Introduction
Facial nerve baroparesis is a rare phenomenon that has been reported in both divers and aviators.Reference Molvaer and Eidsvik1 It is hypothesised to occur as a result of increased pressure on the tympanic segment of the facial nerve through a dehiscence of the horizontal part of the facial canal. The excessive pressure differential between ambient and middle-ear pressure is believed to result in hypoxia and neuropraxia through compression of the vasa nervorum.Reference Molvaer and Eidsvik1 The generally reported experience is a period of facial weakness occurring during flight and resolving after three minutes to several hours.Reference Bennett and Liske2 However, one case has been reported in which the subject took over two months to recover.Reference Rutten and Kunst3 It may be associated with symptoms such as facial pain, facial numbness, ear discomfort, a sensation of pressure and tinnitus.Reference Ardehali, Yazdani and Heidarali4 We present a case report of an aviation-associated right-sided facial nerve palsy lasting 10 minutes on 3 separate flights. The presentation, management and probable pathophysiological mechanisms of facial baroparesis are also discussed, and a literature review of the currently available literature regarding flight-induced facial nerve baroparesis is presented.
Case report
A 43-year-old male presented to our otolaryngology clinic with 3 episodes of aviation induced facial nerve baroparesis. The patient was travelling between the Australian states of Victoria and Queensland and during the flight developed right-sided facial weakness that lasted for 10 minutes and then subsequently resolved. This then happened two weeks later on a similar distance flight between the same states in Australia. The patient frequently flies for work and had never experienced facial palsy previously. He was initially referred to a cardiologist for investigations for assumed cerebral vascular episodes; however, extensive investigations were all normal.
The patient reported no hearing loss, no pain and no tinnitus. He had no significant past medical history and no previous surgical procedures. He reported smoking 20 cigarettes a day for many years. No abnormality was found on clinical examination, including neurotological examination and upper airway nasoendoscopy. The patient was reviewed one month later following audiological assessment, and a high-resolution temporal bone computed tomography (CT) scan was performed. Pure tone audiometry showed a mild right conductive hearing loss at 250, 500 and 8000 Hz. Tympanometry showed negative pressure in the right middle ear. High resolution CT scanning suggested a tympanic facial nerve canal dehiscence. A ventilation tube was subsequently inserted into the right tympanic membrane under local anaesthesia. Upon myringotomy, the patient was found to have a glue ear. The patient had flown multiple times without recurrent symptoms whilst the grommet was in situ. Eight months later, after grommet extrusion, the patient suffered a third episode of transient facial nerve palsy whilst flying with a respiratory tract infection. Over the years, he subsequently had significant recurrent otologic symptoms from airflight that required grommet insertion, but no further facial palsies.
Informed patient in the consent was sought and granted by the case we report in this article.
Materials and methods
The search was conducted using PubMed, Ovid Medline and Embase databases from establishment until January 2020. Abstracts were identified using terms relating to facial palsy (‘barotrauma facialis’, ‘baroparesis facialis’, ‘facial nerve palsy’, ‘facial nerve paralysis’ and ‘alternobaric facial palsy’) and flight (‘flight’, ‘ascent’, ‘aviation’ and ‘high altitude’). Papers that described cases not associated with altitude and animal studies were excluded. There were no language or publication year restrictions imposed. The search strategy performed in January 2020 resulted in 106 articles, resulting in 22 articles that underwent full-text evaluation and 18 studies that fulfilled inclusion criteria for analysis (Figure 1).
Fig. 1. Preferred Reporting Items for Systematic Reviews and Meta-Analyses (‘PRISMA’) flow diagram.
Results
Twenty-three cases (including our own) of aviation-induced facial nerve baroparesis are reported in the literature (Table 1). The median age at diagnosis was 36 years, and the age span was 20–62 years (age data is missing in one case). Of the 23 cases, 16 were male. Twelve cases experienced symptoms on the left, nine on the right, one case had bilateral symptoms in separate instances and one case did not report which side was affected. Six patients described a single episodeReference Ardehali, Yazdani and Heidarali4–Reference Berghaus9 and 17 patients described multiple episodes.Reference Bennett and Liske2,Reference Rutten and Kunst3,Reference Cumming, Matchett, Meller and Saxby5,Reference Cheng and Kaylie10–19
Table 1. Documented cases of barotraumatic facial nerve palsy in aviation or on ascent to high altitudes
* Patient initially presented with a facial nerve schwannoma and underwent nerve decompression and subtotal tumour resection. M = male; F = female; R = right; L = left; CT = computed tomography; MRI = magnetic resonance imaging
Episodes ranged from 5 minutes to 4.5 hours in duration. One patient had a known history of facial nerve schwannoma and had previously undergone a facial nerve decompression and incomplete tumour resection two years prior to his first episode of facial nerve baroparesis.Reference Kung, Roche and Gantz11 Another patient had an iatrogenic facial nerve injury with a baseline House–Brackmann V function.Reference Rutten and Kunst3 Three patients had suffered an upper respiratory tract infection in the weeks preceding their facial nerve baroparesis.Reference Ardehali, Yazdani and Heidarali4,Reference Krywko, Clare and Orabi6
Symptoms experienced by patients included facial weakness (23 patients, 100 per cent), aural fullness (13 patients, 56.5 per cent), otalgia (10 patients, 43.4 per cent) and hearing loss (4 patients, 17.3 per cent). Two patients experienced vertigo during their episodes, and one patient described residual facial pain which persisted for several hours. Nine patients were investigated with CT alone,Reference Ardehali, Yazdani and Heidarali4,Reference Cumming, Matchett, Meller and Saxby5,Reference Berghaus9,Reference Cheng and Kaylie10,Reference Wimmer and Ali14,Reference Ah-See, Shakeel, Maini and Hussain15 three with magnetic resonance imaging (MRI) alone,Reference Rutten and Kunst3,Reference Grossman, Ulanovski, Barenboim, Azaria and Goldstein8,Reference Vivekananda and Omer13 and five patients had both MRI and CT.Reference Krywko, Clare and Orabi6,Reference Kung, Roche and Gantz11,Reference Cada, Hrubá, Jerabek, Cerny, Kluh and Balatkova12,Reference Ah-See, Shakeel, Maini and Hussain15 Two patients were investigated with skull and maxillary sinus X-rays.Reference Bennett and Liske2 One patient did not undergo imaging investigationReference White and Shackleton7 and imaging was not reported in three cases.Reference Motamed, Pau, Daudia and Narula16,Reference Silverstein18,19 Five patients had radiological evidence of facial canal dehiscence.Reference Cumming, Matchett, Meller and Saxby5,Reference Wimmer and Ali14,Reference Ah-See, Shakeel, Maini and Hussain15
In 10 of the reported cases, patients were observed, and the facial nerve baroparesis did not recur after the initial 1 to 3 episodes (this was deemed likely because of an upper respiratory tract infection or other self-limiting cause of Eustachian tube dysfunction). One patient who experienced prolonged symptoms before seeking medical attention was treated with oral prednisolone, and whilst facial motor function was restored to normality, the patient suffered a mild sensorineural hearing loss. Five patients were treated with grommet insertion alone,Reference Ah-See, Shakeel, Maini and Hussain15,Reference Motamed, Pau, Daudia and Narula16,Reference Silverstein18 one was treated with grommet insertion coupled with nasal septum submucous resection and inferior turbinate trimming,Reference Woodhead17 three patients were managed with nasal decongestant spray prior to flyingReference Rutten and Kunst3,Reference Cumming, Matchett, Meller and Saxby5 and one patient was treated with Eustachian tube balloon dilatation.Reference Cheng and Kaylie10 The patient with previously known facial nerve schwannoma underwent a revision facial nerve decompression with subsequent normalisation of symptoms.Reference Kung, Roche and Gantz11 One patient was offered grommet insertion but declined treatment.Reference Cada, Hrubá, Jerabek, Cerny, Kluh and Balatkova12
Discussion
The atmospheric pressure at sea level is 760 mmHg. As an aircraft ascends, the atmospheric pressure decreases, and the gas in the middle ear expands in accordance with Boyles' law. In modern commercial aircraft, the cabins are pressurised to the equivalent of 1500–2500 m.Reference D'Andrea and Frederik20,Reference Mirza and Richardson21 This creates a potential pressure gradient across the tympanic membrane which is normally equalised by passive opening of the Eustachian tube, venting the pressure through the nasopharynx.Reference Brown22
Impaired function of the Eustachian tube may lead to failure of pressure equalisation. This may be caused by conditions which narrow the lumen by oedema, increase the viscosity of the mucous in the lumen or impair the normal opening of the Eustachian tube.Reference Whelan23,Reference King24 Acute rhinitis, nasal septum deviation or other upper airway pathology may be associated with Eustachian tube dysfunctionReference Woodhead17 and a previous report of five cases noted facial baroparesis in divers who descended whilst afflicted with a viral upper respiratory tract infection and presumably had impaired Eustachian tube function.Reference Eidsvik and Molvaer25 Although congenital and traumatic malformations of the nasal skeleton and malocclusion of the teeth and jaw are also recognised to impair Eustachian tube function,Reference King24 it is not clear whether these lead to a predisposition to barotrauma.Reference Ah-See, Shakeel, Maini and Hussain15
The failure to vent air pressure from the middle ear to the nasopharynx during ascent results in an excessive middle-ear pressure, which may then be transmitted to the facial nerve. The most widely accepted hypothesis in the literature for facial baroparesis is ischaemic neuropraxia, based on the quick onset and resolution of facial baroparesis.Reference Molvaer and Eidsvik1 It is theorised that excessive pressure is transmitted through a dehiscence in the facial nerve canal, decreasing the blood flow of the vasa nervorum of the facial nerve. This consequently results in neuropraxia. In cats, facial nerve neuropraxia was induced by applying pressure to an unexposed part of the facial nerve.Reference Roffman, Babin and Ryu26 Subsequently in a guinea pig animal model, it was demonstrated that increasing middle-ear pressures did result in reduced blood flow in the vasa nervorum of the facial nerve.Reference Nagai, Nakashima, Suzuki and Yanagita27 The reported incidence of facial nerve canal dehiscence in humans varies greatly. In anatomical autopsy cases, a dehiscence is shown in 19.7–57 per cent of all human temporal bones.Reference Moreano, Paparella, Zelterman and Goycoolea28–Reference Kida30 However, it must be noted that some cases reported no apparent facial nerve canal dehiscence on CT scan.Reference Ah-See, Shakeel, Maini and Hussain15 The sensitivity and specificity of CT scan detection of facial canal dehiscence is reported at 66–80 per cent and 84–98 per cent, respectively.Reference Keskin, Çetin and Töre31,Reference Fuse, Tada, Aoyagi and Sugai32 A potential explanation for facial baroparesis in patients without a dehiscent tympanic facial canal is the transmission of elevated middle-ear pressure through the fenestra of the chorda tympani;Reference Rutten and Kunst3 however, this hypothesis is less widely acknowledged.
• Facial nerve baroparesis in aviation is a rare phenomenon
• Most patients present with self-limiting facial weakness
• It is thought to occur as a result of ischaemic neuropraxia in the setting of Eustachian tube dysfunction and a dehiscent facial nerve canal
• The most common imaging modalities utilised in diagnosis are computed tomography and magnetic resonance imaging
• Treatment varies from conservative treatment to nasal decongestant sprays and grommet insertion
• Most cases report no further episodes of facial nerve palsy following treatment
Altitude change of the aircraft, opening of the Eustachian tube, myringotomy or an increase in the perfusion pressure of the vasa nervorum will re-establish the nerve's circulation and restore normal nerve function.Reference Rutten and Kunst3 If a prolonged period of nerve ischaemia ensues however, then demyelination and interruption of the facial nerve axons may occur, causing degeneration.Reference Molvaer and Eidsvik1 If pressure interferes with the blood supply of the facial nerve for a sufficiently long time, the nerve may be destroyed and converted to a fibrous cord, with no chance of recovery.Reference Molvaer and Eidsvik1 In cats, the cut-off for irreversible damage was demonstrated to be approximately 3.5 hours.Reference Roffman, Babin and Ryu26
Only 23 subjects (including our case) with aviation induced facial nerve baroparesis are reported in the literature (Table 1). However, it has been suggested that this condition may be under-reported and sometimes misdiagnosed.Reference Molvaer and Eidsvik1,Reference Ah-See, Shakeel, Maini and Hussain15 In 22 of the reported 23 cases, facial nerve baroparesis resolved spontaneously either during flight or during descent of the flight. As such, these cases do not need immediate medical attention as they are transient in character; however, they may be mistaken for cerebrovascular transient ischaemic attacks or other neurological events. Treatment was therefore aimed at preventing recurrence. All except one of the cases reported normalisation as their outcome.
Several treatments have been recommended for facial nerve baroparesis. Patients should be advised to attempt self-equalisation techniques during the flight in an attempt to open up their Eustachian tubes and relieve middle-ear pressure. Prophylactic and therapeutic use of nasal decongestants to prevent or treat middle-ear barotrauma have been recommended and were used in three of the reported cases to good effect.Reference Rutten and Kunst3,Reference Cumming, Matchett, Meller and Saxby5 Oral antihistamines have likewise been recommended in patients with allergies for the prevention of barotrauma.Reference Mirza and Richardson21 In selected cases of recurrent facial nerve baroparesis, ventilation tube insertion would seem to be beneficial. There were no further episodes of facial nerve palsy in cases treated with ventilation tube insertion.Reference Silverstein18,Reference Westerman, Fine and Gilbert33 The senior author's experience supports this, with the patient developing no further facial palsies whilst the ventilation tube was in situ. In the case of persistent facial nerve dysfunction after descent, urgent myringotomy with ventilation tube insertion is indicated to prevent irreversible damage to the facial nerve. Oral steroids have been recommended in cases in which persistent facial paralysis and hearing loss occur.Reference Ardehali, Yazdani and Heidarali4
Conclusion
Facial baroparesis is a rare, mostly temporary paresis of the VIIth cranial nerve, which occurs in both aviation and diving. In this paper, we discussed cases associated with flying only and have added 1 case to the 19 cases already in the literature. While the most widely accepted aetiology is ischaemic neuropraxia, other hypotheses have been suggested. Reported cases usually describe facial paresis, which lasts from a few minutes to several hours; however, one case reported a paresis gradually resolving over two and a half months. Treatment modalities suggested include self-equalisation techniques, nasal decongestants, oral antihistamines, oral steroids and ventilation tube insertion. In the event of long-standing facial nerve palsy after descent of the aircraft, urgent myringotomy should be performed to prevent permanent facial nerve damage. Our literature review demonstrated no current evidence-based management protocol for this condition, and more cases are needed in order to increase our understanding and management of this rare condition.
Competing interests
None declared
