What are the characteristics of diffuse midline glioma H3 K27M-mutant?
Diffuse midline glioma with histone H3 K27M mutation is an entity in the 2016 World Health Organization (WHO) Central Nervous System tumor classification as a WHO grade 4, including those tumors which demonstrate low-grade histologic features on biopsy. The lesions are usually in the pons of young children, which have aggressive clinical behavior and poor prognosis.
Where are the locations of diffuse midline glioma H3 K27M-mutant?
Diffuse midline glioma H3 K27M-mutant localizes throughout the midline structures of the central nervous system: thalami, hypothalamus, third ventricle, pineal region, brainstem (mesencephalic, pontine, medullary), spinal cord.
How is the clinical presentation of diffuse midline glioma H3 K27M-mutant?
Patients with brainstem tumors typically present with multiple cranial nerve palsies, long-tract signs, ataxia, and signs/symptoms of raised intracranial pressure. Other signs may include dysarthria, nystagmus, double vision, swallowing difficulties, slurred speech, and sleep apnea.
What are the radiographic features of diffuse midline glioma H3 K27M-mutant?
The radiographic features are asymmetric enlargement of the pons with the tumor usually centered in the ventral pons, often encircling the basilar artery, which is displaced anteriorly against the clivus. The floor of the fourth ventricle may be flattened, known as the flat floor of the fourth ventricle sign, and obstructive hydrocephalus may be present. These tumors may extend upwards into the midbrain and thalami or downwards into the medulla and spinal cords and may infiltrate the cerebellum. The lesion is T2 hyperintense, occasionally with intratumoral hemorrhage and necrosis, and variable features of contrast enhancement.
How is the treatment of diffuse midline glioma H3 K27M-mutant?
The treatment options include surgery, radiation, chemotherapy, and clinical trials. The tumor is usually treated without biopsy because the risk of histological confirmation has a high rate of complications. A stereotactic biopsy may be a tool for molecular characterization and identifying the type of the mutation and therefore target the chemotherapy or immunotherapy drugs.
There is an expansile mass centred in the pons, abutting, displacing the basilar artery anteriorly, and flattening the floor of the fourth ventricle. The lesion is hyperintense on T2-weighted and FLAIR imaging and low signal on T1-weighted, restricted diffusion with low ADC, presumed to reflect high tissue cellularity. The lesion shows mild peritumoral edema/infiltration. Hydrocephalus is not present.
Impression: Diffuse midline glioma, H3 K27M-altered (WHO 2021).