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Acoustic Neuroma Surgery Discussion
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Acoustic Neuroma Radiosurgery
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What is Acoustic Neuroma Surgery?
Acoustic Neuroma Surgery
In 1977 Maddox described the lateral approach to the acoustic neuroma REFERENCE. The highlights were:
Surgical Approach vs. Size of Acoustic Neuroma
Similarly, Thomsen and colleagues REFERENCE examined the choice of approach in surgery for the acoustic neuroma.
Suboccipital Approach to Acoustic Neuroma:A straight incision is placed approximately 2 cm medial to the mastoid process (back of ear).
Translabyrinthine ApproachThe facial nerve is identified in the lateral internal auditory canal at the transverse crest, and the superior and inferior vestibular and cochlear nerves are disarticulated from the lateral canal. The nerves and tumor are dissected in a lateral-to-medial direction with lateral dissection of the facial nerve and intermittent tumor debulking. Frequent facial nerve identification and stimulation for monitoring response is performed throughout the procedure. Once the entire tumor is removed, the dura is approximated with sutures and abdominal fat is packed into the dural opening for a watertight closure. The eustachian tube and antrum are also packed with muscle, fat, or Surgicel.
Advantages of the Translabyrinthine Approach
Facial NerveFacial Nerve Preservation
Facial nerve preservation has always been considered to be a primary concern in acoustic neuroma surgery, because the nerve is frequently adherent to the surface of the tumor.
Hearing Preservation vs. Size of Acoustic Neuroma
Nadol et. al. described the surgical results in 69 patients with unilateral tumors of the cerebellopontine angle or internal auditory canal in whom total tumor removal was accomplished, and in whom an attempt was made to preserve hearing REFERENCE. The success rate of preservation of hearing and facial nerve function was correlated with the size of the tumor.
A decade later, Glasscock et. al. presented "A systematic approach to the surgical management of acoustic neuroma." REFERENCE
When hearing preservation is to be attempted, some surgeons prefer the middle fossa approach to a posterior fossa approach because the retrosigmoid operation leaves tumor behind in the lateral aspect of the internal auditory canal and places the facial nerve at greater risk.
Monitoring of facial nerve function is routine in order to try to preserve the function of the nerve during the operation. The facial nerve function is monitored by continuous recording of electromyographic (muscle twitches after electrical stimulation) activity with two electrodes, one in the orbicularis oculi (orbit muscle of the eye) and the other in the orbicularis oculus muscles (another eye muscle). Monopolar (single lead) stimulation is used to locate the seventh (facial motor) nerve. Fifth (trigeminal: facial sensory) nerve function is monitored with electrodes placed in the masseter and temporalis (muscles for closure of the jaw) muscles.
Hematoma (Bleeding) and Cerebellar Infarction (Stroke)
During the initial part of the operation attention is focused on occluding the arterial vessels in the muscles as they are encountered. Then during the closure the muscles are again carefully checked for bleeding. A significant blood clot can result with hemorrhage from these blood vessels.
Prior to closure of the dura, the systemic blood pressure is elevated to approximately 140-150 mm Hg to see if it will cause bleeding. Postoperatively the blood pressure is controlled, for as long as necessary.
If the cerebellum is unusually full at the end of the operation and there has been good cerebrospinal fluid drainage, cerebellar stroke or blood clot could be the reason. In this situation a resection of the lateral 1-2 cm of the cerebellum may need to be done.
If the patient does not recover promptly from anesthesia or there is an unexpected significant neurological deficit or delayed neurological worsening, a scan is done immediately to look for cerebellar bleeding or stroke. Prompt removal of a significant blood clot or area of infarction may be necessary.
Cerebrospinal Fluid Leak
If a cerebrospinal fluid leak develops, a lumbar drain is placed for 72 hours; this often resolves the problem. When the leak persists, an operation through the mastoid using an adipose tissue graft is needed.
In one series for translabyrinthine removal of large acoustic neuromas, the rate of spinal fluid leak was 14%, and the rate of meningitis was 4% (Lanman, Brackman et. al: Report of 190 consecutive cases of large acoustic tumors (vestibular schwannoma) removed via the translabyrinthine approach; J. Neurosurgery April 1999 Volume 90 Number 4).
Fortunately, persistent hydrocephalus is rare. Most patients recover spontaneously, a few require a temporary lumbar drain, and only occasionally is a ventriculoperitoneal shunt needed.
When there is postoperative fever with headache or stiffness in the neck, the possibility of either aseptic or bacterial meningitis must be considered. A scan is done to look for an area that might suggest a local infection. A lumbar puncture is then done and administration of broad-spectrum antibiotics is started. Subsequent treatment is guided by the results of the cerebrospinal fluid examination and cultures. If the findings suggest aseptic meningitis, steroids are used.
When the infection is superficial and the organism is sensitive to antibiotics, it may not be necessary to remove the bone flap. If the infection is extensive, debridement of the wound and removal of the bone flap is necessary.
If there is any significant postoperative disability the patient is seen by physical and occupational therapists. Difficulty swallowing due to impaired function in the ninth and tenth nerves should be carefully evaluated with a modified barium swallow and followed by a specialist in swallowing disorders. Often the patient can be given instructions that facilitate their swallowing and prevent aspiration. On rare occasion a gastrostomy is needed.
After suboccipital operation a percentage of patients complain of persistent headache. The magnetic resonance imaging (MRI) scan rarely shows a structural abnormality such as hydrocephalus. In most patients it seems to be a myofascial problem, in a few a neuroma of the occipital nerve, and in some cervical spine degenerative disease. Many patients are benefited by a program of physical therapy and local blocks as indicated.
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