Adult Atypical Teratoid/Rhabdoid Tumors.

Background: Atypical teratoid/rhabdoid tumors (AT/RTs) are highly malignant neoplasms that rarely occur in adults. Due to the complex histology of AT/RTs, the differential diagnosis of these tumors is quite challenging and increasingly relies on demonstration of characteristic SMARCB1/INI1 inactivation in tumor cells.

Case Description: A 51-year-old man presented with diplopia, lethargy, and memory deficit owing to Parinaud syndrome and hydrocephalus. Magnetic resonance imaging revealed a T2-hyperintense and homogeneously enhancing tectal mass that extended to the pineal region. Initial biopsy suggested a World Health Organization grade II myxopapillary astrocytoma. However, subsequent definitive resection revealed an AT/RT, with loss of SMARCB1/INI1 observed through immunohistochemical staining as well as array cytogenetic analysis. Molecular profiling revealed additional mutations in RHPN2(L385I), MDM4(D396G), FLT3(V194M), and NPRL3(D53N).

Conclusions: Pathologic diagnoses in the modern era increasingly integrate molecular data for confirmation as well as prognostication. We present a rare case of a tectal AT/RT in an adult patient and report several novel mutations previously unrecognized in this tumor subtype, in addition to canonical SMARCB1/INI1 loss. Further investigation of these novel variants may improve understanding of the pathogenesis underlying AT/RTs.