In clinical otolaryngology, the term “parapharyngeal space” has been used inclusively to refer to what is described above as the PPS and the carotid space. In this nomenclature scheme, the two distinct compartments were identified as the prestyloid and poststyloid compartments, respectively. For the purposes of consistency in this discussion, the terms PPS (prestyloid compartment) and carotid space (poststyloid compartment) will be used.

The parapharyngeal space (PPS) can be thought of as an inverted pyramid extending from the inferior surface of the petrous bone to the lesser horn of the hyoid bone. Its central location in the deep spaces of the suprahyoid neck results in a complex fascial anatomy (Fig. 1.1). The PPS extends medially to the aerodigestive tract; the visceral fascia is its medial border. The visceral fascia (deepest layer of MLDCF) adheres to the visceral structures of the neck, including the pharynx, larynx, esophagus, trachea, thyroid gland, and parathyroid glands. Anteriorly and laterally, the PPS abuts the masticator and parotid spaces, respectively. The SLDCF splits to envelop these spaces. As such, the anterior and lateral walls of the parapharyngeal space are leaflets of the SLDCF. The DLDCF of the carotid space and that of the lateral margin of the retropharyngeal space demarcate the posterior margin of the PPS. Some texts indicate that there is no fascial separation between the PPS and the submandibular space, allowing direct spread of infection or tumor between the two spaces.

The PPS is predominantly comprised of fat, making it readily identifiable on CT and MRI (Fig. 1.1). Also present are small branches of the mandibular division of the trigeminal nerve (V3), the ascending pharyngeal artery, the internal maxillary artery, lymph nodes, and minor salivary rests (Box 1.1).

When a mass arises in an adjacent space, the fat in the parapharyngeal space can become deformed and displaced. Observation of the direction in which the mass displaces the parapharyngeal fat can help determine the origin of the mass (Fig. 1.2). Box 1.2 summarizes the expected effect of adjacent masses on the parapharyngeal space.

Primary masses of the PPS are rare. More commonly, tumors arise from the deep lobe of the parotid gland or from an adjacent space and extend into the PPS. The most common masses involving the parapharyngeal and the adjacent spaces are listed in Box 1.1.

Of the primary PPS neoplasms, benign tumors account for 80 %. The most common is a pleomorphic adenoma (benign mixed tumor) arising from a minor salivary gland rest. As shown in Fig. 1.3, pleomorphic adenomas are typically well marginated and bright on T2 with heterogeneous enhancement. It is important to distinguish a pleomorphic adenoma arising from a minor salivary gland rest in the PPS from those arising from the deep lobe of parotid gland as this has significant surgical implications: masses centered in the PPS should be fully encompassed by PPS fat. The presence of small branches from V3 gives rise to neurogenic tumors (schwannomas and neurofibromas), which tend to be well defined, but are typically less bright on T2 than pleomorphic adenomas; they may, however, be indistinguishable. This distinction is not vital, as long as the radiologist is confidently able to place the mass in the PPS. Lipomas are rare encapsulated fatty tumors that follow fat signal and density on all MR sequences and CT, respectively. Malignant neoplasms, such as adenoid cystic carcinoma and mucoepidermoid carcinoma are uncommon. As in other spaces, malignant neoplasms are infiltrative and demonstrate avid, though not always uniform, enhancement.