PXA

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Terminology

• • Astrocytic neoplasm with generally favorable prognosis in children and young adults

Imaging

• • Peripherally located hemispheric mass, often involves cortex and meninges

    • Temporal lobe most common

  • Supratentorial cortical mass with adjacent enhancing dural "tail"

    • Cyst and enhancing mural nodule typical

    • Enhancing nodule often abuts pial surface

Top Differential Diagnoses

• • Ganglioglioma

  • Pilocytic astrocytoma

  • Dysembryoplastic neuroepithelial tumor (DNET)

  • Oligodendroglioma

  • Meningioma

Pathology

• • WHO grade II

Clinical Issues

• • Majority of patients have longstanding epilepsy, often partial complex seizures (temporal lobe)

    • Rare but important cause of temporal lobe epilepsy

  • Tumor of children and young adults, majority < 18 years

  • Represent < 1% of all astrocytomas

  • Surgical resection is treatment of choice

Diagnostic Checklist

• • Cortical mass and meningeal thickening in a young adult with long seizure history? Think PXA!

  • Ganglioglioma may mimic PXA clinically and by imaging

TERMINOLOGY

Abbreviations

• • Pleomorphic xanthoastrocytoma (PXA)

Definitions

• • Astrocytic neoplasm with generally favorable prognosis in children and young adults

    • Superficial location in cerebral hemispheres with involvement of meninges

IMAGING

General Features

• • Best diagnostic clue

    • Supratentorial cortical mass with adjacent enhancing dural "tail"

    • Cyst and enhancing mural nodule typical

  • Location

    • Peripherally located hemispheric mass, often involves cortex and meninges

      • 98% supratentorial

    • Temporal lobe most common

      • Parietal > occipital > frontal lobes

    • Rarely found in cerebellum, sella, spinal cord, retina

  • Size: Variable

  • Morphology

    • 50-60% cyst + mural nodule that abuts meninges (may be solid)

    • Discrete round to oval mass typical (may be ill defined)

    • Despite circumscribed appearance, tumor often infiltrates into brain and perivascular spaces

CT Findings

• • NECT

    • Cystic/solid mass: Hypodense with mixed density nodule

    • Solid mass: Variable; hypodense, hyperdense, or mixed

    • Minimal or no edema is typical

    • Ca++, hemorrhage, frank skull erosion (rare)

  • CECT: Strong, sometimes heterogeneous enhancement of tumor nodule

MR Findings

• • T1WI

    • Mass is hypo- or isointense to gray matter

    • Mixed signal intensity may be seen

    • Cystic portion isointense to CSF

    • Associated cortical dysplasia may be seen (rare)

  • T2WI

    • Hyperintense or mixed signal intensity mass

    • Cystic portion isointense to CSF

    • Surrounding edema (rare)

  • FLAIR

    • Hyperintense or mixed signal intensity mass

    • Cystic portion isointense to CSF

  • T1WI C+

    • Enhancement usually moderate/strong, well delineated

    • Enhancement of adjacent meninges, dural "tail" common (approximately 70%)

      • Enhancing nodule often abuts pial surface

    • Rare: Deep tumor extension, distant metastases

Angiographic Findings

• • Typically avascular

  • Vascular blush may indicate necrotic or aggressive PXA

Nuclear Medicine Findings

• • PET: FDG PET may show hypermetabolic foci even in low-grade PXA

Imaging Recommendations

• • Best imaging tool

    • Multiplanar MR is most sensitive

    • CT may be helpful for calvarial changes

  • Protocol advice: Contrast-enhanced MR including coronal images to better evaluate temporal lobes

DIFFERENTIAL DIAGNOSIS

Ganglioglioma

• • Cortically based hemispheric mass, solid/cystic, or solid

  • Mural nodule typical, often not adjacent to meninges

  • Variable enhancement, no enhancing dural "tail"

  • Ca++ is common; may remodel calvarium

Pilocytic Astrocytoma

• • Supratentorial location other than hypothalamus/chiasm is rare

  • Typically solid and cystic or solid mass

  • Enhancement but no dural "tail"

Dysembryoplastic Neuroepithelial Tumor (DNET)

• • Superficial cortical tumor, well demarcated

  • Multicystic "bubbly" appearance

  • T2 hyperintense mass with rare, mild enhancement

  • May remodel calvarium

Oligodendroglioma

• • Heterogeneous, Ca++ mass

  • Typically larger and more diffuse than PXA

  • May remodel/erode calvarium

Meningioma

• • Diffusely enhancing dural-based mass with dural "tail"

  • Usually older patients

Low-Grade Astrocytoma (Grade II)

• • Demarcated but infiltrative white matter mass

  • No enhancement

PATHOLOGY

General Features

• • Etiology

    • May originate from cortical (subpial) astrocytes

    • May arise from multipotential neuroectodermal precursor cells common to both neurons and astrocytes or from preexisting hamartomatous lesions

  • Genetics

    • No definite association with hereditary tumor syndromes

    • Rare reports of PXA in neurofibromatosis type 1 and Sturge-Weber patients

    • PXA with TP53 mutations reported

  • Associated abnormalities

    • PXA may occur with ganglioglioma and oligodendroglioma (rare)

    • PXA reported with DNET and atypical teratoid-rhabdoid tumor

    • Synchronous, multicentric PXA lesions are rare

    • May be associated with cortical dysplasia

Staging, Grading, & Classification

• • WHO grade II

  • PXA with anaplastic features

    • Significant mitoses (5 or more per 10 HPF) &/or necrosis

    • Has been associated with poorer prognosis

      • Increased recurrence and decreased survival

    • Some classify these PXA as WHO grade III

Gross Pathologic & Surgical Features

• • Cystic mass with mural nodule abutting meninges

  • May be completely solid

  • Leptomeningeal adhesion/attachment is common

  • Dural invasion is rare

  • Deep margin may show infiltration of parenchyma

Microscopic Features

• • Superficial, circumscribed astrocytic tumor noted for cellular pleomorphism and xanthomatous change

  • "Pleomorphic" appearance

    • Fibrillary and giant multinucleated neoplastic astrocytes

    • Large xanthomatous (lipid-containing) cells are GFAP positive

    • Dense reticulin network

    • Lymphocytic infiltrates

  • Tumor sharply delineated from cortex, but infiltration may be seen

  • Some positive for synaptophysin, neurofilament proteins, S100 protein

  • CD34 antigen may help differentiate PXA from other tumors

  • Necrosis, mitotic figures rare/absent

    • MIB-1 index generally < 1%

CLINICAL ISSUES

Presentation

• • Most common signs/symptoms

    • Majority with longstanding epilepsy, often partial complex seizures (temporal lobe)

    • Other signs/symptoms: Headache, focal neurologic deficits

Demographics

• • Age

    • Tumor of children and young adults

      • Typically 1st 3 decades

      • 2/3 < 18 years

      • Ranges from 2-82 years, mean 26 years

  • Gender: No definite gender predominance

  • Epidemiology

    • < 1% of all astrocytomas

    • Rare but important cause of temporal lobe epilepsy

Natural History & Prognosis

• • Usually circumscribed, slow growing

  • Recurrence of tumor is uncommon

  • Hemorrhage is rare complication

  • Survival 70% at 10 years

  • Malignant transformation in 10-25% of cases

  • Extent of resection and mitotic index are most significant predictors of outcome

  • Aggressive PXA with malignant progression, dissemination occasionally occurs

Treatment

• • Surgical resection is treatment of choice

  • Repeat resection for recurrent tumors

  • Radiation therapy and chemotherapy show mild improvement in outcome in some cases

DIAGNOSTIC CHECKLIST

Consider

• • Cortical mass and meningeal thickening in young adult with long seizure history? Think PXA!

  • Ganglioglioma may mimic PXA clinically and by imaging

Image Interpretation Pearls

• • Meningioma-like lesion in young patient should raise suspicion of PXA