Pilocytic astrocytoma is a circumscribed, morphologically and biologically distinct astrocytoma subtype. Pilocytic astrocytoma presumably arise from a class of astrocytes that is inconspicuous in normal brain but may become prominent in the reactive gliosis and neoplasia.

Age: Children under 12 years of age and young adults between 40 to 50 years of age.

Incidence: Pilocytic astrocytomas represent only 5% to 10% of all cerebral gliomas but account for nearly one third of pediatric glial neoplasms. It is second overall most common pediatric brain tumor.

Location: Pilocytic astrocytomas are characteristically located around the third and fourth ventricles. Nearly half are found in the optic chiasm and hypothalamus, and about a third are located in the cerebral vermis or hemispheres. Less common locations include the brainstem and basal ganglia. Occasionally, cystic PAs occur in the cerebral hemispheres. The frontal lobes are the most common location of hemispheric PAs; intraventricular and subependymal PAs are the second most frequently encountered site.

Clinical Presentation: Pilocytic astrocytomas are indolent, slowly growing neoplasms. Natural history and presenting symptoms vary with location. The postoperative survival rate for PA is 86% to 100% at 5 years, 83% at 10 years and 70% at 12 years. Patients with gross total tumor resection have survival rate that approach to 100%. Upto one third of Pilocytic astrocytomas may be clinically aggresive. However, frank malignant transformation is uncommon and leptomeningeal dissemination is very rare. Symptoms are cranial nerve palsies, pyramidal tract signs and ataxia.

Pathology: Pilocytic astrocytomas are well-circumscribed but encapsulated mass \"Hairlike\" astrocytic processes; Rosenthal fibres , Cysts with a small, reddish-tan mural nodule are common. Necrosis is absent.

Imaging: On CT-Scan:-  Appears round or oval sharply demarcated and smoothly marginated hypo-or isodense masses. Calcification occurs in about 10% of all pilocytic astrocytomas. Contrast enhancement is strong but variable. Some lesions enhance homogeneously and solidly; others have a small enhancing mural nodule in a large cyst. Because the wall of most cystic astrocytomas consists of nonneoplastic compressed brain, it typically does not enhance , although some cases will occasionally shows mural enhancement. In others the cyst fluid enhances. Obsructive hydrocephalus may occur relatively early and become moderately severe if a pilocytic astrocytoma is located in the vermis or fourth ventricle.

On MRI:- Most Pilocytic astrocytomas are cystic and therefore appear hypo-or isointense on T1W images and hyperintense on T2W images. Mural nodules and solid tumors enhance strongly but somewhat inhomogeneously.