Brain Tumor Diagnosis
When there is a suspicion of a brain tumor, the patients are given an intense neurological examination by their physician. This assesses their mental condition, their coordination, their sensation throughout the body, their reflexes, their strength and the nerves that work the face. Generally, a CT (computed tomography) scan or an MRI (magnetic resonance imaging) scan of the brain is performed. This gives specific information regarding the intracranial condition of the patient. Depending on the type of tumor found, the patient may also have a PET (positron emission tomography) scan, an electroencephalogram (a test measuring the electrical potentials throughout the brain) or a lumbar puncture (a spinal tap) to see if there are any unusual cells within the spinal fluid.
For the malignant gliomas, the strongest factors which determine how patients may do are: age, the type of tumor, the status of the patient's performance and the extent of any surgery which may need to be done. The older the patient, the worse the prognosis with regard to these tumors. Patients who have seizures many times have an earlier diagnosis and, therefore, they might fare a little better with these diseases. The performance status of the patient is very important since it may indicate a smaller amount of tumor. A long duration of the patient's symptoms before the discovery of the tumor may indicate a slower growing tumor and, therefore, a better chance of survival.
Gliomas are divided into relatively benign and malignant types. These are described as grades of tumor extending from Grade I to Grade IV. Grade I tumors are considered benign. Grade II tumors are considered to be low-grade tumors and make up about 15 to 20 percent of all the intracranial gliomas. The more malignant tumors are Grade III (anaplastic astrocytoma) and Grade IV (glioblastoma multiforme). The malignant tumors tend to be very aggressive and have a poor prognosis compared to the Grade II low-grade astrocytomas.
The amount of surgery which can be performed has a direct effect on the prognosis of the patients. Patients who can have a total resection or near total resection do much better in the long run than patients who have a partial resection or a biopsy only. In general, brain tumors are treated with surgical resection followed by radiation therapy, and in some cases, chemotherapy is given. Even when it appears that a tumor cannot be totally removed, some type of surgical procedure, whether it be a biopsy or subtotal resection, tends to be done.
Detailed three-dimensional analysis of a CT scan or an MRI scan by the diagnostic neuroradiologist enables the neurosurgeon to perform a stereotactic biopsy through a small hole drilled in the skull. Debulking surgery is generally indicated when the tumor is in an accessible portion of the brain and is rather large. Postoperative radiation is frequently indicated after partial tumor resections. If there is a significant amount of swelling or edema causing pressure in the brain, then steroids are used to reduce that edema or pressure.
Steroids are also continued during the course of radiation to reduce any edema or irritation which may be caused by the radiation itself. It is important to never stop steroids abruptly. They should be gradually reduced a little bit at a time because they have the effect of shutting down the adrenal glands, and the adrenal glands do need time to recover from the effect of steroid medication.
Low-grade astrocytomas make up 15 to 20 percent of all intracranial gliomas. Seventy-five percent of these occur in the upper portions of the brain. These tumors can be cystic or solid in nature. Usually, the cystic lesions can be cured with surgery alone, while the more solid, less cystic lesions may in fact spread more throughout the brain and be more difficult to resect totally at the time of surgery. In the cystic tumors, the survival is directly related to the completeness of the resection. For the more diffuse tumors, the prognosis appears to be independent of exactly how much tumor can be resected.
There is quite a bit of controversy regarding the use of radiation therapy for the treatment of the low-grade astrocytomas; however, it is important to remember that only about one-third of astrocytomas can be totally resected surgically. In a study performed at the University of California in San Francisco regarding patients with low-grade gliomas, those patients who had postoperative radiation had a longer five-year recurrence-free survival (46 percent) than those patients who had the incomplete resection only (19 percent).
The 10-year survival rates were 35 percent for those with radiation and 11 percent for those who were not irradiated. In that study also, by the time 20 years had passed, all the patients who had not received radiation and had an incomplete resection of their tumor had died. Twenty-three percent of the patients who had received radiation were still alive and free of recurrent disease. In general, patients who have neurologic problems, evidence of a tumor progressing or tumors which become more malignant undergo radiation therapy. There is a trend, however, among some practitioners to defer treatment in asymptomatic patients or those with seizures only.
The proponents of that approach argue that it is not certain whether early radiation has an advantage over delayed radiation or that radiation therapy has an impact at all on the natural history of low-grade glioma. However, one thing is clear: postoperative radiation is not indicated when a complete or near-complete surgical excision has been performed in a pilocystic (cystic) astrocytoma. After a subtotal surgical removal, either immediate radiation therapy or close follow up of treatment reserved for disease progression should be recommended.
The high-grade malignant astrocytomas represent 40 percent of all intracranial primary tumors. The overall five-year survival rate for these patients is less than 10 percent. These are divided into two grades, Grade III and IV, with Grade III tumors being described as anaplastic astrocytomas, and Grade IV tumors being described as glioblastoma multiforme. These tumors have the same neoplastic (malignant) features, except the glioblastomas also contain necrosis (dead areas) within the tumor. Unfortunately, these tumors are very aggressive, and it has been found that most of these patients cannot be cured with surgery and radiation. The median survival for anaplastic astrocytoma is 36 months, while that for glioblastoma multiforme is about nine months.
There are three important prognostic factors in the patients with malignant gliomas. These are age, the extent of surgery and the performance status of the patients. Younger patients (those less than 60 years-of-age) tend to have a better prognosis than older patients. Patients who have a good performance status (out of the hospital, taking care of themselves and getting around reasonably normally) are also in a more favorable group.
There is some indication that a large tumor decompression will allow longer survival than patients who have a biopsy only. Approximately 30 years ago, the primary treatment for patients of malignant gliomas included treatment of the whole brain. With the introduction of the CAT (computerized tomography) scan in the mid 1970s and then the evolution of the MRI (magnetic resonance imaging) scan in the 1980s, localization of tumors within the brain became much more accurate. With this data more concise (smaller) radiation treatment fields were designed.
Despite the fact that autopsy studies have found tumors more than two centimeters away from the contrast enhancing regions of CT scans (supposed edges of the tumors), tumors tend to recur within the primary site as demonstrated on CT scans and MRIs. For that reason, localized treatment with high doses of radiation has become the primary mode of delivery for radiation after surgery in patients with malignant gliomas. Various dose-seeking studies have been performed, and six weeks of radiation was found to be the optimal treatment. This will increase the median survival of these malignant gliomas from approximately 27 weeks to 49 weeks and increases the one-year survival from 20 percent when radiation is not used to 45 percent when radiation is given.
Chemotherapy in Grade III astrocytomas (anaplastic astrocytomas) has been found to increase survival. A combination of CCNU, Procarbazine and Vinblastine has been found to increase survival in these patients with approximately 25 percent having long-term survival. Unfortunately, the survival in patients who have Grade IV astrocytomas (glioblastoma multiforme) has not been enhanced by the use of BCNU chemotherapy.
There have been multiple studies which have demonstrated that BCNU has only a slight influence on survival, except in patients between the ages of 40 and 60, where the two-year survival rate in a Radiation Therapy Oncology Group study increased from eight percent without BCNU chemotherapy to 23 percent with BCNU chemotherapy.
Once the patient has surgery for his tumor and a diagnosis is made, a referral to the radiation oncologist is made. Generally, radiation therapy is not begun until two or three weeks after the completion of the surgical procedure so that adequate healing can take place and the patient can adequately recover from the surgery performed.
At that time, a complete history and physical examination will be performed by the radiation oncologist, and there will be a comprehensive discussion of the type of tumor, the findings, the results of the surgery, the type of radiation, the dose of radiation, the time involved and the results to expect from therapy. It is a good idea for the family to come in with the patient at this time so all may discuss the various options and what to expect since this can be extremely different in each and every patient. Once the initial consultation and discussion have been performed, and the patient and family have decided therapy is to be pursued, a treatment simulation is scheduled. At the time of simulation, an immobilization mask will be manufactured.
The beams to be designed will be quite precise, and it is necessary for the patient to have the cranium in the same position every day so that the entire tumor is treated adequately and portions of the brain which do not need therapy are spared radiation. X-ray films will be made, then a CT scan will be performed with the immobilization device in place. The CT scan will be transferred to the treatment planning system and three-dimensional treatment planning, as well as possibly intensity-modulated radiation therapy (IMRT) plans will be designed to offer the most precise dosage to the tumor with the maximum sparing of surrounding normal brain tissue. Initially, the tumor margins will be quite wide to cover the entire contrast-enhancing tumor as seen on the MRI, as well as the edema with the margin around that.
After approximately two-thirds of the length of the treatment, the radiation fields will be reduced to cover only the area of tumor plus a two-centimeter margin. Generally, a dosage of 60 gray delivered in six weeks (30 fractions five days a week) will be utilized in the treatment of these tumors. Once the treatment has begun, it is given daily, Monday through Friday, until completion.
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