Contributed by Lincy Thomas, MD1, Naina Gross, MD2, Spencer Thompson, MD3, Rene McNall-Knapp, MD1, David Ellison, MD, PhD4, Jason Chiang, MD, PhD4, Jo Elle Peterson, MD5, Kar-Ming Fung, MD, PhD5 , Abhishek Bavle, MBBS1.
1Jimmy Everest Section of Pediatric Hematology-Oncology, University of Oklahoma;
2Department of Neurosurgery, University of Oklahoma; 3Department of Radiation Oncology, University of Oklahoma;
4Department of Pathology, St. Jude Children's Research Hospital, 5Department of Pathology, University of Oklahoma, Oklahoma City, Oklahoma, USA.
A 4-year-old girl presented with right hemiparesis and ataxia. Her symptoms progressed rapidly and she could no longer ambulate without assistance. Her exam was remarkable for severe right-sided weakness of both upper and lower extremities. The MRI showed a left thalamic, hemorrhagic mass measuring up to 42 x 33 x 38 mm (Figs. 1a, 1b). Mass effect on the third ventricle was noted with resultant acute obstructive hydrocephalus. Interval placement of an EVD at the time of presentation helped mildly improve ventricle size. Gross total resection was performed by a parietal craniotomy and inner hemispheric, transcallosal approach.
Histology revealed a hypercellular tumor with small blue cells, scant cytoplasm, nuclear pleomorphism, and increased mitotic activity (Fig. 1c). Tumor cells stained diffusely for synaptophysin (Fig. 1e) and were negative for GFAP (Fig. 1d). Due to its midline location and atypical morphology, immunostaining for the mutant histone H3 p.K27M protein and H3 K27Me3 were also performed. Tumor cells stained negative for H3K27Me3 (Fig. 1g) and positive for H3K27M (Fig. 1f). What is your diagnosis?