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Enhanced retrosigmoid exposure with posterior semicircular canal resection
Enhanced retrosigmoid exposure with posterior semicircular canal resection LTC MOISESARRIAGA, MD, FACS,*and MAJ MICHAEL GORUM, MD, Lackland AFB, Texas A subset of patients with acoustic neuromas and useful hearing have tumors that are inadequately approached by both middle fossa and retrosigmoid techniques. The enhanced retrosigmoid technique combines the hearing preservation of posterior semicircular canal ablation to achieve lateral internal auditory canal exposure with the ample cerebellopontine angle exposure of the standard retrosigmoid technique. (Otolaryngol Head Neck Surg 1996;115:46-8.)
T h e increasing proportion of acoustic tumors in patients with useful hearing has heightened interest in hearing-preservation acoustic tumor surgery. The surgical approaches for hearing preservation are the middle cranial fossa approach and the retrosigmoid (suboccipital) approach. Middle fossa surgery provides excellent exposure of the internal auditory canal (IAC) from the porous acousticus to the fundus; however, exposure of the cerebellopontine angle (CPA) is limited.' In contrast, the retrosigmoid approach offers excellent CPA exposure; however, access to the distal IAC is limited by the posterior semicircular canal if hearing preservation is attempted. 2 Controlled, systematic opening of the inner ear is compatible with preserved cochlear function. The advent of posterior semicircular canal ablation procedures has documented the consistent ability to open and occlude portions of the inner ear with preserved hearing. 3 We describe a surgical approach that combines posterior semicircular canal occlusion/resection with extradural skeletonization of the IAC and retrosigmoid CPA exposure.
SURGICAL TECHNIQUE The patient is positioned supine on the operating table with the head turned and the affected side up. After a
From the Departments of Otology/Neurotology(Dr. Arriaga) and Neurosurgery (Dr. Gorum), WilfordHall Medical Center. The views expressed in this article are those of the anthors and do not reflect the official policy of the Department of Defense or other departments of the U.S. government. *Dr. Arriaga is currently affiliated with Allegheny Neuroscience Institute and Pittsburgh Ear Associates. Received for publicationAug. 4, 1995; accepted Nov. 10, 1995. Reprint requests: Moises Arriaga, MD, FACS, Pittsburgh Ear Associates, 420 East North Ave., Suite 402, Pittsburgh, PA 15212. 23/1/70644 46
postauricular incision, a complete mastoidectomy permits identification of the labyrinth, skeletonization of the presigmoid posterior fossa dura, and wide exposure of the posterior fossa dura. With high magnification, the bone of the posterior semicircular canal is unroofed, carefully preserving the membranous labyrinth. The canal is then sealed with bone wax to occlude the membranous labyrinth. By systematic advancement of the bone wax as the canal is drilled, the posterior canal is resected from its entry to the vestibule (ampullated end) to its junction with the superior semicircular canal (common crus). Without the obstruction from the posterior canal, the IAC can be skeletonized before the dura is opened (Fig. 1). (Alternatively, the IAC can be skeletonized in a standard "intradural" retrosigmoid fashion after transmastoid resection of the posterior semicircular canal.) Drilling the bone of the porous acousticus before opening the dura requires generous retrosigmoid bone removal to permit extradural retraction of the posterior fossa dura and sigmoid sinus, with the suction-irrigator in one hand while drilling proceeds with the other. Surgery proceeds with a retrosigmoid dural opening to expose the CPA. A cerebellar retractor is not necessary because drainage of cerebrospinal fluid from the CPA cistern and cisterna magna provides adequate cerebellar relaxation. Only a dural cuff surrounds the IAC contents if the drilling is done before the dura is opened (Fig. 2). After the CPA tumor is debulked, the dura of the IAC may be opened sharply to expose the contents, By gentle reflection of the IAC contents inferiorly, the facial nerve is identified in the anterior-superior compartment. Thus tumor dissection may proceed from both a medial-tolateral (brain stem to IAC) direction and a lateral-tomedial direction. Abdominal fat and standard closure techniques are used.
Otolaryngology Head and Neck Surgery
Volume 115 Number 1
Fig. i. Schema of right enhanced retrosigmoid approach. After completion of mastoidectomy and skeletonization of the sigmoid sinus (compressed by the suction), the posterior semicircular canal (dotted lines) is occluded with b o n e wax (black dots). The IAC is skeletonized (arrow). L, Lateral semicircular canal; S, superior semicircular canal.
ARRIAGA and GORUM
47
Fig. 2. Schema or right retrosigmoid CPA exposure with the e n h a n c e d retrosigmoid approach. Sigmoid sinus is reflected anteriorly with a dural cuff (sutures holding dural cuff). The cochleovestibular nerve c o m p l e x is shown entering the IAC dura (arrow) medial to where the posterior semicircular canal was resected (dotted lines).
REPRESENTATIVE CASE A 58-year-old man with asymmetric hearing loss and tinnitus was diagnosed with a 1.9-cm acoustic neuroma. The speech reception threshold was 55 dB and speech discrimination was 72% on the affected side, and 35 dB and 92%, respectively, on the tmaffected side. The patient was interested in hearing preservation; however, his tumor exceeded our team's limits of CPA tumor extension for the middle cranial fossa approach. In addition, the tumor involved the lateral third of the IAC, making direct visualization of the lateral extent of the tumor unlikely with the retrosigmoid approach if the posterior semicircular canal was preserved. The modified procedure was explained to the patient, and he consented to the enhanced retrosigmoid approach with posterior canal resection. The tumor was removed entirely with preservation of the facial and cochlear nerves. The patient had an uncomplicated postoperative course with normal facial function and hospital discharge on postoperative day 4. Figure 3 is a postoperative computed tomography scan of his IAC. The audiogram taken 3 weeks after surgery revealed a speech reception threshold of 55 dB, with 88% speech discrimination and a flat tympanogram with a 15-dB air-bone gap on the operated side. The patient retains his hearing 6 months after surgery. OVERALL EXPERIENCE
Three patients have undergone the enhanced retrosigmold technique. A 62-year-old patient with a 2-cm
Fig. 3. PostoperativelACcomputedtomographyscanafter enhanced retrosigmoid removal of a right acoustic neuroma. Posterior bone of the IAC is removed, exposing the lateral third for tumor resection. C, Cochlea; F, fat filling mastoid; I, IAC.
acoustic neuroma has retained his hearing for 24 months after surgery without evidence of recurrence or deterioration in hearing or facial function. The third patient had a 2.4-cm tumor that presented with sudden hearing loss and hearing return after systemic steroid therapy. This patient also underwent enhanced retrosigmoid surgery but lost all hearing after a dramatic "pop" sensation and the onset of severe tinnitus on the third postoperative day.
48
Otolaryngology Head and Neck Surgery July 1996
ARRIAGA and GORUM
DISCUSSION
The middle cranial fossa and retrosigmoid approaches are viable techniques for safe tumor removal with an opportunity for hearing preservation. In our institution, middle fossa surgery is the procedure of choice for tumors involving the IAC with less than 0.6 cm of CPA extension. Retrosigmoid surgery is offered to patients who are candidates for hearing preservation and have acoustic tumors less than 2.5 cm in diameter and sparing the lateral third of the IAC. The enhanced retrosigmoid approach is a hearing-preservation procedure designed for patients with useful hearing and tumors in the lateral I A C and greater than 0.6 cm of extension into the CPA. The hearing results of posterior canal ablation surgery prove that controlled entry into the inner ear is compatible with hearing preservation2 In tumor surgery, House's experience with superior canal transection in middle fossa surgery showed that even transection of the membranous labyrinth was compatible with hearing preservation. 4 Hirsch et al. 5 published a series of enhanced skull base exposures and hearing preservation with partial labyrinthine resections in neoplasms not affecting the IAC. The most dramatic report of translabyrinthine hearing preservation acoustic neuroma surgery was by McElveen et al. in 1991. 6 With that approach all three semicircular canals and the vestibule are opened before IAC skeletonization. The vestibule is then refilled with fluid and sealed. Unfortunately, our team has been unsuccessful in duplicating this maneuver with success in hearing preservation. A less destructive approach may increase the opportunity for hearing preservation. The recent description of the posterior canal ablation procedure and its success in preserving hearing when performed by different surgeons at various centers is provocative. The success of semicircular canal ablation surgery prompted us to combine the retrosigmoid approach with controlled removal of the posterior canal, which is the anatomic barrier to visualization of the lateral I A C in hearing-preservation retrosigmoid tumor surgery. We note two advantages of the en-
hanced retrosigmoid technique over standard retrostgmold surgery: First, this approach offers lateral IAC exposure while retaining the opportunity for hearing preservation. Second, the I A C drilling may be performed before the dura is opened, and bone dust does not have the opportunity to mix with the cerebrospinal fluid spaces. Thus a potential cause of aseptic meningitis and postoperative headaches is eliminated. Two pitfalls of the technique are that the endolymphatic sac and duct must be violated and that the lateral IAC facial nerve identification cannot use the vertical crest (Bill's bar). Postoperative hydrops must be considered in these patients. CONCLUSION
The enhanced retrosigmoid approach with posterior semicircular canal resection is applicable in hearingpreservation IAC tumor surgery with 0.6 cm or more CPA tumor extension and involvement of the lateral IAC. Although this is a preliminary report, we believe that this modified approach should be considered in those acoustic tumors that do not meet the criteria for middle fossa or retrosigmoid surgery because of CPA e x t e n s i o n and lateral IAC involvement, respectively. Further study of this approach is warranted.
REFERENCES
1. Shelton C, Brackmann D, House W, et al. Middle fossa acoustic tumor surgery: results in 106 cases. Laryngoscope 1989;99:405-8. 2. Jackler RK. Overview of surgical neurotology. In: Jackler RK, Brackmann DE, eds. Neurotology. Mosby-Year Book, Inc., 1994: 651-84. 3. Parnes LS, McClure JA. Posterior semicircular canal occlusion in the normal hearing ear. Otolaryngol Head Neck Surg 1991;104: 52-7. 4. Malony TB, Kwartler JA, House WF, et al. Extended middle fossa and retrolabyrinthineapproachesin acoustic neuroma surgery: case reports. Am J Otol 1992;13:360-3. 5. Hirsch BE, Cass SR Sekhar LN, et al. Translabyrinthine approach to skull base tumors with hearing preservation. Am J Otol 1993; 14:533-43. 6. McElveen JT, Wilkins RH, Erwin A, et al. Modifying the translabyrinthine approach to preserve hearing during acoustic tumor surgery. J Laryngol Otol 1991;105:34-7.
T h e increasing proportion of acoustic tumors in patients with useful hearing has heightened interest in hearing-preservation acoustic tumor surgery. The surgical approaches for hearing preservation are the middle cranial fossa approach and the retrosigmoid (suboccipital) approach. Middle fossa surgery provides excellent exposure of the internal auditory canal (IAC) from the porous acousticus to the fundus; however, exposure of the cerebellopontine angle (CPA) is limited.' In contrast, the retrosigmoid approach offers excellent CPA exposure; however, access to the distal IAC is limited by the posterior semicircular canal if hearing preservation is attempted. 2 Controlled, systematic opening of the inner ear is compatible with preserved cochlear function. The advent of posterior semicircular canal ablation procedures has documented the consistent ability to open and occlude portions of the inner ear with preserved hearing. 3 We describe a surgical approach that combines posterior semicircular canal occlusion/resection with extradural skeletonization of the IAC and retrosigmoid CPA exposure.
SURGICAL TECHNIQUE The patient is positioned supine on the operating table with the head turned and the affected side up. After a
From the Departments of Otology/Neurotology(Dr. Arriaga) and Neurosurgery (Dr. Gorum), WilfordHall Medical Center. The views expressed in this article are those of the anthors and do not reflect the official policy of the Department of Defense or other departments of the U.S. government. *Dr. Arriaga is currently affiliated with Allegheny Neuroscience Institute and Pittsburgh Ear Associates. Received for publicationAug. 4, 1995; accepted Nov. 10, 1995. Reprint requests: Moises Arriaga, MD, FACS, Pittsburgh Ear Associates, 420 East North Ave., Suite 402, Pittsburgh, PA 15212. 23/1/70644 46
postauricular incision, a complete mastoidectomy permits identification of the labyrinth, skeletonization of the presigmoid posterior fossa dura, and wide exposure of the posterior fossa dura. With high magnification, the bone of the posterior semicircular canal is unroofed, carefully preserving the membranous labyrinth. The canal is then sealed with bone wax to occlude the membranous labyrinth. By systematic advancement of the bone wax as the canal is drilled, the posterior canal is resected from its entry to the vestibule (ampullated end) to its junction with the superior semicircular canal (common crus). Without the obstruction from the posterior canal, the IAC can be skeletonized before the dura is opened (Fig. 1). (Alternatively, the IAC can be skeletonized in a standard "intradural" retrosigmoid fashion after transmastoid resection of the posterior semicircular canal.) Drilling the bone of the porous acousticus before opening the dura requires generous retrosigmoid bone removal to permit extradural retraction of the posterior fossa dura and sigmoid sinus, with the suction-irrigator in one hand while drilling proceeds with the other. Surgery proceeds with a retrosigmoid dural opening to expose the CPA. A cerebellar retractor is not necessary because drainage of cerebrospinal fluid from the CPA cistern and cisterna magna provides adequate cerebellar relaxation. Only a dural cuff surrounds the IAC contents if the drilling is done before the dura is opened (Fig. 2). After the CPA tumor is debulked, the dura of the IAC may be opened sharply to expose the contents, By gentle reflection of the IAC contents inferiorly, the facial nerve is identified in the anterior-superior compartment. Thus tumor dissection may proceed from both a medial-tolateral (brain stem to IAC) direction and a lateral-tomedial direction. Abdominal fat and standard closure techniques are used.
Otolaryngology Head and Neck Surgery
Volume 115 Number 1
Fig. i. Schema of right enhanced retrosigmoid approach. After completion of mastoidectomy and skeletonization of the sigmoid sinus (compressed by the suction), the posterior semicircular canal (dotted lines) is occluded with b o n e wax (black dots). The IAC is skeletonized (arrow). L, Lateral semicircular canal; S, superior semicircular canal.
ARRIAGA and GORUM
47
Fig. 2. Schema or right retrosigmoid CPA exposure with the e n h a n c e d retrosigmoid approach. Sigmoid sinus is reflected anteriorly with a dural cuff (sutures holding dural cuff). The cochleovestibular nerve c o m p l e x is shown entering the IAC dura (arrow) medial to where the posterior semicircular canal was resected (dotted lines).
REPRESENTATIVE CASE A 58-year-old man with asymmetric hearing loss and tinnitus was diagnosed with a 1.9-cm acoustic neuroma. The speech reception threshold was 55 dB and speech discrimination was 72% on the affected side, and 35 dB and 92%, respectively, on the tmaffected side. The patient was interested in hearing preservation; however, his tumor exceeded our team's limits of CPA tumor extension for the middle cranial fossa approach. In addition, the tumor involved the lateral third of the IAC, making direct visualization of the lateral extent of the tumor unlikely with the retrosigmoid approach if the posterior semicircular canal was preserved. The modified procedure was explained to the patient, and he consented to the enhanced retrosigmoid approach with posterior canal resection. The tumor was removed entirely with preservation of the facial and cochlear nerves. The patient had an uncomplicated postoperative course with normal facial function and hospital discharge on postoperative day 4. Figure 3 is a postoperative computed tomography scan of his IAC. The audiogram taken 3 weeks after surgery revealed a speech reception threshold of 55 dB, with 88% speech discrimination and a flat tympanogram with a 15-dB air-bone gap on the operated side. The patient retains his hearing 6 months after surgery. OVERALL EXPERIENCE
Three patients have undergone the enhanced retrosigmold technique. A 62-year-old patient with a 2-cm
Fig. 3. PostoperativelACcomputedtomographyscanafter enhanced retrosigmoid removal of a right acoustic neuroma. Posterior bone of the IAC is removed, exposing the lateral third for tumor resection. C, Cochlea; F, fat filling mastoid; I, IAC.
acoustic neuroma has retained his hearing for 24 months after surgery without evidence of recurrence or deterioration in hearing or facial function. The third patient had a 2.4-cm tumor that presented with sudden hearing loss and hearing return after systemic steroid therapy. This patient also underwent enhanced retrosigmoid surgery but lost all hearing after a dramatic "pop" sensation and the onset of severe tinnitus on the third postoperative day.
48
Otolaryngology Head and Neck Surgery July 1996
ARRIAGA and GORUM
DISCUSSION
The middle cranial fossa and retrosigmoid approaches are viable techniques for safe tumor removal with an opportunity for hearing preservation. In our institution, middle fossa surgery is the procedure of choice for tumors involving the IAC with less than 0.6 cm of CPA extension. Retrosigmoid surgery is offered to patients who are candidates for hearing preservation and have acoustic tumors less than 2.5 cm in diameter and sparing the lateral third of the IAC. The enhanced retrosigmoid approach is a hearing-preservation procedure designed for patients with useful hearing and tumors in the lateral I A C and greater than 0.6 cm of extension into the CPA. The hearing results of posterior canal ablation surgery prove that controlled entry into the inner ear is compatible with hearing preservation2 In tumor surgery, House's experience with superior canal transection in middle fossa surgery showed that even transection of the membranous labyrinth was compatible with hearing preservation. 4 Hirsch et al. 5 published a series of enhanced skull base exposures and hearing preservation with partial labyrinthine resections in neoplasms not affecting the IAC. The most dramatic report of translabyrinthine hearing preservation acoustic neuroma surgery was by McElveen et al. in 1991. 6 With that approach all three semicircular canals and the vestibule are opened before IAC skeletonization. The vestibule is then refilled with fluid and sealed. Unfortunately, our team has been unsuccessful in duplicating this maneuver with success in hearing preservation. A less destructive approach may increase the opportunity for hearing preservation. The recent description of the posterior canal ablation procedure and its success in preserving hearing when performed by different surgeons at various centers is provocative. The success of semicircular canal ablation surgery prompted us to combine the retrosigmoid approach with controlled removal of the posterior canal, which is the anatomic barrier to visualization of the lateral I A C in hearing-preservation retrosigmoid tumor surgery. We note two advantages of the en-
hanced retrosigmoid technique over standard retrostgmold surgery: First, this approach offers lateral IAC exposure while retaining the opportunity for hearing preservation. Second, the I A C drilling may be performed before the dura is opened, and bone dust does not have the opportunity to mix with the cerebrospinal fluid spaces. Thus a potential cause of aseptic meningitis and postoperative headaches is eliminated. Two pitfalls of the technique are that the endolymphatic sac and duct must be violated and that the lateral IAC facial nerve identification cannot use the vertical crest (Bill's bar). Postoperative hydrops must be considered in these patients. CONCLUSION
The enhanced retrosigmoid approach with posterior semicircular canal resection is applicable in hearingpreservation IAC tumor surgery with 0.6 cm or more CPA tumor extension and involvement of the lateral IAC. Although this is a preliminary report, we believe that this modified approach should be considered in those acoustic tumors that do not meet the criteria for middle fossa or retrosigmoid surgery because of CPA e x t e n s i o n and lateral IAC involvement, respectively. Further study of this approach is warranted.
REFERENCES
1. Shelton C, Brackmann D, House W, et al. Middle fossa acoustic tumor surgery: results in 106 cases. Laryngoscope 1989;99:405-8. 2. Jackler RK. Overview of surgical neurotology. In: Jackler RK, Brackmann DE, eds. Neurotology. Mosby-Year Book, Inc., 1994: 651-84. 3. Parnes LS, McClure JA. Posterior semicircular canal occlusion in the normal hearing ear. Otolaryngol Head Neck Surg 1991;104: 52-7. 4. Malony TB, Kwartler JA, House WF, et al. Extended middle fossa and retrolabyrinthineapproachesin acoustic neuroma surgery: case reports. Am J Otol 1992;13:360-3. 5. Hirsch BE, Cass SR Sekhar LN, et al. Translabyrinthine approach to skull base tumors with hearing preservation. Am J Otol 1993; 14:533-43. 6. McElveen JT, Wilkins RH, Erwin A, et al. Modifying the translabyrinthine approach to preserve hearing during acoustic tumor surgery. J Laryngol Otol 1991;105:34-7.