Astroblastoma

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Astroblastomas are rare glial tumors usually found in the cerebral hemispheres of young adults and children.

Epidemiology

They occur at all ages range from early childhood to 6th decade but are most commonly seen in children, adolescents, and young adults with a mean age between 10-30 years . A female predilection has been suggested in some reports .

Pathology

Astroblastomas, along with choroid gliomas of the third ventricle and angiocentric gliomas, are grouped as other neuroepithelial tumors in the current (2016) version of the WHO classification of CNS tumors .

They have not yet been given a WHO grade, but do have a range of histological appearance and biological behavior ranging from relatively indolent (astroblastoma) to aggressive (anaplastic or malignant astroblastoma) .

Macroscopic appearance

They are well-demarcated masses with areas of cystic degeneration and necrosis giving it a bubbly appearance. Hemorrhage and adjacent brain infiltration are rare.

Microscopic appearance

Astroblastomas have elongated glial cells with abundant eosinophilic cytoplasm and a broad, or “stout”, GFAP positive process extending radially towards a central blood vessel, forming "astroblastic pseudorosettes", reminiscent to the perivascular pseudorosettes of ependymomas, which are a characteristic feature of this tumor. The central vessel tends to be hyalinized.

Although no agreed-upon criteria have been accepted, anaplastic/malignant histological features include :

  • increased mitotic activity (>5 mitoses per 10 high-powered fields)
  • high cellularity 
  • anaplastic nuclear features
  • microvascular proliferation
  • palisading necrosis 
  • usually Ki-67 >10%
Immunophenotype

Radiographic features

Astroblastomas are usually fairly sizable, peripherally located, supratentorial lobulated solid cystic masses with little if any associated vasogenic edema . Multiple cysts are common and can give it a bubbly appearance. Calcification is very common and seen in 85% of cases, and usually in a punctate pattern.

MRI

Reported signal characteristics include

  • T1: iso- to hypointense
  • T2/FLAIR: heterogeneously hyperintense
  • T1 C+ (Gd): heterogeneous enhancement

Treatment and prognosis

Surgical resection is the treatment of choice with adjuvant radiation therapy and chemotherapy reserved for high-grade lesions. Recurrence after complete surgical resection of low-grade tumors is uncommon .

Differential diagnosis

Possible imaging differential considerations include: