A rare high-grade glioma with a histone H3 K27M mutation in the hypothalamus of an adult patient: a case report.

"Diffuse midline glioma, H3 K27M-mutant" is a new tumor entity described in the revised 2016 World Health Organization classification. It is most frequently observed in children, and develops in midline structures including the brainstem, thalamus, and spine. We describe a rare diffuse midline glioma with an H3 K27M mutation arising in the hypothalamus of an adult.A 27-year-old woman was admitted to our department complaining of amenorrhea, polydipsia, and diuresis for the previous 3 months, as well as headache and lethargy for approximately 10 days. Computed tomography showed an oval isodense solid mass extending from the pituitary towards the suprasellar cistern. A Gadolinium-enhanced magnetic resonance imaging (MRI) showed a strongly heterogeneous enhanced solid lesion and non-enhanced cystic lesion. The patient underwent surgery as well as chemoradiotherapy with temozolomide. Histological and immunohistochemical analyses revealed H3 K27M-mutant diffuse midline glioma. The patient underwent another resection for a recurrent tumor 5 months after the first surgery. Three months after the second operation, the patient relapsed, with MRI revealing spinal cord and meningeal metastases; she died shortly afterwards.Diffuse midline glioma with an H3 K27Mmutation occurring in the hypothalamus of an adult is rare, but should be considered in differential diagnoses. As histone H3K27M mutations are associated with aggressive clinical behavior and poor prognosis, molecular analyses should be used to determine the clinical and histopathological features of such tumors. This will contribute to developing targeted drugs and gene therapy going forward.