Abstract
Hallermann-Streiff syndrome, also known as oculomandibulofacial syndrome, is a rare congenital disorder affecting growth and cranial, dental, ocular, pilocutaneous, and mental development. In addition to routine audiologic testing in patients with this syndrome, high-resolution computed tomography of the temporal bones should be performed in those with documented or suspected sensorineural hearing loss. Cochlear implantation may be considered, as in other children with syndromic hearing loss and certain inner ear abnormalities, if the appropriate audiologic, psychosocial, and medical criteria are met. The current case report radiographically and clinically characterizes inner ear dysplasia in an 8-year-old patient with Hallermann-Streiff syndrome. High-resolution computed tomography of the temporal bones revealed a hypoplastic bony island between the vestibule and horizontal semicircular canals, as well as incomplete bony coverage of the posterior semicircular canal crura bilaterally. To our knowledge, this is the first report of a pediatric patient demonstrating bilateral posterior semicircular canal dehiscence.
Introduction
Hallermann-Streiff syndrome (HSS), also known as oculomandibulofacial syndrome, is a rare congenital disorder affecting growth and cranial, dental, ocular, pilocutaneous, and mental development. It was first described by Hallermann in 1948 1 and Streiff in 1950. 2 Patients with HSS typically have distinctive malformations of the craniofacial region, including a broad, short head, frontal bossing, and mandibular hypoplasia. Hypotrichosis is common, as are congenital cataracts, dysplastic dentition, and high-arched palate.
The exact incidence of HSS is unknown, although it is believed to occur sporadically and thus cannot be predicted from family history or genetic testing. 3 Multiple developmental systems are involved in the pathophysiology of HSS, yet prior case reports have not described abnormalities in inner ear development. Moreover, the incidence of hearing loss in these patients has not been well characterized.
Case report
An 8-year-old boy with HSS presented to the Department of Otolaryngology–Head and Neck Surgery with poor speech development and suspected hearing loss. He had failed both his initial newborn hearing screen and a follow-up hearing screen. He was scheduled for subsequent testing by auditory brainstem response audiometry, but this appointment was not kept.
The patient was not seen again until he presented at age 8. Speech therapy had been instituted at age 7 for findings of delayed speech. The patient was in a physical therapy program, as well, and he had gross motor skills at the level of a 7-year-old along with good performance of his activities of daily living.
At the time of his visit, the patient did not have otorrhea, ear pain, or other evidence of ear infections. He had visual impairment, lumbar scoliosis, premature adrenarche, and follicular plugging. Physical examination revealed a child of short stature with reduced body hair and a hypoplastic mandible. The pinnae appeared well developed, and the ear canals were patent and without abnormalities, while the tympanic membranes on both sides were clear and mobile. The patient had a normal gait, although further balance testing was limited. Audiometry was performed to evaluate the degree and nature of the suspected hearing loss.
Figure. Axial CTS demonstrate dehiscence of the bone overlying the right posterior semicircular canal (A) and a similar finding on the left side (B).
Pure-tone audiometry revealed bilateral, symmetric, sloping, moderate to severe sensorineural hearing loss. Speech reception thresholds of 45 dB on the right and 60 dB on the left were obtained, while type A tympanograms were found bilaterally. The patient was fitted for hearing aids and began immediate rehabilitation in an effort to improve his speech and language skills.
High-resolution computed tomography (HRCT) of the temporal bones was performed to evaluate for the presence of an inner ear malformation. Axial, coronal, and sagittal images were obtained. Bilateral posterior semicircular canal dehiscences were identified (figure). The bony island between the vestibule and the horizontal semicircular canal was also hypoplastic. The width of this bony island, as measured from the inner apex of the canal to the midpoint between the vestibule and the canal, was 2.5 mm on the left and 2.4 mm on the right (normal ranging from 2.8 to 4.2 mm). Cochlear and internal auditory canal morphology appeared normal on both sides. The vestibular aqueducts on both sides were not enlarged. Magnetic resonance imaging was not obtained, nor was electronystagmography performed.
Discussion
Congenital severe to profound hearing loss occurs in approximately 1 out of every 1000 births, with up to 60% of these cases resulting from genetic mutations. 4 While most genetic causes of hearing loss are nonsyndromic, roughly 20% of cases have an association with a definable syndrome. 4 HSS is characterized by abnormalities involving cranial, dental, ocular, and pilocutaneous development.1,2 Patients with HSS often have significant growth problems, as well as respiratory and airway issues in infancy, and it is possible that hearing evaluations might be delayed as a result. While hearing loss in patients with HSS has not been well delineated in prior reports, the current case report describes a patient with HSS and bilateral sensorineural hearing loss.
In addition to history, physical examination, and appropriate audiologic testing, HRCT has been an extremely valuable tool in screening patients with various forms of hearing loss, including those with congenital hearing loss. 5 More recently, HRCT has also allowed for the precise measurement of specific inner ear anatomic structures, thereby establishing normative data for comparison in patients with hearing loss. 5 Abnormalities in cochlear height, horizontal semicircular canal bony island width, and vestibular aqueduct width have correlated well with the presence of hearing loss. 5
In the current case, the horizontal semicircular canal bony island widths of 2.4 mm and 2.5 mm represent a hypoplastic developmental process (normal: 2.8 to 4.2 mm). It is unclear whether this is directly related to the patient's observed sensorineural hearing loss, but prior studies suggest that such abnormal radiographic findings correlate well with the presence of hearing loss. 5
HRCT also allows for the identification of superior and posterior semicircular canal abnormalities, although the incidence of these abnormalities is much lower than those of horizontal canal, cochlear, and vestibular aqueduct abnormalities. 5 In a recent study of 131 consecutive pediatric patients undergoing HRCT of the temporal bones, 4% of patients demonstrated findings of semicircular canal dehiscence, with the superior canal being dehiscent three times more often than the posterior canal. 6 In the current case, both posterior semicircular canals demonstrated areas of bony dehiscence.
Because posterior semicircular canal dehiscence is relatively rare, its clinical implications remain unclear, particularly in a case with bilateral involvement. Symptoms of vertigo in patients with radiographic findings of posterior semicircular canal dehiscence have been reported, but further experience with this rare condition is required before clinical extrapolations can be made. 7
In conclusion, HSS is a rare disorder of unknown etiology that affects multiple organ systems. As with other syndromes, a high degree of suspicion must be maintained to diagnose less obvious developmental abnormalities, including those affecting the cochleovestibular apparatus. In such cases, early hearing screening with repeat testing for equivocal results is essential. HRCT of the temporal bones provides further diagnostic information in cases with documented or suspected sensorineural hearing loss and readily identifies anatomic inner ear abnormalities.
Amplification with hearing aids, in addition to aggressive speech therapy, should be instituted early in such cases, with cochlear implantation reserved for those children with profound sensorineural hearing loss who fail amplification.