brainstem glioma

Brainstem gliomas consist of a heterogeneous group which vary greatly in histology and prognosis.

Terminology

Unless otherwise specified the term brainstem glioma usually refers to the most common histology, the diffuse brainstem glioma, and in children this is most likely a diffuse midline glioma H3 K27M–mutant.

Epidemiology

Brainstem gliomas account for ~25% of all posterior fossa tumors and are most common in children between 7 and 9 years of age . There is no recognized gender or racial predilection.

Brainstem gliomas are also recognized in adults, although they are rare accounting for only 2% of adult brain tumors . They typically occur in younger adults (third and fourth decade) and tend to be of low grade (WHO I or II) .

Clinical presentation

Although the exact presentation will vary according to location and size of the tumor, in general patients will exhibit a combination of  :

The duration of symptoms is usually much shorter in diffuse gliomas, in which the history is typically very short (a few days) . Additionally, diffuse gliomas more frequently have multiple cranial nerve palsies.

Pathology

Histology

Recognized histological types include:

  • diffuse astrocytoma
  • focal glioma
  • (dorsally) exophytic glioma
    • Low-grade astrocytoma 
    • ganglioglioma
  • NF1 associated brainstem glioma
    • seen in up to 9% of NF1 patients
    • most frequently seen in the medulla
    • appears similar to a sporadic focal brainstem glioma but has an even better prognosis, with little if any progression
Classification

The most frequently used classification system is to divide these tumors into four types :

  • diffuse brainstem glioma
  • focal brainstem glioma
  • (dorsally) exophytic
  • cervicomedullary
    • probably an artificial group made up of the downward extension of true brainstem gliomas or upward extension of upper cervical cord intramedullary spinal cord tumors
  • Associations
    Location

    As a general rule mesencephalic tumors tend to be of a lower grade than those in the pons and medulla .

    • pontine
      • most common location
      • classic location for the childhood 'brainstem glioma' which tends to refer to a diffuse pontine glioma, the majority of which are diffuse midline gliomas, H3 K27M–mutant
      • focal dorsally exophytic brainstem glioma is an uncommon variant accounting for only 10% of pontine tumors, and has a much better prognosis, as it usually represents a pilocytic astrocytoma
      • overall survival of pontine gliomas is 10% at 5 years
    • mesencephalic
    • medullary
      • least common location
      • includes focal dorsally exophytic, focal, diffuse and cervicomedullary junction variants
      • cervicomedullary junction tumors usually represent upper cervical tumors extending superiorly
      • most common location for NF1 associated tumors

    Radiographic features

    MRI

    MRI is the imaging modality of choice. The appearance will vary with the tumor type, thus please refer to individual articles.

    DSA/angiography

    May show anterior displacement of the basilar artery.

    Treatment and prognosis

    Again, both treatment and prognosis are significantly influenced by tumor type, morphology and location. Radiation is a key part of treatment.

    As a general rule, dorsal exophytic tumors and cervicomedullary tumors tend to do best with surgery, whereas surgery has no role in the management of diffuse brainstem gliomas.

    Prognosis
    • diffuse
      • terrible prognosis
      • 90-100% patients die within 2 years of diagnosis
    • focal (tectal glioma)
      • excellent long-term survival with CSF shunting (essentially benign lesions)
    • focal (other)
      • good long-term prognosis with surgery
    • (dorsally) exophytic tumors
      • good long-term prognosis with surgery​