Atypical Teratoid Rhabdoid Tumor With TTF-1 Expression: A Case Report and Possible Insight Into Its Embryologic Origin.

Atypical teratoid rhabdoid tumor (AT/RT) of the brain is a highly malignant (CNS WHO grade 4) embryonal neoplasm. Majority of AT/RTs occur in the posterior fossa although supratentorial examples may also be observed. Pathologically, the tumor typically consists of cells with rhabdoid morphology that are immunoreactive for synaptophysin, EMA, and variably for GFAP. Diagnosis is typically confirmed by observing loss of INI-1 or BRG-1 expression from the nucleus of the tumor cells. Little is known regarding the embryogenesis of AT/RT. We therefore present here a case of supratentorial AT/RT in a 3-year-old male who presented with fatigue, irritability, left facial drop, left sided weakness of arm and leg, headaches, and vomiting. Neuroimaging revealed a large tumor involving the basal ganglia and foramen of Monro. Neuropathologic examination of the resected tumor revealed morphologic, immunohistochemical, and molecular evidence of an AT/RT (Group 1, SHH subtype). The tumor cells additionally exhibited immunoreactivity for TTF-1 (also known as NKX2.1), which has been reported to be expressed in GABAergic precursor cells in the medial ganglionic eminence. This example may provide at least a small insight into embryonic origins of supratentorial AT/RT.