Teaching Case

Pharyngeal pain and a left cervical swelling. Swelling was seen to be pushing the soft palate towards the midline at endobuccal clinical examination.

The patient consulted for pharyngeal pain and a left cervical swelling. This swelling was seen to be pushing the soft palate towards the midline at endobuccal clinical examination. CT scan and MRI were performed.

Pleomorphic adenoma is the most common salivary gland tumor and represents about 80% of all benign tumors of the major salivary glands. 84% of them occur in the parotid gland, where 10% arise in the deep lobe. In about two-thirds of these deep lobe tumors the lesion is attached to the parotid gland only by a thin isthmus of tissue and develops in the parapharyngeal space. For the surgeon it is very important to know whether the mass originates in the parotid or in the parapharyngeal space, as this will determine the surgical approach. The tumor presents both on CT an MRI as a sharply delineated, round, oval or lobulated mass in the parapharyngeal space. On CT scan, the tumor is hypodense compared to surrounding parotid parenchyma, and does not enhance significantly on contrast enhanced studies. On MRI, signal intensity is intermediate on T1-weighted images. A mixture of intermediate and high intensity areas is seen on T2-weighted images, the latter corresponding to pockets of mucoid matrix. Study of the interface between the para-pharyngeal space tumor and the parotid gland is essential for revealing its origin. If a fat plane is seen on all axial images, the lesion is extra-parotid in origin. Although the soft tissue detail is better depicted on MR images, thin slices in the axial plane through the tumor should be obtained. In about 20% of cases, the tumor is in fact extra-parotid but it is so large that it obliterates the fat plane by compression or it originates from the gland capsule. In the very rare case of extraparotid tumor with parotid gland invasion, the differential diagnosis should include minor salivary gland tumors, neuromas and glomus tumors.