Pleomorphic xanthoastrocytoma

Pleomorphic xanthoastrocytomas (PXA) are a type of rare, low-grade astrocytoma (WHO Grade II) found in young patients who typically present with temporal lobe epilepsy.

They usually present as cortical tumours with a cystic component and vivid contrast enhancement. Features of slow growth may be present, such as no surrounding oedema and scalloping of the overlying bone. A reactive dural involvement expressed by a dural tail sign can be found. Calcifications are rare. 

They are rare tumours accounting for only 1% of primary brain tumours 2-3,6. Typically these tumours are found in young patients (children or young adults), with a peak incidence in the second and third decade of life (10-30 years-of-age) 6

As these tumours have a predilection for the temporal lobe, they most frequently present with seizures (~ 75% of cases) 1,2. Other findings include dizziness, and headache or rarely patients are asymptomatic 5.

Grading

Pleomorphic xanthoastrocytomas are considered WHO grade II tumours. If mitoses are more frequent (>5 mitoses per 10 high-power fields) then a diagnosis of anaplastic pleomorphic xanthoastrocytoma (WHO grade III) should be made 6

Location

Pleomorphic xanthoastrocytomas are almost invariably (98%) located supratentorially, typically located superficially (peripherally) abutting the leptomeninges, involving the cortex and overlying leptomeninges but actual dural involvement is rare. Approximately half are located in the temporal lobe with rest of lesions are more common in frontal and then parietal lobes 4,6.

Macroscopic appearance

Macroscopically these tumours appear well circumscribed, often with cystic component and involvement of the overlying leptomeninges 1,3.

Microscopic appearance

Microscopically the margins are not as well defined. The histological features are variable (thus the term 'pleomorphic') with spindle cells, polygonal cells, multinucleated cells and lipid-laden xanthomatous astrocytes are all identified 6. Even more pleomorphic is the appearance of the nuclei, with common nuclear inclusions, and highly variable nuclear size 6

Immunophenotype

Immunohistochemistry demonstrates expected glial marker reactivity. Less obviously, there is also variable reactivity for neuronal markers 3,6:

Ki-67 proliferation index: <1% 6

Genetics

Pleomorphic xanthoastrocytomas, as well as pilocytic astrocytomas (and many non-CNS tumours), exhibit BRAF mutations 6,7. The only reported association is with neurofibromatosis type 1, although this is not a strong association 6

Pleomorphic xanthoastrocytomas appear as a solid enhancing nodule, frequently with peripheral eccentric cystic component (50-60%). Due to their peripheral location and leptomeningeal involvement, they are one of the tumours that may exhibit a dural tail. This is reactive rather than due to true direct dural invasion, which is rare 2,6. As these lesions are very slow growing and superficial remodelling of the adjacent skull is characteristics and vasogenic oedema is variable 5

CT

Pleomorphic xanthoastrocytomas are typically hypodense or isodense and may be well or poorly demarcated, usually with no or little surrounding oedema. Calcification is rare. Due to its superficial location it may cause scalloping of the overlying bone 2.

MRI
  • T1 
    • solid component iso to hypointense c.f. grey matter
    • cystic component low signal
    • leptomeningeal involvement seen in over 70% of cases 2
  • T1 C+ (Gd)
    • solid component usually enhances vividly
  • T2 
    • solid component iso to hyperintense c.f. grey matter
    • cystic component high signal
    • on T2 FLAIR sequence, cystic areas show hyperintensity relative to CSF due to higher protein contents
    • little surrounding vasogenic oedema
DSA - angiography

Despite vivid enhancement, pleomorphic xanthoastrocytomas are usually avascular on angiography 2

Although prognosis is good following surgical excision, with a 5-year survival of 90% and 5-year-disease-free-survival of 70% 1,3,6, local recurrence and malignant transformation (to WHO grade III lesion or GBM) are common, encountered in up to 20% of cases 2.

Neither radiotherapy nor chemotherapy has a significant effect on these tumours 2, although radiotherapy may have a role to play in patients with incomplete resection or those with recurrent disease 3

Main differential diagnosis is that of other cortical tumours, with helpful distinguishing features including 1-4

Astrocytic tumour
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Article Information

rID: 1895
Section: Pathology
Synonyms or Alternate Spellings:
  • Pleomorphic xanthoastrocytoma (PXA)
  • PXA
  • Pleomorphic xanthastrocytoma

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Cases and Figures

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    Case 3: in the Heschl's gyrus
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