Small cell carcinoma of the brain without extracranial involvement by serial CT, MRI and PET

The author reports herein a case of small cell carcinoma of the brain without extracranial tumors by serial imaging modalities. A 75-year-old man presented with headache. Brain CT and MRI revealed a solitary cystic tumor (5 x 6 x 7 cm) in the left occipital lobe. Blood laboratory test revealed no significant findings. Preoperative diagnosis was a primary or metastatic brain tumor. Preoperative systemic examinations including CT, MRI and PET revealed no extracranial tumors. Tumorectomy was performed. Pathologically, the tumor was small cell carcinoma positive for four types of pancytokeratins, cytokeratin (CK) 7, CK 18, thyroid transcriptional factor-1 (TTF-1), CD56, chromogranin, synaptophysin, neuron-specific enolase, p53 protein, KIT, PDGFRA, and Ki-67 antigen (labeling = 100%). It was negative for high molecular weight CK, CK5/6, CK14, CK19, CK20, PE10, epithelial membrane antigen, vimentin, CEA, desmin, S100 protein, CA19-9, alpha-smooth muscle actin, CD34, p63, and CD68. The pathologic examination strongly suggested primary small cell lung carcinoma. However, repeated serial imaging modalities including systemic CT, MRI and PET revealed no extracranial tumors. The serial sputum cytology was always negative. The patient was treated with radiation and cisplatin-based chemotherapy, and no tumors were found seven months after the operation. The present case suggests that there are small cell carcinomas with a solitary brain metastasis without a radiologically detected primary site. In the present case, primary small cell brain carcinoma cannot be excluded completely, although such a case has not been reported in the literature.