Use of the KTP-532 Laser in Acoustic Neuroma Surgery

The potassium titanyl phosphate (KTP-532) laser has been applied to otologic surgery with a proven record of both safety and efficacy. The aim of this study was to demonstrate the use, safety, and advantages of laser dissection in the surgical treatment of acoustic neuromas. The authors' experience with 111 patients in whom laser surgery was used in acoustic neuroma is presented, with emphasis on surgical technique employed and facial nerve functional outcome. The method of laser dissection did not result in deleterious neurologic sequelae or laser-specific complications. In addition, laser dissection afforded certain advantages to traditional techniques, especially in larger tumors. The facial nerve functional outcome as assessed by the House-Brackmann grading system revealed that 90.2% of small tumors, 72.2% of medium tumors, and 75.0% of large tumors achieved satisfactory (grades I and II) functional results. These results compare favorably with the literature describing nonlaser dissection techniques. The observations and results reported in this article demonstrate the safety of the KTP-532 laser in the posterior cranial fossa, and specific advantages that this technology may offer to the surgical armamentarium of the neuro-otologist are outlined.     

Clinical experience with vestibular schwannomas: epidemiology, symptomatology, diagnosis, and surgical results

The Danish model for vestibular schwannoma (VS) surgery has been influenced by some historical otological events, taking its origin in the fact that the first attempt to remove CPA tumors was performed by an otologist in 1916. In approximately 50 years VS surgery was performed by neurosurgeons in a decentralized model. Highly specialized neuro- and otosurgeons have been included in our team since the early beginning of the centralized Danish model of VS surgery in 1976. Our surgical practice has always been performed on the basis of known and proven knowledge, but we spared no effort to search for innovative procedures. The present paper reflects the experience we have gained in two decades of VS surgery. Our studies on the incidence, symptomatology, diagnosis, expectancy and surgical results are presented. Received: 26 February 1997 / Accepted: 7 July 1997     

Acoustic Evoked Response Following Transection of the Eighth Nerve in the Rat

Summary ? Object. The auditory brainstem response (ABR) is the most widely used means of intra-operative monitoring of the integrity of the auditory nerve and brainstem pathways during surgery in the cerebellopontine angle (CPA). Reliability of this and other electrophysiological techniques has been questioned because of persisting potentials in direct nerve recordings despite complete eighth nerve section.  The study was designed to assess the extent to which an acoustic evoked response persists after the cochlear nerve is lesioned in the CPA of the adult rat.  Methods. The eighth nerve was exposed microsurgically via a lateral suboccipital approach without damage to surrounding structures. The auditory brainstem response to monaurally presented click stimuli was recorded using needle electrodes and a bandpass of 10 to 5000 Hz.  Findings. Complete sharp sectioning of the nerve in the CPA resulted in immediate disappearance of brainstem-generated potentials but persistence of a large primary, vertex-positive wave in all but one case. This response was also abolished in recordings three days later and after emptying the inner ear canal. Provided that the cochlea remained intact, two weeks later a single, vertex-positive potential in the latency range of wave Ia of the ABR reappeared, reaching its peak amplitude six weeks after sectioning of the nerve.  Conclusions. The short-latency electrical potential recorded following damage of the eighth nerve in the cerebellopontine angle can be mistaken for an indication that nerve function is still preserved. The evoked injury potential is probably the major contributor to this potential that resembles wave I of the ABR. Monitoring of functional auditory integrity must neither be limited to early components of the ABR, nor to the electrocochleogram (EcoG) and the peripheral compound nerve action potential (CNAP), respectively.     

Fractionated Stereotactic Radiotherapy for Acoustic Neuromas: Long-term Outcomes

AimsAcoustic neuromas are rare, benign intracranial tumours. There are a variety of treatment options, with no clear optimal management strategy and wide variation in treated outcomes. We report the outcomes from a 15 year cohort of patients treated at our centre using fractionated stereotactic radiotherapy (52.5 Gy in 25 fractions).Materials and methodsWe analysed a retrospective case series. Patients were identified from patient records and a retrospective review of case notes and imaging reports was undertaken. We assessed tumour response using RECIST criteria and recorded toxicity. Progression-free survival was estimated using the Kaplan–Meier method. The study was conducted according to the STROBE guidelines.ResultsIn total, 93 patients were identified; 83 patients had follow-up data, with a median follow-up period of 5.7 years. The overall control rate using RECIST criteria was 92%. Data on complications were available for 90 patients, with six (7%) experiencing a reduction in hearing, one (1%) developing trigeminal nerve dysfunction and one (1%) a deterioration in facial nerve function. Other toxicities included four (4%) patients who developed hydrocephalus, requiring the placement of a shunt and one (1%) patient who developed radiation brainstem necrosis. After further evaluation this patient was deemed to have been treated within acceptable dose constraints.ConclusionThese data suggest that a good control rate of acoustic neuromas is achievable using fractionated stereotactic radiotherapy to a dose of 52.5 Gy in 25 fractions. Toxicity is considered acceptable but the episode of radiation brainstem necrosis remains of concern and is the subject of further work.     

Directional Hearing,Temporal Order and Auditory Pattern in Peripheral and Brain Stem Lesions

Tests have been applied to the following subjects: (1) 25 normal individuals; (2) the same individuals during temporary impairment of the brain stem by barbiturate (3 mg/kg); (3) 32 patients affected by acute nucleo-reticular vestibular syndrome; (4) 7 patients affected by unilateral Menière's disease, and (5) 1 patient affected by acoustic neuroma with well preserved hearing

Directional hearing was tested by changing the DLi and DLt two pure tones (400 and 600 Hz) presented through earphones or two fixed loudspeakers placed at 30 from the azimuth and with balanced intensity: temporal order and auditory patterns were tested with the same frequencies by changing the DLt or the order of presentation of the stimuli at fixed intensity

On the basis of the results obtained in the normal subjects, a distinction can be made between the patients affected by brain stem impairment and those affected by Menière's disease. In these patients it was very difficult to obtain reliable discriminations due to the failure of the affected cochlea, especially during an acute phase of the disease, to perform adequate time, intensity and frequency analysis

In brain stem patients, spontaneous or pharmacological, the directional hearing judgments were impaired whereas temporal order and auditory pattern discrimination were normal. It is suggested, therefore, that these various central-hearing tests do not investigate analogous performances, but on the contrary different ones. This difference can be attributed to different structures, or to different performance along the same pathways but also to an identical structure of different sensitivity to the noxious agents     

Early Rehabilitation of Facial Nerve Deficit after Acoustic Neuroma Surgery

Objective—To determine whether an early physical rehabilitative program could improve and/or accelerate recovery from a postoperative deficit of facial nerve (FN) function.Material and Methods—A retrospective study of the charts of patients who presented a postoperative FN deficit after surgery for acoustic neuroma (AN) was carried out. Twenty-nine patients were enrolled and divided into 2 groups: 18 who underwent early physical rehabilitation and 11 who did not undergo rehabilitation. All the AN patients underwent translabyrinthine removal and were classified preoperatively according to the House–Brackmann staging system. Physical rehabilitation was performed according to Kabat (i.e. neuromuscular facilitation). FN function was assessed postoperatively and classified according to the House–Brackmann grading system.Results—In Grade IV and V patients, early rehabilitation allowed a faster and better recovery with respect to AN patients for whom rehabilitation was not carried out.Conclusion—Early physical rehabilitation has proved to be effective as a helpful tool for recovery from FN deficit and it is therefore advisable to use it soon after surgery, especially for FN deficits worse than Grade IV.