The Parapharyngeal Compartment and its Fascial Relations

Abstract

Introduction An accurate understanding of the arrangement of cervical fascia and its associated compartments is essential for differential diagnosis, predicting the spread of disease and surgical management. As surgical technology advances it becomes imperative to have a thorough understanding of the anatomy of these compartments. Current descriptions of one such compartment, the parapharyngeal compartment (PPC), are inconsistent in terms of its borders, communications and contents. Methods This thesis comprises two main elements. Firstly, a review of descriptions of cervical fascia in contemporary reference texts recommended by the Royal Australasian College of Surgeons, followed by a detailed review of the scientific and clinical literature. Secondly, an investigation of the anatomy of the PPC utilising a combination of techniques: cadaver dissection of 10 half heads (eight embalmed, two fresh; 3 male, 7 female; mean age 81 years) via several different approaches (lateral to medial, medial to lateral [transoral], and posterior to anterior); serial histological sections in two additional half heads; and magnetic resonance imaging (MRI) of cadaver specimens and 20 patients (9 male, 11 female; mean age 53 years) independently and blindly analysed by an experienced head and neck radiologist and the author to compare fascial arrangements seen on MRI and dissection. Results The current terminology used to describe the cervical fascia and its compartments is replete with confusing synonyms and inconsistencies, creating important interdisciplinary differences in understanding. Analysis of the scientific and clinical literature revealed numerous anatomical controversies relating to the PPC. Dissection findings showed that the PPC has a dihedral shape, tapering to a point superiorly at the skull base, widening in its central portion, and tapering to its inferior limit at the greater cornu of the hyoid bone. The lateral and superior boundary of the PPC was formed by the tensor veli palatini muscle, which was intimately related to the medial pterygoid muscle. Structures lying between the tensor veli palatini and medial pterygoid muscles were contents of the masticator compartment. The carotid sheath formed a distinct, robust fascia separating the PPC and carotid compartment. There was no ‘styloid diaphragm’ encompassing the styloid process and its associated muscles. However, the styloid muscles are key contents of the PPC that can be used to guide surgical dissection. The PPC also contained fat and neurovascular structures. It communicated with the submandibular compartment in all specimens, with the parotid compartment in some, but a communication with the carotid and retropharyngeal compartments was not identified. Conclusions A revised nomenclature underpinned by evidence-based anatomical and radiological findings is proposed in order to enhance understanding of the cervical fascia and its compartments and facilitate clearer interdisciplinary communication. The three-dimensional anatomy of the PPC is complex; it is a deep compartment that is difficult to access and not oriented along traditional imaging planes. This study has clarified the borders, communications and contents of the PPC, which should help to optimise minimally invasive surgical approaches (particularly transoral approaches), intraoperative orientation within the compartment, and reduce the risk of inadvertent damage to regional neurovascular structures