Seventh nerve palsy
The seventh or facial cranial nerve may be affected, causing ‘facial baroparesis’. Recorded in both aviators and divers, this disorder sometimes follows middle ear barotrauma. It manifests as a unilateral facial weakness similar to Bell’s palsy, and it tends to recur in the same patient if the cause is not corrected.
The reason for this disorder is explained by the anatomy of the facial canal. This is open to the middle ear in some people and so shares its barotraumatic pathology. Also, middle ear air expands during ascent and could force its way into this seventh nerve canal.
Paralysis of the facial nerve makes frowning impossible, prevents the eye from closing on that side and causes drooping of the lower eyelid (which may result in tears running down the face because they do not drain into the nasolacrimal duct). The cheek is smooth, and the mouth is pulled to the normal side. Whistling becomes impossible, and food collects between the cheek and gum. A metallic taste may be noticed at the start of the illness, as may impaired taste in the anterior part of the tongue on the same side, from chorda tympani involvement. Hyperacusis may result from paralysis of the stapedius muscle.
Early treatment could include inhalation of 100 per cent oxygen for some hours, based on the theoretical pathophysiology involved, to remove air from the seventh nerve canal.
Both physicians and otologists frequently omit to interrogate patients with Bell’s palsy regarding their swimming, diving and aviation exposure.
CASE REPORT 7.2: This diver, who had been exposed to gunfire in the past, experienced considerable pain and difficulty in equalizing both middle ears during a dive to 10 metres. He continued to dive despite the pain and performed forceful autoinflations. He noted tinnitus, and he also experienced ear pain and vertigo during ascent. Otoscopic examination of the tympanic membrane revealed the effects of barotrauma. The diver became progressively more deaf, with a sensorineural pattern in both ears, over the next few days. Transient episodes of vertigo were noted. Exploratory surgery was performed. A fistula of the round window was observed, together with a frequent drip of perilymph fluid into the middle ear. The round window was packed. A similar procedure was performed 5 days later in the other ear, with the same result. Subsequent audiograms over the following month revealed a considerable improvement in hearing.
Diagnosis: inner ear barotrauma (with perilymph fistula of the round window) caused by middle ear barotrauma of descent and forceful autoinflation, resulting in sensorineural hearing loss.
Although not frequent, otitis media is an occasional complication of middle ear barotrauma, with the middle ear collecting fluid that forms a medium for growth of organisms (see Chapter 29). Thus, ear pain developing hours or days after middle ear barotrauma should be considered to indicate a middle ear infection. This not only is a serious illness in its own right, but is also a possible cause of narrowing of the Eustachian tube and further middle ear barotraumas.
The mastoid, being part of the middle ear cleft, responds in the same way as the middle ear to a negative pressure situation. Thus, the production of fluid and blood in the mastoid, especially during descent, can develop and produce the conditions conducive to bacterial growth.
Under these circumstances, the patient usually has pain and tenderness over the mastoid, and the pathological features can be demonstrated by CT scans of the temporal bone.
Although rare, meningitis is a possible extension of otitis media, mastoiditis, sinusitis and so forth and a complication of both labyrinthine fistula and pneumocephalus.
Another rare complication from the middle ear cleft and mastoid air cells is pneumocephalus, resulting from the expansion of gas in a space that is now occupied by blood and fluid from descent barotrauma. A rupture into the cranial cavity, with air and/or fluids, produces a sudden and excruciating headache, with the pathological features demonstrated by CT brain scans and magnetic resonance imaging (see Chapter 8). The bony roof over the middle ear–mastoid space, the tegmen tympani of the petrous temporal bone, is frequently very thin or incomplete, allowing for the contents of this space (air, blood) to rupture into the middle cranial fossa, into the epidural or sub-dural areas.