eighth cranial nerve schwannomas are benign tumors that are more likely to occur in the internal auditory canal ( iac ) or in the cerebellopontine angle ( cpa ) cistern than within the cochlea . although , most schwannomas are sporadic , they may be associated with neurofibromatosis type ii . intracochlear schwannomas are a rare cause of unilateral hearing loss , with fewer than 80 cases reported in the literature . within the labyrinth , these lesions are composed of schwann cells and tend to occur in the modiolus and the basal turn of the cochlea along the path of spiral ganglion dendrites . we present a case of an intracochlear schwannoma demonstrating atypical imaging features on mri , contributing to a delay in diagnosis and treatment . a 33-year - old woman presented with 3  years of progressively worsening left - sided hearing loss , aural fullness , and intermittent vertigo . mri of the internal auditory canals ( iacs ) performed on a 1.5  t scanner showed a diffuse enhancement of the left cochlea on t1 post - gadolinium images ( fig .  1 ) . short - term follow - up mris showed a qualitative decrease in the degree of enhancement , and the acute process causing these mri changes was thought to have improved.fig . 1axial ( top ) and coronal ( bottom ) post - contrast t1-weighted images ( obtained on a 1.5  t siemens sonata scanner ) show diffuse enhancement of the left cochlea . there is no abnormal enhancement of the left internal auditory canal or vestibule axial ( top ) and coronal ( bottom ) post - contrast t1-weighted images ( obtained on a 1.5  t siemens sonata scanner ) show diffuse enhancement of the left cochlea . there is no abnormal enhancement of the left internal auditory canal or vestibule the patient presented 3  years later with worsening symptoms . repeat mri , this time performed on a 3  t scanner , again showed smooth diffuse enhancement of all three half - turns of the cochlea ( fig .  2 ) . steady - state imaging continued to show no evidence of a focal nodular lesion ( fig . audiologic examination revealed normal hearing in the right ear and moderate - to - severe sensorineural hearing loss in the left ear with a speech reception threshold of 45  db and word discrimination score ( wrs ) of 44% . repeated audiologic exam several months later demonstrated stable hearing thresholds , but a worsening wrs of 8% . due to the lack of serviceable hearing and intractable vertigo , the patient underwent left transmastoid labyrinthectomy with a bone - anchored hearing aid ( baha ) placement.fig . 2axial ( top ) and coronal ( bottom ) post - contrast images obtained on a 3  t siemens verio scanner continue to show faint diffuse enhancement of all turns of the left cochleafig .  3multiple axial steady - state free precession ( ssfp ) images obtained on a 3  t siemens verio scanner show normal cochlear anatomy . there is no evidence of a focal nodular lesion axial ( top ) and coronal ( bottom ) post - contrast images obtained on a 3  t siemens verio scanner continue to show faint diffuse enhancement of all turns of the left cochlea multiple axial steady - state free precession ( ssfp ) images obtained on a 3  t siemens verio scanner show normal cochlear anatomy . there is no evidence of a focal nodular lesion at surgery , a mass ( dimensions 0.4    0.3    0.1  cm ) was found to be confined to the labyrinth and was removed as part of the labyrinthectomy . on pathology , a schwannoma was found arising from within the cochlea . the lesion consisted of schwann cells appearing as spindle cell proliferation , and the s100 marker was positive on immunohistochemical staining . verocay bodies , which consist of a group of fusiform cells arranged in whorls or palisades , were also evident ( fig the arrow indicates a verocay body , which consists of a group of fusiform cells arranged in whorls or palisades histopathology of the labyrinthine lesion consistent with schwannoma , appearing as spindle cell proliferation . the arrow indicates a verocay body , which consists of a group of fusiform cells arranged in whorls or palisades although the majority of patients present with progressive hearing loss , as in our case , 31% of patients with intralabyrinthine schwannomas have sudden sensorineural hearing loss . diagnosis of intracochlear schwannoma is difficult and often delayed because these presenting symptoms are shared with other otologic diseases , particularly meniere s disease . in one series of 19 patients , although auditory brainstem response ( abr ) testing is highly sensitive for schwannomas larger than 1  cm , it is inferior to gadolinium - enhanced mri , which is the gold standard for diagnosis . in one study of intralabyrinthine schwannomas , mri was diagnostic in 96% of patients ( one patient had an incidental finding of intracochlear schwannoma at cochlear implant surgery ) . current mri evaluation of the inner ear includes axial and coronal thin - section gadolinium - enhanced sequences to detect the presence of an enhancing lesion as well as a steady - state free precession sequence ( ssfp , also known as fiesta or ciss ) for improved spatial resolution . although mri is useful in making the diagnosis , it too , is limited by tumor size . small intralabyrinthine lesions may be particularly difficult to see on mri , and may be seen only in retrospect . mri is usually ordered when asymmetric hearing loss raises the question of a possible acoustic neuroma . however , the expensive use of frequent mris to diagnose intracochlear schwannoma is a concern , especially as many initial screening scans are negative . once diagnosed , not all the patients with intracochlear schwannomas require surgery ; the decision for treatment depends on size and extent of tumor as well as patient symptoms . large tumors with extra - labyrinthine extension usually undergo surgical treatment or stereotactic - guided radiotherapy . in patients with small tumors and serviceable hearing , conservative management with repeat mris when patients have small tumors without useful hearing and when vestibular symptoms indicate the need for treatment , as in our case , surgery is planned . both translabyrinthine and transotic approaches have been described ; the transotic approach is superior for more extensive tumors . because of the risks of surgery , some authors advocate conservative management whenever possible : in his series from 1992 to 2002 , kennedy describes only 30% of patients with intralabyrinthine schwannomas requiring operative management . we present an unusual appearance of an intracochlear schwannoma . although the vast majority of these tumors are seen as focal nodular enhancing masses on mri , smooth diffuse enhancement of the cochlea does not exclude the presence of a schwannoma . in patients with a prolonged clinical presentation atypical for an inflammatory or infectious lesion , diffuse cochlear enhancement should not exclude the possibility of an intracochlear schwannoma .
intracochlear schwannoma is a rare , treatable , cause of unilateral hearing loss . due to the small size , position , and variable clinical and imaging features 
 , diagnosis presents a significant challenge and is often delayed . 
 we present a case of a patient with an intracochlear schwannoma presenting as a diffuse enhancement of the cochlea , mimicking an infectious or inflammatory process . 
 the absence of focal nodularity in this lesion on multiple high - resolution mri examinations led to a delay of over 3 years from the patient s initial presentation to surgical diagnosis . 
 clinical history and examination , imaging features , pathologic findings , and surgical management options are described .