A Brain Tumor Primer: Common Tumors and Presentation
Pankaj A. Gore, M.D.
Neurosurgeon and medical director,
Brain tumor and skull base surgery
Providence Brain and Spine Institute
How brain tumors present is significantly related to their location, size and rate of growth. Tumors associated with the pituitary gland can manifest endocrine effects related to pituitary hypofunction or hyperfunction, for example, while many slow-growing tumors, such as meningiomas and pituitary tumors, may be discovered incidentally upon unrelated cranial imaging.
Generally MR imaging should be ordered for any new, persisting or dramatically changed headache, any subacute progressive neurologic deficit (motor, sensory, visual, cognitive or cranial nerve) or new seizure. In a patient with history of systemic cancer, the threshold for obtaining imaging in the setting of a new headache is even lower. Sudden onset or severe headache should prompt an urgent referral to the emergency room.
Meningiomas account for approximately 30 percent of intracranial neoplasms. They arise from the arachnoid cap cells of the meninges. More than 90 percent of these tumors tend to be benign, with the remainder falling into atypical (7 percent) and malignant (2 percent) categories.
Meningiomas typically grow 1 to 2 millimeters per year. Tumors less than 2 centimeters in size tend to be asymptomatic, but this is heavily dependent on location. Stable, asymptomatic lesions or slow-growing tumors in patients over 70 are typically followed with serial imaging.
Surgical resection is the first line of treatment in healthy patients. Gamma Knife radiosurgery can be utilized for tumors smaller than 10 cubic centimeters in patients with a higher risk of surgical morbidity or for control of postoperative residual or recurrence. External beam radiation is usually reserved for postoperative unresectable residual or recurrence that is too large for Gamma Knife.
Patients who are postresection of a meningioma need to be followed long-term, as recurrence rates can range from 10 to 20 percent, even with gross total resection.
This heterogeneous group of tumors arises from the “support cells” of the brain, the glia. They account for 45 percent of CNS tumors in patients ages 20 to 34. Eighty percent of low-grade gliomas present with seizure. Patients have a variable course ranging from two to 20 years before malignant degeneration of the tumor occurs.
Surgery is first-line treatment with the goal of maximal safe resection. Adjuvant radiation alone improves seizure control and progression-free survival by two years but does not affect overall survival. Radiation followed by PCV chemotherapy significantly improves overall survival by five years in higher-risk patients (subtotal tumor resections or age older than 40).
Favorable prognostic factors include oligodendroglia pathology, age younger than 40, gross total resection of tumor, IDH-1 mutation, and 1p19q chromosomal deletions.
These tumors are classified as WHO grade III and grade IV gliomas. The incidence is 5 per 100,000, and 14,000 new cases are diagnosed annually. Seventy percent of these are glioblastoma, the most common malignant brain tumor. GBM is frequently diagnosed in the sixth decade. Symptoms onset is typically short (less than three months). Headache, seizure and neurological deficit are all common presentations.
Left: An MRI scan showed a large acoustic neuroma in a 32-year-old woman with balance difficulties and hearing loss. She underwent uncomplicated resection of the lesion with full preservation of facial nerve function. Right: A postoperative MRI showed no evidence of residual tumor. The patient continues to do well clinically.
Surgical resection of at least 95 to 98 percent of glioblastoma has been shown to improve prognosis. Standard adjuvant therapy consists of concurrent radiation and TMZ chemotherapy followed by maintenance TMZ. Tumor treatment fields is a novel FDA-approved technology in which electric fields are used to interfere with mitotic spindle formation and cancer cell division.
Overall prognosis for GBM is poor. Median survival is 14.6 months. Positive prognostic factors are extent of resection, age older than 60, Karnofsky performance score more than 70 and a cell proliferation index less than 20 percent. MGMT is a gene involved in DNA replication. MGMT promoter methylation in GBM increases the two-year survival rate to 46 percent compared with 14 percent without MGMT methylation.
Pituitary adenomas are quite common. Cadaver studies indicate that more than 10 percent of the population may harbor small pituitary tumors. Many are incidentally found. Symptomatic tumors present via mass effect on the normal gland, the optic chasm, the cavernous sinus or via hormonal effects. Pituitary apoplexy is a hemorrhagic or ischemic infarction of the pituitary gland, which can result in severe headache, visual loss and/or diplopia. Presentation is typically acute and warrants referral to the emergency room.
Hormone-secreting tumors are known as functional tumors. These make up slightly less than 50 percent of tumors and are predominantly of the prolactin, growth hormone or ACTH-secreting variety. Many “nonfunctioning” tumors actually produce FSH and LH but are clinically silent.
Smaller, nonfunctional tumors can be followed. Prolactinomas are treated first-line with dopamine agonist therapy. Surgery is indicated for all other functional tumors and larger tumors with suprasellar extension.
Metastatic brain tumors, as a group, are actually the most common brain neoplasm. They outnumber primary brain tumors by almost three to one. Like gliomas, symptoms are related to location. There is a predilection for the periphery of the cerebrum, but any structure in the nervous system or adjacent areas can be affected. Headache, seizure and neurologic deficit are common presentations.
Lung cancer is the most common type of brain metastasis. Breast cancer, melanoma, renal cancer and colorectal cancer will also commonly metastasize to the brain. Radiation therapy is the mainstay of treatment. Surgery is indicated in certain patients with solitary tumors or significant mass effect, or if tissue diagnosis is necessary. Stereotactic radiosurgery may also be used in lieu of whole-brain radiation in certain patients.