temporal)bone)encephalocele… · 2016. 9. 15. ·...
TRANSCRIPT
Temporal Bone Encephalocele Presenting with Conductive Hearing Loss
ABSTRACT
INTRODUCTION
CASE REPORT DISCUSSION
CONCLUSIONS
Dennis Bojrab II, MD1; Robert Hong, MD1,2; Aaron Metrailer, MD2; Dennis Bojrab, MD1,2
1Wayne State University, 2Michigan Ear Institute
Outcome Objectives:1. Describe-‐ Conductive hearing loss has numerous potential causes. This case report presents a patient with an intact tympanic membrane, aerated middle ear, and no history of ear disease or trauma who developed unilateral, conductive hearing loss as an adult secondary to temporal bone encephalocele.
2. Recognize-‐ In a patient with conductive hearing loss and partially intact acoustic reflexes, a temporal bone encephalocele impeding movement of the ossicles in addition to the more common etiology of third window disorders must be considered.
Methods:We present a case report of a 50-‐year-‐old woman with conductive hearing loss and aural fullness who presented to our clinic in late 2013. She initially underwent a negative middle ear exploration for suspected otosclerosis. Subsequently, she was found to have a temporal bone encephalocele with resolution of conductive hearing loss after transmastoid and middle cranial fossa repair.
Results:Temporal bone encephalocele can cause conductive hearing loss and partially absent acoustic reflexes with an unremarkable neurotological examination including a well aerated middle ear.
Conclusion:This case demonstrates the role of imaging and importance of close evaluation for temporal bone encephaloceles when evaluating conductive hearing loss, particularly when acoustic reflexes are not completely absent.
Conductive hearing loss is the result of any process that attenuates the sound energy reaching the cochlea. The differential diagnosis for conductive hearing loss is broad; however a thorough patient history in conjunction with the physical examination, audiologic testing, and imaging may narrow the differential diagnosis. The most common cause of progressive conductive hearing loss in the absence of chronic otitis media is otosclerosis, yet other entities causing ossicular chain fixation, ossicular discontinuity, and third window phenomena should be considered [1].
In this report, we present the unusual case of a patient who underwent middle ear exploration for presumed otosclerosis, but who was ultimately found to have a temporal bone encephalocele as the etiology of conductive hearing loss. Preoperative evaluation did not reveal any specific signs or symptoms strongly suggestive of this diagnosis, with an aerated middle ear and inconclusive imaging studies. Temporal bone encephaloceles can present with conductive hearing loss, though usually in the context of persistent middle ear effusion or otorrhea. However, as this case demonstrates, they can also be the cause of conductive hearing loss in the presence of a normal otoscopic exam.
A 50 year old healthy female was referred for evaluation of unilateral hearing loss. The patient weighed 250 lbs with body-‐mass index of 41. Hearing loss began 6 months prior with associated aural fullness. She denied tinnitus, vertigo, disequilibrium, sound or pressure-‐induced dizziness, otorrhea, otalgia, history of ear disease, or trauma. She also denied a family history of hearing problems.
On examination, the right ear tympanic membrane was intact and the middle ear aerated. Tuning fork examination was consistent with a significant conductive hearing loss in the right ear. The remaining neurotological examination and the general head and neck examination were unremarkable.
Audiologic testing revealed a right mixed hearing loss with an air-‐bone gap at all frequencies (most pronounced at 2000 to 4000 Hz) and type A tympanograms bilaterally (Figure 1). Right ipsilateral acoustic reflexes were absent. Left contralateral reflexes were present at 500 Hz, 1000 Hz, and 2000 Hz, and absent at 4000 Hz (Figure 2). A high resolution CT scan of the temporal bone was obtained to evaluate for the possibility of cochlear otosclerosis (given the mixed hearing loss) as well as a third window disorder (given the presence of acoustic reflexes). CT imaging was essentially normal, with no evidence of cochlear otosclerosis or a third window disorder. The tegmen appeared thin in places but was not clearly dehiscent. Scant opacification was noted in the mastoid.
The patient elected to have a right middle ear exploration to address the conductive hearing loss. Intraoperatively, no specific ossicular abnormality was identified. Scant middle ear fluid was present and the possibility of an encephalocele with associated CSF (cerebrospinal fluid) otorrhea was entertained, though an encephalocele was not directly visualized. A small amount of fluid was collected and sent for beta-‐2 transferrin (though this test was ultimately negative).
Given the intraoperative findings, a magnetic resonance imaging (MRI) of the brain was ordered postoperatively to evaluate for possible encephalocele (Figure 3). Possible encephalocele was identified, and there appeared to be more extensive opacification of the mastoid compared to the preoperative CT scan. A repeat CT scan of the temporal bone was obtained, again suggesting increased opacification of the mastoid, as well as an area of tegmen dehiscence (Figure 4). As such, the patient underwent a combined transmastoid and middle cranial fossa repair, with intraoperative confirmation of the encephalocele and CSF leak. Postoperatively, the patient had an uneventful recovery, with postoperative audiogram demonstrating resolution of conductive hearing loss.
A patient who presents with progressive conductive hearing loss without evidence of chronic otitis media is often presumed to have an ossicular etiology of hearing loss, most commonly otosclerosis. However, more recently, third window disorders such as superior semicircular canal dehiscence have been demonstrated to cause similar hearing loss [1]. Third window disorders include dehiscence of any semicircular canal, dilated vestibular aqueduct, inner ear malformations causing dehiscence of the cochlea or vestibule, and Paget’s disease of the temporal bone [2]. Patients with an enlarged vestibular aqueduct or superior semicircular canal dehiscence can present with conductive hearing loss as the primary complaint [3].
Given the multiple possible diagnoses, acoustic reflex testing is an important tool in the armamentarium of an otolaryngologist in the evaluation of conductive hearing loss in the setting of a normal ear exam. Its use is advocated to help differentiate between ossicular and third window etiologies prior to middle ear surgery, with the presence of reflexes necessitating additional workup for third window disorders to minimize the risk of negative middle ear explorations [4].
In the acoustic reflex test the reflex arch starts with stimulation of the cochlea, which in turn stimulates the cochlear nerve, ventral cochlear nuclei, superior olive, facial nerve, and finally causing the stapedius muscle to contract. In patients with conductive hearing loss that has progressed to the point of considering surgery, the reflexes are typically absent with otosclerosis. In contrast, acoustic reflexes may be present when superior semicircular canal dehiscence or enlarged vestibular aqueduct is responsible for the conductive hearing loss [5, 6]. When at least one reflex is present, CT imaging of the temporal bone is advocated to evaluate for 3rd window etiologies [4]. We suggest that careful attention should also be paid to the tegmen on such imaging, as a temporal bone encephalocele overlying the ossicles may also lead to such hearing loss and result in a significantly different recommendation for surgery
The presence of middle cranial floor defects occurs in 20-‐33% of adult temporal bones, but the occurrence of encephaloceles is much less common [7]. Depending on the location and size of the encephalocele, patient presentation can be quite variable. Several studies have shown that encephaloceles can cause a conductive hearing loss [8]. Other articles had both pre and post-‐encephalocele repair audiology testing, which revealed that the conductive hearing loss either stayed relatively stable or improved [9, 10].
This case demonstrates that close evaluation for temporal bone encephaloceles is important when evaluating conductive hearing loss and this diagnosis should be considered prior to middle ear exploration, particularly when acoustic reflexes are present. In this case, the encephalocele was touching the heads of the ossicles, leading to a conductive hearing loss that was not corrected until the encephalocele was repaired via a combined transmastoid/middle cranial fossa approach. To our knowledge this is the first report of a case with conductive hearing loss, a normal otoscopic exam, and presence of at least some acoustic reflexes where the final etiology of hearing loss was determined to be an encephalocele.
There are multiple potential diagnoses for an adult patient presenting with progressive conductive hearing loss. In addition to a thorough history and examination, it may also be important to obtain audiometric and radiologic evaluation. In this report, the patient had no history of ear disease or trauma, an unremarkable otoscopic examination who presented with worsening conductive hearing loss because of an encephalocele impeding normal ossicular movement. Now temporal bone encephalocele must also be considered when evaluating a patient with conductive hearing loss and partially intact acoustic reflexes.
Figure 1This is the patient’s pre-operative audiogram revealing mixed hearing loss in the right ear, with an air-bone gap at all frequencies, most pronounced at 2000 to 4000 Hz.
Figure 2This is the patient’s pre-operative tympanogram and acoustic reflexes. Bilateral type A tympanograms. Right ipsilateral acoustic reflexes were absent. Left contralateral reflexes were present at 500 Hz, 1000 Hz, and 2000 Hz, and absent at 4000 Hz
Figure 3T1 coronal MRI scan post contrast demonstrating encephalocele involving epitympanum
Figure 4Coronal CT scan revealing tegmen dehiscence and encephalocele in the region of the epitympanum coming into contact with the ossicles.
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