Pilocytic Astrocytoma

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Pilocytic Astrocytoma
Axial MRI of JPA
Tumor Class	Astrocytoma
WHO Grade	I
Survival	80% at 10 years
Treatment	Surgery
Histologic Features Gross Usually cystic lesion with an associated nodule Micro Defined by mitotic figures and Rosenthal fibers
Radiographic Features
MRI	Usually cystic with an enhancing nodule. May be homogeneously non enhancing and solid as well

Definition

Pilocytic astrocytoma is a circumscribed, slowly growing astrocytic neoplasm of young life and early adulthood. Histologically, pilocytic astrocytomas are biphasic tumors consisting of compacted bipolar cells with Rosenthal fibers and loose textured multipolar cells with microcysts and granular bodies. Pilocytic astrocytoma corresponds to WHO Grade I astrocytoma.

Epidemiology

Pilocytic astrocytoma typically occurs in the first two decades of life. See Pilocytic Astrocytoma in adults.

Localization

Pilocytic astrocytoma may occur throughout the neuraxis. More prevalent sites of growth include the optic nerve, hypothalamus, thalamus and basal ganglia, cerebral hemispheres, cerebellum and brainstem.

Clinical presentation

Patients most commonly present with focal neurological deficit or evidence of increased intracranial pressure.

Imaging

On MRI, pilocytic astrocytomas are well circumscribed, contrast-enhancing lesions. Cyst formation is common.

Sagittal T1 weighted MRI with contrast showing a diffusely enhancing lesion in the cerebellum.

Macroscopy

Pilocytic astrocytoma is a discrete, soft lesion, often readily discernible from the surrounding brain. Intra- or peri-tumoral cyst formation in common.

Histopathology

Pilocytic astrocytoma is a biphasic tumor of low cellularity composed of compacted bipolar cells with Rosenthal fibers and loose textured multipolar cells with microcysts and granular bodies. Rare mitosis, occasionally hyperchromatic nuclei, microvascular proliferation and infiltration of the meninges may be seen, and are not a sign of malignancy.

Molecular genetics

TP53 mutations do not play a role in the development of these lesions. Pilocytic astrocytomas may demonstrate loss of chromosome 17q, with subsequent deletion of the NF1 gene.

Prognosis

Because pilocytic astrocytoma is a discrete lesion, surgery offers the opportunity for cure. Many of these lesions, however, are unresectable by the nature of their localization. In these cases, the biology of the tumor demonstrates it to be slow-growing, with very low risk of metastatic behavior, and rarely malignant degeneration.