Parapharyngeal space tumors: anatomical and image analysis findings

The parapharyngeal space (PS) is defined as the deepest space in the neck and it consists of the pre- and post-styloid regions. PS tumors originating in these regions are thought to dislocate the carotid artery (CA) in either the posterior or anterior direction. To determine the precise anatomy of the PS and its relationship with the CA in diagnostic images, we conducted cadaveric and imagining analysis.

We examined the posterior and lateral aspects of the PS in three cadavers. We also examined 17 patients who suffered from PS tumors, in which the carotid artery was dislocated (CA), then compared the results with surgical and pathological findings.

The anterior part of the PS was mainly composed of fatty tissue and is generally referred to as the pre-styloid region of the PS. In the posterior of this fatty region, blood vessels and nerves were tightly covered with muscles and adjacent fascias to form a compact musculo-fascial structure containing the CA, jugular vein, vagal, glossopharyngeal, accessory and sympathetic nerves, and a portion of the hypoglossal nerves. The hypoglossal nerves emerged from the hypoglossal canal posterior to this structure and coursed behind it, entering it at the upper third of the PS. These anatomical findings indicated that the PS was actually comprises of three regions. Image analysis showed that the CA was dislocated in the postero-lateral direction by a pleomorphic adenoma originating from the parotid gland and by a trigeminal schwannoma, both of which were pre-styloid tumors. On the other hand, the post-styloid tumors did not always dislocate the CA in the anterior direction. Tumors that developed within the musculo-fascial structure such as those of the carotid body tumor or sympathetic nerve schwannoma dislocated the CA from both the antero- to the postero-lateral directions. A hypoglossal nerve schwannoma originating from the most posterior part of the PS, which was behind the musculo-fascial structure dislocated the CA in the anterior direction.

The present findings indicated that the post-styloid region of the PS is considered to consist of two regions. As the CA is a component of this musculo-fascial structure, tumors originating from it that are defined as post-styloid did not always displace the CA in the anterior direction. Such anatomical recognition is helpful for diagnostic imaging of PS tumors.