What are Astrocytomas?
Gliomas account for 70% of all primary brain tumours, the vast majority (about 80%) of which are astrocytoma. They originate from astrocytes, which are the most abundant cells in the brain. Most astrocytomas are diffuse because of their infiltration of adjacent brain structures, regardless of grade.
Little is known about the cause of astrocytomas. Most cases are sporadic, although familial predispositions exixs. In some well-defined familial cancer syndromes astrocytic tumours occur.
Astrocytomas represent a continuum with a grading dependent on the presence or absence of anaplastic features. Astrocytomas are graded from Grade 1 to 4, according to the histological type and how they are likely to grow and spread. Tumours graded 1 and 2 are called low grade and are slow-growing but with diffuse infiltration of neighbouring brain tissue. Tumours that are graded 3 and 4 are malignant and fast-growing being more aggressive. Gliomatosis cerebri is by definition a diffuse glial tumour infiltrating the brain extensively so as to involve more than two lobes of the brain, and often bilaterally or extending into the spinal cord.
They are graded as follows:
- Grade I- Pilocytic astrocytoma, Pleomorphic Xanthoastrocytoma, SEGA
- Grade II- Diffuse astrocytoma
- Grade III- Anaplastic astrocytoma
- Grade IV- Glioblastoma Multiforme
Grade I astrocytoma – Pilocytic astrocytoma
Pilocytic tumours are circumscribed tumours occurring predominantly in younger age groups and have an equal incidence among males and females. It is seen in 10% of the people with neurofibromatosis type I, an inherited genetic condition that makes prone to have certain tumours. They arise mostly in cerebellum (especially in children causing imbalance in gait) and in temporal lobe, but also in optic pathways (affecting vision) and thalamic region. These tumours differ from the diffuse astrocytoma by the absence of infiltration of adjacent brain tissue; if completely resected most patients are cured.
In MRI, it is noted as circumscribed and enhancing lesion with pressure effect and edema. Often they present with a cystic lesion with an enhancing mural nodule.
Subependymal Giant Cell Astrocytoma is a type of grade I tumours that arise from the ventricles of the brain. It is usually associated with tuberous sclerosis, which is again a genetic disorder.
Grade II astrocytoma – Diffuse astrocytoma
Diffuse astrocytomas always do not have well-defined borders. They are usually slow-growing but can recur as grade II or grade IV tumours. They are seen in adults within the age group of 25 to 40 years and are more common in males than females.
Gemistocytic astrocytoma is a low-grade tumour with poorer prognosis when compared to other grade II tumours. They have a higher risk of progression to glioblastoma or grade IV tumours. The hallmark of these tumours are the gemistocytes- they are large cells with abundant cytoplasm.
Grade III astrocytoma – Anaplastic astrocytoma
Anaplastic refers to cells which do not resemble any normal structure and are cells that divide rapidly. They are known to be malignant tumours and recur even after treatment.
They are seen in adults between the age of 30 to 70 years of age and are also more common in males.
Grade IV astrocytoma- Glioblastoma
GBM, the most malignant astrocytic tumour is histologically characterized by necrosis and/or endothelial proliferation. They can either develop de-novo or from a less malignant precursor lesion.
Diagnosis of Astrocytoma
Neurological examination- When you are suspected of having a brain tumour, the neurologist will test your nervous system, which includes your alertness, vision, hearing, muscle strength, reflexes and coordination.
Radiology – A Computed tomography (CT) or a Magnetic Resonance Imaging (MRI) scan gives the exact location and size of the tumour along with the extent of spread of the tumour. It also gives an idea of operability of the tumour and helps to decide the treatment plan.
Biopsy – A biopsy is done by removing a small portion of the tumour for examination under the microscope. This report, given by a pathologist, gives information on the cell of origin and the grade of the tumour.
Treatment options for astrocytoma include:
- Surgery to remove the tumour: The neurosurgeon aims to remove as much of the tumour from the brain without damaging the normal surrounding brain tissue. Though this may be curative in some low-grade patients, some may require additional treatments such as chemotherapy or radiotherapy.
- Radiotherapy: Radiation Therapy involves high-energy radiation infractions that target the tumour bed. This therapy is recommended after surgery if the cancer was not able to be completely removed by surgery, or was of a higher grade with a high chance of recurrence. Palliative Radiotherapy, along with chemotherapy, may be used to treat tumours that cannot be operated upon.
- Chemotherapy: This is administered as pills as an adjunct after surgery to destroy any residual cancer cells and to reduce the chances of recurrence.
Prognosis:
The prognosis of astrocytomas is mainly determined by tumour grade. With a median survival of 5-10 years, low-grade astrocytoma has the best outcome. Large studies reported a median survival in grade III astrocytoma of 2-4 years and of grade IV of 9-12 months. Recent trials show that for some subsets of patients, the outcome may be improved by combined modality treatment.
Dr. Thimappa Hedge, Dr. Kiran M, Dr. Komal Prasad, Dr. Shibu Pillai, Dr. Sumana Palegar, Dr. Sathyanarayan L D and
Dr. Vishwas from the Department of Neurosurgery | Mazumdar Shaw Medical Center, Bommasandra, Bangalore