Oligodendroglioma

Oligodendrogliomas occur with equal frequency in members of all races and ethnic groups. The brain is made up of many supporting cells that are called glial cells. Any tumor of these glial cells is called a glioma. Oligodendrogliomas are tumors that arise from a type of glial cell called oligodendrocytes. These cells are the specialized cells of the brain that produce the fatty covering of nerve cells (myelin). Oligodendrogliomas can grow in different parts of the brain, but they are most commonly found in the frontal or temporal lobes of the cerebrum. || Within the tumor, branching blood vessels are seen and divide the cells into discrete clusters. Most of these tumors arise from a common oligodendrocyte precursor termed the oligodendrocyte type-2 astrocyte. For the most part, these tumors are slow-growing tumors, but it can evolve into an aggressive tumor. The histologic classification of central nervous system states that oligodendroglial tumors are that the slow growing tumor in this classification is called a oligodendroglioma and the aggressive tumors are called anaplastic oligodendroglioma. T PrimaryTumor TX Primary tumor cannot be assessed T0 No evidence of primary tumor Supratentorialtumor T1 Tumor <5 cm in greatest dimension;limited to one side T2 Tumor >5 cm in greatest dimension; limitedto one side T3 Tumor invades or encroaches on theventricular system. T4 Tumorcrosses the midline of the brain, invades the opposite hemisphere or invadesinfratentorially N Nodal Involvement Not defined for thissite M Distant Metastases MX Presenceof distant metastases cannot be assessed MO Nodistant metastases M1 DistantMetastases || Possible late radiation complications are radiationnecrosis, diffuse leukoencephalopathy, hearing loss, retinopathy, cataract,visual changes, endocrine abnormalities, decreased short term, and decreasedproblem-solving skills memory. || The prognosis factors for Oligodendrogliomas are mostly the same for all intracranial tumors. The most important are age, tumor type, seizure symptoms, duration of symptoms, performance status, surgery outcomes, and radiation doses and the kind of treatment given. ||
 * Epidemiology: || Oligodendrogliomas is a type of glioma. It is an intracranial tumor. These tumors account for approximately 5% of intracranial tumors. Oligodendroglioma is an incurable but slowly progressive malignant brain tumor. These tumors occur in males and females with a male predominance of 2:1. Oligodendrogliomas occur most commonly in young children and middle aged adults with the median age at diagnosis to be 35-50 years old, but the disease has been seen in all ages.
 * Etiology: || The etiology is unknown for oligodendrogliomas. Viruses have been linked to be the cause on some studies done. ||
 * Signs & Symptoms: || The onset of seizure activity is normally the first symptom for fifty to eighty percent of cases. Another common symptom is headaches combined with intracranial pressure. The location of the tumor plays a big role in neurological symptoms such as: visual loss, motor weakness, and cognitive decline. Occasionally patients can present with stroke-like attacks or with intracerebral hemorrhage. ||
 * Diagnostic Procedures: || Assessment of the patient begins with a complete history and physical of the patient and history from the family members. Complete neurologic examination should be performed. Routine labs are not helpful. Cerebral spinal fluid cytology can be essential for staging the tumor. The most important part of the work-up is the use of diagnostic imaging studies. MRI is the preferred modality for diagnosis. When contrast is used during the imaging of the MRI, the tumor will not show up enhanced unless it is behaving unusually aggressively or has an anaplastic astrocytic component. Definite diagnosis can be confirmed by stereotactic or open biopsy of the lesion. Today, MR spectroscopy is performed regularly in some centers to differentiate this particular tumor from other benign lesions and also to define the aggressiveness of the tumor. A brain biopsy is the only method of definitive diagnosis. ||
 * Histology: || Unfortunately it is very hard to differentiate an oligodendrogliomas from other brain lesions solely by their clinical or radiographic appearance. These are primary glial tumors. It is very interesting that the Greek meaning of ‘oligo’ means “few” and ‘dendro’ means “trees”. The lesion is generally composed of cells with small to slightly enlarged round nuclei with dark, compact nuclei and a small amount of eosinophilic cytoplasm. Many times these cluster of cells are referred to as “fried eggs”. Please see the following photo to demonstrate the cells of a oligodendrogliomas: || [[image:Picture1.jpg caption="Picture1.jpg"]] ||
 * Picture1.jpg ||
 * Lymph Node Drainage: || There is no lymph node drainage. Intracranial primary neoplasms do not metastasize through lymphatics. ||
 * Metastatic Spread: || They grow slowly and ordinarily do not invade surrounding brain or spinal cord tissue.Brain Metastases and metastases to the cerebral spinal fluid can be seen in these tumors, but it is very rare. Lower lumbar back pain, bowel or bladder dysfunction can sometimes indicate cerebral spinal fluid metastasis. ||
 * Grading: || Oligodendrogliomas and other primary brain tumors are diagnosed, or staged, in grades of severity from I to IV. Grade I tumors have cells that are not malignant and are nearly normal in appearance. Grade II tumors have cells that appear to be slightly abnormal.Grade III tumors have cells that are malignant and clearly abnormal. Grade IV,the most severe type of brain tumors ,contain fast-spreading and abnormal cells. Well-defined oligodendrogliomas are generally stage I or stage II tumors. Anaplastic oligodenrogliomas are generally stage III or stage IV tumors. ||
 * Staging: || TMN Staging of brain tumors:
 * Radiation Side Effects: || Possible acute radiation complications are alopecia,fatigue, nausea, vomiting and radiation dermatitis. These symptoms usually subside within 4 to 6weeks after radiation.
 * Prognosis: || Careful monitoring by the medical team will be required. A median survival of up to 16.7 years has been reported for low grade oligodendrogliomas. Repeat surgery may be necessary for oligodendrogliomas because these tumors sometimes redevelop.
 * Treatments: || Steroids are used to stabilize neurologic symptoms. Oligodendroglioma treatment recommendations for adults is safe resection of the tumor, Under the age of 40 years old it is recommended to closely observe the patient with MRI’s. If progression is seen, radiation therapy is given 50-54 Gy. Post-op radiation can be used immediately following surgery, but does not improve survival outcomes. The radiation will delay reoccurrence. Over the age of 40, radiation therapy is used. These patients are followed with an MRI 2-6 weeks after RT, then an MRI every 6 months for 5 years and then annually.

The standard treatment for all grades of oligodendrogliomas is surgery to remove the tumor completely. This surgery is generally aided by an image guidance system that allows the surgeon to determine the most efficient route to location of the tumor. Approximately half of oligodendroglioma patients gain relief of the increased intracranial pressure after complete removal of their tumors. The others require a spinal fluid shunt to allow drainage of the excess fluid. In some instances of oligodendroglioma, the tumor is inoperable or cannot be completely removed. Patients with inoperable oligodendrogliomas are generally treated with radiation therapy. Oligodendrogliomas are among the only brain tumors that can be successfully treated with a type of chemotherapy called PCV (Procarbazine, CCNU or lomustine, and Vincristine). Chemotherapy is usually used only in cases of recurrent anaplastic oligodendrogliomas. Radiotherapy may be used following, or in some cases in place of, resection of the tumor. Forms of radiotherapy used for brain cancer include external beam radiation therapy, interstitial brachytherapy and in more difficult cases, stereotactic radiosurgery.
 * // External beam radiation //**// : //

The radiation treatment set-up should be reproducible. The head should be positioned so that it is not tilted. Many different techniques and immobilization devices can be used to achieve reproducibility. Radiation will usually begin 2 to 4 weeks following surgery to allow for wound healing. Total doses of 50-65 Gy are given in 25-30 fractions with a daily dose of 1.8 to 2.0 Gy. Whole Brain 50Gy Partial Brain 60Gy Brainstem 54Gy Spinal Cord 45Gy Chiasm 50-54Gy Retina 45Gy Lens 10Gy Inner Ear 30Gy Brainstem 12Gy Optic nerve and Chiasm 8Gy Visual Pathway 12Gy The best rule of thumb for designing intracranial treatment portals is to have generous margins that include all of the radiographic evidence of tumor and associated edema. Many radiation techniques can be used to treat intracranial tumors depending on their location. - Parallel opposed fields can be used to treat bilateral or medial cerebral hemispheric tumors. - A tumor that is located laterally or asymmetrically it can be treated with a combination of 6/20 MV to provide better dose distributions. - For frontal tumors located in the anterior parts of the lobe benefit from being treated with anterior and lateral isocentric perpendicular beams. The use of wedges in the beams can optimize the dose distribution. - The best treatment for midcerebral tumors is the use of parallel opposed anterior,posterior, and lateral portals. - Posterior and lateral isocentric beams with wedges are best suited for posterior parietal, unilateral cerebellar or occipital tumors. - The temporal lobe tumors are treated with lateral portals. - Parallel opposed lateral portals combined with a posterior midline portal can adequately treat brainstem tumors. - Boost fields are always much smaller fields compared to the primary treatment portals.
 * //__ Dose ToleranceGuidelines using 1.8-2.0 Gy: __//**
 * //__ Stereotactic Radiosurgery Dose Tolerance: __//**

IMRT is the treatment modality of choice due to the beam arrangement minimizing the volume of the brain irradiated to a high dose. Multiple planar and noncoplanar fields can be used which should include the tumor and the surrounding edema with an appropriate margin. The 95% isodose line should include your treated volume. Conventional external beam 'whole brain radiotherapy treatment' (WBRT) or 'whole brain irradiation' may be suggested if there is a risk that other secondary tumors will develop in the future. Please see the following photos of an IMRT plan done on an oligodendroglioma tumor. ||  ||
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 * [[image:20110603121103856_0001.jpg width="432" height="231" caption="20110603121103856_0001.jpg"]] ||
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 * [[image:20110603121121470_0001.jpg width="378" height="285" caption="20110603121121470_0001.jpg"]] ||
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Hyperfractionated therapy has been investigated with trials but has concluded that there is no clear benefit. Volume || Organ |||| 1/3 |||| 2/3 |||| 3/3 ||
 * // Radiosurgery or Stereotactic Irradiation //**// : // Target area should not exceed 3-4 cm and must be a great distance from surrounding critical structures. The optic nerves and brainstem should not be included in the high dose treatment area.
 * // Interstitial Brachytherapy: //** Tumor should be located in one hemisphere, can not have any spread to the transcallosal or subependymal areas, must be smaller than 5-6 cm, very easily defined on CT or MRI imaging, and must be located in an area that is accessible for implant.
 * TD5/5: || TD5/5 (Gy)
 * TD5/5: || TD5/5 (Gy)
 * Brain || 60 || 59.90 || 50 || 50.27 || 45 || 44.82 ||
 * Brain stem || 60 || 59.86 || 53 || 53.39 || 50 || 49.73 ||

**End point:** Necrosis/ infraction

References/Resources:


 * 1) Website Article,Oligodendroglioma Cancer: found at []. Accessed 6-1-2011.
 * 2) Website Article,Oligodendroglioma Cancer: found at [|www.cancer.net/patient/cancer+types/Oligodendroglioma] .Accessed 6-1-2011
 * 3) Website Article,Oligodendroglioma Cancer: found at [|www.medicineNet.com] .Accessed 6-3-2011
 * 4) Chao C, Perez C, BradyL .//Radiation Oncology.2nd ed//. Philadelphia, PA: Lippincott Williams& Wilkins; 2002:129-154.
 * 5) Hansen E., Roach M. //Handbookof Evidence-based Radiation Oncology//. Springer+Business Media, LLC, NewYork, NY. 2007:17-24.