A technique for placing ventriculoperitoneal shunts in a neonatal model of hydrocephalus.

Induction of hydrocephalus in a neonatal animal with subsequent surgical decompression is the most analogous situation to the clinical state of infantile hydrocephalus. Described in detail is a reliable method for the placement of pressure-dependent ventriculoperitoneal shunts in neonatal kittens with hydrocephalus. Successful decompression can be quantified using ultrasound. This model allows for observation of hydrocephalic changes that may persist or be corrected after shunting, be they morphological, behavioral or biochemical. In addition, potential pitfalls in performing the procedure and in postoperative care of the kittens are addressed.

Syringomyelia as a postoperative sequela of the resection of a chordoma of the clivus: case report.

Syringomyelia has been described frequently in association with various abnormalities of the skull base but rarely with tumors of the skull base. Syringomyelia as a postoperative sequela of surgery of the skull base has not been reported. The authors describe a case of cervical syringomyelia developing after the partial resection of a chordoma and combined conventional and proton beam irradiation. The possible mechanisms causing this abnormality are discussed.

Intraoperative mapping of the trigeminal nerve root: technique and application in the surgical management of facial pain.

A method for intraoperative topographic mapping of the trigeminal nerve root using electrophysiological methods is described. A series of 15 patients under general anesthesia during microvascular decompression and selective posterior fossa trigeminal rhizotomy was studied. This method was used to study the localization of fibers of individual subdivisions of the intradural portion of the trigeminal nerve and as a guide for performing physiologically controlled, selective, microsurgical trigeminal rhizotomy.

Effects of hydrocephalus and surgical decompression on cortical norepinephrine levels in neonatal cats.

Norepinephrine (NE) changes during hydrocephalus, and the effects of surgical decompression on these changes, were studied using a new model of neonatal hydrocephalus. Kittens 4 to 10 days old received intracisternal injections of a sterile solution of 25% kaolin. Control kittens were injected similarly with sterile injectable saline. Ultrasonography was used to follow the progression of ventriculomegaly and the initial effects of the shunts. A subgroup of hydrocephalic animals was shunted using a cerebrospinal fluid lumbar-peritoneal catheter. Hydrocephalic animals were killed at approximately 25 days of age (16-21 days after kaolin injection). Surgical decompression was performed at 12, 16, and 17 days after kaolin injection; these animals were killed 30 days after the shunts were inserted. Control animals were killed at 29 and 53 days of age, to correlate with the ages of the hydrocephalic and shunted animals, respectively. Cortical samples equivalent to Brodmann's areas 4, 22, and 17 were measured for NE using high-performance liquid chromatography. Hydrocephalus caused NE levels to decrease significantly in all cortical areas. These alterations followed a rostrocaudal gradient in severity, with mean reductions of 65.8, 83.9, and 95.8% in areas 4, 22, and 17, respectively. Partial recovery occurred in animals that received shunts 16 and 17 days after kaolin injection, such that NE reductions of 75.7, 56.2, and 81.6% were noted in areas 4, 22, and 17, respectively. Shunting at 12 days after kaolin injection produced complete recovery in areas 4 and 22, with only a 67.7% decrease in area 17. These results suggest that the projection fibers from the locus ceruleus are damaged by the direct effects of hydrocephalus. Axotomy or neuropraxia of these fibers could result in decreases in NE throughout the cerebral cortex. In addition, there appears to be a period of time during which surgical decompression will allow neuropraxic fibers to recover with partial restoration of NE levels. Earlier insertion of a shunt appears to allow for more recovery than later decompression.

Improvement of cortical morphology in infantile hydrocephalic animals after ventriculoperitoneal shunt placement.

As a sequel to our previous descriptions of the pathological changes induced by hydrocephalus in the infantile cerebral cortex, the study presented here has evaluated the effects of surgical decompression on cortical cytology and cytoarchitecture. Hydrocephalus was induced in 14 kittens by the intracisternal injection of kaolin at 4 to 11 days of age. Nine of these hydrocephalic animals received low-pressure ventriculoperitoneal shunts at 9 to 15 days after kaolin injection; these animals were monitored preoperatively and postoperatively by ultrasound and were killed at various postshunt intervals up to 30 days. Five normal or saline-injected animals served as age-matched controls. At the time of shunt placement, the ventricular index confirmed that all recipient animals had attained moderate or severe degrees of ventriculomegaly. Within 3 days after shunt placement, the size of the lateral ventricles had decreased to control levels and was accompanied by rapid and dramatic improvements in behavior and skull ossification. When the animals were killed, gross inspection revealed that about half of the animals exhibited mild to moderate ventriculomegaly, with cortical mantles 50 to 80% their normal thickness. Tissue from frontal (primary motor), parietal (association), and occipital (primary visual) cortical areas was processed for light microscopic analysis. Pyknotic or dark shrunken neurons, which are found typically in hydrocephalic brains, were observed only occasionally in the cortex of shunted animals. Gliosis and mild edema were prevalent, however, in the periventricular white matter. The laminae of the cerebral cortex could be identified in all shunted animals. In those animals with mild residual ventriculomegaly, the entire cortical mantle was somewhat compressed, as evidenced by an increased packing density of neurons. Furthermore, the somata of some neurons were disoriented. Overall, these results indicate that most of the morphological characteristics of the cerebral cortex are preserved after surgical decompression and suggest that ventriculoperitoneal shunts may prevent neuronal damage and/or promote neuronal repair.

Posterior cervical spine fusion with tension-band wiring.

In this study the authors detail their experience with posterior tension-band wiring for stabilization of the subaxial cervical spine. Fifty-five patients underwent fusion for trauma (41 patients), degenerative disease (13 patients), and tumor (one patient). The fusion rate was 96% (50 of 52 patients) and postoperative immobilization was accomplished by means of a Philadelphia collar in the majority of cases. Tension-band wiring provides a stable construct that is simple to perform, requires fusion of a minium number of motion segments, and allows early mobilization with only a hard collar needed for support. The details of the technique, which has been modified from preliminary descriptions, are discussed.

Anomalous cross-modal plasticity following posterior fossa surgery: some speculations on gaze-evoked tinnitus.

A unique and intriguing form of subjective tinnitus evoked by eye gaze is reviewed. A new perspective is presented because this condition is sufficiently different from other forms of subjective tinnitus and its manifestation cannot be adequately explained by existing models or conceptual frameworks. Our examination of this topic considers pathophysiologic changes in the central nervous system in the context of deafferentation-induced plasticity. Potential neuroanatomical areas contributing to this effect include a number of distributed and functionally diverse areas in the brainstem and neocortex involved in the auditory control of eye movements. We also consider contemporary psychophysical methods to evaluate the perceptual correlates of this phenomenon and tools for the development of objective tinnitus measurements. Although theoretical and speculative in nature, this article is intended to stimulate interest in, advance knowledge of, and provide a better understanding about this condition.

Light-induced genetic toxicity of thimerosal and benzalkonium chloride in commercial contact lens solutions.

Several commercial solutions used for daily care of contact lenses were tested for mutagenicity in 4 strains of Salmonella and for their ability to induce repairable DNA damage in the E. coli DNA polymerase A- assay. 5 of the 13 solutions tested were positive in the polymerase A- assay. These products demonstrated an increased level of genetic toxicity when the assay was conducted under conditions of illumination with visible light. Investigation of the genetic toxicity of some of their components, specifically the preservatives, indicated that thimerosal and benzalkonium chloride were capable of causing repairable DNA damage. Thimerosal was active only when the plates were incubated under conditions of illumination, and thus was light-induced. Benzalkonium chloride was active under conditions of dark incubation, and its genetic toxicity was enhanced when the plates were irradiated with visible light. These results were confirmed in a parallel experiment, in which cells were treated with the test agent and irradiated for a short period in liquid culture and viable cells then determined. None of the commercial products and none of the components tested, were mutagenic in the Salmonella assay.

Intraoperative loss of auditory function relieved by microvascular decompression of the cochlear nerve.

BACKGROUND: Brainstem auditory evoked potentials (BAEP) are useful indicators of auditory function during posterior fossa surgery. Several potential mechanisms of injury may affect the cochlear nerve, and complete loss of BAEP is often associated with postoperative hearing loss. We report two cases of intraoperative auditory loss related to vascular compression upon the cochlear nerve. METHODS: Intra-operative BAEP were monitored in a consecutive series of over 300 microvascular decompressions (MVD) performed in a recent twelve-month period. In two patients undergoing treatment for trigeminal neuralgia, BAEP waveforms suddenly disappeared completely during closure of the dura. RESULTS: The cerebello-pontine angle was immediately re-explored and there was no evidence of hemorrhage or cerebellar swelling. The cochlear nerve and brainstem were inspected, and prominent vascular compression was identified in both patients. A cochlear nerve MVD resulted in immediate restoration of BAEP, and both patients recovered without hearing loss. CONCLUSION: These cases illustrate that vascular compression upon the cochlear nerve may disrupt function, and is reversible with MVD. Awareness of this event and recognition of BAEP changes alert the neurosurgeon to a potential reversible cause of hearing loss during posterior fossa surgery.

Microvascular decompression for trigeminal neuralgia. Surgical technique and long-term results.

In summary, it can be concluded that MVD has a long-term success rate equal or superior to percutaneous procedures without the higher rate of permanent neurologic sequelae. It is a safe operation with an almost negligible mortality and low morbidity in skilled hands. If the goal in the treatment of TGN remains obtaining a pain-free state without the need for medication and no permanent neurologic deficit, then MVD remains the definitive procedure of choice for typical TGN.

Comparison of tension band wiring and lateral mass plating for subaxial posterior cervical fusion.

BACKGROUND: Two instrumentation methods for subaxial posterior cervical fusion are compared in terms of efficacy, morbidity, and significant cost-related variables. METHOD: Thirty-four patients with tension band wiring and 14 patients with lateral mass plating are retrospectively compared in a single surgeon's experience between 1989 and early 1995. RESULTS: Both groups were similar in regard to operative indication (about 40% trauma, 30% degenerative changes in each group), postoperative immobilization (hard collar only used in 82% of patients wired and 79% of patients plated), and number of levels fused (mean, 1.7 in each group). Mean follow-up is 23 months for wiring and 35 months for plating. Pseudoarthrodesis occurred in one patient undergoing wiring and in none of the patients plated. Both methods resulted in complications (7 in 34 cases of wiring, 4 in 14 cases of plating), but no patient experienced neurologic decline. Statistically significant differences between the two groups were found for estimated blood loss, operating room time, and hardware cost, but not for postoperative orthosis or length of stay. CONCLUSION: In some instances when subaxial posterior fusion is performed, tension band wiring may be more cost-efficient. Tension band wiring and lateral mass plating seem to have comparable efficacy and morbidity, but the indications for each technique differ.

Functional outcome and the effect of cranioplasty after retromastoid craniectomy for microvascular decompression.

BACKGROUND: While the efficacy of retromastoid craniectomy for microvascular decompression for hyperactive cranial nerve syndromes is well established, there is no real information regarding the functional outcome of these operations. The purpose of this retrospective questionnaire study is to assess functional outcome regarding presence and duration of postoperative headache, incisional pain, and the time to return to normal activity in patients undergoing retromastoid craniectomy for microvascular decompression. The effect of closure with bone chips or cranioplasty in the defect upon these functional outcomes was studied, as was the influence of the particular nerve that was the object of decompression. METHODS: Four-hundred and ninety-five consecutive patients were contacted and 320 (65%) returned questionnaires with enough information to be suitable for analysis. RESULTS: The incidence of postoperative headache was initially 60.1%, dropping to 28.8% at 1 month and 16.8% at 6 months. Incisional pain likewise declined with time, noted in 25.8% at 1 month and only 13.1% at 6 months. Use of a cranioplasty made no significant difference in influencing either postoperative headache or incisional pain, nor was the nature of the procedure a significant factor. CONCLUSION: Twenty-five percent of patients resumed normal activity by 3 weeks, 50% by 1 month, and 90% by 3 months. Overall, 98% of patients responding reported returning to normal activity. Therefore, although there is an incidence of postoperative headache and incisional pain, these decrease with time and do not seem to interfere with the return to normal activity, nor are they affected by placement of a cranioplasty or the nature of the operation.

Delayed facial weakness after microvascular decompression of cranial nerve VII.

BACKGROUND: Retromastoid craniectomy and microvascular decompression of cranial nerve VII for hemifacial spasm is a well accepted and effective treatment. Risks of the operation relate to the surgical approach in general and to the seventh nerve in particular. Delayed facial weakness is an unusual and little-described complication of the procedure. The purpose of this review is to describe this complication and the characteristics of the patients so affected. METHODS: Between 1972 and 1996, 985 patients have undergone microvascular decompression for hemifacial spasm. During this time, 28 patients (2.8%) undergoing decompression of the facial nerve and 1 patient undergoing decompression of the cochlear nerve for tinnitus developed delayed facial palsy. RESULTS: The weakness was at least a House Grade III or worse and was complete in 11 of the patients. The time to occurrence averaged 12 days, with a tight range of 7 to 16 days. There were no factors such as duration of symptoms, intraoperative findings, or preoperative botulinum injections that were predictive of this postoperative weakness. In all patients there was almost complete recovery (House Grade I or II). CONCLUSIONS: Delayed facial weakness after MVD of CN VII can occur in up to 3% of cases. The onset of weakness after operation is consistent in its timing, occurring on average 12 days after the procedure. Although the etiology of this complication is uncertain, the palsy spontaneously resolves with a good or excellent outcome.

Degenerative cervical spondylolisthesis: diagnosis and management in five cases.

Five cases of degenerative subaxial spondylolisthesis of osteoarthritic etiology associated with significant cervical spondylotic myelopathy are described with treatment recommendations. Diagnostic studies included cervical plain films with flexion/extension, magnetic resonance imaging, and computed tomography/myelography. All patients had at least 2 mm of spondylolisthesis at one or more levels, and two patients had movement evident on flexion/extension films. Posterior laminectomy with AME (American Medical Electronics, Richardson, TX, U.S.A.) lateral mass plate and bone fusion was successfully performed in all five patients, three of whom improved one grade on the Nurick classification, whereas the rest improved within the same grade.

Surgical management of geniculate neuralgia.

BACKGROUND: Geniculate ganglion or nervus intermedius neuraigia is an unusual condition resulting in deep ear pain with or without signs of atypical trigeminal neuralgia, deep face, or throat pain. This article describes an experience with 14 patients who came to the neurosurgical service at the University of Pittsburgh Medical Center with a diagnosis of geniculate neuralgia. METHODS: After failing conservative treatment and after undergoing neurologic, otologic, and dental evaluations, these 14 patients underwent 20 intracranial procedures consisting of retromastoid craniectomies with microvascular decompression of cranial nerves V, IX, and X with section of the nervus intermedius in most cases. RESULTS: At operation, vascular compression of the nerves and nervus intermedius was found, which implicated vascular compression as an etiology of this disorder. Initially, 10 of 14 patients had an excellent outcome (71.5%), 3 experienced partial relief (21.5%), and there was 1 failure (7%). Ten patients were available for long-term (> 12 months) follow-up. Of these 10, 3 retained the excellent result (30%), 6 experienced partial relief (60%), and there was 1 failure (10%). Complications included one transient facial paresis, one facial numbness, one paresis of cranial nerves IX and X, one chemical meningitis, two cerebrospinal fluid leaks, and one superficial wound infection. Of those that fell from the excellent to partial category, this usually involved a return of atypical facial pain, but otalgia remained resolved. CONCLUSIONS: Overall, good results (with excellent or partial relief) were found long term for 90% of patients in this series. The authors recommend microvascular decompression of cranial nerves V, IX, and X with nervus intermedius section for the treatment of geniculate neuralgia.

The value of provocative facet blocking as a predictor of success in lumbar spine fusion.

Studies attempting to correlate facet blocking with successful relief of pain after fusion have reached unfavorable results. These studies, however, did so in a retrospective fashion, and facet blocking was not the sole criterion by which surgical candidates were chosen. The current study is the first to use facet blocking in a prospective fashion and as the definitive criterion by which patients were chosen. Ninety-one patients with chronic low back pain who responded to bracing underwent 197 facet blocks. Twenty-eight patients who had > 70% relief of their pain for >6 h on three separate occasions were surgical candidates and underwent fusion along with two others with mechanical abnormalities but negative blocks. Pre- and postoperative Prolo (Prolo DJ, Oklund SA, Butcher M: Toward uniformity in evaluating results of lumbar spine operations. A paradigm applied to posterior lumbar interbody fusions. Spine 11:601-606, 1986) outcome scores were assigned and the patients underwent self-assessment. Twenty-three of 30 patients had successful fusion. Nineteen of 23 described 90% relief, 3 patients had 50-90% partial relief, and 1 failed by self-assessment. A preoperative mean Prolo score of 3.95 (range 2-7) improved to 7.7 (range 3-10) with fusion. Provocative facet blocking can be used to successfully predict outcome in patients undergoing arthrodesis for chronic low back pain.

Factors influencing hearing preservation in acoustic tumor surgery.

In patients who underwent neurosurgery for excision of acoustic tumors, we used correlation and multivariate logistic regression analysis to study relationships among nine variables thought to have value in predicting hearing preservation. These variables included auditory perceptual, auditory neurophysiologic, and imaging-related characteristics of acoustic tumor dimensions. The univariate correlations showed two general trends. The first trend demonstrated relationships among imaging-related acoustic tumor dimensions (size or porus acousticus widening) with either postoperative hearing or brainstem auditory evoked potential (BAEP) abnormalities (tumor size and postoperative hearing; porus acousticus widening and postoperative hearing; tumor size and preoperative BAEP abnormalities). The second trend reflected interrelationships among preoperative audiometric variables that were not related to postoperative hearing outcome. Logistic regression analysis of eight independent variables on the presence or absence of postoperative hearing found that porus acousticus widening was the best prognostic indicator for hearing outcome. When the porus acousticus was widened, the odds ratio was 11:1 that hearing would be lost postoperatively. Viewed as a whole, the literature on prognostic variables related to hearing preservation has been limited, almost entirely, to univariate relationships. To determine more accurately which preoperative variables have unique prognostic value, more complex multivariate, analysis procedures will be required. Additionally, standardized criteria for assessment and reporting of auditory test results are also needed.