Oligodendroglioma

oligodendrogliomaOligodendroglioma is a primary brain tumor derived from glial cells.


Description

Oligodendroglioma is a type of brain tumor, which originates from the oligodendrocytes or glial precursor cells. Neuroglia are the supporting cells, which nourish neurons and produce myelin –  a substance that surrounds the axons of the nerve cells and increases the speed of the nerve impulses.

Oligodedrogliomas develop in the brain hemispheres. Usually they are located supratentorially. The most common site for this type of tumors is the frontal lobe (55%), followed by parietal (20%) and temporal (17%) lobe. Less commonly oligodendroblastomas arise from in the occipital lobe. In rare cases, these tumors affect the cerebellum, brain stem and spinal cord (1%).

 

Incidence

The tumor is more common in adults (aged 40-60 years), although it may also be detected in children. Oligodendrogliomas comprise approximately 3% of all the brain tumors. A peak incidence of these tumors is 35-44 years. Males are more likely to develop the tumor than females.

 

Causes
The causes of the tumor development are not known. However, in the abnormal cells  deletions of 1p and 19q are identified.

 

Classification

According to the WHO classification, there are 3 subtypes of oligodendrogliomas:

  • oligodendroglioma;  
  • mixed  oligoastrocytoma;
  • anaplastic (malignant) oligodendroglioma.

 

Symptoms

The tumor grows slowly, so it takes from months to years (up to 29 years) before the symptoms occur.

The symptoms of the tumor vary, according to the site of oligodendroglioma, and may include the following:

  • Simple, complex partial or generalized seizures refractory to anticonvulsant therapy;
  • Increased intracranial pressure causes headaches (painkillers don’t alleviate the pain, it is associated with nausea, vomiting and vertigo; papolloedema is characteristic for intracranial neoplasms);
  • Behavioral and cognitive change (mood swings, memory impairment etc.), speaking disturbances;
  • Visual loss (altered vision or visual hallucinations), hemianopsia;
  • Ataxia (gait abnormality due to lack of muscle control);
  • Muscular weakness, loss of movements control or paralysis (usually on one side of body);
  • Distorted sensations (strange smells, hallucinations);
  • Tumors arising in the ventricles may disseminate via cerebrospinal fluid.

 

Diagnosis

  • EEG to see the abnormal brain activity;
  • Serum electrolyte studies;
  • MRI:

T1 images – a hypointense or mixed hypointense and hyperintense mass is identified;

T2 images – a hyperintense mass with or without edema around is detected

  • CT scan reveals an area of calcification and hemorrhage;
  • Positron  emission tomography  (PET) helps to differentiate low-grade oligodendroglioma from astrocytoma, according to the methionine uptake.
  • Biopsy of the lesion: the tumor appears as solid pinkish gray neoplasm with areas of calcification, necrosis and hemorrhages. Microscopically oligodendroglioma consists of round cells with a small central nucleus;

 

Grading system

According to the WHO grading system the cells appear “almost normal” on the grade I, “slightly abnormal” – on the II grade, “definitely abnormal” – on the III grade, and “very abnormal” – on the grade IV.

See also: Rathke pouch tumor

Treatment

The treatment depends on the aggressiveness of the tumor, its location and symptoms severity.

Low grade tumors may be monitored with regular CT or MRI scans. If the low grade tumor causes many symptoms and compress the brain structures the surgical removal of the neoplasm is indicated. Sometimes it is impossible to remove oligodendroglioma totally, though the surgeon will try to delete as much as possible.

Radiation therapy is performed with doses between 40 Gy and 50 Gy.

High grade oligodendroglioma has to be removed. After the surgery radiotherapy will follow in order to avoid the tumor recurrence.

Chemotherapy is indicated for those who have a 1p19q co-deletion.

 

Applicable medicines

Commonly procarbazine, lomustine (CCNU), and vincristine, as a chemotherapy regimen (PCV) is administered in the treatment of oligodendroglioma.

A methylating agent temozolomide is indicated for patients with recurrent gliomas.

 

Prognosis

The mean survival rate is from 3 (malignant oligodendroblastoma) up to 10 years.