Otologists have long debated the importance of the mastoid in determining the success or failure of tympanic membrane reconstruction. The pneumatic spaces within the mastoid represent an "air reservoir" which can be drawn upon during periods of eustachian tube dysfunction and buffer the middle ear against the development of detrimental negative pressures. Mastoid inflammatory disease, if untreated, may result in recurrent suppuration and graft failure. Small mastoid volume, aside from its well known association with chronic infectious middle ear disease, has been shown to effect adversely graft survival following myringoplasty. In 48 patients undergoing myringoplasty with simple mastoidectomy, neither small mastoid size nor inflammatory mastoid disease significantly decreased the rate of graft healing. This suggests that simple mastoidectomy is an effective means of repneumatizing the mastoid and eradicating mastoid sources of infection. The successful surgical creation of a pneumatized mastoid cavity in communication with the middle ear was confirmed by postoperative computerized tomographic (CT) scans. In failed cases, CT scanning predictably identified residual mastoid disease. Simple mastoidectomy is considered to be a safe and useful adjunct to myringoplasty in selected cases of chronic otitis media with perforation.

Since only one third of patients show pathologic tympanic membrane changes, and since complaints of otalgia, fever, and tenderness are inconstant, subperiosteal mastoid abscess is frequently a delayed diagnosis. The clinical presentation, pathogenesis, and routes of abscess spread are presented with photographic and radiographic illustration. Medical and surgical management is reviewed, and methods for accurate diagnosis are emphasized.

Sensory deafness may be associated with partial or total obliteration of the cochlear scalae. Before undertaking cochlear implant surgery, a preoperative assessment of cochlear patency with high‐resolution computed tomography (CT) is indicated. To determine the accuracy of pre‐implant CT, a review of the radiographic and surgical findings in 36 implanted ears was performed. An abnormal CT scan was found to be a reliable predictor of compromised cochlear patency at operation. These findings help the surgeon to select the side most favorable for implantation and to anticipate problems that may be encountered during device insertion. A normal pre‐implant CT scan, however, does not exclude the possibility of compromised cochlear patency. A 46% false negative rate was encountered, presumably because subtle degrees of osseous or fibrous obliteration of the cochlea are beyond the resolution by current generation CT scanners. In our opinion, the radiographic finding of cochlear ossification is not a contraindication to an attempt at cochlear implantation. The only assured way of determining the extent of cochlear patency is by performing an ‘exploratory cochleostomy’ with fenestration of the basal cochlear turn. Drilling anteriorly through an ossified basal scala tympani will often expose an adequate lumen and permit insertion of even a long multichannel electrode into a partially ossified cochlea. Nevertheless, it is essential that the implant team be prepared with devices appropriate for whatever existing or surgically created lumen may be available.

A series of psychoacoustic experiments was conducted in subjects implanted with a permanent intracochlear bipolar electrode. These experiments were designed to reveal the nature of the sensation evoked by direct sinusoidal electrical stimulation of the acoustic nerve. A series of single unit experiments in the inferior colliculus of cats was then conducted, using intracochlear stimulus electrodes identical to those implanted in human subjects in all respects except size, and using identical stimuli. These physiological experiments were designed to reveal how sounds evoked by intracochlear electrical stimulation in humans are generated and encoded in the auditory nervous system. Among the results were the following: 1) The sensation arises from direct electrical stimulation of the acoustic nerve. It is not “electrophonic” hearing arising from electro-mechanical excitation of hair cells. 2) While sounds are heard with electrical stimulation at frequencies from below 25 to above 10,000 Hz, the useful range of discriminative hearing is limited to frequencies below 400–600 Hz. 3) There is no “place” coding of electrical stimuli of different frequency. Tonal sensations generated by electrical stimulation must be encoded by the time order of discharge of auditory neurons. 4) The periods of sinusoidal electrical stimuli are encoded in discharges of inferior colliculus neurons at frequencies up to 400–600 Hz. 5) Both psychoacoustic and physiological evidence indicates that the low tone sensations evoked by electrical stimulation are akin to the sensations of “periodicity pitch” generated in the normal cochlea. 6) Most cochlear hair cells are lost with intracochlear implantation with this electrode. Most ganglion cells survive implantation. Implications of these experiments for further development of an acoustic prosthesis are discussed.

A quantitative analysis of the afferent innervation of the organ of Corti was made on normal and vestibular nerve-sectioned guinea pigs. Section of the vestibular nerve at the internal auditory meatus provided an efficient means of eliminating the efferent innervation to the cochlea without significant loss of afferent fibres. Nerve counts on normal and de-efferented animals revealed that about 10-15 % of the cochlear afferent innervation supplies the outer hair cells. The remaining 85-90% of afferent fibres innervate the inner hair cells. As in cats, all tunnel spiral bundle fibres and upper tunnel crossing fibres were efferent to outer hair cells. Since unmyelinated fibres in the osseous spiral bundle were not counted, quantitative analysis of the efferent innervation to inner hair cells could not be made. However, a significant loss of myelinated fibres in the osseous spiral lamina after vestibular nerve section confirms that many myelinated efferent fibres are present in this region.