Shigeki Kamata

Changes of the auditory system after cerebellopontine angle manipulations.

The current tendency in acoustic neuroma surgery to attempt the preservation of hearing function and the problem of accidental hearing loss caused by microsurgical neurovascular decompression operations for hemifacial spasm or trigeminal neuralgia prompted us to study the exact surgical vulnerability of the auditory system. The surgical procedures for operation on the cerebellopontine angle of dogs were carried out according to the sequence of the posterior fossa transmeatal operation for acoustic neuroma. The operation was tentatively divided into three stages: (a) craniectomy and dural opening, (b) cerebellar retraction, and (c) identification of the cochlear nerve in the unroofed internal auditory canal (IAC). The postoperative behavior of the auditory system was evaluated electrocochleographically (EcochG) and histologically. Overzealous retraction of the cerebellar hemisphere caused transient disturbance of the EcochG pattern. Mechanical stretching of both the cochlear nerve and the internal auditory artery may cause a disturbance in the synchronized discharge of the cochlear neurons. Various manipulations at the porus acusticus internus or the IAC (such as pinching the nerve with forceps or electrocoagulation) produced thoroughly distorted EcochG patterns. From the histological findings, the main causative factor for these labyrinthine damages was considered to be vascular insufficiency. The current need for neurosurgical operations to preserve hearing is discussed in the light of these findings.

Neurotological findings in syphilis of the labyrinth.

The audiometric findings in five patients with syphilis of the labyrinth were classified as progressive type or fluctuating type. However, they were not peculiar to this disease.Disturbances of equilibrium detected by Manns test and a marked reduction of caloric response were common in all cases. A significant reduction of VOR gain observed in the computerized rotation test was useful in the diagnosis of this disease.

Experimental Studies on Allergic Endolymphatic Hydrops

Jiro Hozawa, Shigeki Kamata, Takashi Ishida and Noriko Kimura (Hirosaki University) The labyrinths of guinea pigs sensitized by horseradish peroxidase (HRP) were investigated by electronmicroscopy after challenging this antigen through the foram. stylomastoideum. Horizontal nystagmus toward the contralateral side was observed about fifteen minutes after challenging. The animals sacrified in this stage did not show endolymphatic hydrops, however, particles of HRP were observed in intracellular vesicles and basal lamina of the Reissners membrane. This particles were took in dark cells of the stria vascularis, too. In the animals sacrified forty-eight hours after challenging HRP, endolymphatic hydrops could be observed. These findings were not observed in the control study and suggested that hyperpermeability of the Reissners membrane and hypersecretion of the stria vascularis induced by antigen-antibody reactions were probable causes of endolymphatic hydrops.