Internal Auditory Canal Stenosis and Congenital Facial Nerve


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Internal Auditory Canal Stenosis and Congenital Facial Nerve Palsy
Susan L. Fulmer, MD1; Valerie Flanary, MD1
1Department of Otolaryngology and Communication Sciences, Medical College of Wisconsin, Milwaukee, WI

INTRODUCTION
Internal Auditory Canal (IAC) Stenosis •12% of congenital sensorineural hearing loss (SNHL) is associated with a narrow internal auditory canal (<3mm)1 •Typically facial nerve function is preserved in IAC stenosis2 •2-8 mm is the normal range for the IAC3
Facial Nerve Paralysis in the Newborn •Primarily traumatic in etiology and complete recovery expected in 89-91% of cases •16-22% of congenital facial nerve palsy is developmental in etiology4,5 •Developmental facial nerve paresis typically accompanies other craniofacial abnormalities • Möbius syndrome • Goldenhar syndrome • asymmetric crying facies
METHODS
•Subjects •Children seen in the otolaryngology clinic at the Children’s Hospital of Wisconsin from June 1996 to June 2009 with each of the following findings • Congenital facial nerve palsy • Congenital sensorineural hearing loss • Internal auditory canal stenosis •Exclusion criteria • Diagnosis of a syndrome or other major congenital abnormalities
•Retrospective chart review of the two identified subjects

Case one
History •9 year-old healthy male referred to the otolaryngology clinic for hearing loss •Failed routine school hearing screening and was found to have a profound left SNHL on subsequent audiogram •Subject did not recall a time when he could hear from his left ear •Unable to close left eye and has had facial asymmetry since birth •Birth history • No perinatal, ototoxic medications • No perinatal infections • No hx of jaundice or hyperbilirubinemia • Full-term cesarian section • Apgar scores unremarkable •Family history- mother has Diabetes Mellitus Type I
Physical Exam •House—Brackmann facial-nerve grading system: IV/VI • Asymmetric face at rest with decreased expression of left nasolabial fold • Incomplete closure of his left eye • No movement of his left forehead • Mouth is symmetric at rest and with movement •Left ear has lop ear deformity with absence of antihelical fold •Cranial nerves intact except left CN 7 and 8
Diagnostics •Audiogram • Profound left SNHL throughout all frequencies • Normal right hearing •High-resolution computed tomography (Figure 1) • Narrow left internal auditory canal (1.0 mm) • Normal right internal auditory canal (4.0 mm) • Bony anatomy of bilateral external, middle, inner ears were otherwise normal

Figure 1. Coronal CT scan demonstrating a normal right internal auditory canal in Subject 1 (image on the left) and a narrow left internal auditory canal (image on the right).

Case two

History •5 month-old healthy female referred to the otolaryngology clinic for hearing loss, facial weakness, and bilateral pre-auricular skin tags •Had failed her newborn hearing screening •Left facial weakness since birth with inability to close her eye; had had no improvement in function •Birth history • No perinatal, ototoxic medications • No perinatal infections • No hx of jaundice or hyperbilirubinemia • Full-term spontaneous vaginal delivery • Apgar scores unremarkable •Family history- mother has Diabetes Mellitus Type II, multiple paternal relatives with pre-auricular skin tags
Physical Exam •House—Brackmann facial-nerve grading system: V/VI • Asymmetric face at rest • Incomplete closure of his left eye, mild exposure keratitis evident • No movement of his left forehead • Mouth is asymmetric at rest •Left preauricular skin tag and two right pre-auricular skin tags •Cranial nerves intact except left CN 7 and 8
Diagnostics •Audiology • Abnormal left auditory brainstem response (ABR) and absent left otoacoustic emissions (OAE) •Electroneuronography • No response of left orbicularis oculi or nasalis •Electromyography • Decreased muscle unit action potentials (MUAPs) in orbicularis oris and frontalis on left and absent spontaneous or voluntary activity in orbicularis oculi •High-resolution computed tomography (Figure 2) • Narrow left internal auditory canal • Normal right internal auditory canal • Bony anatomy of bilateral external, middle, inner ears were otherwise normal •Magnetic resonance imaging • Hypoplastic left 7th and 8th cranial nerves.

Figure 2. Axial CT scan demonstrating a normal right internal auditory canal in Subject 2 (image on the left) and a narrow left internal auditory canal (image on the right).
DISCUSSION
•Congenital internal auditory canal stenosis is rarely associated with both facial nerve palsy and ipsilateral sensorineural hearing loss.
•There are less than five reported cases7,8,9
•Theories explaining the association of Hearing Loss with IAC Stenosis6
•1st theory: The 8th cranial nerve is hypoplastic secondary to an abnormal chemotactic environment or a lack of end organs. The bony canal is narrow as a result of the thin or absent 8th nerve. •2nd theory: Stenosis is a primary defect that then inhibits the growth of the 8th cranial nerve. •Major argument against the 2nd theory is that facial nerve function is typically preserved; these two cases counter that argument against the 2nd theory.
•IAC stenosis should be considered in the differential diagnosis of developmental facial nerve palsy
•Facial nerve function may be less likely to recover in setting of IAC stenosis
REFERENCES
1.Jackler RK, et al. Congenital malformations of the inner ear: a classification based on embryogenesis. Laryngoscope, 97 (1987) 2-14. 2.Shelton C, et al. The narrow internal auditory canal in children: a contraindication to cochlear implants. Otolaryng. Head Neck Surg., 100 (1989) 227-231. 3.Valvassori GE, et al. The normal internal auditory canal. Am. J. Radiol., 92 (1964) 1232-1241. 4.Smith JD, et al. Facial paralysis in the newborn. Otolaryngol. Head Neck Surg., 89 (1981) 1021-1024. 5.Falco NA and Eriksson E. Facial nerve palsy in the newborn: Incidence and outcome. Plastic and Reconstructive Surgery., 85 (1990) 1-4. 6.Rothschild MA, et al. Isolated primary unilateral stenosis of the internal auditory canal. Int. J. Pediatr. Otorhinolaryngol., 50 (1999) 219-224. 7.Lin KM, et al. Congenital unilateral facial palsy and internal auditory canal stenosis. Pediatric Neurology, 39 (2008) 116-119. 8.Nakumura K, et al. Stenosis of the internal auditory canal with VIIth and VIIIth cranial nerve dysfunctions. ORL J Otorhinolaryngol Relat Spec., 61 (1999) 16-18. 9.Sakina MS, et al. Internal auditory canal stenosis in congenital sensorineural hearing loss. Int. J. Pediatr. Otorhinolaryngol., 70 (2006) 2093-2097.

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Internal Auditory Canal Stenosis and Congenital Facial Nerve