HYPOGLOSSAL nerve palsy is a rare occurrence usually associated with other cranial nerve palsies and long tract signs. Twelfth-nerve palsies have frequently been reported in association with the following conditions: tumors (metastatic, chordoma, nasopharyngeal mass, lymphoma), head trauma, stroke, hysteria, multiple sclerosis, carotid endarterectomy, Guillain-Barré syndrome, and infection. Hypoglossal nerve palsies usually present unilaterally, associated with involvement of other cranial nerves and neurologic structures, and present as signs rather than symptoms. 1,2 

Isolated bilateral 12th-nerve palsy is an unusual finding. These patients have dysarthria; accumulation of saliva, forcing the patient to swallow frequently; dysphagia due to inability to propel food to the pharynx; and respiratory embarrassment due to prolapse of the tongue into the pharynx (mainly in the supine position). Examination shows bilateral tongue atrophy and fasciculations.

We describe a patient with isolated bilateral 12th-nerve paralysis complicating transoral intubation for general anesthesia presenting with breathing distress and airway obstruction after extubation. To our knowledge, a bilateral hypoglossal nerve palsy after transoral intubation has not been reported previously.

A 63-yr-old man with a history of hypertension and an abdominal aortic aneurysm was admitted to hospital for sudden onset of abdominal pain. Examination showed that the patient was hypotensive (blood pressure, 90/60 mmHg), diaphoretic, and tachycardic. A diagnosis of rupture of the aneurysm and hypovolemic shock (systolic arterial pressure decreasing to 50 mmHg) was made, requiring emergency surgery and rapid infusion of plasma expanders, platelets, and erythrocytes. The patient underwent aneurysm excision and replacement with a graft via  a standard open procedure. Administration of general anesthesia and endotracheal intubation proceeded without difficulty: laryngoscopy was performed with a Macintosh blade, and an 8-mm-diameter endotracheal tube was inserted atraumatically on the first try and was then fixed to the right angle of the mouth. The cuff of the tube was inflated and attached to a pressure gauge to keep the cuff pressure less than 20 cm H2O. No adjustment of cuff volume was made postoperatively. A Guedel airway was in place during surgery. Surgery was performed with the patient in the supine position and lasted 240 min.

The patient tolerated the procedure well. He was taken to the intensive care unit and underwent mechanical ventilation. The patient was sedated postoperatively with morphine, and there was no significant period of coughing or gagging before the first attempted extubation. Four days after surgery, before removal of the endotracheal tube, the patient was breathing adequately. He was weaned from ventilatory support gradually, but after extubation, respiratory obstruction, dysphagia, dysarthria, and pooling of saliva in the mouth developed. He underwent reintubation. The patient continued to have airway obstruction each time extubation was attempted. The situation remained unchanged 2 weeks after surgery, so a tracheostomy was performed, and nasogastric tube feeding was started.

Neurologic assessment was performed 5 days after surgery. Examination revealed pronounced dysarthria and slurred speech and inability to move and protrude his tongue, which was observed at rest in the floor of the mouth. Bilateral atrophy and fasciculations, dysphagia, and pooling of saliva in the mouth with frequent swallowing were noted. Detailed neurologic examination revealed no other evidence of central or cranial nerve involvement. Therefore, a diagnosis of isolated bilateral hypoglossal nerve paralysis was considered. The electromyographic examination (6 days after surgery) showed denervation of the tongue with minimal active contraction of single motor units, fibrillation potentials, and positive sharp waves.

Laboratory tests, including serologic studies to exclude infections, such as herpes viruses or Borreliae , yielded normal results. Radiography of the skull and the chest, computerized tomography of the head, and magnetic resonance imaging of the brain and cervical spine showed no abnormalities.

No specific treatment was administered. The hypoglossal palsy improved slowly. The patient was able to extend his tongue symmetrically 1 month after surgery. He was placed on a soft food diet and experienced no difficulty with swallowing either saliva or food 2 months after surgery. Closing of the tracheostomy was tolerated 3 months after surgery. Three months later, mobility of the tongue was normal. In an electromyogram 8 months after the initial episode, normal potentials were observed on minimal and on maximal contractions.

Palsies of the hypoglossal cranial nerve rarely occur in isolation and are usually accompanied by other cranial neuropathies. Keane 1summarized his experience with 100 cases of 12th cranial nerve palsy encountered over a 26-yr period. In the majority, the 12th cranial nerve involvement was of minor discomfort to the patient. Twelfth cranial nerve palsies usually presented as signs rather than symptoms, but their appearance was ominous (tumors were involved in almost half of the cases).

Isolated hypoglossal nerve palsies are an uncommon complication after otolaryngologic procedures, such as prolonged direct laryngoscopy, 3,4tonsillectomy, 5aortic arch surgery, 6use of a laryngeal mask airway, 7extraction of a tooth, 8or transoral intubation for general anesthesia. 9These patients usually experience an excellent outcome. To our knowledge, development of an isolated severe bilateral 12th cranial nerve palsy as a result of transoral intubation for general anesthesia has not been previously reported. The following mechanisms of injury have been proposed in published cases: pressure to the lateral roots of the tongue during routine intubation using the McIntosh blade with hyperextension of the head, 5and a difficult intubation in which cricoid pressure or forceful laryngoscopy are used, 10which can result in hypoglossal nerve injury.

Anatomically, the hypoglossal nerve rests on the most lateral prominence of the anterior surface of the transverse process of C1. If hyperextension of this joint occurs, it is possible that this nerve would be stretched against this prominence. 8This case does not follow this pattern, but the mechanism has been reported frequently in cases of traumatically induced hypoglossal nerve palsy in which initial plain radiographs and computed tomography scans have failed to show any causative lesion. 11Inadvertent extubation of the trachea with the cuff inflated, leading to compression and stretch of the nerve against the greater horn of the hyoid bone, has been postulated as the cause of the hypoglossal palsy. 12Two factors have been reported influencing 12th-nerve damage: a calcified ligamentum stylohyoideum 9and the presence of a skull base malformation. 13Both were excluded in this patient. There was no clear mechanism of injury to the hypoglossal nerves in this patient. Because all other nerves were spared and the computed tomography scan and magnetic resonance image of the brain were normal, intracranial pathology was unlikely. We postulate that low blood pressure and prolonged but unnoticed overinflation of an endotracheal cuff resting high in the larynx, just below the cords, might have been a source of bilateral nerve compression. A change in the position of the neck at some point, compression by the endotracheal tube, and pressure to the lateral roots of the tongue with the McIntosh blade could be additional mechanisms. The progressive recovery of function suggests a neuropraxic type of nerve damage.

Isolated bilateral hypoglossal nerve palsy is a rare finding. It should be considered in patients after transoral intubation for general anesthesia who report respiratory obstruction, dysphagia, and dysarthria when extubation is attempted.

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