Introduction
The glossopharyngeal (IXth cranial) nerve is complex, with both sensory and motor functions. It transmits general sensation from the tonsils, pharynx and middle ear; general and taste sensation from the posterior third of the tongue; and visceral sensation from the carotid bodies and sinus. It also supplies motor function to the stylopharyngeus, supplies parasympathetic fibres to the parotid gland via the otic ganglion and contributes to the pharyngeal plexus. Injury to this nerve can therefore result in a variety of symptoms and morbidities.
The glossopharyngeal nerve is particularly prone to injury during tonsillectomy because of its position in the tonsillar bed. Well-recognised symptoms of injury include referred otalgia and transient dysgeusia, usually due to neurapraxia or transient nerve paresis. However, true palsy of the nerve is uncommon and usually unilateral;Reference Uzun, Adali and Karasalihoglu1 thus, bilateral palsy is even rarer. We present a case of bilateral nerve palsy in conjunction with palatal weakness, and discuss the challenges of managing such a difficult complication. To our knowledge, this complication has been reported only once before.
Case report
A 31-year-old Caucasian woman underwent bipolar dissection tonsillectomy for recurrent tonsillitis with no intra-operative complications. As the operation was performed at a different institution, specific intra-operative technical details of how the dissection was performed were not available. On post-operative day one, the patient began experiencing dysgeusia, manifested as all food having a bad taste, particularly sweet substances. She also began experiencing a strong, unpleasant burning sensation in her mouth, which worsened after brushing her teeth. She returned to her local ENT department on post-operative day 13 and was treated with a tapered regimen of 20 mg/day prednisolone for 5 days, followed by 10 mg/day for 5 days.
On post-operative day 15, she noticed that her soft palate had ‘dropped’ and become dry (xerostomia), resulting in nasal speech and the feeling of a lump in her throat, which caused gagging. Upon examination, her soft palate was seen to be low lying, with the uvula resting on the posterior tongue. It was decided to adopt a watchful waiting approach, based on a presumed diagnosis of bilateral glossopharyngeal nerve neurapraxia (supported by intra-operative photographs obtained from the original hospital; Figure 1) that should resolve with time. However, at follow up on post-operative day 40, her symptoms were persistent and had worsened. She commenced self-medicating for dysgeusia with 50 mg/day zinc sulphate, with little long-term effect.
Intra-operative photographs showing the vulnerability of the glossopharyngeal (IXth cranial) nerve to injury during routine tonsillectomy.
On post-operative day 70, she was referred to speech and language therapists owing to increasing problems with her speech and swallowing secondary to soft palate palsy, which was deemed to be permanent. On day 80, she began snoring and started to experience areas of numbness on her soft palate, the back of her throat and along the dorsum of her tongue, starting from the posterior third and extending along the midline to the tip. She was unable to sense temperature on her posterior tongue when drinking hot or cold fluids and the xerostomia had worsened. Examination revealed the posterior third of her tongue and palate to be very dry; she was prescribed artificial saliva.
By post-operative days 100–120, she had developed troublesome paraesthesia on the dorsum and tip of her tongue and a feeling of ‘tightness’ of the tonsillar fauces. More than one year after the surgery, she requested to be referred to the Smell and Taste Clinic at the James Paget University Hospital, where we first examined her. She was evaluated using a taste strip test and scored 8 out of 32. Correct responses were largely given only for salty stimuli and the pattern was symmetrical for both sides of the tongue. The patient subsequently tried both pentoxifylline and gabapentin treatments, without success. With respect to her snoring, the patient is currently awaiting assessment for coblation palatoplasty at the Snoring and Sleep Disorders Clinic at the James Paget University Hospital.
Discussion
The glossopharyngeal nerve has complex functions; therefore, its injury can result in a plethora of symptomatology. Dysgeusia usually results from injury to the lingual branch of the glossopharyngeal nerve, which innervates taste receptors in the posterior third of the tongue. However, injury to the tonsillar branches and soft palate is also thought to contribute.Reference Scinska, Jodkowska, Korkosz, Kukwa and Sienkiewicz-Jarosz2 Dysgeusia can result in a very poor quality of life. In 2002, Ohtsuka et al. made an anatomical study of the lingual branch of the glossopharyngeal nerve in 107 tonsillar fossae of 83 cadavers.Reference Ohtsuka, Tomita and Murakami3 They showed that in approximately a quarter of the cases, the lingual branch of the glossopharyngeal nerve travelled inferiorly to the styloglossus muscle and laterally to the superior constrictor pharyngeal muscle over its whole course to the base of the tongue such that the palatine tonsil was clearly separated from the lingual branch of the glossopharyngeal nerve. In just over half of the cases, the muscle lining of the tonsillar bed was discontinuous, and thin muscle bundles derived from the stylopharyngeus (palatopharyngeus or superior constrictor pharyngeal muscle) partially covered the tonsillar capsule. In the remainder, the lingual branch of the glossopharyngeal nerve was firmly adherent to the tonsillar capsule because of the complete absence of muscles lining the tonsillar bed. The intra-operative findings place our patient in the latter category: despite dissection within the correct planes, there was almost complete exposure of the nerve near the tongue base upon removal of the tonsils. The relatively unprotected state of the nerve could have rendered it more susceptible to thermal and traumatic injury. In 2004, also through cadaveric dissections (20 nerves in 10 cadavers), Ford and Cruz localised the glossopharyngeal nerve and its lingual branch more specifically: the former is a mean distance of 10.7 mm from the postero-superior tonsillar fossa and its main trunk, and the latter a mean distance of 6.5 mm from the postero-inferior tonsillar fossa.Reference Ford and Cruz4 This group was the only other to describe bilateral palsy of the glossopharyngeal nerve following tonsillectomy. Magnetic resonance imaging (MRI) of their patient was not performed to rule out other causes. As the patient's symptoms developed immediately after tonsillectomy, surgery was presumed to be the direct cause; therefore, MRI was not performed. However, where there is doubt about the cause of dysgeusia, MRI is the investigation of choice.
The patient's low-lying palate is likely to result from injury to the glossopharyngeal nerve contributions to the pharyngeal plexus. This plexus, which also receives fibres from the vagus nerve and the cranial part of the hypoglossal nerve, provides sensation to the oro- and laryngopharynx and innervates most of the pharyngeal muscles. An exception is the stylopharyngeus, which is solely innervated by the glossopharyngeal nerve. Thus, injury to this plexus during tonsillectomy can lead to velopharyngeal insufficiency.Reference Haapanen, Ignatius, Rihkanen and Ertama5 The patient's xerostomia was probably due to a lack of the basting effect of the uvula, which coats the posterior oropharynx with saliva.Reference Back, Nadig, Uppal and Coatesworth6
• Bilateral glossopharyngeal nerve palsy is a rare tonsillectomy complication
• Its association with different comorbidities reflects its complex functions
• Knowledge of the anatomical variations in the nerve course within the tonsillar bed can help prevent injury
• Careful dissection within tissue planes close to the tonsil is essential to prevent nerve injury
• If the nerve is suspected of being particularly vulnerable, ‘hot’ dissection methods should be avoided
Overall, it is clear that this patient suffered a disabling neuronal injury for which there is no easy remedy: treatment is largely supportive. Hence, for this type of injury, prevention is always better than cure, highlighting the need for care when using diathermy in the tonsillar bed.
Conclusion
Bilateral glossopharyngeal nerve palsy is an exceedingly rare complication of tonsillectomy. It is associated with a plethora of comorbidities, which reflect the complex functions of the glossopharyngeal nerve. It is important that surgeons performing tonsillectomy are aware of the natural variations in the nerve's anatomical course within the tonsillar bed. Careful dissection within tissue planes close to the tonsil, especially near the tongue base, is essential to prevent nerve injury. Where the nerve is suspected to be particularly vulnerable, ‘hot’ methods of dissection should be avoided wherever possible.
