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 are most frequently present with seizures (~75% of cases) 1,2. Other findings include dizziness, and headache or rarely patients are asymptomatic 5.
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.
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 the remainder of the lesions more common in the frontal than the parietal lobes 4,6.
Macroscopically these tumours appear well-circumscribed, often with a cystic component and involvement of the overlying leptomeninges 1,3.
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.
Immunohistochemistry demonstrates expected glial marker reactivity. Less obviously, there is also variable reactivity for neuronal markers 3,6:
- GFAP: positive, although often only weakly
- S100: positive
- neuronal markers including synaptophysin, MAP2 and neurofilament: variable
Ki-67 proliferation index: <1% 6
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 a 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, superficial remodelling of the adjacent skull is characteristic and vasogenic oedema is variable 5.
Pleomorphic xanthoastrocytomas are typically hypodense or isodense and may be well or poorly demarcated, usually with little or no surrounding oedema. Calcification is rare. Due to its superficial location it may cause scalloping of the overlying bone 2.
- solid component iso to hypointense cf. grey matter
- cystic component low signal
- leptomeningeal involvement is seen in over 70% of cases 2
T1 C+ (Gd)
- solid component usually enhances vividly
- solid component iso to hyperintense cf. 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
Treatment and prognosis
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:
- can look very similar
- contrast enhancement often less prominent
- calcification in ~50% of cases
- no dural tail sign
dysembryoplastic neuroepithelial tumours (DNET)
- contrast enhancement uncommon
- 'bubbly appearance' common
- calcifications common
desmoplastic infantile ganglioglioma
- young children
- dural involvement prominent
- large often multiple lesions
- cystic meningioma
- 1. Koeller KK, Rushing EJ. From the archives of the AFIP: pilocytic astrocytoma: radiologic-pathologic correlation. Radiographics. 24 (6): 1693-708. doi:10.1148/rg.246045146 - Pubmed citation
- 2. Rumboldt Z, Castillo M, Huang B et-al. Brain Imaging with MRI and CT. Cambridge University Press. (2012) ISBN:1139576399. Read it at Google Books - Find it at Amazon
- 3.Rippe DJ, Boyko OB, Radi M et-al. MRI of temporal lobe pleomorphic xanthoastrocytoma. J Comput Assist Tomogr. 1992;16 (6): 856-9. Pubmed citation
- 4. Crespo-Rodríguez AM, Smirniotopoulos JG, Rushing EJ. MR and CT imaging of 24 pleomorphic xanthoastrocytomas (PXA) and a review of the literature. Neuroradiology. 2007;49 (4): 307-15. doi:10.1007/s00234-006-0191-z - Pubmed citation
- 5. Yu S, He L, Zhuang X et-al. Pleomorphic xanthoastrocytoma: MR imaging findings in 19 patients. Acta Radiol. 2011;52 (2): 223-8. doi:10.1258/ar.2010.100221 - Pubmed citation
- 6. Louis DN, Ohgaki H, Wiestler OD, Cavenee WK "WHO Classification of Tumours of the Central Nervous System. 4th Edition Revised" ISBN: 9789283244929
- 7. Dias-Santagata D, Lam Q, Vernovsky K et-al. BRAF V600E mutations are common in pleomorphic xanthoastrocytoma: diagnostic and therapeutic implications. PLoS ONE. 2011;6 (3): e17948. doi:10.1371/journal.pone.0017948 - Free text at pubmed - Pubmed citation
Related Radiopaedia articles
- WHO classification of CNS tumours
- WHO grading of CNS tumours
- VASARI MRI feature set
- diffuse astrocytoma grading
- grade I:
- grade II:
- grade III
- grade IV:
- glioblastoma vs cerebral metastasis
- radiation-induced gliomas
- gliomatosis cerebri (growth pattern)
- specific locations
- treatment response
- Stupp protocol
- glioma treatment response assessment in clinical trials
- multicentric glioblastoma
- multifocal glioblastoma
- prognostic genetic markers