[Our experience in neuroma surgery]

Our 24-year experience with acoustic neuroma surgery is reported. Three approaches were used in 34 patients: translabyrinthine (11 cases), transtemporal (2 cases), and retrosigmoid (21 cases). Prolonged facial paralysis occurred in 27% of patients with the translabyrinthine approach and in 15% with the retrosigmoid approach. Facial nerve monitoring was used in all operations with the retrosigmoid approach. In the translabyrinthine approach, 5 patients had CSF leak, 2 required secondary surgery, and 2 developed meningitis. With the retrosigmoid approach, 5 patients had CSF leak, 2 required secondary surgery, 3 developed meningitis (1 died), and 1 patient required emergency reoperation for posterior cranial fossa hematoma. Auditory function was preserved in one patient. The advantages of the retrosigmoid approach have become apparent: good exposure, speed, and preservation of the facial and cochlear nerves.

[Hearing preservation and tinnitus following removal of acoustic neurinomas]

Thirty-five cases of unilateral acoustic neurinomas were analyzed with special reference to the postoperative eighth cranial nerve function. An additional three cases of bilateral acoustic neurinomas associated with neurofibromatosis were also analyzed. Out of a total of 40 neurinomas in all, 38 cases were retrospectively reviewed. The thirty-five cases of unilateral acoustic neurinomas were summarized as follows. The patients' age ranged from 23 to 69 years old. The tumor size varied as follows; 7 cases were confined to the internal acoustic meatus, 4 cases were 20 mm or less in their maximum diameter, 13 cases were 30 mm or less, and 11 cases were more than 30 mm. The consistency of the tumor was classified as being solid in 27 cases, and being cystic in 8 cases. Hearing had been maintained in 27 cases on admission, serviceable in 17 cases, unserviceable in 10 cases and deaf in 8 cases. Operations were performed via the retromastoid suboccipital approach in all cases. The facial nerve was anatomically preserved in all cases. On the other hand, the cochlear nerve was anatomically preserved in 14 out of 35 cases (40%). The preservation ratio of the cochlear nerve showed a negative correlation to the tumor size. In 17 cases with preoperative serviceable hearing, preservation of the cochlear nerve was attempted, which resulted in a 65% anatomical preservation. However, hearing was preserved in 4 cases (36%). Serviceable hearing was preserved in only 2 cases. Tinnitus developed in 20 cases preoperatively, and then occurred postoperatively in 11 cases. Tinnitus was prominently aggravated in 2 cases in which the cochlear nerves were preserved, which resulted in unserviceable hearing. There was a statistically significant correlation between cochlear nerve preservation and the postoperative presence of tinnitus (Fisher's exact probability test: P = 0.0106 < 0.05). Tinnitus was aggravated just after the operation. However, it gradually improved and vanished as the hearing showed a recovery to a slight degree in one case. Three cases of bilateral acoustic neurinomas in neurofibromatosis were also summarized. One case received the operation only on the unilateral side. The remaining two cases were operated bilaterally. To preserve serviceable hearing on at least one side, partial removal of the tumor was performed under the monitoring of auditory brain stem response and/or cochlear microphonic potential. Serviceable hearing on at least one side was maintained in all three cases. In conclusion, hearing preservation can be expected after removal of the acoustic neurinomas under the following situations; hearing acuity of less than 50-60dB in preoperative pure tone audiogram, tumor size of less than 20 mm in maximum diameter, cases with preservation of cochlear nerve and of the internal auditory artery during the operation, and no injury to the labyrinth during the operation. In some cases, tinnitus becomes aggravated in the case with cochlear nerve preservation associated with unserviceable hearing. Furthermore, the degree of tinnitus shows a decrease as postoperative hearing improves in some cases.

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.

Surgical management of transcranial hypoglossal schwannomas

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.

Facial nerve neuromas: diagnosis and management

Facial nerve neuromas are uncommon tumors that involve the facial nerve. There is no classic presentation of these tumors. This study presents a series of 22 patients with facial neuromas managed from 1977 to 1993. Facial nerve dysfunction was the most common complaint, present in 90.5% of cases. Hearing loss was the second most common complaint and was found in 76.2% of cases. High resolution computed tomography and magnetic resonance imaging with gadolinium proved to be the most accurate methods of preoperative assessment of these tumors and are complementary in selected cases. Different surgical approaches were performed according to tumor location and preoperative hearing level. In all cases long-term follow-up showed no tumor recurrence, and acceptable return of facial function was noted in 80% of cases.

[Intraoperative monitoring of the lower cranial nerves during skull base surgery: evoked electromyographic technique]

Functional preservation of the lower cranial nerves is an important issue in the surgery of the skull base to avoid postoperative serious complications such as aspiration pneumonia and respiratory disorders. We presented our experience of intraoperative monitoring of the lower cranial nerves during skull base surgery. The evoked electromyographic (EMG) activities were successfully recorded from the muscles innervated by the lower cranial nerves. These EMG recordings are helpful to guide the surgeon intraoperatively and to avoid careless severing of these nerves. Although the glossopharyngeal nerve that innervates only one small muscle in the pharynx (M. stylopharyngeus) cannot be monitored with the evoked EMG technique described in this paper, the position of this nerve can be deduced from the position of the vagus nerve.

Intracranial facial neuromas: total tumor removal with facial nerve preservation: a new surgical technique

Neuromas of the facial nerve are uncommon tumors. The majority of cases involve the intratemporal and parotid areas. Since their description in 1930, there have been only 26 cases of intracranial facial neuroma reported in the world literature. Of these, 19 involved the middle cranial fossa, and only seven tumors extended into or originated in the posterior cranial fossa. In this location, the seventh nerve is surrounded by a very delicate and thin arachnoid casing. Thus, although these tumors are encapsulated, there is usually no obvious plane of separation between the tumor and perineurium. As a result, the seventh nerve has been sacrificed routinely. Two patients with posterior fossa facial neuromas underwent total tumor removal with a new surgical technique permitting preservation of the nerve fascicles via a translabyrinthine approach. Each patient has good recovery of seventh nerve function with no evidence of recurrence six and nine years later, respectively. Leaving the nerve fascicles intact appears to result in good reinnervation following total tumor removal. The potential value of this technique is best considered in the context of diagnostic and therapeutic options for facial neuromas in general. Neurotologists should find this a useful addition to their surgical armamentarium for selected cases.

Precocious puberty in children with neurofibromatosis type 1

We undertook a comprehensive study of children with neurofibromatosis type 1 (NF-1) cared for in a large multidisciplinary clinic to determine the prevalence of precocious puberty and its relationship to optic pathway tumors (OPTs). Precocious puberty was diagnosed in 7 of 219 children with NF-1 (5 boys and 2 girls) examined between Jan. 1, 1985, and April 20, 1993. All seven children had OPTs involving the optic chiasm; they represented 39% of children with NF-1 and chiasmal tumors (95% confidence interval, 17% to 64%). Eleven prepubertal children (aged 2 to 10 years) with NF-1 and OPTs, and age- and sex-matched NF-1 control subjects without OPTs, underwent luteinizing hormone-releasing hormone (LH-RH) stimulation tests. Two boys with OPTs had pubertal luteinizing hormone (LH) responses, and testosterone levels > 10 ng/dl. Basal LH levels were also elevated in these two boys when tested with a very sensitive immunochemiluminometric assay. None of the children without an OPT had either a pubertal response to LH-RH or an elevated basal LH level. We conclude that precocious puberty in children with NF-1 is found exclusively in those who have OPTs involving the optic chiasm; it is a common complication in those children. With the use of a highly sensitive LH assay, biochemical evidence of hypothalamic-pituitary-gonadal axis activation may be demonstrated, even without provocative testing.

On the site of transcranial magnetic stimulation of the facial nerve: electrophysiological observations in two patients after transection of the facial nerve during neuroma removal

The site of stimulation of the facial nerve after transcranial temporo-occipital magnetic stimulation is being controversially discussed, particularly whether the nerve is stimulated in the root exit zone in the cerebellopontine angle or whether stimulation originates within the bony canal of the facial nerve. In two case reports, the neurophysiological findings after the surgical transection of the facial nerve during the extirpation of a large acoustic and a facial nerve neuroma are presented. In both cases, transcranial magnetic stimulation of the facial nerve produced compound muscle action potential 4 and 2 days after the dissection of the facial nerve at the internal auditory canal and in the supralabyrinthine portion. These findings indicate that the site of stimulation in transcranial magnetic stimulation can be located to the course of the facial nerve within its bony petrosal canal distal to the external genu.

Facial nerve involvement in patients with acoustic neurinomas. Examination with magnetic single- and bi-stimulation

The diagnosis of acoustic neurinomas is usually made by auditory and vestibular testing and magnetic resonance imaging. As clinical involvement of the facial nerve is infrequent, occurring only in large tumours, only little is known about the subclinical involvement of the facial nerve. Transcranial magnetic stimulation of the VIIth cranial nerve in the temporal bone, adjacent to acoustic neurinoma growth, seems to be an adequate instrument for electrophysiological measurements of minimal nerve lesions without clinically obvious facial palsy. In 70% out of 97 patients with surgically and histologically confirmed acoustic neurinomas, obvious elongation of the intratemporal conduction time of the facial nerve was found. This affection was dependent on tumour size. No correlation was found to preoperative or postoperative facial nerve function and hearing function. The latencies of the conduction time showed a tendential increase in patients with a more difficult grade of surgery and of facial nerve preparation due to fibrous adhesions and nerve spreading on the tumour capsule. A completely new stimulation modality, the application of two magnetic stimuli in quick succession, was applied for the first time in acoustic neurinoma patients, and revealed facial nerve involvement by acoustic neurinoma growth. Facial nerve involvement in acoustic neurinoma can be detected by transcranial magnetic stimulation even in patients with small and medium sized tumours but with clinically normal facial function.

Evaluation of fifth nerve dysfunction in 136 patients with middle and posterior cranial fossae tumors

One-hundred thirty-six patients operated on for extra-axial tumors of the posterior and middle cranial fossae were retrospectively evaluated to define the relevance of trigeminal nerve dysfunction and to correlate clinical and surgical observations. The following data are reported: tumor types, presence of specific trigeminal symptoms and signs, mean duration of symptomatology, anatomical relation between tumor and fifth nerve. Trigeminal symptoms were present in 45 subjects (33.08%) with a mean duration of 23.56 months. Frequency of symptoms was different in various oncotypes. Fifth nerve disturbances were the symptom of onset in 18 subjects (13.23%). A tumoral involvement of the nerve was reported at surgery in 73 patients (53.67%) and was defined as contact, compression or infiltration. Postoperatively, 12 patients showed an improvement of fifth nerve disturbances. A statistically significant difference (p < 0.05) was found in: (1) the incidence of symptoms in patients with and in those without anatomical trigeminal involvement: (2) the incidence of signs in the same groups; (3) the incidence of postoperative relief in patients with fifth nerve compression compared to patients with different surgical findings; (4) the incidence of postoperative relief in patients with typical trigeminal neuralgia compared to those with other symptoms.

Natural history of optic pathway tumors in children with neurofibromatosis type 1: a longitudinal study

To assess the natural history of optic pathway tumors (OPT) in children with neurofibromatosis type 1 (NF-1), from January 1985 through May 1993 we performed a prospective, longitudinal study of OPT in an unselected population of children with NF-1. Of 227 children with NF-1 seen in a specialty clinic, 176 (77%) underwent neuroimaging. Children in whom tumors were identified were followed closely by both repeated neuroimaging and ophthalmologic examinations to detect tumor growth or visual deterioration. Thirty-three children (19%) were found to have OPT at a median age of 4.2 years. The median age of children who had ophthalmologic complaints was significantly lower than that of children who had no such complaints (1.9 vs 5.3 years; p < 0.001). Although eight tumors were discovered because of ophthalmologic complaints or evidence of precocious puberty, 25 children (76%) were free of symptoms at the time of diagnosis. Twenty-one children (64%) had normal ophthalmologic findings at diagnosis; six children, all with chiasmal tumors, had previously unrecognized decreased visual acuity. Only three children (9%) had evidence of either tumor growth or deteriorating vision after diagnosis; the median duration of neuroimaging follow-up was 2.4 years (range, 0.2 to 7.2 years) and of ophthalmologic examinations 3.4 years (range, 0.2 to 8.1 years). All symptomatic OPT were diagnosed before 6 years of age. We conclude that OPT rarely progress during the next few years in children with NF-1 once the OPT have been discovered. The utility of screening neuroimaging for OPT in symptom-free children with NF-1 appears very limited.

Stereotactic radiosurgery for acoustic nerve tumors in patients with useful preoperative hearing: results at 2-year follow-up examination

Twenty patients with acoustic nerve tumors (mean diameter < or = 30 mm) and useful preoperative hearing were examined 2 years after stereotactic radiosurgery to determine the effectiveness of the surgery in the control of tumor growth and the preservation of cranial nerve function. Results showed tumor volume stabilization (12 cases) or reduction (seven cases) was achieved in a total of 19 patients (95%). Useful hearing (defined as Gardner and Robertson Class I or II) preservation was obtained in 100% of cases immediately postoperatively, 50% at 6 months, and 45% at both 1 and 2 years. Two years after stereotactic radiosurgery, facial nerve function was preserved in 90% of patients and 75% continued to have normal trigeminal nerve function. All patients returned to and maintained their preoperative functional status within 3 to 5 days after radiosurgery. These findings indicate that stereotactic radiosurgery with multiple isocenters and narrow radiation beams is a safe and effective management strategy for progressive acoustic nerve tumors. Auditory, facial, and trigeminal nerve function can be preserved in most patients. Prevention of further growth and preservation of cranial nerve function appear to be satisfactory goals in the current management of patients with acoustic neuromas.

Optic gliomas in neurofibromatosis type 1: role of visual evoked potentials

Optic gliomas occur in 15% of patients with neurofibromatosis type 1 (NF 1) and are a significant cause of morbidity. Of these tumors, 20-30% become symptomatic, usually before age 10 years. Previous studies have suggested that visual evoked potentials (VEPs) are a sensitive method for the detection of asymptomatic optic gliomas. Because routine neuroimaging of children with NF 1 is currently not recommended, the role of pattern-shift VEPs (PS VEPs) as a screening test for optic gliomas was evaluated. PS VEPs were performed on 10 children with NF 1 and optic gliomas and 20 children with NF 1 and normal visual pathways (as defined on MRI). PS VEPs had 90% sensitivity for detecting optic gliomas, with an increase in sensitivity to 100% when hemifield stimulation was used. The specificity of the test was 60%. Four of 20 children without optic gliomas had thickened optic nerves on computed tomography which represented dural ectasia with normal visual pathways on MRI; PS VEPs were normal in these patients. The efficacy of PS VEPs as a routine screen for optic gliomas is limited by the age at which children will cooperate with the test procedure and the high incidence of false-positive results; however, VEPs do provide a useful adjunct to routine clinical ophthalmologic assessment in the detection of optic gliomas in children with NF 1. Abnormal test results provide a stronger indication for neuroimaging. The early detection of optic gliomas allows for close monitoring of tumor progression and earlier intervention prior to significant visual loss.

Surgical treatment of meningiomas of the orbit and optic canal: a retrospective study with particular attention to the visual outcome

A series of 57 patients affected either by optic nerve sheath meningiomas (15 patients) or by secondary meningiomas extending into the orbital apex or optic canal (42 patients) has been reviewed. Proptosis (80%), progressive visual loss (76%), and visual fields defects (63%) were the most common pre-operative complaints. All patients underwent transcranial surgery. Radical tumour resection was possible in 9 out of 15 primary and 22 out of 32 secondary tumours. Overall, 27% of the patients obtained improved postoperative visual acuity, 62% remained unchanged, and 11% were worse. The postoperative visual outcome was related to the degree of pre-operative visual impairment. In a period between 38 and 68 months, 5 meningiomas recurred. The time to progression of partially resected lesions ranged between 9 and 68 months.

[Ophthalmologic symptoms in meningioma of the orbits and in the anterior and medial cranial fossa]

The records of 182 patients treated for a meningioma of the orbit or the periorbital region between 1971 and 1989 were analyzed.

PATIENTS

There were 138 women (76%) and 44 men (24%). Twenty patients had a meningioma of the optic nerve sheath, 78 patients a meningioma involving the sphenoid wing, 29 a meningioma within the sella region, 36 patients a meningioma of the anterior cranial fossa and 19 patients a meningioma of the medial cranial fossa.

RESULTS

As an initial symptom 53% complained of decreased vision, 25% of headaches and 16% had exophthalmos. At the first ocular examination visual acuity was decreased below 0.1 in 22%. In 58 eyes we found papilledema and in 60 eyes optic atrophy. Other manifestations were visual field defects, ocular motility deficits in 20%. Histologically the meningiomas were most commonly of the endotheliomatous type (72%). In 23% of the patients, the tumor recurred, which manifested itself in a third by ocular symptoms.

Trigeminal involvement in intracranial tumours. Anatomical and clinical observations on 73 patients

Neoplastic involvement of the trigeminal nerve was observed in 73 patients operated on in our institution for extra-axial tumours of the posterior and middle cranial fossae. It was defined as contact, compression, or infiltration. The nerve root was involved in 58 patients, the ganglion and/or the peripheral divisions in 9, all portions of the Vth nerve system in 6. A clinical trigeminal dysfunction was present in 44 patients (60%). Anatomico-surgical findings are correlated with clinical features and with tumour type. Typical trigeminal neuralgia was the complaint in 7 subjects; all of them presented an involvement of the sensory root. Post-operatively, 11 patients were relieved of their symptoms. The outcome is correlated with the anatomical findings and with the extent of surgical removal of the tumours. The importance of a careful evaluation of patients with trigeminal symptomatology is stressed.

A newly designed nerve monitor for microneurosurgery: bipolar constant current nerve stimulator and movement detector with a pressure sensor

The authors describe a newly designed nerve monitor which is useful for numerous microneurosurgical procedures. Standard bipolar forceps are used to apply constant current stimulation. Muscle contraction evoked by the stimulation is detected by a small disc-shaped pressure sensor taped to the overlying skin. The responses are monitored both quantitatively on a liquid crystal display and qualitatively through an on-off auditory signal. Surgery can proceed without interruption. This apparatus can safely and reliably monitor the facial nerve, nerves involved in eye movements, lower cranial nerves and spinal nerves. This portable system weights only 1.8 kg and can easily be used by a neurosurgeon.

The sensitivity of auditory brainstem response testing in small acoustic neuromas

Auditory brainstem response (ABR) testing is a reliable and sensitive test for retrocochlear pathology in neurotologic diagnosis. Several investigators have reported the sensitivity of ABR testing as 95% or greater. Fifty-one consecutive patients with surgically confirmed acoustic neuromas were examined. Forty patients had sufficient hearing preoperatively for assessment with ABR. In addition, all had been evaluated with gadolinium-enhanced magnetic resonance imaging and conventional electronystagmography. Overall, 34 of 40 patients (85%) had abnormal ABRs. One of 25 patients with extracanalicular tumors had a normal ABR for a false-negative rate of 4%; however, 5 of 15 patients with intracanalicular tumors had normal ABRs for a false-negative rate of 33%. Tumor size and nerve of origin were important factors affecting the ABR sensitivity. The ABR was less sensitive in detecting intracanalicular tumors than in detecting extracanalicular tumors.

Spontaneous visual improvement in chiasmal gliomas

Three untreated patients with presumed chiasmal gliomas had spontaneous visual improvement, although serial magnetic resonance imaging in two of the patients showed the lesions to be unchanged. Two patients had evidence of neurofibromatosis. Three other patients with similar disease courses have been documented in the medical literature. These cases demonstrate that conservative management of optic chiasmal gliomas may sometimes be associated with favorable outcomes.

Promontory electrical stimulation in postoperative acoustic tumor patients

Complete deafness can follow acoustic tumor surgery and results from labyrinthine injury, auditory nerve trauma, and/or vascular compromise. A central auditory prosthesis is one potential rehabilitative strategy in such patients. Anatomical studies suggest that some spiral ganglion cells may survive after vascular occlusion, and we have demonstrated responses to electrical stimulation in patients after labyrinthectomy. It was thus hypothesized that patients deafened after a hearing conservation attempt, but maintaining an intact auditory nerve, could utilize an intracochlear implant. To investigate this possibility, promontory electrical stimulation was performed on three patients who had tumors less than 2 cm and who had serviceable preoperative hearing, but no responses postoperatively. Behavioral responses and electrically evoked auditory brainstem and middle latency responses were obtained from two patients, one of whom was 6 years postsurgery. These data indicate that a cochlear implant may be possible after acoustic tumor surgery.

Facial nerve repair by interposition nerve graft: results in 22 patients

Resection of tumors of the posterior cranial base may incorporate a segment of the facial nerve because of tumor infiltration, or may result in unplanned nerve injury. Immediate repair of the facial nerve by resuture or with an autogenous nerve graft is highly desirable to ensure optimal recovery of facial function. Twenty-four patients who underwent extensive surgery of the posterior skull base and facial nerve reconstruction were studied. Of these, 12 patients had preoperative facial weakness and 3 had facial palsy. All patients underwent graft reconstruction from the subarachnoid or labyrinthine portion of the facial nerve to the fallopian or extracranial segment. The greater auricular nerve was used as a graft in 14 patients, and the sural nerve in 10. Two patients died of their disease soon after surgery, and, therefore, were excluded from our follow-up. In the remaining 22 patients, the median follow-up time was 20 months. As evaluated by the House-Brackmann grading system, 45% (10/22) of the surviving patients achieved a good recovery of facial function, 36% (8/22) attained a fair recovery, and 18% (4/22) had minimal or no recovery. There was no statistical correlation between the length of the graft used and the degree or timing of clinical recovery. The surgical result obtained in all patients with complete preoperative facial palsy and in one patient with dense facial paresis was poor.

Visual hallucinations after acute visual loss in a young child

A four-year-old boy developed complex visual hallucinations consisting of moving figures, animals and other familiar objects one week after becoming totally blind. This followed a six-month period of gradually deteriorating vision and was precipitated by the debulking of a large optic nerve glioma. Although visual hallucinations are well recognised in adults with visual loss, secondary to both ophthalmological and neurological causes, they have not been reported in young children.