Cranial nerve injuries from a laryngeal mask airway
2009-10-06

Editor, The laryngeal mask airway is a well tolerated, supraglottic airway device for general anaesthesia that provides an alternative to tracheal tubes. Complications include oropharyngeal bleeding, vocal cord palsy, pulmonary aspiration, dental damage and the inability to properly ventilate the patient for different reasons. Isolated cranial nerve injuries of the lingual, hypoglossal and recurrent laryngeal nerve have been reported in a few case reports and were related to suboptimal use of the laryngeal mask airway [1]. We report the case of a 32-year-old female patient (body mass index 29.8 kg m−2) who had multiple cranial nerve injuries after the use of a laryngeal mask airway during otherwise uneventful anaesthesia for knee arthroscopy. The patient presented with damage of the left retropatellar cartilage. In the past, she had had multiple surgical interventions with different forms of anaesthesia. On the day of surgery, the patient received midazolam 3.75 mg per os 1 h before the start of anaesthesia. Anaesthesia was induced with sufentanil 0.1 μg kg−1 and propofol 4 mg kg−1. The laryngeal mask airway (4) was inserted with an Esmarch manoeuvre after being lubricated with a water-based gel. The cuff was inflated to 50 cmH2O. After 1 h of surgery, the laryngeal mask airway was withdrawn without force after the cuff had been deflated. Back on the ward, the patient reported of numbness of the left half of the tongue. Clinical examination revealed the loss of taste in the left tongue, loss of sensory function in the anterior tongue, a tongue deviation to the right side, uvular deviation to the left side and a deficit of the hypopharyngeal reflex. No specific treatment was initiated. Four days later, cranial nerve function had been recovered and the patient was discharged. Here we report the combined injuries of three cranial nerves including the glossopharyngeal nerve caused by a laryngeal mask airway after unproblematic placement of the device. The patient developed transient nerve injuries of the left lingual nerve, the right hypoglossal nerve and the right glossopharyngeal nerve. A few similar reports have described isolated lesions of the lingual, hypoglossal and recurrent laryngeal nerves [1], but until now damage to the glossopharyngeal nerve has been reported only in connection with a cuffed oropharyngeal airway [2]. The lesion of the lingual nerve was most probably caused by the pressure of the rigid tube of the laryngeal mask on the hard palate as the lingual nerve enters the mouth below the inferior border of the superior constrictor and continues against the periosteum of the mandible posterior to the third molar [1,3,4]. The lesion of the hypoglossal nerve was caused by the inflated cuff and is due to compression of the nerve when it crosses the hyoid bone [3]. The recurrent laryngeal nerve is at risk of compression as it enters the larynx, where it passes under the lower border of the inferior constrictor; injury can result in dysarthria, stridor or postoperative aspiration [1]. The glossopharyngeal nerve could also be vulnerable to compression from the cuff where the nerve passes between the superior and middle constrictor muscles near the hyoid bone [5,6]. Previously, long duration of laryngeal mask placement was thought to be responsible for the described cranial nerve lesions [7]. In our case, however, the mask was in place for only 60 min. Another possibility is that a haematoma caused by forced insertion or bleeding into the tissue could lead to compression of neural structures. And, finally, chemical neuritis through the use of aggressive lubricants or cleaning fluids could result in cranial nerve damage. In our case, we hypothesize that the multiple cranial nerve damage developed from a subluxation of the temporomandibular joint, which might have caused a stretch trauma of the glossopharyngeal, hypoglossal and lingual nerves. Anatomically, these cranial nerves lie close to the mandibula and the temporomandibular joint.