Revision 50 for 'Pleomorphic xanthoastrocytoma'

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

Epidemiology

They are rare tumors accounting for only ~ 1% of primary brain tumors 2-3

Clinical presentation

Typically these tumors 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.

Pathology

Macroscopically these tumors 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. 

Pleomorphic xanthoastrocytomas, as well as pilocytic astrocytomas (and many non-CNS tumors) exhibit BRAF mutations 6,7

Markers

These tumors are GFAP positive, although often only weakly 3.

Location

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.

Radiographic features

Often there is a cystic component (50-60%) with an enhancing mural nodule or only solid nodule. Additionally, they are one of the tumors 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 edema is variable 5

CT

PXAs are typically hypo or isodense and may be well or poorly demarcated, usually with no or little surrounding edema. 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 edema
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 tumors 2, although radiotherapy may have a role to play in patients with incomplete resection or those with recurrent disease 3

Differential diagnosis

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

See also

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