Fibrous dysplasia mimicking a pediatric endolymphatic sac tumor

A 15-year-old female presented for evaluation of progressive hearing loss over a year. Computed tomographic imaging revealed a 11 x 6 × 6 mm osseous lesion with 'groundglass' appearance within the left posterior petrous bone lateral to vestibular aqueduct suspicious for an endolymphatic sac tumor. Surgical excision revealed fibrous dysplasia on histological analysis. Fibrous dysplasia of the temporal bone is not uncommon, but few cases of extension causing sensorineural hearing loss exist in the literature. We describe the first reported case of fibrous dysplasia mimicking an endolymphatic sac tumor; interestingly, the patient also showed hearing improvement immediately following removal.