Angiocentric glioma

Angiocentric gliomas are rare superficial slow-growing WHO grade 1 brain tumours typically presenting in pediatricpaediatric patients with intractable partialfocal epilepsy ^1-6. 

Epidemiology

Angiocentric gliomas are very rare tumours with relatively few reported cases. They usually affect children and young adults ^1,6. No reported gender predilection has been reported ¹. 

Clinical presentation

Seizures are the classical presentation, with over 95% of patients presenting with intractable seizures ³.

Pathology

Angiocentric gliomas are considered pediatricpaediatric-type diffuse low-grade gliomas and designated as WHO grade 1 tumour in the current WHO brain tumour classification ^1-3,7. The exact aetiology of angiocentric gliomas remains unclear although some features are similar to ependymomas ^1,6. In fact, sometimes, a distinct ependymoma component may co-exist ¹.

Microscopic appearance

These tumours demonstrate a monomorphic population of elongated spindle-shaped bipolar cells with a strikingly perivascular orientation, somewhat reminiscent of perivascular pseudorosettes ^1,6. Although tumour cells do extend into the surrounding parenchyma, a strong predilection for perivascular spread is evident ⁶. Subpial growth along the surface of the cortex is also a prominent feature ^1,6.

Immunophenotype

The immunophenotype shares some similarities to ependymomas ¹. 

• GFAP: positive
• EMA: both surface and perinuclear cytoplasmic dot may be present

Ki-67 index is usually <5% ¹. 

They do not demonstrate neuronal markers (e.g. synaptophysin, chromogranin-A, neuronal nuclear antigen) and they are isocitrate dehydrogenase (IDH) negative.

Associations

Cortical dysplasia may be associated.

Radiographic features

Angiocentric gliomas are usually cortical or subcortical (grey-white matter junction), typically well-delineated, supratentorial tumours that tend to expand affected gyri. They exhibit a propensity to spread horizontally in the subpial plane and deeply along vessels ¹.

CT

Typically appear as an expansile non-enhancing cortical tumour.

MRI

• T1
  • hypointense
  • hyperintense rim may be seen
• T2 / FLAIR
  • hyperintense
  • extension toward the ventricles along vessels
  • may have cystic-appearing areas
• T1 C+ (Gd): no enhancement

History and etymology

Angiocentric glioma was initially identified in 2005 in two separate case reports ^2,5 and then introduced in the WHO classification of CNS tumours in 2007.

Differential diagnosis

Given their rarity, on purely imaging grounds it is difficult to distinguish these tumours from more common diffuse gliomas (both astrocytoma and oligodendroglioma). Other imaging differential considerations include:

• focal cortical dysplasia
• cortical tuber (forme fruste of tuberous sclerosis)
• DNET 
  • "bubbly" cortical and subcortical lesion
  • rim of high signal on FLAIR
  • minimal surrounding oedema
• perivascular spaces
  • total nulling on the FLAIR sequence
• ganglioglioma/gangliocytoma
  • usually enhance
  • well defined
• multinodular and vacuolating neuronal tumours
  • subcortical cluster of cystic-like lesions