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Biomedical subjects

H F Schuknecht

Publications and source records attributed to H F Schuknecht.

At least 19 recordsLinked to original sources

Myths in neurotology.

For many diseases the etiology of disordered function is unknown and therapy is either symptomatic or empirical. The empirical approach to therapy is acceptable to many physicians, particularly if a treatment can be based on some attractive, although unproven, concept of pathogenesis. A hypothetical explanation of disordered function can become widely popular in spite of a serious lack of scientific support. When evidence emerges that refutes the logic of a concept of pathogenesis, then that concept becomes a myth. Human temporal bone studies have identified several myths in neurotology that deserve our attention. Among these myths are the following: (1) cochlear otosclerosis is a common cause for sensorineural hearing loss, (2) idiopathic sudden sensorineural hearing loss is a vascular disorder that should be treated as a medical emergency, (3) the conductive component of hearing loss in Paget's disease is caused by ossicular fixation and therefore should be surgically correctable, (4) vascular loops should be considered as a possible cause for otherwise unexplained otologic symptoms, (5) surgical manipulations on the endolymphatic sac are scientifically sound therapies for selected cases of Meniere's disease, and (6) perilymph fistulas are a common cause for audiovestibular symptoms that are not related to a stressful incident.

Ear Diseases

Autosomal dominant sensorineural hearing loss. Pedigrees, audiologic findings, and temporal bone findings in two kindreds.

We report the clinical and otopathologic findings in three persons from two kindreds affected with adult-onset autosomal dominant progressive sensorineural hearing loss. The primary pathologic change is a deposit of acid polymucosaccharide ground substance in the cribrose areas; in the spiral ligament, limbus, and spinal lamina of the cochlea; and in the stroma of the maculae and cristae. These deposits obstruct the channels that accommodate the dendritic nerve fibers to the auditory and vestibular sense organs. The end result is strangulation and degeneration of dendrites followed by retrograde neuronal degeneration in association with varying degrees of atrophic change in the sense organs.

Adult

Blockage of longitudinal flow in endolymphatic hydrops.

The external shunt operation on the endolymphatic sac is based on the concept that it will drain excess endolymph and thus arrest the progression of endolymphatic hydrops. We performed histological studies on 46 temporal bones from 13 cases of bilateral and 20 cases of unilateral Meniere's disease to evaluate the status of the pathways of longitudinal flow of endolymph to the sac. The endolymphatic ducts were blocked in 8 specimens (17%), the endolymphatic sinuses in 9 (19.5%), the utricular ducts in 12 (26%), the saccular ducts in 7 (15%), and the ductus reuniens in 27 (59%). These blockages arrested longitudinal flow from both the pars superior and inferior in 21 cases (46%), the pars superior only in 3 (6.5%), and the pars inferior only in 16 (35%). In the 6 ears with all pathways open, 2 were found to have fistulae between the saccules and the perilymphatic spaces, which theoretically results in internal shunting, thus alleviating the need for the external shunt procedure. In the aggregate, therefore, 42 (91%) of 46 ears showed either areas of blockage of longitudinal flow or internal shunts that would theoretically negate the value of external endolymphatic shunt procedures. These temporal bones, however, are from an autopsy population and the severity of pathological changes is probably greater than it would have been at an earlier age when external shunt surgery might have been a therapeutic consideration.

Adult

The anterior inferior cerebellar artery in the internal auditory canal.

It has been proposed that compression of the auditory and vestibular nerve trunks by vascular loops might be the cause of otherwise unexplained hearing loss, tinnitus, and vertigo, as well as Meniere's disease. We studied the human temporal bone histological collection at the Massachusetts Eye and Ear Infirmary to determine whether audiovestibular symptoms could be correlated with the presence of the anterior inferior cerebellar artery within the internal auditory canal. Anterior inferior cerebellar artery loops were found within the internal auditory canals of 12.3% of 1327 temporal bones, about half the number found when preparations with intact brains are studied. This difference can be attributed to avulsion of the anterior inferior cerebellar artery during removal of the brain at autopsy. There were 5 cases of unexplained unilateral hearing loss with anterior inferior cerebellar artery loops: 3 in the opposite ear and 2 in both ears. There were 2 cases with unilateral unexplained tinnitus with anterior inferior cerebellar artery loops: 1 in the involved ear and 1 in the opposite ear. A case with bilateral tinnitus had an anterior inferior cerebellar artery loop in 1 ear. There were 29 cases of vertigo with no peripheral histopathological correlate or central nervous system disorder; anterior inferior cerebellar artery loops were found in the internal auditory canals of 7 (12.5%) of the 56 ears in this group, which is not significantly different from the 12.3% incidence recorded for the entire collection. In 23 cases of unilateral Meniere's disease, there were anterior inferior cerebellar artery loops in the hydropic ears in 3, the opposite ear in 1, and both ears in 1. We can find no correlation between unexplained hearing loss, tinnitus, vertigo, or Meniere's disease and the presence of the anterior inferior cerebellar artery in the internal auditory canal.

Adult

In search of pathologic correlates for hearing loss and vertigo in Paget's disease. A clinical and histopathologic study of 26 temporal bones.

Mixed sensorineural and conductive hearing loss is a common clinical manifestation of Paget's disease of the temporal bone, and while there are numerous clinical and pathologic reports on the condition, none have identified a consistent pathologic explanation for the hearing loss. We performed histologic studies on 26 temporal bones exhibiting Paget's disease from 16 persons, of whom 7 had audiometric testing performed. Contrary to common opinion, the conductive hearing loss is not caused by ossicular fixation; in fact, no cause could be found in the seven ears with documented conductive hearing losses. While the sensorineural hearing losses were greater than normal for age, we could not identify cochlear disorders that could be attributed to Paget's disease. It is concluded that the hearing losses in Paget's disease are caused by changes in bone density, mass, and form that serve to dampen the finely tuned motion mechanics of the middle and inner ears.

Adult

The Siamese twins, Eng and Chang: their lives and their hearing losses.

Eng and Chang were conjoined twins who were born in Thailand and settled in the United States at the age of 18 years. Numerous surgeons in the United States and Europe examined them and almost all of them believed that an attempt at separation would be fatal. They married sisters and lived on a farm in North Carolina where they loved to hunt wild game. Both used shotguns placed on their right shoulders. At the age of 58 years, it was noted that Chang, who was located to the left of Eng, had a hearing loss in both ears and that Eng had a loss that was greater in the left ear. It is proposed that these hearing losses may have been caused by muzzle-blast injury from hunting and that only the right ear of Eng was privileged to experience the protective effect of head shadow.

Hearing Loss

Experimental study of sacculotomy in endolymphatic hydrops.

Thirty-nine guinea pigs were used for four groups of experiments: 1. sacculotomy only, 2. sacculotomy and simultaneous obliteration of the endolymphatic duct, 3. sacculotomy followed by obliteration of the endolymphatic duct, and 4. obliteration of the endolymphatic duct followed by sacculotomy. Sacculotomy alone caused only minimal cochlear pathology, whereas sacculotomy on hydropic ears produced severe atrophy of the organ of Corti and cochlear neurons as well as connective cells of the limbus. There was histological evidence that Reissner's membrane in hydropic ears was ruptured by the sacculotomy procedure. The primary cause for the severe atrophic changes is thought to be the toxic effect of intermixing perilymph with a large volume of endolymph. The surgically induced saccular tears appeared to be healed in all ears, and the procedure had no significant effect on the course of endolymphatic hydrops. Although two out of eleven specimens in which sacculotomy was performed on hydropic ears showed tears and collapse of Reissner's membrane, since others with similar tears showed extensive hydrops, the possibility of artifact could not be ruled out. In one specimen with simultaneous sacculotomy and obliteration of the duct, persisting fistulae were noted at the sites of accidental fracture of the osseous spiral lamina; this ear is the only one which failed to develop hydrops following obliteration of the duct. The results of this experiment, namely sacculotomy on hydropic guinea pig ears, suggest that sacculotomy is not a rational procedure for the control of endolymphatic hydrops in Ménière's disease for the following reasons: 1. surgically induced tears in the saccular wall are followed by rapid healing and 2. intermixing of perilymph and a large volume of endolymph causes toxic atrophy of the limbus, organ of Corti and cochlear neurons.

Animals

Experiences with type IV tympanomastoidectomy.

Tye IV tympanoplasty was performed on 72 patients having advanced suppurative disease of the middle ear and mastoid with total loss of the middle ear sound transmission system. The principal features of the method consist of a postauricular wide-field mastoidectomy, canalplasty, meatoplasty, Type IV tympanoplasty with cutaneous exteriorization of the footplate and mastoid obliteration. The method achieved a postoperative bone-air gap of 30 db or less in 59 percent of cases with a 15 percent incidence of recrudescence requiring some further surgery.

Adolescent

Pathophysiology of endolymphatic hydrops.

Endolymphatic hydrops of the nonprogressive type occurs in response to a single traumatic or toxic insult of limited duration and although it may result in permanent deficits in sensorineural function, there is total subsidence of vestibular symptoms. Endolymphatic hydrops of the progressive type, on the other hand, appears to be the result of permanent impairment of endolymph resorption and is caused principally by disorders of the endolymphatic sac. It occurs in Menière's disease, syphilitic labyrinthitis and the delayed hydrops syndrome. In addition to deafness of varying extent, it is characterized by episodic vertigo and sometimes by Hennebert's sign. Histological studies suggest that the acute vertiginous episodes are caused by potassium intoxication following ruptures of the membranous labyrinth and that Hennerbert's sign is caused by vestibular fibrosis.

Aged

Myringoplasty.

Myringoplasty is a deceptively difficult procedure in which surgical finesse and experience dictate success in terms of hearing improvement as well as closure rate. In essence, it is the complete removal of epidermal ingrowth followed by the placement of a non-epithelialized graft on the medial surface of the tympanic membrane which has withstood the test of time.

Ear Canal

Human cochlear changes in noise induced hearing loss.

The temporal bone histopathological findings in 14 ears with noise induced hearing loss are presented. The morphological changes consist mainly of hair cell loss, which is more severe in the 9 mm to 13 mm region of the cochlear duct. Within the area of maximum hair cell loss, there is a greater loss of outer hair cells than of inner hair cells. There is a good correlation between the permanent auditory threshold shifts and the spatial location of the sensory lesion according to the anatomical frequency scale.

Auditory Threshold

A morphological study of human vestibular sensory epithelia.

Surface preparations were made of the vestibular sense organs of humans from membranous labyrinths removed within ten hours of death. Total sensory cell counts and surface area measurements were made from composite photographic reconstructions. The general topographical and cytoarchitectural arrangements were found to be similar to those previously described for the guinea pig and squirrel monkey. The surface areas and sensory cell populations of the human cristae were only slightly greater than those recorded for these animals; however, the figures for the human maculae were twofold to fourfold greater. It seems possible that this exceptional enlargement of the sensory epithelia of the static labyrinth is in response to a physiological need generated by the evolutionary transition of primates from the quadruped to the biped stance.

Adult

Ossiculoplasty.

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Ear Ossicles