Cerebellar astrocytoma (CA) arises in the cerebellum, present in the posterior fossa of the brain. Other common tumors in the posterior fossa of the brain include medulloblastoma, ependymoma, and brainstem glioma. CA is the second most common pediatric posterior fossa tumor (25-30%) after medulloblastoma; approximately, 70-80% of all CAs are found in children. CA also accounts for 15% of all intracranial tumors, and 5% of all gliomas (neuroglial tumors). The WHO classifies all astrocytomas into four histologically distinct grades, that range from benign (non-cancerous) tumors (pilocytic astrocytoma) to highly malignant (cancerous) tumors (glioblastoma multiforme – GBM).
Based on the gross pathological appearance, CAs can be classified as cystic, or solid or mixed tumors. The cystic lesions tend to dominate the cerebellar hemispheres while the solid tumors are common in the midline near the vermis and potentially invade the brainstem.
The clinical features depend mainly on the anatomic location of the tumor. The mean age of presentation of CAs in children and adults is 6.5 years and 14.5 years, respectively, with a median duration of symptoms (before diagnosis) of around 3 months. The early symptoms are:
The late symptoms are consequences of raised intracranial pressure (ICP) and include:
Papilledema (swelling around the nerve of the eye)
The other clinical signs associated with CAs are ataxia (poor neuromuscular control), dysmetria (poor action-distance assessment), diplopia (blurred/double vision), and hydrocephalus (bulging of the head due to excess accumulation of extracellular fluid). In infants, the early clinical signs are irritability, developmental delay, an increasing head circumference, and regression in intellectual and motor ability as the child grows older.
The diagnosis of cerebellar astrocytoma is made by correlating the clinical presentation with neuro-radio-imaging (CT and MRI scans). CT scan is phenomenally successful (>95%) in detecting posterior fossa tumors. These tumors appear isodense/hypodense to the surrounding brain tissue on unenhanced images. MRI detects the infiltrating type of CAs that invade the brainstem, due to its better multi-planar visualization than CT. These tumors appear iso/hypointense to the surrounding brain tissue on T1-weighted images and hyperintense on T2-weighted images, on MRI.
Preoperative management is dictated by the clinical condition of the patient at the time of diagnosis. An asymptomatic patient with an incidentally detected tumor is only closely monitored without surgical intervention unless otherwise required. A symptomatic patient showing the classic signs of raised ICP (headache, nausea, vomiting) is put on a high dose of dexamethasone for as long as needed until surgery is performed. Relief from raised ICP is an emergency in patients presenting with mental confusion, lethargy, and cardiorespiratory instability (a condition presenting with abnormal heart rate and breathing, high blood pressure, and low blood-oxygen saturation), and is managed with an external ventricular shunt (EVD) or an endoscopic third ventriculocisternostomy (ETV). Gross total resection (GTR) is the treatment of choice for grade-I tumors, with a survival rate of >95% at 5 years and 70-80% at 10 years. Grade-II tumors have only a 50% survival rate at 5 years, and the prognosis of grades III & IV is extremely poor. Benign, well-circumscribed tumors, confined to cerebellar hemispheres have a better chance at GTR, hence, a better prognosis than the infiltrating type and/or those in the cerebellar midline. Subtotal resection (STR) is reserved for lesions not feasible for GTR due to their insidious location or malignant histology. Such tumors also require adjuvant chemotherapy and/or radiotherapy.