The aim of the present study was to confirm the hypothesis that the cochlear efferent system is involved in the mechanisms underlying the "toughening" effect at high frequencies. The toughening effect is defined as a progressive threshold shift reduction when repeated exposures to the same noise are applied. Vestibular neurectomy was performed through a posterior cranial fossa approach in six healthy pigmented guinea pigs, and it assured the interruption of both crossed and uncrossed olivocochlear bundles to one ear only, before their entrance in the internal auditory meatus. The animals were then implanted with permanent electrodes for the electrocochleographic findings. Ten days after the operation the animals were exposed to octave-band toughening noise, centered at 4 kHz, at 85-dB SPL, for 10 consecutive days, 6 hours on/18 hours off. The hearing threshold was registered before and at the end of each exposure session. The behavior of the hearing threshold in the operated ears was then compared to that of the controlateral, nonoperated ears. Complete recovery from TS in the control ear began after four days of exposure, whereas in the operated ear hearing loss increased to day 7 (55 dB), with only a partial reduction (45 dB) beyond ten days of exposure. The results of the present study clearly demonstrated that sectioning of the OCB in guinea pigs causes persistent hearing loss during noise-exposure conditioning, in comparison to the contralateral, nonoperated ear. Thus, one can assume that the lack of decrease of TS during intermittent noise exposure could be due to the loss of the protective effect of the efferent fibers, perhaps mediated by the lateral OC neurons that synapse beneath the IHCs.

Using laser Doppler flowmetry, cochlear blood flow was assessed in Mongolian gerbils exposed to noise. Anesthetized animals were surgically implanted with permanent electrodes and then exposed for 10 consecutive days (6 h on/18 h off) to an octave band noise centered at 4 kHz (85 dB SPL). The auditory brainstem responses and the blood flow in the basal turn of the cochlea were compared with those of gerbils not exposed to noise. The exposed animals developed an initial threshold shift, followed by a progressive reduction in threshold shift up to complete recovery at the end of the test. In the exposed animals, a reduction in the cochlear blood flow during the first 4 days of exposure was observed, which was then followed by a progressive increase up to the end of the test. The results of this study exclude a possible role of the microvasculature of the lateral cochlear wall in determining the resistance to 4 kHz frequency noise exposure.

Using laser Doppler flowmetry, cochlear blood flow was assessed in Mongolian gerbils exposed to noise. Anesthetized animals were surgically implanted with permanent electrodes and then exposed for 10 consecutive days (6 h on/18 h off) to an octave band noise centered at 4 kHz (85 dB SPL). The auditory brainstem responses and the blood flow in the basal turn of the cochlea were compared with those of gerbils not exposed to noise. The exposed animals developed an initial threshold shift, followed by a progressive reduction in threshold shift up to complete recovery at the end of the test. In the exposed animals, a reduction in the cochlear blood flow during the first 4 days of exposure was observed, which was then followed by a progressive increase up to the end of the test. The results of this study exclude a possible role of the microvasculature of the lateral cochlear wall in determining the resistance to 4 kHz frequency noise exposure.

Arachnoid cysts (AC) often present with symptoms depending on their anatomical location within the skull; while supratentorial cysts grow causing relatively few symptoms, infratentorial ones may impair liquor circulation at the level of the fourth ventricle, giving rise to intracranial hypertension, or may stretch the complex nerve network in the cerebello-pontine angle. We report the singular clinical history of a 54-year-old male, who suddenly began to feel dizzy while sitting at his workplace, complaining of left tinnitus and aural fullness, in a classic clinical picture of Ménière's disease. The anomalous findings at otoneurological examination (markedly the left deviation at the Fukuda test) made a magnetic resonance image (MRI) scan mandatory and a huge AC was found in the left fronto-parietal lobe. The mass provoked an evident clockwise rotation of the brainstem that we suppose to be the cause of acoustico-facial bundle stretching explaining the vestibular symptomatology.

Sigmoid sinus thrombosis (SST) usually follows acute as well as chronic otitis media with coalescent mastoiditis. A singular case of noncoalescent mastoiditis complicated with thrombosis of deep cerebral sinuses occurring in a young child is presented. A genetic thrombophilic disorder (prothrombin G20210A allele mutation) was identified as the predisposing factor for this unusual complication. Particular emphasis is placed on the course of the disease, which showed regression only after surgical exploration and additional anticoagulant therapy. We conclude that a thorough and early assessment of coagulation factors should always be performed, especially in the population at risk, in order to rule out unusual aetiologies of these rare but still life-threatening pathological processes.