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”.
