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.
Typically these tumours are found in young patients (children or young adults), and as they 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.
Macroscopically these tumours appear well circumscribed, often with cystic component and involvement of the overlying leptomeninges 1,3.
Microscopically the margins are not as well defined. Spindle cells, polygonal cells, multi-nucleated cells and lipid laden xanthomatous astrocytes are identified. Even more pleomorphic is the appearance of the nuclei. Endothelial proliferation is rare.
These tumours are GFAP positive, although often only weakly 3.
PXAs are almost invariably (98%) located supratentorially, typically located superficially (peripherally) abutting the leptomeninges, involving the cortex and overlying leptomeninges but 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.
Often there is a cystic component (50-60%) with an enhancing mural nodule or only solid nodule. Additionally, they are one of the tumours that may exhibit a dural tail, which is reactive rather than due to direct dural invasion, which is rare 2. As these lesions are very slow growing and superficial remodelling of the adjacent skull is characteristics and vasogenic oedema is variable 5.
PXAs are typically hypo 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.
- 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
- 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, PXAs are usually avascular on angiography 2
Treatment and prognosis
Although prognosis is good following surgical excision, with a 5-year survival of 70 -80% 1,3, local recurrence and malignant transformation (to WHO grade III lesion or GBM) are common (up to 20% 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
- WHO classification of CNS tumours
- WHO grading of CNS tumours
- VASARI MRI feature set
- diffuse astrocytic tumours
- prognostic markers
- diffuse astrocytoma grading
- low grade astrocytoma
- anaplastic astrocytoma
- glioblastoma variant
- glioblastoma vs cerebral metastasis
- treatment response
- Stupp protocol
- glioma treatment response assessment in clinical trials
- multicentric glioblastoma
- multifocal glioblastoma
- radiation-induced gliomas
- gliomatosis cerebri (growth pattern)
- localised astrocytic tumours
- specific locations
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