Posterior semicircular canal occlusion in the normal hearing ear LORNE S. PARNES, MD, and JOSEPH A. McCLURE, MD, London, Ontario, Canada
This report outlines our experience with posterior semicircular canal occlusion, a new operative procedure for intractable benign paroxysmal positional vertigo (BPPV). We postulate that the resulting solid canal “plug” prevents endolymph movement within the posterior canal, which effectively fixes the cupula. This selectively abolishes the receptivity of the posterior canal to both angular acceleration and gravity without influencing the other inner ear receptors. We previously reported the success of this procedure in two patients with BPPV and a co-existing profound sensorineural hearing loss in the affected ear. Since that report, a slightly modified technique has been used to occlude six more posterior canals-five in normal hearing ears. While our follow-up times range from only 3 to 18 months, all eight patients continue to be relieved of their BPPV. Temporary mixed hearing losses occurred in three of the five ears with normal preoperative hearing. Hearing in all five patients ultimately returned to the preoperative state. We believe this procedure is a simpler and safer alternative to singular neurectomy for the treatment of intractable benign paroxysmal positional vertigo. (OTOLARYNGOL HEAD NECK SURG 1991;104:52,)
I n a recent report, we described a new operative procedure used successfully to treat two patients with intractable benign paroxysmal positional vertigo (BPPV).’ With this procedure, an attempt is made to completely and permanently occlude the membranous posterior semicircular canal. It is postulated that this canal plug abolishes movement within the posterior canal, thereby preventing cupular displacement. It has been shown in cats that posterior canal occlusion abolishes this canal’s response to angular acceleration without influencing the receptivity of the other vestibular receptors.’ In theory, it should abolish the gravitational effect upon a fixed cupular deposit, so-called cupulolithiasis, which is the presumed pathophysiologic mechanism of the permanent form of BPPV.3 As reported previously, our initial two patients were relieved of their BPPV symptoms after posterior canal occlusion. Both maintained lateral semicircular canal function, as measured by bi-thermal caloric testing. Thus, the animal study showing selective abolition of posterior canal function after occlusion is borne out in
the human inner ear. The immediate relief both patients obtained from BPPV suggests an underlying mechanical fluid problem, which supports the gravitational differential density theory (cupulolithiasis) as the cause of permanent BPPV. The two previously reported patients had occlusions in ears with pre-existing profound deafness. Therefore, the effect of this procedure on hearing in the normal human ear was unknown. In a previous study, we plugged the posterior semicircular canals of eleven guinea pigs and measured the effect on hearing using brainstem auditory evoked responses (BAER) . 4 There were minimal changes in the baseline BAER after canal plugging (follow-up time, 50 days), suggesting little or no cochlear damage. On the basis of this animal finding, we carried out six more posterior canal occlusions subsequent to our previous report-five in patients with normal hearing ears. The results from these occlusions form the basis of this report. We also include additional follow-up from both the original guinea pig study and the two patients reported previously. METHODS
~
From the Department of Otolaryngology, University of Western Ontario. Presented at the Annual Meeting of the American Neurotology Society, Palm Beach, Fla., April 27-29, 1990. Received for publication March 17, 1990; accepted Aug. 8, 1990. Reprint requests: Lome S. Pames, MD, University Hospital, 339 Windennere Road, London, Ontario, Canada N6A 5A5. 231 1 I24404
Follow-up animal study. This section is a continuation of a previous study in which we reported the short-term (50 days) effect on BAER after posterior semicircular canal occlusion in guinea pigs.4 BAERs were subsequently obtained after a further 6-month period. The animals were then perfused intravitally with 10% formalin and killed. Harvested temporal bones
52 Downloaded from oto.sagepub.com at University of Sussex Library on June 4, 2016
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Fig. I . A and B. Histologic section through two representative posterior semicircular canals in the guinea pig. Note central core of neo-ossification (arrows).corresponding to the drill-bit pathway.
were processed in celloidan for examination of the operative site under light microscopy. Follow-up human canal occlusions. These two patients had posterior semicircular canal occlusions for intractable BPPV. ' Both had preoperative profound sensorineural hearing loss in the affected car. One patient is now 26 months, and the other 23 months postocclusion. Current medical histories and physical examinations have been obtained. Both patients had thin-section axial temporal bone CT scans I year postocclusion. New Cases
Six more canal occlusions have been performed since the last report-five in normal hearing ears. A new occlusion technique, modified from the original two cases, is now used for all patients. The posterior canal
exposure through a postauricular mastoidectomy remains the same. Once the posterior canal otic capsule bone is identified, the canal is "blue-lined" with progressively smaller diamond burs. The posterior canal target area is at or just inferior to the area bisected by the lateral canal. As this part of the posterior canal is furthest from the ampulla and vestibule. manipulation in this region is least likely to induce damage to other inner ear structures. A 3- to 4mm segment of canal is skeletonized 180 degrees around its outer circumference down to endosteum. If endosteum is violated and perilymph leaks, all drilling ceases. Dry bone chips, previously gathered from the mastoidectomy, are mixed with one drop of fast-acting human fibrinogen glue (Tisseel; Immuno, Vienna, Austria). Once set, it forms an easily workable plug with
Downloaded from oto.sagepub.com at University of Sussex Library on June 4, 2016
OtolaryngologyHead and Neck Surgery
54 PARNES and McCLURE
Fig. 2. A, Preoperative axial CT scan (first patient) through reglon of posterior semicircular canal to undergo occlusion. B, Postoperative CT scan at the same level. Note complete bony occlusion of the canal (arrow).
a firm consistency. The endosteal bone removal with fine hooks allows perilymph to escape, whereby the membranous labyrinth becomes visible. Great care is taken not to suction directly on the perilymph or membranous labyrinth. The plug, fashioned slightly larger than the canal opening, is gently but fimily inserted into the canal. The intent is to completely fill the lumen throughout the fenestrated area and thereby compress the membranous labyrinth closed. An oversized piece of temporalis fascia, maintained in place by several more
Fig. 3. A, Preoperativeaxial CT scan (secondpatient) through region of posterior semicircular canal to undergo occlusion. B, Postoperative CT scan at same level.Note soft tissue density in the canal confluent with mastoid mucosa (arrow).
drops of fibrinogen glue, covers the fenestra and surrounding bone and the wound is closed in layers. RESULTS
Follow-up animal study. One guinea pig died of unknown causes before follow-up BAER. The BAER at 6 months in all other guinea pigs showed no significant auditory threshold changes from the 50-day postocclusion BAER reported previously. Light microscopy findings of the posterior canal region were virtually identical in all guinea pigs. The canals were completely
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Posterior semicircular canal occlusion in normal hearing ear 55
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This report outlines our experience with posterior semicircular canal occlusion, a new operative procedure for intractable benign paroxysmal positional vertigo (BPPV). We postulate that the resulting solid canal “plug” prevents endolymph movement within the posterior canal, which effectively fixes the cupula. This selectively abolishes the receptivity of the posterior canal to both angular acceleration and gravity without influencing the other inner ear receptors. We previously reported the success of this procedure in two patients with BPPV and a co-existing profound sensorineural hearing loss in the affected ear. Since that report, a slightly modified technique has been used to occlude six more posterior canals-five in normal hearing ears. While our follow-up times range from only 3 to 18 months, all eight patients continue to be relieved of their BPPV. Temporary mixed hearing losses occurred in three of the five ears with normal preoperative hearing. Hearing in all five patients ultimately returned to the preoperative state. We believe this procedure is a simpler and safer alternative to singular neurectomy for the treatment of intractable benign paroxysmal positional vertigo. (OTOLARYNGOL HEAD NECK SURG 1991;104:52,)
I n a recent report, we described a new operative procedure used successfully to treat two patients with intractable benign paroxysmal positional vertigo (BPPV).’ With this procedure, an attempt is made to completely and permanently occlude the membranous posterior semicircular canal. It is postulated that this canal plug abolishes movement within the posterior canal, thereby preventing cupular displacement. It has been shown in cats that posterior canal occlusion abolishes this canal’s response to angular acceleration without influencing the receptivity of the other vestibular receptors.’ In theory, it should abolish the gravitational effect upon a fixed cupular deposit, so-called cupulolithiasis, which is the presumed pathophysiologic mechanism of the permanent form of BPPV.3 As reported previously, our initial two patients were relieved of their BPPV symptoms after posterior canal occlusion. Both maintained lateral semicircular canal function, as measured by bi-thermal caloric testing. Thus, the animal study showing selective abolition of posterior canal function after occlusion is borne out in
the human inner ear. The immediate relief both patients obtained from BPPV suggests an underlying mechanical fluid problem, which supports the gravitational differential density theory (cupulolithiasis) as the cause of permanent BPPV. The two previously reported patients had occlusions in ears with pre-existing profound deafness. Therefore, the effect of this procedure on hearing in the normal human ear was unknown. In a previous study, we plugged the posterior semicircular canals of eleven guinea pigs and measured the effect on hearing using brainstem auditory evoked responses (BAER) . 4 There were minimal changes in the baseline BAER after canal plugging (follow-up time, 50 days), suggesting little or no cochlear damage. On the basis of this animal finding, we carried out six more posterior canal occlusions subsequent to our previous report-five in patients with normal hearing ears. The results from these occlusions form the basis of this report. We also include additional follow-up from both the original guinea pig study and the two patients reported previously. METHODS
~
From the Department of Otolaryngology, University of Western Ontario. Presented at the Annual Meeting of the American Neurotology Society, Palm Beach, Fla., April 27-29, 1990. Received for publication March 17, 1990; accepted Aug. 8, 1990. Reprint requests: Lome S. Pames, MD, University Hospital, 339 Windennere Road, London, Ontario, Canada N6A 5A5. 231 1 I24404
Follow-up animal study. This section is a continuation of a previous study in which we reported the short-term (50 days) effect on BAER after posterior semicircular canal occlusion in guinea pigs.4 BAERs were subsequently obtained after a further 6-month period. The animals were then perfused intravitally with 10% formalin and killed. Harvested temporal bones
52 Downloaded from oto.sagepub.com at University of Sussex Library on June 4, 2016
Volume 104 Number 1 Jonuory 1991
Posterior semicircular canal occlusion in normal hearing ear
53
Fig. I . A and B. Histologic section through two representative posterior semicircular canals in the guinea pig. Note central core of neo-ossification (arrows).corresponding to the drill-bit pathway.
were processed in celloidan for examination of the operative site under light microscopy. Follow-up human canal occlusions. These two patients had posterior semicircular canal occlusions for intractable BPPV. ' Both had preoperative profound sensorineural hearing loss in the affected car. One patient is now 26 months, and the other 23 months postocclusion. Current medical histories and physical examinations have been obtained. Both patients had thin-section axial temporal bone CT scans I year postocclusion. New Cases
Six more canal occlusions have been performed since the last report-five in normal hearing ears. A new occlusion technique, modified from the original two cases, is now used for all patients. The posterior canal
exposure through a postauricular mastoidectomy remains the same. Once the posterior canal otic capsule bone is identified, the canal is "blue-lined" with progressively smaller diamond burs. The posterior canal target area is at or just inferior to the area bisected by the lateral canal. As this part of the posterior canal is furthest from the ampulla and vestibule. manipulation in this region is least likely to induce damage to other inner ear structures. A 3- to 4mm segment of canal is skeletonized 180 degrees around its outer circumference down to endosteum. If endosteum is violated and perilymph leaks, all drilling ceases. Dry bone chips, previously gathered from the mastoidectomy, are mixed with one drop of fast-acting human fibrinogen glue (Tisseel; Immuno, Vienna, Austria). Once set, it forms an easily workable plug with
Downloaded from oto.sagepub.com at University of Sussex Library on June 4, 2016
OtolaryngologyHead and Neck Surgery
54 PARNES and McCLURE
Fig. 2. A, Preoperative axial CT scan (first patient) through reglon of posterior semicircular canal to undergo occlusion. B, Postoperative CT scan at the same level. Note complete bony occlusion of the canal (arrow).
a firm consistency. The endosteal bone removal with fine hooks allows perilymph to escape, whereby the membranous labyrinth becomes visible. Great care is taken not to suction directly on the perilymph or membranous labyrinth. The plug, fashioned slightly larger than the canal opening, is gently but fimily inserted into the canal. The intent is to completely fill the lumen throughout the fenestrated area and thereby compress the membranous labyrinth closed. An oversized piece of temporalis fascia, maintained in place by several more
Fig. 3. A, Preoperativeaxial CT scan (secondpatient) through region of posterior semicircular canal to undergo occlusion. B, Postoperative CT scan at same level.Note soft tissue density in the canal confluent with mastoid mucosa (arrow).
drops of fibrinogen glue, covers the fenestra and surrounding bone and the wound is closed in layers. RESULTS
Follow-up animal study. One guinea pig died of unknown causes before follow-up BAER. The BAER at 6 months in all other guinea pigs showed no significant auditory threshold changes from the 50-day postocclusion BAER reported previously. Light microscopy findings of the posterior canal region were virtually identical in all guinea pigs. The canals were completely
Downloaded from oto.sagepub.com at University of Sussex Library on June 4, 2016
Volume 104 Number 1 Januav 1991
Posterior semicircular canal occlusion in normal hearing ear 55
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