Differential Diagnosis for Cerebellar Tumor
Single Most Likely Diagnosis
- Medulloblastoma: Although medulloblastomas are more common in children, they can occur in adults. The high Ki-67 index (approximately 70%) and positivity for synaptophysin support this diagnosis, as medulloblastomas are known for their high proliferation rates and expression of neuronal markers like synaptophysin.
Other Likely Diagnoses
- Atypical Teratoid/Rhabdoid Tumor (AT/RT): While less common, AT/RT can present in adults and may express cytokeratins and have a high Ki-67 index. However, the presence of TTF-1 and the specific combination of markers might make this less likely compared to medulloblastoma.
- Primitive Neuroectodermal Tumor (PNET): PNETs can occur in the cerebellum and may have a high Ki-67 index. They can express synaptophysin, but the expression of TTF-1 and cytokeratins might be less typical.
Do Not Miss Diagnoses
- Metastatic Small Cell Lung Cancer: Given the patient's age and the tumor's positivity for TTF-1 and cytokeratins, along with a high Ki-67 index, metastatic small cell lung cancer is a critical diagnosis not to miss. Small cell lung cancer can metastasize to the brain and cerebellum, and TTF-1 positivity is common in lung primaries.
- Lymphoma: Although less likely given the specific marker profile, primary central nervous system lymphoma (PCNSL) or metastatic lymphoma could present with a high Ki-67 index. The clinical context and additional diagnostic tests (e.g., flow cytometry) would be crucial in distinguishing this.
Rare Diagnoses
- Desmoplastic Small Round Cell Tumor (DSRCT) with CNS Involvement: This is an extremely rare tumor that typically affects the abdominal cavity but can, in very rare instances, involve the CNS. The expression of cytokeratins and a high proliferation index could fit, but the clinical context and additional markers (e.g., WT1) would be necessary to consider this diagnosis.
- Cerebellar Neuroblastoma: A rare primitive neuroectodermal tumor of the cerebellum, which could express synaptophysin and have a high Ki-67 index. However, the specific combination of markers provided might not be typical for this entity.