M. Berg

The enlarged middle cranial fossa approach for surgery of the temporal bone and of the cerebellopontine angle

SummaryDue to the fact that the temporal bone has broad segments of bone anterior to and behind the internal auditory canal which are empty of functionally important structures, a broad exposure of the cerebellopontine angle may be obtained from above. This technique is adequate for the management of acoustic neurinomas up to 3 cm in diameter. A low postoperative morbidity and a high percentage of hearing preservation with total tumor removal were obtained in a series of 190 cases. This report underlines the advantages of the procedure and points to various other indications.

Clinical Survey of Meniere's Disease: 574 cases

Only 27% out of 574 patients suffering from Meniéres disease initially started with the typical Meniéres triad. A great advantage in order to diagnose Meniéres disease can be established with the telemetric-ENG. With this equipment it is possible to verify a nystagmus outside the clinic (at home, at work) at any time in patients suffering from vertigo attacks. Most of our patients showed an omnifrequent sensorineural hearing loss on the affected side. Many of our patients with Meniéres disease suffered from internal diseases (e.g. hypotonia, hyperlipidemia, diabetes mellitus), allergy or an affection of the paranasal sinuses, which may constitute co-factors triggering Meniéres disease.

Delayed hearing loss after surgery for acoustic neurinomas: clinical and electrophysiological observations.

In a series of 26 patients with medium-sized and large acoustic neurinomas and documented hearing before surgery, 7 patients had preservation of hearing initially after the procedure but then developed delayed hearing loss. The most prominent intraoperative electrophysiological finding in these cases was a gradual deterioration of brain stem auditory evoked potentials (BAEP), especially of Wave V. Four additional patients with a similar gradual intraoperative loss of BAEP and severe postoperative hearing deterioration received vasoactive treatment after surgery (low-molecular weight dextran). In all 4 patients, including 1 patient with documented total deafness after surgery, hearing was preserved. Initial preservation of cochlear nerve function after the removal of an acoustic neurinoma does not guarantee postoperative hearing. Intraoperative BAEP help to identify patients at risk for delayed postoperative hearing loss. The pathophysiological mechanism can be attributed to disturbances of the microcirculation in endoneurial vasa nervorum caused by the mechanical manipulation of the cochlear nerve.

Topographical Anatomy of the Internal Auditory Canal: Implications for Functional Surgery in the Cerebello-Pontine Angle

For exposure of the cerebello-pontine angle by an enlarged middle-fossa approach without destruction of the inner ear, bone removal anterior and posterior to the internal auditory meatus (c.a.i.) can be performed with orientation at landmarks. Based on the experience of more than 300 interventions and documented by a series of 10 temporal bone micro-dissections, rules have been established for reliable localization of the following structures: geniculate ganglion, Fallopian canal, vertical crest at the fundus of the c.a.i., basal coil of the cochlea, and ampulla of the superior semicircular canal. The surgical technique has enabled the authors to remove acoustic neurinomas of up to 3.5 cm with preservation of hearing in 51%.

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.

Transcranial magnetic stimulation of the facial nerve in small and medium-sized acoustic neurinomas.

The expanding mass of an acoustic neurinoma in the internal auditory meatus and the cerebellopontine angle induces symptoms dependent on the time period of the tumor growth. Initial signs of acoustic neurinoma are hearing impairment and tinnitus as well as disturbances of equilibrium. The clinician interpretes affections of the facial, trigeminal, or other cranial nerves as indications of a large tumor mass. The size of the tumor and the initial symptoms are not strictly correlated. Patients with small intrameatal tumors can be deaf and vice versa. The subclinical lesions of the facial nerve by tumor growth have been evaluated earlier by stimulation of the extratemporal part of the facial nerve [8, 7]. Transcranial magnetic stimulation (TMS) was first described in 1985 [1] and is now widely used in the diagnosis of neurological disorders [3, 6]. TMS is a noninvasive instrument for stimulation of the facial nerve in its labyrinthine portion, close to the site of the growing tumor [10, 14].

Otochirurgische Neurolyse des VIII. Hirnnerven bei progressiven, cochleo-vestibulären Störungen

SummaryOto-microsurgical exploration of the VIII. nerve within the internal auditory canal and the cerebello-pontine angle was performed in 16 cases of progressive sensorineural hearing loss with vestibular disturbances. The indications included Menières disease with severe attacks of vertigo, resistant to conservative treatment. The CT-scan with air-cisternography had always outruled an eighth nerve neurinoma, but sometimes evidenced abnormal courses of nerves or vessels at the internal porus acusticus. By a transtemporal exposure of the cerebello-pontine angle pathological abnormalities such as dislocation of the VIII. nerve, scar tissue or arterial vessel loops could be visualized and removed. The preliminary results evidenced a beneficial effect of the operation on the vestibular symptoms, while its influence on hearing and tinnitus was different. Follow up studies remain necessary. The observations underline earlier assumptions of Dandy (1934), Janetta (1980) et al. regarding the effect of neurovascular compression on the function of cranial nerves.

Neurootologische Verlaufsbeobachtungen nach Neurektomie des N. vestibularis bei M. Menière

SummaryThirty-seven patients suffering from Menières disease resistant to conservative treatment underwent neurectomy of the vestibular nerve. Preoperatively the vestibular test results often showed a fluctuating character depending on the phase of the disease (irrigation — or interval phase). Of the cases 62% had a hypoactivity in the caloric reaction on the diseased side. The postoperative vestibular examination results in the follow up correlated with the subjective feeling of vertigo. In all cases a decrease of the nystagmus intensity was present. As final result (16 cases with follow up examinations between 3 and 8 years) the patients usually showed a slight positioning nystagmus, a minimal disturbance of the vestibulo-spinal reaction with eyes closed and sometimes a slight preponderance of the nystagmus in the pendular chair. The vertigo attacks stopped in 32 of the 37 cases and were reduced and not so frequent in four cases (97%). The tinnitus diminished or disappeared in more than 50% after vestibular nerve resection. Special complications or risks of this vestibular nerve resection have not to be mentioned.