Many benign brain tumors occur in adults. It is important to remember, however, that in the brain, benign tumors can be life-threatening if not treated successfully. Because of their benign histologic nature there is sometimes a tendency to undertreat them because of the fear of long-time side-effects, particularly the effects of radiation therapy. Today’s technology makes most of these fears unfounded.
Meningiomas are slow-growing tumors that arise from the thick, fibrous lining of the brain called the dura. Most commonly they are on the surface of the brain, but other sites include the base of the brain and the falx, a fibrous sheath dividing the right and left hemispheres of the brain. Small lesions on the surface of the brain can often be watched (with no immediate treatment), since they may change so slowly as to never cause symptoms. For tumors in more critical areas, or if documented progression takes place, surgery is a very successful treatment if a complete resection can be performed; in this case, the patient needs no further treatment. Many lesions, however, particularly those in the base of the brain or around the optic nerves, are not resectable without major risks. It has been shown that these patients benefit from radiation therapy, either radiosurgery or more conventional, fractionated radiation therapy. Even patients with part of their tumor removed benefit as well. Because these tumors do not readily infiltrate into the surrounding brain, but rather push it aside as they grow, all of the new technologies, which allow the discrete treatment of the tumor without much irradiation of the surrounding brain, are helpful in preventing long-term radiation complications.
Pituitary adenomas are benign, very slow-growing tumors arising from the pituitary gland, which is located deep in the skull at the base of the brain.
The pituitary gland produces a number of important hormones in the brain; therefore, since these tumors are derived from pituitary tissue, they may produce abnormal quantities of pituitary hormones, although many do not. Results of excessive hormone production can include excessive growth, excessive lactation (milk production in the breasts), and weight gain. Because the symptoms can be unusual, hormone-producing adenomas are often small when diagnosed and can be easily removed. The most common operation is called a transsphenoidal hypophysectomy; the surgeon reaches the pituitary gland through the nose and sphenoid sinus (which is a hole in the facial bones between the nasal cavity and the pituitary gland).
Pituitary adenomas that do not produce hormones can grow to a large size and cause symptoms by pressure on the optic nerves, causing vision disturbances, or by invading the cavernous sinus, which is located beside the pituitary gland. Through this sinus run the nerves that control eye motion on the same side; thus, involvement of this area by the tumor can cause numbness in the face or difficulty with eye movement. Tumors of this size cannot often be removed, and radiation therapy may be beneficial. Because these tumors are benign, very focal irradiation is appropriate; as in meningiomas, modern techniques that spare normal tissue are optimal.
Acoustic schwannomas (neuromas) are benign, slow-growing tumors arising from the eighth cranial nerve, the nerve responsible for hearing. Symptoms usually include hearing loss on the affected side. These tumors generally occur in people over the age of fifty. Treatment is preferably radiosurgery, although surgery may be preferred for schwannomas larger than 3 cm. Fractionated radiation therapy has also been used. With any of these treatments it is often difficult to preserve hearing.