Cochleosacculotomy

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Chapter 39 Cochleosacculotomy

Harold F. Schuknecht ^∗, Michael J. McKenna, K. Paul Boyev,

The surgical treatment for Meniere’s disease can be classified into two groups, according to mode of action: (1) procedures that have the objective of total or partial ablation of vestibular function, and (2) procedures that are intended to enhance the drainage of endolymph by fistulization of the membranous labyrinth and decompression of the endolymphatic sac. Endolymphatic drainage procedures can be divided further into external shunts that attempt to drain excessive endolymph from the endolymphatic sac into the mastoid or subarachnoid space, and internal shunts that attempt to drain excessive endolymph into the perilymphatic space. The cochleosacculotomy operation falls into the latter group—an internal shunt procedure.

PHYSIOLOGIC, ANATOMIC, AND PATHOLOGIC RATIONALE

Meniere’s disease is characterized pathologically by progressive endolymphatic hydrops that is probably related to a disturbance in endolymphatic sac function. This condition must be differentiated from nonprogressive endolymphatic hydrops, in which the hydrops is the result of a single traumatic or inflammatory insult to the labyrinth, causing a permanent but not progressive endolymphatic hydrops.¹

The symptoms of progressive endolymphatic hydrops can be correlated with two principal types of pathologic change: (1) distentions and ruptures of the endolymphatic system,^2,³ and (2) alterations in the cytoarchitecture of the auditory and vestibular sense organs, sometimes accompanied by atrophic changes. Coincident with rupture, there is sudden contamination of the perilymphatic fluid with neurotoxic endolymph (140 mEq/L of potassium) that causes paralysis of the sensory and neural structures and is expressed clinically as episodic vertigo, fluctuating hearing loss, or both. The American Academy of Otolaryngology–Head and Neck Surgery (AAOHNS)⁴ recommended that these episodes be designated the “definitive” symptoms of Meniere’s disease.

As the disease progresses, there are changes in the cytoarchitecture of the sense organs that consist of distortion and atrophy of the sensory cells and supporting cells, and disruption and deformation of their gelatinous aprons. These alterations impair the motion mechanics of the sense organs, resulting in permanent functional deficits. The symptoms for the auditory system are hearing loss and tinnitus, and for the vestibular system are constant or recurring sensations of unsteadiness, described as being off-balance, floating, tilting, falling, or spinning, and are often aggravated by head movement. The AAOHNS recommended that they be known as “adjunctive” symptoms. To be successful, surgical procedures based on facilitating drainage of endolymph should alleviate definitive symptoms and arrest the progression of adjunctive symptoms.

Internal shunt procedures include the sacculotomy of Fick,^5,⁶ the tack operation of Cody,^7,⁸ the otic-perotic shunt of Pulec and House,⁹ and the cochleosacculotomy.¹⁰ In the sacculotomy and tack procedures, picks are introduced through the footplate of the stapes to puncture the saccule with the hope of producing a permanent fistula in the saccular wall by which excessive endolymph can drain into the perilymphatic space. This approach fails to consider, however, the histopathologic observation that in Meniere’s disease, the distended saccule often fills the vestibule; its distended wall is adherent to the footplate and could not be fistulized into the perilymphatic space by these maneuvers.¹¹ The otic-perotic shunt, as conceived by House and Pulec, involves the placement of a platinum tube through the basilar membrane to connect the scala media and scala tympani; however, the procedure is not surgically feasible because of the small size of the cochlear duct.

The cochleosacculotomy operation consists of creating a fracture-disruption by impaling the osseous spiral lamina and cochlear duct with a pick introduced through the round window. The rationale is supported by two histopathologic observations and muted by a third:

1. Histologic study of the temporal bones from patients with Meniere’s disease shows that the distended membranous labyrinth may fistulize permanently in any area. Such spontaneous fistulization may account for the long remissions and even permanent arrest of symptoms of episodic vertigo and fluctuating hearing loss in some patients.

2. Animal experiments have shown that surgical disruption of Reissner’s membrane ¹² or the walls of the utricle, saccule, or semicircular canals¹³ results in prompt healing of the fistulas. It has been shown in experimental studies on cats¹⁴^–¹⁶ and guinea pigs,¹⁷ however, that fracture-disruption of the osseous spiral lamina and cochlear duct can sometimes result in a permanent communication between the endolymphatic and perilymphatic spaces. Those experiments show that such fistulas exist without impairing the hearing for frequencies other than those tonotopically located immediately adjacent to the fistulas.

3. A histopathologic finding in human temporal bones of patients with Meniere’s disease that militates against the success of internal shunts is that the distended membranes in some cases block the flow of endolymph toward such a fistula.¹⁸ For this reason, a successful cochleosacculotomy fistula does not relieve symptoms in all instances.