ABSTRACT
Hypoglossal schwannomas are rare cranial base neoplasms that originate in the posterior cranial fossa and extend through the hypoglossal canal in a dumbell fashion. Recent experience with this unusual neoplasm prompted a search for an operative approach to remove the lesion with a minimization of postoperative morbidity from bleeding and iatrogenic cranial nerve deficits. This report describes the use of the transcondylar approach with monitoring of the lower basal cranial nerves to totally remove a transcranial hypoglossal schwannoma with no new-onset cranial nerve palsies. The regional anatomy of the hypoglossal nerve and canal is reviewed in relation to the operative approach.
Subject(s)
Cranial Nerve Neoplasms/surgery , Hypoglossal Nerve/surgery , Neurilemmoma/surgery , Cranial Nerve Neoplasms/diagnosis , Cranial Nerve Neoplasms/physiopathology , Humans , Male , Middle Aged , Neurilemmoma/diagnosis , Neurilemmoma/physiopathology , Surgical Procedures, Operative/methods , Tomography, Emission-Computed , Tomography, X-Ray ComputedABSTRACT
The efficacy of monitoring facial nerve activity in decreasing long-term morbidity has promoted an interest in monitoring other at-risk cranial nerves during procedures that involve manipulation of the basal cranial nerves. This presentation details practical techniques for monitoring the lower cranial nerves, which have been experientially developed over the past 9 years. Emphasis is placed on the selection of electrodes and procedural changes required for reliable and safe stimulation of the basal cranial nerves. Either paired hook-wire or tethered needle electrodes can be used for monitoring glossopharyageal, accessory, and hypoglossal nerve function. Several options for monitoring vagus nerve function are discussed. Of these, the transoral placement of paired hook-wire electrodes remains the most reliable, cost-effective, and least morbid technique. Electrical stimulation of the glossopharyngeal and vagus nerves carries the risk of unanticipated, potentially irreversible disturbances in cardiovascular function. Guidelines for type and optimal placement of stimulating electrodes and recommended intensity levels to prevent unfavorable reactions are presented.
ABSTRACT
The transtemporal or translabyrinthine approach is generally regarded as the most reliable method of ensuring total tumor removal and preservation of facial nerve function in the resection of a cerebellopontine angle tumor. This is particularly true in removing a tumor that has a significant extension into the patient's internal auditory canal. An anticipated deficit associated with the approach is a total hearing loss in the patient's hearing on the operated side. We have encountered a patient, however, who was serially documented as having serviceable hearing after a transtemporal removal of an acoustic schwannoma. Plausible reasons for the functional preservation of some of this patient's hearing are included in the discussion.
Subject(s)
Cerebellopontine Angle/surgery , Facial Nerve/physiology , Hearing Disorders/prevention & control , Neuroma, Acoustic/surgery , Postoperative Complications/prevention & control , Temporal Lobe/surgery , Cerebellopontine Angle/pathology , Ear, Inner/surgery , Female , Hearing Disorders/etiology , Hearing Loss, Conductive/etiology , Hearing Loss, Conductive/prevention & control , Humans , Magnetic Resonance Imaging , Middle Aged , Neuroma, Acoustic/diagnosis , Neuroma, Acoustic/pathology , Postoperative Complications/etiologyABSTRACT
Auditec cassette tape recordings of NU-6 word lists were used to obtain performance-intensity functions for phonetically balanced words (PI-PB) from 25 subjects with normal hearing, 19 subjects with presumed cochlear disorders, and 9 subjects with confirmed retrocochlear lesions. A rollover index greater than .35 differentiated retrocochlear hearing loss from cochlear hearing loss, although some retrocochlear subjects scored well below that level. Factors that may contribute to differences among PI-PB studies are discussed.
