A Case of Cerebrospinal Fluid Hypovolemia with Bilateral Mixed Hearing Loss

Cerebrospinal fluid (CSF) hypovolemia is characterized by orthostatic headache, loss of CSF, and diffuse pachymeningeal gadolinium enhancement on MRI. The audiometric finding that has so far been associated with CSF-hypovolemia is sensorineural hearing loss. We report the case of a 52-year-old woman with bilateral mixed hearing loss in CSF-hypovolemia. She complained of headache upon rising, nausea, and bilateral earfullness. Her MRI showed a diffuse pachymeningeal gadolinium enhancement with decreased ventricle size, indicating CSF-hypovolemia. Her tympanic membranes were normal and tympanograms were type A, but her audiogram showed bilateral mixed hearing loss. Her audiogram also showed a normal air-conduction threshold and hyper sensitivity to bone conduction (−10, −15 dB), and an air-bone gap remained after she recovered from the CSF-hypovolemia. The original air-bone gap had apparently developed into mixed hearing loss as a result of the sensorineural hearing loss with CSF-hypovolemia. In this case, a wide cochlear aqueduct may have acted as a third mobile window in the inner ear, resulting in an air-bone gap and hypersensitivity to bone-conducted sound stimuli. Moreover, this third window may have been related to the onset of sensorineural hearing loss with CSF-hypovolemia. The air-bone gap in this case should perhaps be called “pseudo-conductive loss”.