Aggressive clinical behavior of desmoplastic myxoid tumor of the pineal region, SMARCB1-mutant: expanding the biological spectrum of a rare central nervous system neoplasm.

Desmoplastic myxoid tumor of the pineal region, SMARCB1-mutant (DMT-SMARCB1) is a rare central nervous system neoplasm, with only approximately 15 reported cases. Published cases suggest a relatively indolent clinical course with low proliferative activity and no radiologically documented disseminated disease. We report a 47-year-old woman with a pineal region mass who developed aggressive recurrence and focal leptomeningeal dissemination following ventriculoperitoneal shunt placement and Gamma Knife radiosurgery. Histologically, the tumor was composed of discohesive rhabdoid cells embedded within a prominent myxoid stroma and focal collagenous matrix. Immunohistochemistry demonstrated loss of INI1 expression. DNA methylation profiling, interpreted in conjunction with histopathological and immunohistochemical findings, supported the diagnosis of DMT-SMARCB1 and demonstrated molecular proximity to other SMARCB1-deficient central nervous system neoplasms. Literature review revealed no previous reports of radiologically documented leptomeningeal dissemination. This case expands the clinicopathologic spectrum of DMT-SMARCB1 and highlights the potential for aggressive biological behavior despite relatively low-grade histologic features.