Acoustic neuromas are benign, slow growing tumors that may also be called vestibular schwannomas, neurinomas, or nerve sheath tumors. The tumors are derived from Schwann cells, which are the insulating cells of nerves. Most frequently, the tumors arise from the cells insulating one of two vestibular nerves, which are involved with relaying balance information to the brain. The auditory nerve, which relays hearing information, and the facial nerve, which controls motion of the face, travel together with the vestibular nerves through the bony internal auditory canal and thus may also be affected by these tumors. All of these functions can be injured both by tumor growth and (temporarily or permanently) by any type of treatment. If allowed to grow, acoustic neuromas eventually cause compression of the brainstem leading to additional neurologic damage and death.

The schwann cells of the superior vestibular nerves within the internal auditory canal are the usual site of origin of acoustic neuromas. A typical tumor first grows within the confines of the canal, pressing on the nerves running there. It then continues to grow in the direction offering the least resistance, which is along the nerves toward the brain, since there are bony boundaries in all other directions (link to diagram). If a tumor is allowed to continue to grow, it will then form mass that, as it gets larger, presses more and more on the brainstem and cerebellum. This may cause additional problems with coordination due to pressure on the cerebellum or the brainstem. Other cranial nerves may also become involved, leading to problems with facial sensation, face pain, or difficulties swallowing.

Before the modern techniques of diagnosis and treatment were developed, most patients had very large tumors before they came to medical attention. Most patients had had a long history of hearing loss in one ear and balance problems, but it took the development of other problems as well, including headache, facial weakness, sensory problems, incoordination, or even coma, before the tumor could be confirmed. Even if the tumor was diagnosed earlier, operations were so risky that they were delayed until the patient developed a serious or life-threatening problem due to the tumor. An operation was considered successful merely if the patient survived, even if he or she was left with numerous neurologic problems. These goals have now changed. Total tumor removal is now the rule in experienced hands.

The first major advance in the improvement in treatment of acoustic neuromas was the development of the operating microscope in the 1960's. This allowed precise operations to be done in which the tumor could be separated from the facial nerve and from the brain itself. It was during this time that the standards for success began to be raised. In the following decade, new techniques for operating and for monitoring were developed that allowed the rates for successful treatment of these tumors to increase drastically. However, tumors still needed to grow to a relatively large size before they could be accurately diagnosed. It was not until the 1980's that Magnetic Resonance Imaging (MRI) was developed (link to image). Using this technique, very small tumors could be seen, and their treatment could be initiated early. This allowed even greater success, especially in regard to the preservation of facial nerve function and hearing preservation, both of which are much more easily accomplished in patients with smaller tumors.

The skull base surgical team at OHSU has developed a national and international reputation for excellence in the management of skull base tumors. Patients from Oregon, Washington, Idaho, Florida, Alaska, California, Montana, and Utah are all routinely treated, as well as patients from as far away as Taiwan and Thailand.