They are rare tumors accounting for only ~ 1% of primary brain tumors 2-3.
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.
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.
These tumors are GFAP positive, although often only weakly 3.
PXAs are almost invariably (98%) located supratentorially, typically located superficially (peripherally), involving the cortex and overlying leptomeninges. Approximately half are located in the temporal lobe 2.
Often there is a cystic component ( 50-60% ) with an enhancing mural 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.
PXAs are typically hypo or isodense and may be well or poorly demarcated, usually with little surrounding edema. Calcification is rare. Due to its superfical location it may cause scalloping of the overlying bone 2.
- iso to hypointense c.f. grey matter
- solid component usually enhances vividly
- leptomeningeal involvement seen in over 70% of cases 2
- iso to hyperintense c.f. grey matter
- 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 not uncommon (up to 20% cases) 2
Neither radiotherapy nor chemotherapy have 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.
General imaging differential considerations include
- pilocytic astrocytoma: usually posterior fossa
- DNET: usually little if any enhancement
- meningioma: cystic component uncommon