Primary diffuse leptomeningeal atypical teratoid/rhabdoid tumor diagnosed by cerebrospinal fluid cytology: case report with molecular genetic analysis.

Atypical teratoid/rhabdoid tumors (AT/RT) are rare malignant neoplasms that mainly affect infants and young children, and are typically located in the cerebellar hemispheres. These tumors are histologically characterized by varying proportions of rhabdoid cells, and nuclear INI1 immunonegativity. Here, we report a case of a 15-year-old male with primary diffuse leptomeningeal AT/RT. The patient had symptoms similar to those of meningitis. Magnetic resonance imaging revealed leptomeningeal thickening. Cytological examination using cerebrospinal fluid was repeatedly performed and revealed rhabdoid cells with loss of INI1 reactivity, and shortly after, the diagnosis of AT/RT was confirmed by tissue biopsy. Multiplex ligation-dependent probe amplification analysis revealed compound heterozygous microdeletion of the SMARCB1/INI1 locus. Leptomeningeal AT/RT without primary mass is extremely rare - only four cases have been previously reported to date. To the best of our knowledge, this is the first case report of primary leptomeningeal AT/RT with detailed genetic information.