Imaging Findings

Diffuse brainstem gliomas infiltrate and occupy large portions of the brainstem, best seen as expansile hyperintense lesions on T2WI. They are hypodense on CT, of low T1 signal, and usually with minimal or no enhancement. Areas of necrosis, cystic change, hemorrhage, and focal enhancement may be present. Tumors most commonly arise in the pons and can infiltrate into the mesencephalon, medulla, or cerebellar peduncles. Exophytic growth with effacement of the basilar cisterns and engulfing of the basilar artery is frequently present. Appearance on diffusion imaging varies, usually from slightly brighter to slightly darker compared to the normal brain. MR spectroscopy shows nonspecific elevated choline and decreased NAA; increased lactate appears to be a poor prognostic sign. Focal brain stem tumors occupy less than 50% of the axial diameter of the brainstem, have well-defined margins and frequently an exophytic component.

Pertinent Clinical Information

The mean age at diagnosis is around 8 years, brainstem gliomas rarely occur in adults. Clinical presentation includes multiple cranial neuropathies, long tract signs, and ataxia. Diffuse pontine tumors are the most common and have the worst prognosis with a median survival of 9–18 months. A short duration of symptoms appears to be associated with worse prognosis. MRI is the main diagnostic modality, while biopsy is usually not performed because of the associated risks.

Differential Diagnosis

Pilocytic Astrocytoma (173)

1. • usually well-defined margins

2. • usually homogenous contrast enhancement

3. • very high ADC values