A labyrinthine concussion is a condition which occurs following trauma to the head and/or inner ear or can also present without well-defined radiological injury and is characterized by inner ear symptoms such as tinnitus, dizziness, and high-frequency sensorineural hearing loss.
Labyrinthine concussion, also known as inner ear concussion, or commotion labyrinthitis /otitis interna vasomotoria [1] is characterized by a sensorineural hearing loss in the high frequencies. It follows vestibular or head trauma and may or may not be associated with vertigo. Some patients may report symptoms despite the absence of radiological evidence of labyrinthine injury [2] [3].
Typical features of labyrinthine concussion are a reversible hearing loss, dizziness, and tinnitus on the ipsilateral side, although they can also be seen on the contralateral side of the temporal bone fracture [1] or can be bilateral [4]. The symptoms are noticed either immediately or within an hour or even days after the injury [4]. Nystagmus and alteration in hearing are a prerequisite to label the condition as labyrinthine concussion [4]. Nystagmus is initially in the ipsilateral direction, horizontal, torsional or directional and later changes direction towards the contralateral side. The hearing loss is in the high frequencies and can be either mild to moderate or even profound. Patients may witness with recruitment [4].
The causes of labyrinthine concussion are unknown and it is presumed that injury of the saccule and utricle occurs following trauma to their encasing bony labyrinth with resultant hemorrhage, ischemia or rupture of parts of the membranous labyrinth [5] [6].
History, examination findings, audiological evaluation and psychological assessment are necessary to distinguish between labyrinthine concussion from post-concussion syndrome and whiplash syndrome, which may be concurrent [4]. All these patients can complain of dizziness, although a migraine and headaches are more common in post-concussion syndrome while patients with whiplash syndrome may have long-standing shoulder and neck pain with tinnitus and hearing loss. Benign positional vertigo (BPPV) may be noticed in all the three groups of patients [4]. However, patients with a labyrinthine concussion recover faster as compared to other syndromic patients.
A complete otolaryngological and neurologic examination is performed along with the tuning forks test to document hearing loss. Slight nystagmus on fistula test is indicative of oval or round window fistulae [7] while strong nystagmus can indicate superior semicircular canal dehiscence. Dix-Hallpike maneuver is administered as part of the examination. Caloric testing will not reveal central problems and cerebellar signs will be absent. Pure tone audiometry is helpful to document the degree and type of hearing loss while tympanometry is useful to assess the tympanic membrane and middle ear status. Hearing loss is usually sensorineural and more often in the higher frequencies [3]. Electronystagmography (ENG) is performed to differentiate between central and peripheral vertigo [4].
High resolution computed tomography (CT) scan of the temporal bone can detect fractures which can be either transverse or longitudinal. The incidence of vestibular injury is higher with transverse fractures. Magnetic resonance imaging (MRI) of the temporal bone and internal auditory canal (IAM), help to exclude associated tumors.