CONGENITAL POSTERIOR FOSSA POLAR SPONGIOBLASTOMA

Purpose: 'Polar spongioblastoma' is a historical microscopic description of a tumor pattern that can be observed in a variety of high-grade pediatric and adult CNS neoplasms. It is characterized by bipolar neoplastic cells arranged in distinctive palisades. It is not recognized as a diagnostic entity in the current W.H.O. CNS tumor classification, though some argue it is indeed a unique tumor entity. The purpose of this case study is to increase awareness and encourage continued reporting of this rare congenital brain neoplasm. Methods: Following IRB approval, the medical record of an infant classified as having congenital posterior fossa 'polar spongioblastoma' was abstracted for demographic information, diagnostic details, tumor histopathology and overall clinical course. The medical literature pertaining to congenital CNS tumors, young-age medulloblastoma and 'polar spongioblastoma' was surveyed. Results: A 3 month old presented with progressive irritability, back arching and poor feeding since birth. Scans revealed a large rim-enhancing posterior fossa mass. Gross total resection was performed. There were no metastases. The tumor was comprised nearly exclusively of palisading columns of bipolar cells with a brisk MIB-1 index (10%). There were no morphologic features of medulloblastoma or glioma. Atypical teratoid/rhabdoid tumor was excluded by strong INI-1 immunostaining. There was patchy weak synaptophysin (neuronal) and focal GFAP (glial) staining. A diagnosis of malignant 'polar spongioblastoma' was assigned based on the distinctive histology of this embryonic glioneuronal neoplasm. Conclusions: Whether 'polar spongioblastoma' is a unique tumor entity, rather than a description of tumor cell palisading that can be commonly seen in a variety of high-grade CNS tumors, is controversial. We suggest that the unique feature of virtual complete cellular palisading, in the absence of diagnostic features which would otherwise categorize the tumor into a known neuroepithelial tumor class (e.g., medulloblastoma), should prompt ongoing discussions about the nomenclature for this rare condition. The infant discussed here represents the youngest reported case of polar spongioblastoma. We suggest ongoing reporting of this condition.