Nontumorous Enlargement of the Internal Auditory Canal: A Risk Factor for Sensorineural Hearing Loss? A High Resolution CT-Study

Abstract

Purpose: First aim of the study was to define normal shape and diameter of the internal auditory canal (IAC). In the second part the clinical relevance of IAC-enlargement was analyzed, considering also lesions of the subtle structures at the fundus of the internal auditory canal.

Materials and Methods: 440 high resolution CT-scans of the temporal bone were used for retrospective analysis of the internal auditory canal and its fundus region.

Results: The mean value of the IAC diameter in axial and coronal plane was determined. In 20 of 440 patients IAC enlargement was found. In the group with pronounced enlargement (3fold SD) nearly all patients suffered from hearing impairment. In some of them we found structural abnormalities near the IAC fundus in the CSF/perilymph border zone.

Conclusion: A new CT-based definition of normal shape and diameter of the internal auditory canal is presented. There is some evidence that a pathologic transmission of CSF-pressure in case of IAC-enlargement and/or abnormal fistulous communications could play an important role in the pathophysilogy of hearing loss.

Key points:

• New CT-based definition of normal internal auditory canal.

• Nearly all patients showing pronounced IAC-enlargement suffer from hearing impairment.

• Possible pathomechanism: Transmission of CSF-pressure on the inner ear.

Citation Format:

• Stimmer H, Niedermeyer HP, Kehl V et al. Nontumorous Enlargement of the Internal Auditory Canal: A Risk Factor for Sensorineural Hearing Loss? A High Resolution CT-Study. Fortschr Röntgenstr 2015; 187: 450 – 458

Zusammenfassung

Ziel: Erstes Anliegen der Studie war es die normale Form und Größe des inneren Gehörganges (IAC) auf CT-Basis zu definieren. Im zweiten Teil sollte die klinische Relevanz einer Erweiterung des inneren Gehörganges untersucht werden, wobei insbesondere auch begleitende Läsionen am Fundus des inneren Gehörganges bzw. am angrenzenden Innenohr berücksichtigt werden sollten.

Material und Methoden: 440 HR-CT’s des Felsenbeins wurden retrospektiv unter besonderer Berücksichtigung des inneren Gehörganges und dessen Fundus-Region ausgewertet.

Ergebnisse: Der CT-basierte Mittelwert des IAC-Durchmessers in axialer und koronarer Ebene wurde bestimmt, in 20 von 440 Fällen zeigte sich eine Erweiterung. In der Gruppe mit ausgeprägter Erweiterung (3-fache SD) zeigten nahezu alle Patienten eine Hörminderung. Einige hiervon wiesen Auffälligkeiten der knöchernen Struktur in der Region des IAC-Fundus an der Grenzzone Liquor/Perilymphe auf.

Schlussfolgerung: Die Untersuchung erlaubt eine neue CT-basierte Definition des normalen IAC-Durchmessers sowie auch von dessen Form. Zudem erbringt die Studie Hinweise auf eine pathophysiologische Bedeutung der Übertragung von Liquordruck auf das Innenohr bei erweitertem inneren Gehörgang oder angrenzenden Fistelverbindungen in der Entwicklung einer Schwerhörigkeit.

Kernaussagen:

• Neue CT-basierte Definition der normalen Form und Größe des inneren Gehörganges.

• Nahezu alle Patienten mit stark erweitertem inneren Gehörgang zeigen Hörverlust.

• Knöcherne Defekte begünstigen pathologische Liquordruckübertragung auf das Innenohr.

Key words

head/neck - CT - hearing loss - inner ear - perilymph

• References

• 1 Valvassori GE, Potter GD, Hanafee WN et al. Radiology of the Ear, Nose and Throat. Stuttgart, New York: Thieme; 1982: 96-98
• 2 Valvassori GE. The internal auditory canal revisited. The high definition approach. Otolaryngol Clin North Am 1995; 28: 431-511
• 3 Duvoisin B, Fernandes J, Doyon D et al. Magnetic resonance findings in 92 acoustic neuromas. Eur J Radiol 1991; 13: 96-102
• 4 Salzmann KL, Davidson HC, Harnsberger HR et al. Dumbbell schwannomas of the internal auditory canal. Am J Neuroradiol 2001; 22: 1368-1376
• 5 Tsunoda A, Komatsuzzaki A, Suzuki Y et al. Three dimensional imaging of the internal auditory canal in patients with acoustic neuroma. Acta Otolaryngol Suppl 2000; 542: 6-8
• 6 Ueyama T, Tamaki N, Kondoh T et al. Cerebellopontine angle ependymoma with internal auditory canal enlargement and pineal extension – case report. Neurol Med. Chir 1997; 37: 762-765
• 7 Samii M, Nakamura M, Mirzai S et al. Cavernous angiomas within the auditory canal. J Neurosurg 2008; 105: 581-587
• 8 Aquilina K, Nanra JS, Brett F et al. Cavernous angioma of the internal auditory canal. J Laryngol Otol 2004; 118: 368-371
• 9 Fleck SK, Baldauf J, Langner S et al. Arachnoid cyst confined to the internal auditory canal – endoscope-assisted resection: case report and review of the literature. Neurosurgery 2011; 68: E267-E270
• 10 Kitamura K, Senba T, Komatsuzaki A. Bilateral internal auditory canal enlargement without acoustic nerve tumor in von Recklinghausen neurofibromatosis. Neurofibromatosis 1989; 2: 47-52
• 11 Propst EJ, Blaser S, Gordon KA et al. Temporal bone findings on computed tomography imaging in branchio-oto-renal syndrome. Laryngoscope 2005; 115: 1855-1862
• 12 Crain MR, Dolan KD. Internal auditory canal enlargement in Paget´s disease appearing as bilateral acoustic neuromas. Ann Otol Rhinol Laryngol 2005; 99: 833-834
• 13 Blaser S, Propst EJ, Martin D et al. Inner ear dysplasia is common in children with Down syndrome (trisomy 21). Laryngoscope 2006; 116: 2113-2119
• 14 Weinberg PE, Kim KS, Gore RM. Unilateral enlargement of the internal auditory canal: a developmental variant. Surg Neurol 1981; 15: 39-42
• 15 Kokai H, Oohashi M, Ishikawa K et al. Clinical review of inner ear malformation. Nippon Jibinkoka Gakkai Kalho 2003; 106: 1038-1044
• 16 Migirov L. Patulous internal auditory canal. Acta Otolaryngol Head Neck Surg 2003; 129: 992-993
• 17 Valvassori G. The radiological diagnosis of acoustic neuromas. Arch Otolaryng 1966; 83: 92-97
• 18 Swartz JD, Harnsberger HR. The otic capsules and otodystrophies. Swartz JD, Harnsberger HR, In: (eds) Imaging of the temporal bone. New York Stuttgart: Thieme; 1998: 240-317
• 19 Phelps PD, Reardon W, Pembrey M et al. X-linked deafness, stapes gusher and a distinctive defect of the inner ear. Neuroradiology 1990; 33: 326-330
• 20 Kumar G, Castillo M, Buchmann CA. X-linked stapes gusher: CT findings in one patient. Am J Neuroradiol 2003; 24: 1130-1132
• 21 Papadaki E, Prassopoulos P, Bizakis J et al. X-linked deafness with stapes gusher in females. Eur J Radiol 1998; 29: 71-75
• 22 Cremers CW, Huygen PL. Clinical features of female heterozygotes in the x-linked mixed deafness syndrome (with perilymphatic gusher during stapes surgery). Int J Pediatr Otorhinolaryngol 1983; 6: 179-185
• 23 Cremers CW. Audiologic features of the X-linked progressive mixed deafness syndrome with perilymphatic gusher during stapes surgery. Am J Otol 1985; 6: 243-246
• 24 Phelps PD, King A, Michaels L. Cochlear dysplasia and meningitis. Am J Otol 1994; 15: 551-557
• 25 Magliulo G, Stasolla A, Collichio MG et al. Enlarged internal auditory canal and sudden deafness. J Laryngol Otol 2010; 124: 931-933
• 26 Ciuman RR. Communication routes between intracranial spaces and inner ear function, pathophysiologic importance and relations with inner ear disease. Am J Otolaryngol 2009; 30: 193-202
• 27 Marchbanks RJ, Reid A. Cochlear and cerebrospinal fluid pressure: their interrelationship and control mechanisms. Br J Audiol 1990; 24: 179-187
• 28 Marchbanks RJ, Reid A, Martin AM et al. The effect of raised intracranial pressure on intracochlear fluid pressure: three case studies. Br J Audiol 1987; 21: 127-130
• 29 Masaaki K, Mikio S, Akira K. Equilibrium of inner and middle ear pressure. Acta Otolaryngol Suppl 1994; 510: 113-115
• 30 Murakami S, Gyo K, Goode RL. Effect of increased inner ear pressure on middle ear mechanics. Otolaryngol Head Neck Surg 1998; 118: 703-708