Abstract
Mucoepidermoid carcinoma is the most common malignant salivary gland tumour. Central mucoepidermoid carcinomas (CMC) are an exceedingly rare subgroup, representing 2–4% of all cases. The authors report on a case of CMC in a patient who presented with trigeminal neuropathy, trismus and distant metastasis. The possible pathogenesis of CMC and criteria for diagnosis are discussed.
Mucoepidermoid carcinoma is the most common malignant salivary gland tumour. These tumours mainly arise in the parotid gland and account for about 15% of all salivary gland tumours. Central mucoepidermoid carcinomas (CMC) are an exceedingly rare subgroup, representing 2–4% of all cases.
In August 2008, a 55-year-old man was referred to the Medical Admissions Unit by the Emergency Department with a ‘pre-syncopal’ episode and ‘numbness’ to the right side of his tongue and lip, along with altered taste sensation to the right side of his tongue. His electrocardiogram (ECG) was normal and a magnetic resonance image (MRI) of the brain and stem was organised for an outpatient visit. The MRI only imaged the skull base and excluded the mandible. This scan was normal and patient was discharged.
In October 2009, the same patient was referred to the Oral and Maxillofacial unit by his dentist with increased pain to the right side of his mandible and complete paraesthesia to the lower right lip. He reported he had limited jaw movement and had suffered persistent agonizing headaches over the last few months. On examination, the patient had trismus, but there was no apparent intra-oral pathology. An orthopantogram (OPG) ( Fig. 1 ) demonstrated an unerupted lower right third molar with 1 cm diameter radiolucency around the crown of the tooth. The radiolucency was overlying the inferior dental canal and had irregular ill-defined borders. A computed tomography (CT) scan of the thorax, abdomen and pelvis was performed and demonstrated multiple ‘cannon ball’ pulmonary lesions, representing metastases. The MRI of the right mandibular area demonstrated normal overlying mucosa, but a high signal was seen in the mandible on T2-weighted images, extending from the anterior body up to the angle and into the ascending ramus, with perforation of the lateral cortex. There were a number of suspicious nodes in the neck. A repeat MRI of the brain showed at least 6 new ring-enhanced lesions scattered throughout the brain on T2-weighted images. They looked like cystic lesions, highly suspicious of cystic metastases ( Fig. 2 ).
The patient underwent removal of the third molar and wide local resection of the associated abnormal bone. Histology from the right angle of the mandible confirmed normal superficial oral mucosa but the deep tissue of the mandible revealed the lesion to be mucoepidermoid carcinoma. The patient was treated with palliative radiotherapy to the brain. At the time of submitting this paper the patient is alive.
Discussion
Mucoepidermoid carcinoma is the second most common malignant salivary neoplasm which accounts for 15% of all salivary gland tumours . Just over 50% occur in the major salivary glands with 45% seen in the parotid gland. The most common minor salivary gland site is in the palate. Mucoepidermoid carcinoma is a malignant epithelial tumour composed of mucous, epidermoid, intermediate, columnar, and clear and occasionally oncocytic cells ( Fig. 3 ). It often demonstrates prominent cystic growth and is divided into low, intermediate and high grade types on the basis of morphological and cytologic features. This case is a rare subtype known as a central mucoepidermoid carcinoma, which represents 2–4% of mucoepidermoid carcinomas. The commonest site of presentation is in the third molar region of the mandible, and only rarely is the anterior segment affected. They occur in the maxilla, where they tend to occur in the molar region, but they are four times more common in the mandible . These tumours arise in tissue that does not normally contain salivary gland tissue, but approximately 50% of CMC are associated with an unerupted tooth.
