Cerebellar Astrocytoma

The common lesions of posterior fossa are: Brain Metastasis , Granulomas, Abscess, Glioma, Medulloblastoma, Hemangioblastoma, Meningioma, Arachnoid cyst, Acoustic Schwannoma, Epidermoid, etc.

Cerebellar Astrocytoma is the commonest primary intra-parenchymal tumor of the cerebellum in all age groups.

Common clinical presentation of cerebellar astrocytoma : 

Initially patient may present with headache, vomiting , instability while walking and gait disturbance ( postural instability) and on examination patient may have papilledema and positive cerebellar signs. At a later stage patient may become unconscious due to the tonsillar herniation and on examination patient may have bradycardia, hypertension and respiratory irregulaties ( Cushing Reflex due to raised intra-cranial pressure).

Management: The tumor of the cerebellum shoud be treated on urgent basis because of the risk of ventricular compression  ( obstruction of the fourth ventricle ) , compression of the brain stem, acute hydrocephalus and  tonsillar herniation.

Investigation

MRI brain with contrast with MR spectroscopy is the investigation of choice. It will depict:

1        Location of the lesion, whether it is intra-axial or extra-axial. Glioma is an intraaxial lesion because there will the brain parenchyma all around the lesion. On the contrary, Meningioma is an extra-axial lesion, which arises from the arachnoidal cap cells and grossly it appears  adherent to the dura, with broad dural base attachment and there is no brain parenchyma  on one side of the tumor.

2      Contrast image may show enhancement  of a part of the dura close to the tumor base, it is known as dural tail sign.

        3  Cerebellar astrocytoma is an intra-axial lesion and this tumor arises from the cerebellar parenchyma and is usually situated inside the cerebellar lobes. T1,T2, FLAIR, DWI sequences should be examined in conjunction with contrast image and MR spectroscopy. It may appear iso to hypointense on T1 weighted image and iso to hyperintense on T2 weighted image . The FLAIR ( Flow Attenuation Inversion Recovery) image may depict perilesional edema.

4    Contrast image can differentiate the astrocytoma from abscess ( hypointense on 1 weighted image, hyperintense on T2 weighted image, thick abscess wall which enhances on on contrast administration, MR spectroscopy may suggest infective pathology ), meningioma ( omogenous contrast enhancement, broad dural attachment, associated perilesional edema, dural tail sign, bony chages), Epidermoid, hemangioblastoma (cystic lesion with contrast enhancing mural nodule ) and other common lesions of the posterior fossa.

   5.  Asociatied brain stem compression , ventriculomegaly  or tonsillar herniation may be seen.

   6. MRI will give an idea about the consistency of the lesion, vascularity of the lesion and will be the most important tool for the preoperative surgical planning.
   Treatment:

If patient presents in an unconscious state and CT scan reveals a posterior fossa lesion with hydrocephalus then without wasting time, ventricular tap shoud be done to save life of the patient.

If patient presents in routine out- patient department setting , then neurosurgeon has some time to investigate the patient, however, at the outset antiedema measures should be started. Acetazolamide (Diamox 250 mg Thrice a day in an adult patient), Steroid ( Dexamethasone 4 mg four times a day in an adult patient ) should be initiated.

Suboccipital Craniectomy and tumor decompression should be done and depending upon the grade of the tumor patient should be given chemoradiation therapy.