56, neuron-specific enolase, CD68, KIT, and PDGFRA. The positive CK7 and negative CK20 suggested lung origin, and cytokeratin profiles and positive CK5/6 and p63 suggested a squamous differentiation. The pathological diagnosis was undifferentiated carcinoma with squamous differentiation probably of lung origin. Later, systemic CT, MRI and PET were performed, and they detected a small lung tumor (8 mm) in the right apex. The lung biopsy revealed an undifferentiated carcinoma with focal squamous differentiation; the immunohistochemical findings were the same as those of the brain tumor. These findings suggest that occult very small lung carcinoma can metastasize to brain and such a metastasis may mimic cavernous hemangioma radiologically. Pathologic observations using many antibodies are very useful to determine the origin and histological type in solitary brain nodule.