About Acoustic Neuroma Surgery
Acoustic neuromas are slow-growing, benign tumors which frequently start in the internal auditory canal of the inner ear. They usually originate in the Schwann cells that surround the vestibular (balance) nerve. If left untreated, they may eventually break out of the IAC and enter the area at the base of the brain known as the cerebellopontine angle. This part of the brainstem contains many of the 12 cranial nerves.
The most common symptoms of this type of tumor are unilateral (one-sided) hearing loss or tinnitus (buzzing, ringing or whistling sound) and balance problems. Options for treatment include surgery, gamma knife or other forms of radiation, and observation (depending on the size and location of the tumor and the age or health of the patient). If the recommended option is surgery, it may be performed by a neurotologist and/or a neurosurgeon.
Surgery to remove an acoustic neuroma is a delicate, involved procedure. Depending on the skill of the surgeon and the size of the tumor, surgery can take from two and one-half hours to over 12 hours. The following pictures taken through a surgical microscope represent some of the phases in the removal of a 1.8 x 2.0 cm tumor. The "translabyrinthine" approach was used. This approach involves drilling through the mastoid bone behind the ear, and removing the semicircular canals.
Translabyrinthine surgery will leave the patient without hearing on the affected side and with only one functioning vestibular nerve. The amount of time for the patient to adapt to the use of the remaining vestibular nerve varies, and that length of time is somewhat determined by how severely the nerve is impaired prior to surgery. In general, the more impaired the vestibular nerve is preoperatively, the shorter the recovery time postoperatively. The translabyrinthine approach is one of the safest approaches for removing an acoustic neuroma, and is the approach preferred in tumors in which hearing preservation is not an issue, and the location and size of the tumor warrant its use.
In the initial phase, the patient is prepared for surgery, the incision made, and bone in the mastoid is drilled out. It is not uncommon for this phase of surgery to take three hours. It is very important that the facial nerve is monitored during acoustic neuroma surgery. Since these tumors usually originate on the vestibular nerve, they frequently are wrapped around or adjacent to the facial nerve. Additionally, the facial nerve goes through the mastoid bone, and it is important that the surgeon have feed-back as the facial nerve is approached. Facial nerve monitoring involves placing electrodes on the face to monitor the muscle activity of the various portions of the face. The nerve will react to heat, cold, direct touch and stretching. If the facial nerve is stimulated, these facial muscles will fire off, giving an audible and visual waveform on a monitoring machine which is used for this specific purpose.
Surgery Steps and Photographs
Caution: These photographs are graphic in nature. More sensitive visitors may want to view only the text below.
Figure 1. The mastoid bone has been exposed and partially drilled out. Water is constantly flushed over the drill tip to keep it cool, and bone chips, etc., are suctioned away from the site. Various sizes and types of drill bits are used, including diamond bits. The temporal bone contains some of the densest bone in the body, and has to be drilled away very carefully.
Figure 2. The vestibular nerve is cut with precision surgical scissors in order to get to the tumor. The white object below the scissors is a small "cottonoid" which is used to absorb liquids in the area and increase visibility.
Figure 3. The tumor, which is remote from the facial nerve, is cauterized and removed bit by bit.
Figure 4. The tumor is carefully separated from a portion of the facial nerve.
Figure 5. With part of the tumor removed, cranial nerves and blood vessels adjacent to the tumor can be seen.
Figure 6. The tumor is now completely removed, and various cranial nerves can be seen.
Figure 7. A piece of fascia, or tissue, is placed over the opening to help seal and protect the underlying structures.
Figure 8. Fat is removed from an incision in the abdomen and placed over the fascia to further protect and fill the hole. After this, the surgical site is closed with sutures, dressing is placed, and the surgery is over.
Where Is the Skull Base?
The skull base is the bottom part of the skull. While the sides, front, back, and top of the skull are essentially smooth, thin walls of bone, the skull base is dramatically more complex. The skull base is complex because every nerve in the body that carries signals to and from the brain crosses the skull base. Additionally, the large vessels that carry blood to and from the brain run through the skull base.