Stephen G. Harner

Stereotactic radiosurgery using the gamma knife for acoustic neuromas

PURPOSE To assess the efficacy and toxicity of stereotactic radiosurgery using the gamma knife for acoustic neuromas. METHODS AND MATERIALS Between January 1990 and January 1993, 36 patients with acoustic neuromas were treated with stereotactic radiosurgery using the gamma knife. The median maximum tumor diameter was 21 mm (range: 6-32 mm). Tumor volumes encompassed within the prescribed isodose line varied from 266 to 8,667 mm3 (median: 3,135 mm3). Tumors < or = 20 mm in maximum diameter received a dose of 20 Gy to the margin, tumors between 21 and 30 mm received 18 Gy, and tumors > 30 mm received 16 Gy. The dose was prescribed to the 50% isodose line in 31 patients and to the 45%, 55%, 60%, 70%, and 80% isodose line in one patient each. The median number of isocenters per tumor was 5 (range: 1-12). RESULTS At a median follow-up of 16 months (range: 2.5-36 months), all patients were alive. Thirty-five patients had follow-up imaging studies. Nine tumors (26%) were smaller, and 26 tumors (74%) were unchanged. No tumor had progressed. The 1- and 2-year actuarial incidences of facial neuropathy were 52.2% and 66.5%, respectively. The 1- and 2-year actuarial incidences of trigeminal neuropathy were 33.7% and 58.9%, respectively. The 1- and 2-year actuarial incidence of facial or trigeminal neuropathy (or both) was 60.8% and 81.7%, respectively. Multivariate analysis revealed that the following were associated with the time of onset or worsening of facial weakness or trigeminal neuropathy: (a) patients < age 65 years, (b) dose to the tumor margin, (c) maximum tumor diameter > or = 21 mm, (d) use of the 18 mm collimator, and (e) use of > five isocenters. The 1- and 2-year actuarial rates of preservation of useful hearing (Gardner-Robertson class I or II) were 100% and 41.7% +/- 17.3, respectively. CONCLUSION Stereotactic radiosurgery using the gamma knife provides short-term control of acoustic neuromas when a dose of 16 to 20 Gy to the tumor margin is used. Preservation of useful hearing can be accomplished in a significant proportion of patients.

Improved Preservation of Facial Nerve Function With Use of Electrical Monitoring During Removal of Acoustic Neuromas

Continuous spontaneous electromyographic activity and responses to electrical stimulation of the facial nerve in the surgical field were monitored in 48 patients undergoing primary removal of an acoustic neuroma. The operative and postoperative results in these patients were compared with the results in 48 patients who were matched for age and size of tumor and who underwent the same surgical procedure without intraoperative monitoring. Eighty-three percent of the patients had preoperative evidence of facial neuropathy, which was more severe with larger tumors. Postoperative facial nerve function was most accurately predicted on the basis of the extent of facial neuropathy on preoperative electrophysiologic testing. Anatomic preservation of the facial nerve in patients with large tumors was substantially improved in the monitored patients (67%) in comparison with those without monitoring (33%). No difference was noted in facial nerve function in the two groups of patients immediately postoperatively. By 3 months, the degree of improvement in the monitored group exceeded that in those who were not monitored, particularly in patients with medium-sized and large tumors.

Long-term follow-up of transtympanic gentamicin for Ménière's syndrome.

Objective Recent studies have shown that transtympanic gentamicin for Méniéres syndrome is effective. Current treatment protocols vary. One concept has been to perform a chemical ablation; the other has been to perform a chemical alteration. Ablation requires multiple injections and is effective in controlling the vertigo, but it is associated with a significant incidence of hearing loss. Chemical alteration uses a minimal dose to reduce vestibular function without affecting cochlear function. Study Design Prospective. Setting Tertiary medical center. Patients Patients had classic unilateral Méniéres syndrome that was unresponsive to medical therapy. Intervention A single injection of gentamicin is given, and the patient is seen 1 month after injection. If indicated, the patient receives another injection and is reevaluated 1 month later. Main Outcome Measures Control of vertigo and maintenance of hearing using the American Academy of Otolaryngology–Head and Neck Surgery (AAO-HNS) guidelines (1995). Results Fifty-six patients have documented follow-up for 2 years or more, and 21 have 4 years or more of follow-up. This article presents the 4-year results as outlined by the AAO-HNS guidelines. Vertigo classes A and B were seen in 82% of patients. The patients followed 2 to 4 years had 86% vertigo class A and B results. Those followed 4 years or more show 76% with a vertigo class A or B result. In this study there has been minimal cochlear loss. There was vestibular change clinically, which was documented by electronystagmography. Conclusions It appears that a single transtympanic gentamicin injection is effective in controlling the vertigo of Méniéres syndrome. Cochlear impact has been minimal. It is most useful for those patients who have failed medical management and are severely affected but not totally incapacitated by the disease.

Ossicular reconstruction with Titanium prosthesis

Objectives To evaluate the results when using titanium total ossicular replacement prosthesis (TORP) or partial ossicular replacement prosthesis (PORP) in chronic ear disease.

Low-dose intratympanic gentamicin and the treatment of Meniere's disease: preliminary results.

The most disabling symptom for most patients with unilateral Menieres disease is vertigo. Eradication of the diseased end organ is effective in eliminating the vertigo. Labyrinthectomy remains the “gold standard”; unfortunately, residual hearing is sacrificed to obtain this end. The purpose of this study is to evaluate low‐dose intratympanic gentamicin for the control of vertigo and for the preservation of hearing. A single dose of gentamicin(10‐80 mg) was injected into the middle ear space of 23 patients with unilateral Menieres disease as an office procedure. Eighty‐four percent of the patients had no episodes of vertigo during the last 6 months of follow‐up. Pure tone average and word discrimination scores were unchanged as a group. Ninety‐five percent of patients had a hearing loss at 6 and 8 kHz that averaged 7.5 dB. Caloric function was reduced in 93%. Low‐dose intratympanic gentamicin is a safe, simple, office procedure that is effective in controlling the definitive vertiginous episodes in most patients with unilateral Menieres disease. Control of vertigo can be obtained with preservation of hearing.

Impact of cranioplasty on headache after acoustic neuroma removal.

We reported previously the incidence of headache after the retrosigmoid removal of an acoustic neuroma as 23% at 3 months, declining to 9% at 2 years after surgery. In an attempt to reduce the incidence and the severity of these headaches, we made one change in our surgical procedure, which was to perform a cranioplasty with methyl methacrylate. Twenty-four patients underwent the cranioplasty and were followed for at least 3 months postoperatively. These patients were matched to 24 patients who did not undergo a cranioplasty. We found a 4% incidence of headache in the cranioplasty group and a 17% incidence in the matched group. No complications were related to this change in our procedure.

Longitudinal Followup of Patients with Meniere's Disease

The etiology, pathophysiology, and natural history of Menieres syndrome are poorly understood. The reported studies have had inadequate followup or insufficient numbers of patients to allow conclusions about the natural history. Our study group was 119 patients who had the classic symptom complex of episodic vertigo, tinnitus, and hearing loss in the year 1970. After initial review of these charts, follow-up information was obtained by questionnaire, telephone interview, chart review, or repeat examination, when possible, both in 1983 and in 1988, for a total followup of 18 years. In the patients with followups of at least 14 years, vertiginous episodes had disappeared completely in 50% of patients and somewhat resolved in 28%; hearing was absent in 48% and worse in 21%. Surprisingly, 43% of patients underwent surgery at some point for control of vertigo. Bilateral disease was present initially in 13% and developed subsequently in 45% of patients. Other areas reviewed included the efficacy of long-term medical treatment, frequency and severity of vertiginous attacks, and contralateral ear symptoms.

Venous air embolism in sitting and supine patients undergoing vestibular schwannoma resection.

OBJECTIVE This study retrospectively compares the incidence of venous air embolism (VAE) detection and morbidity in the sitting and supine positions. All patients underwent vestibular schwannoma resection via the retrosigmoid approach by a single surgical team. METHODS A total of 432 consecutive operations were reviewed, 222 of which were performed with the patients in the sitting position and 210 of which were performed with the patients in the supine position. Charts were reviewed for evidence of intraoperative VAE, intraoperative hypotension secondary to VAE, postoperative morbidity related to VAE, and other variables to compare the groups. RESULTS This study demonstrated a 28% incidence of VAE detection when patients were in the sitting position compared to a 5% incidence of VAE detection when patients were in the supine position (P < 0.0001). Intraoperative hypotension secondary to VAE was noted in 1.8% of the sitting patients and 1.4% of the supine patients (P=0.72, no significant difference). Postoperative morbidity caused by VAE was noted in one sitting patient (0.5%) (pulmonary edema) and in no supine patients (P=0.48, no significant difference). Blood loss was slightly greater in the supine group, and operative times were similar in both groups, despite that the average tumor size of patients operated on in the sitting position was 2.8 cm versus 2.2 cm in the supine group (P < 0.0001). CONCLUSION Our results indicate that although there is a higher incidence of VAE detection in sitting patients, the morbidity is not statistically greater. We conclude that because morbidity from VAE is similar in either position, patient positioning should be based on surgical team preference.

Intraoperative monitoring of the facial nerve

Anatomic preservation of the facial nerve, with maximal facial function, is one of the goals of acoustic neuroma surgery. Application of electrophysiologic monitoring techniques is useful in achieving this goal. Preoperative electromyography and nerve conduction studies provide important prognostic information for preservation of the nerve and postoperative function. Intraoperative electromyography alerts the surgeon to facial nerve proximity and potential injury. Direct nerve stimulation is utilized to confirm the location and integrity of the nerve. Matched‐pair analysis of two groups of patients demonstrated an increased ability to preserve the facial nerve with less postoperative facial deformity.

Relationship of the Optic Nerve to the Paranasal Sinuses as Shown by Computed Tomography

Restricted exposure and inconsistencies in sinus pneumatization place the optic nerve at risk during operations on the sphenoid sinus and posterior ethmoid cells. In this study, computed tomography was used to examine these relationships. We reviewed 80 patients who underwent high-resolution computed tomographic scanning for ophthalmologic complaints in which the scan was negative. Forty-eight percent of posterior ethmoid cells are separated from the optic nerve by the thin bony lamina of the optic canal. Nearly 90% of sphenoid sinuses contact the ipsilateral optic nerve and 10% contact both nerves. Eight percent of posterior ethmoid cells override the ipsilateral sphenoid sinus and contact the optic nerve on that side. Paraxial reformatted displays allowed estimation of the degree of projection of the optic nerve into adjacent sinus cavities. Three percent of optic nerves have significant projection into the posterior ethmoid cell, and 23% project significantly into the sphenoid sinus. The width of the bony plate that separates the optic nerve from the sinus cavity was the same for sphenoid and ethmoid sinuses. Although sinus pneumatization varies among individuals, right and left sides are generally similar within one person.