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Skull Base. 2003 February; 13(1): 59–63.
PMCID: PMC1131831

Current Abstracts

DIAGNOSIS

Michael Beenstock. Predicting the stability and growth of acoustic neuromas. Otol Neurotol 2002; 23:542–549

Hypothesis: Acoustic neuroma (AN) growth can be predicted using information gathered at the time the AN is initially diagnosed.

Background: Knowledge of AN growth is essential for treatment planning. Previous studies have not been able to identify predictors of AN growth.

Methods: A multivariate statistical analysis was carried out using two independent sets of secondary data from the natural histories of ANs. Logit, probit, and censored regression techniques were used to test alternative hypotheses of AN growth between the initial and second measurements, as well as between subsequent measurements.

Results: In one data set, AN growth between the first and second measurements varied significantly and inversely with age. It was much greater if the AN was on the left side and if there were more symptoms. It did not depend on initial tumor size or the measurement interval. In the other data set, AN growth was also greater for left–sided tumors and depended on symptoms. However, it varied inversely with tumor size and directly with the measurement interval. There was also some evidence that tumors that were more stable between the initial two measurements were more likely to remain stable between the second and third measurements. However, this did not apply to AN growth between the third and fourth measurements.

Conclusions: AN growth is predictable but the prediction model is not apparently independent of the policy for selecting ANs for conservative management.

Fred F. Telischi, Orlando Gomez–Marin, Barden Stagner, Glen Martin. Effect of acoustic tumor extension into the internal auditory canal on distortion–product otoacoustic emissions. Ann Otol Rhinol Laryngol 2002;111:912

We studied the effects on distortion–product otoacoustic emissions (DPOAEs) of internal auditory canal (IAC) extension of acoustic neuromas (ANs) with the hypothesis that cochlear patterns of DPOAEs would be more commonly observed when the IAC was completely filled with tumor because of direct tumor involvement of either the inner ear or its blood supply. In a retrospective analysis of 86 patients with surgically proven ANs, DPOAEs were classified as having cochlear or noncochlear patterns on the basis of comparisons with the behavioral pure tone thresholds. The results of behavioral audiometry and DPOAEs were compared with the extension of the tumor into the IAC, which was categorized as full or partial. Of the 86 patients, 58 had tumors with full IAC extension, and 28 had tumors with partial IAC involvement. Cochlear patterns of DPOAEs were found in 55.2 % of the tumors in the full IAC group and in 71.4 % of those in the partial IAC group (not statistically different). It was concluded that the extent of IAC involvement by ANs was not significantly related to the negative effects of the tumor on cochlear function as represented by DPOAEs.

SURGICAL ANATOMY

Amitabha Chanda, Anil Nanda. Partial labyrinthectomy petrous apicectomy approach to the petroclival region: An anatomic and technical study. Neurosurgery 2002;51:147–160

Objective: The petroclival region generally is thought to be an inaccessible area in the intracranial compartment. A number of ways of reaching this area during surgery have been described, including the presigmoid petrosal approach. The partial labyrinthectomy petrous apicectomy approach is a relatively new approach to this region and is a variant of the presigmoid petrosal approach. This study aims to demonstrate the technique and the microsurgical anatomy of the partial labyrinthectomy petrous apicectomy approach and to provide a quantitative study of its exposure to compare it with other common approaches to this region, particularly the presigmoid petrosal approach.

Methods: Bilateral stepwise dissections were performed on 15 formalin–fixed and dye–injected cadaveric heads (30 side) under ×3 to ×40 magnification. A temporal craniotomy was performed after a complete mastoidectomy. A partial labyrinthectomy and petrous apicectomy were performed next. The amount of dura exposed was measured before and after the partial labyrinthectomy and the petrous apicectomy. By measuring the angles of exposure, the approach was examined to analyze how much increased access was gained.

Results: This approach provided wide exposure to the pectroclival region, the cerebellopontine angle, Meckel's cave, the cavernous sinus, and the prepontine region. On average, there was an increase of 10.8 mm in horizontal exposure as compared with the retrolabyrinthine approach. The average angle of vision achieved with the clival pit as the target was 58.9 degrees. In most of the specimens, an area from the IIIrd to the IXth cranial nerves was easily visible without any significant brain retraction. A high jugular bulb did not reduce the exposure.

Conclusion: The partial labyrinthectomy petrous apicectomy approach converts two narrow tunnels into a wide corridor. It increases the angle of exposure markedly, providing easy and excellent exposure of the otherwise difficult-to-access petroclival region, and it may also preserve hearing.

Daniel I. Choo, David L. Steward, Myles L. Pensak. Clinical Note. Meningioma involving Meckel's cave: Transpetrosal surgical anatomy and clinical considerations. Ann Otol Rhinol Laryngol 2002; 111:850

Meningiomas originating in Meckel's cave (MC) are uncommon lesions that represent 1 % of all intracranial meningiomas. Innovations in skull base surgery have enabled resection of these lesions with less morbidity, but require an intimate knowledge of both lesional pathology and regional microneuroanatomy. To review the surgical and clinical considerations involved in the management of MC meningiomas, we retrospectively reviewed data from patients who underwent transpetrosal resection of primary MC meningiomas between 1984 and 1998. Of 146 patients who underwent transpetrosal removal of meningiomas, 7 were believed to have tumors originating in MC. All 7 patients presented with trigeminal dysfunction, facial pain, and/or headache. Complete tumor removal was achieved in 5 of the 7 patients. Facial hypoesthesia or anesthesia, paralysis of cranial nerve VI, and ophthalmoplegia were among the postoperative complications encountered. Meningiomas of MC represent treatable lesions whose diagnosis requires prompt imaging of patients with trigeminal dysfunction and symptoms of facial pain and headache.

SURGICAL TECHNIQUES

Sheng–Po Hao. Modified facial translocation technique to prevent necrosis of bone graft. Laryngoscope 2002;112:1691–1695

Objective: To assess the efficacy of a modified facial translocation technique in preventing translocated facial bone graft from necrosis, which is the most common complication of facial translocation.

Study Design: Prospective.

Methods: A lateral nasal flap was preserved and transposed to resurface the inner surface of the translocated facial bone graft in a facial translocation approach to skull base tumors in 35 patients including 24 patients with radiation therapy between July 1998 and December 2000.

Results: Only one patient had bone graft necrosis. Thirty–four (97 %) of 35 patients had intact mucosa covering the inner surface of the translocated facial bone graft. The outcome was not affected by preoperative or postoperative radiation therapy.

Conclusions: A modified facial translocation technique using a lateral nasal flap to resurface the inner defect of the translocated facial bone graft significantly improved the viability of the translocated facial bone graft, especially in patients who underwent radiation therapy. The use of a lateral nasal flap does not interfere with the detection of early local recurrence.

John A. Jane, Jr., Kamal Thapar, George J. Kaptain, Nicholas Maartens, Edward R. Laws, Jr. Pituitary surgery: Transsphenoidal approach. Neurosurgery 2002;51:435–444

The transsphenoidal approach for sellar tumors has evolved significantly since it was described initially during the first decade of the 20th century. The approach currently incorporates technological advancements and refinements in patient selection, operative technique, and postoperative care. Although many of these innovations are considered indispensable, the operative technique, as performed by contemporary neurosurgeons, is not standardized. This variability is a reflection of surgeon's preference, the lessons of experience, and the bias inherent in neurosurgical training. The methods and preferences described herein embody the distillation of an experience gained from 3900 transsphenoidal operations.

OUTCOMES

D. M. Baguley, P. Axon, I. M. Winter, D. A. Moffat. Review. The effect of vestibular nerve section upon tinnitus. Clin Otolaryngol 2002;27:219–226

This paper reviews the published evidence regarding the effect of vestibular nerve section upon tinnitus. This is of relevance not only for those performing and undergoing this procedure, but also for those considering the hypothesis that auditory efferent system dysfunction may be influential in tinnitus perception. The auditory medial efferent fibres within the internal auditory canal run within the inferior vestibular nerve, only joining the cochlear nerve at the anastomosis of Oort, a bundle of 1300 fibres running from the saccular branch of the inferior vestibular nerve to the cochlear nerve. Vestibular nerve section procedures therefore section this efferent olivocochlear pathway, and ablate efferent influence upon that cochlear. If auditory efferent dysfunction is involved in tinnitus perception, this ablation might influence the tinnitus status of that patient. A literature search identified 18 papers mentioning tinnitus status after vestibular nerve section, describing the experiences of a total of 1318 patients. The proportion of patients in whom tinnitus was said to be exacerbated postoperatively ranged from 0 % to 60 %, with a mean of 16.4 % (standard deviation 14.0). The proportion of patients in whom tinnitus was unchanged was 17 % to 72 % (mean 38.5 %, standard deviations 15.6), and in whom tinnitus was said to be improved was 6 % to 61 % (mean 37.2 %, standard deviation 15.2). In the majority of patients undergoing this procedure, ablation of auditory efferent input (and thus total efferent dysfunction) to the cochlea was not associated with an exacerbation of tinnitus. The finding of this review is that efferent dysfunction after vestibular nerve section does not consistently worsen tinnitus.

Jan Maurer, Torsten Frommeld, Wolf Mann. Vestibular function after acoustic neuroma removal with preservation of one branch of the vestibular nerve. Otol Neurotol 2002;23:749–754

Background: Vestibular compensation after acoustic neuroma surgery is affected by many parameters. Apart from surgical approach, age of the patient, and comorbidity, the use of rehabilitative vestibular training and the degree of preoperative vestibular compensation play their respective roles.

Objective: To examine whether and how surgical preservation of one branch of the vestibular nerve affects the compensation process in patients after acoustic neuroma removal.

Study Design: Prospective study involving 29 patients with acoustic neuromas. In 15 patients operated on by the middle fossa or retrosigmoid approach, one branch of the vestibular nerve could be preserved intraoperatively, and the course of the compensation process was followed (Group 1). Fourteen other patients with acoustic neuroma, who were operated on via a translabyrinthine approach, served as a control group (Group 2).

Main Outcome Measure: The evaluation of vestibular compensation was accomplished clinically, by electronystagmography, and by dynamic posturography.

Results: An accelerated vestibular compensation was found in all examinations for Group 1, and 3 months after surgery 47 % of the patients in this group were back to work without substantial restrictions, compared with 29 % of Group 2. At the end of 6 months, however, there was no more significant difference between the two groups.

Conclusion: The long–term results of vestibular compensation do not seem to be influenced by partial preservation of the vestibular nerve, whereas the compensation process seems to be accelerated when the nerve is partially preserved.

Isabelle Mosnier, Françoise Cyna–Gorse, Alexis Borzog Grayeli, Bernard Fraysse, Christian Martin, Alain Robier, Bertrand Gardini, Larbi Chelikh, Olivier Sterkers. Management of cholesterol granulomas of the petrous apex based on clinical and radiologic evaluation. Otol Neurotol 2002; 23:522–528

Objective: The purpose of this study was to analyze the imaging characteristics of 12 cholesterol granulomas as a function of their clinical symptoms. The results of the different surgical approaches and the management of these lesions are discussed.

Study Design: Retrospective case review.

Setting: Five tertiary referral centers.

Patients: Twelve patients managed for a cholesterol granuloma of the petrous apex.

Interventions: All patients were evaluated via computed tomography and magnetic resonance imaging. Eight patients required surgical drainage: through a conservative approach in seven patients (infralabyrinthine, n = 5; infracochlear, n = 2) and a transotic approach in one patient. Clinical and radiologic follow–up without surgery was the mode of treatment for four patients. The mean follow–up period was 18 months for patients who underwent operations and ranged from 6 months to 10 years for patients without operations.

Results: Four patients of clinical symptoms were noted; retrocochlear signs by an involvement of the internal auditory meatus (n = 8), headaches by a traction of the dura (n = 4), serous otitis media by a compression of the eustachian tube (n = 2), and asymptomatic lesions with no involvement of the adjacent structures (n = 2). Hearing and facial functions were preserved in all the cases treated by a noninvasive procedure. No recurrence or complication was reported in the patients who underwent operations. None of the noninvasively treated patients with cholesterol granulomas showed significant enlargement on follow–up imaging.

Conclusion: Clinical manifestations of cholesterol granulomas depend on their anatomic location and the involvement of the adjacent structures. Aggressive lesions in patients with residual hearing can be drained via an infralabyrinthine or an infracochlear approach with minimal morbidity. Follow–up must be preferred for patients with nonaggressive lesions. Although magnetic resonance imaging provides a specific diagnosis tool for cholesterol granulomas, computed tomography is essential for an accurate evaluation of the location of the cyst and choice of the surgical procedure.


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