The hypoglossal nerve is responsible for the motor supply to the tongue and innervates the genioglossus, hypoglossus, chondroglossus, inferior belly of the omohyoid and other intrinsic tongue muscles.3
The nuclei of this nerve is situated in the median eminence of the dorsal medulla.4
Although the exact trajectory of this cranial nerve is variable, it can broadly be classified into three distinct parts: cisternal, intracranial and extracranial. The hypoglossal canal is situated above the occipital condyle and lies in an anterolateral direction.5
The purpose of the canal is to transmit the hypoglossal nerve and aids the differentiation the intracranial and extracranial components of the nerve. It opens into the skull base above the anterior third of the condyle.
The tongue has dual supranuclear innervation and consequently unilateral upper motor neuron lesions will not result in lingual weakness.4
In comparison, lower motor neuron lesions can result in atrophy, fasciculations and lingual weakness, as demonstrated in our case report. Skull metastasis causing unilateral hypoglossal nerve palsy has been described in previous studies,1
however, in such cases, the palsy is more commonly found in conjunction with other co-existing cranial nerve palsies. This is largely due to its anatomical relation to other important anatomical structures throughout its course.6
Although tumours account for a substantial proportion of the aetiology of hypoglossal nerve palsies, it is important to exclude other possible causes such as trauma, medullary infarctions, multiple sclerosis, Guillain–Barre neuropathy and infection.6
MRI remains the imaging investigation of choice for visualisation of the hypoglossal canal. In addition electromyography studies of the tongue may be useful in differentiating a flaccid from a spastic paralysis.7
Treatment of the palsy is focused on the management underlying aetiology. The treatment rationale should be made with consideration to the patient's comorbidities and underlying diagnosis. In our case, a surgical intervention was deemed inappropriate and radiotherapy or conservative management were offered to the patient.
- Metastatic infiltration must be a differential for any unilateral cranial nerve palsy.
- Skull metastasis causing unilateral hypoglossal nerve palsy is more commonly found in association with other cranial nerve palsies.
- Treatment of cranial nerve palsies is focused on the management underlying aetiology.
- Management options for a cranial nerve palsy associated with skull metastasis may include neurosurgery, radiotherapy or conservative management.