Diffuse midline medullary glioma - H3 K27M–mutant

Case contributed by Dr Bálint Botz

Presentation

No significant prior illness. Sudden out of hospital cardiac arrest (due to aspiration) and CPR. Hiccups and moderate swallowing difficulty for approximately two days before. Positive family history of neurofibromatosis type 1.

Patient Data

Age: 25 years
Gender: Female
  • An inhomogeneous mass is seen in the region of the medulla and pons. The lesion is partially hypodense suggesting necrosis or cystic internal structure
  • The fourth, third and lateral ventricles as well as the quadrigeminal cistern are mildly dilated due to resultant partial obstruction of CSF flow. 
  • Note is also made of the marked dilatation of the intraorbital segment of the right and the retrorbital part of the left optic nerve and the distension of the perioptic CSF space on the right. 
  • Complete right and partial left lower lobe collapse on chest CT due to aspiration (not shown)

An urgent brain MRI with IV contrast was therefore performed. 

  • There is an inhomogeneous mass showing predominantly peripheral enhancement, involving the medulla, pons, the left cerebellar peduncles, as well as the vermis.
  • The lesion also infiltrates the fourth ventricle causing moderate dilatation of the intracerebral CSF spaces cranially. 
  • The intraorbital part of the right optic nerve, as well as the retroorbital segment os the left optic nerve shows fusiform dilatation without abnormal enhancement. Considering the family history these findings are in line with bilateral optic gliomas. 
  • The right perioptic CSF space is distended. 

Case Discussion

The imaging appearance was initially more suggestive of pilocytic astrocytoma, considering the serpiginous peripheral enhancement pattern, and the first preliminary intraoperative histology was in agreement with this. Further morphological analysis of the surgical specimen with light microscopy demonstrated a glial-like tumor tissue with numerous Rosenthal fibers, also favoring a pilocytic astrocytoma in this respect. Immunohistological assessment however showed that the tumor cells were overwhelmingly H3K27me3 negative, and showed nuclear staining on H3K27M-specific immunohistology. The morphological appearance and the immunohistological status seemingly contradict each other. However, it has been shown recently that a substantial minority of H3K27M mutant midline glial spectrum tumors may show morphology other than a "typical" high-grade glioma, including a pilocytic astrocytoma morphology 1

Thus, the final diagnosis was diffuse midline glioma H3 K27M–mutant which is known to be associated with neurofibromatosis type 1

Bilateral optic nerve gliomas are explained are caused by the inherited NF1.

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