Teaching Case

Patient with progressive dysphagia and a large submucosal oral tumour.

The patient was admitted to the hospital via the emergency department with total dysphagia. He has been experiencing progressive dysphagia since several weeks, and had noted progressive deformity of his face. On admission, a large intra-oral soft tissue swelling was seen on the left side, superficially ulcerated. Some adenopathies were palpated in the neck. A subsequent contrast-enhanced CT study of the head and neck showed the presence of a very large soft tissue tumour centered on the left parapharyngeal space, causing severe narrowing of the oropharyngeal lumen. The lesion appeared inhomogeneously and showed large areas of low density. The mass lesion extended laterally into the infratemporal space, deforming the mandibular ramus, and reached the deep lobe of the parotid gland. The internal carotid artery and internal jugular vein were displaced posterolaterally. Cranially, the lesion extended to the nasopharyngeal level; it also reached against the left pterygoid process and maxillary tuber, causing some erosion of these structures. Caudally, the tongue base appeared compressed but not invaded. No clear separation could be made between the mass lesion and the left submandibular salivary gland, which was enlarged and showed increased contrast enhancement. Thickening of the lateral wall of the left vallecula and left lateral wall of the hypopharynx was noted. Some slightly enlarged lymph nodes were seen along the left internal jugular vein (figures 1-8). Since the lesion could not be well delineated from the surrounding structures, appeared partially necrotic, and showed evidence of bone destruction, the possibility of a malignant lesion was suggested, such as a largely submucosally growing squamous cell carcinoma of pharyngeal origin, an atypical lyphoma, sarcoma or dedifferentiated pleomorphic adenoma. The lesion was surgically approached from anterior by splitting the mandible and soft tissues of the oral cavity; the mass could be removed relatively easily by blunt dissection. Pathological examination revealed a tumour with a variable histological aspect. Some areas contained a lot of polygonal epithelial cells, while others areas appeared myxoid, chondroid or frankly necrotic. The overall picture corresponded with a pleomorphic adenoma; there was no evidence of malignancy.

Pleomorphic adenoma is the most common benign tumor of the salivary glands, and is predominantly encountered in the parotid gland; it occurs less commonly in the submandibular gland and minor salivary glands. Pleomorphic adenoma is more often seen in women and the majority presents in the fifth decade. Histologically, both epithelial and mesenchymal elements are found (hence the name mixed tumours). The CT and MRI appearance of these tumours is variable. They usually appear well circumscribed, but may be lobulated. Tumours of the deep lobe of the parotid gland extend in the parapharyngeal space and become symptomatic when compressing the pharyngeal wall. Sometimes a more unsharp demarcation is noted, related to peritumoural inflammation. Malignant transformation of the epithelial component of a pleomorphic adenoma (called "carcinoma ex pleomorphic adenoma" or "malignant mixed tumour") is the primary reason why all pleomorphic adenomas should be surgically removed. Malignant transformation occurs typically in tumors already present for a very long time, and manifests itself clinically by a sudden increase in tumor volume, sometimes accompanied by pain and facial nerve paralysis. The appearance of a malignant mixed tumour on CT and MRI may be unremarkable compared to the "benign" mixed tumour, or it may show infiltration in the surrounding structures. The parapharyngeal space can be displaced or invaded by pathology arising from the surrounding spaces. Tumours arising from the deep lobe of the parotid gland commonly extend into the prestyloid compartment of the parapharyngeal space. Differentiation from a primary prestyloid lesion may be difficult. The most reliable sign of a primary parapharyngeal tumour is the presence of a fat layer separating the tumour from the deep lobe of the gland. The presented case is atypical, mainly because of the size of the tumour. Although pleomorphic adenoma is the most common tumour of the prestyloid part of the parapharyngeal space, some findings suggested the lesion was of malignant nature. Retrospectively, the bone alterations observed on CT were presumably induced by pressure from the tumour. Similarly, the enlargement and increased enhancement of the left submandibular salivary gland was likely caused by compression on Wharton's duct, leading to retro-obstructive sialadenitis. The poor delineation from a number of structures, such as the pharyngeal walls, was likely due to peritumoural inflammation.