Teaching Case

Anatomy of the suprahyoid spaces

Modern cross sectional imaging has deeply modified the perception of the anatomy of the head and neck because it permits direct identification of the main deep structures. A reappraisal of the anatomy has been proposed by H.R. Harnsberger (1) and has become common ground among head and neck radiologists (although other descriptions exist (2)). The concept of space is superimposed to the traditional presentation of areas (oropharynx, nasopharynx, oral cavity and pharyngo larynx…). French anatomists originally described these spaces in the nineteenth century (3); they are defined by the course of the three layers of the deep cervical fascia (not directly visualized): superficial layer (investing fascia), middle layer (buccopharyngeal fascia), deep layer (prevertebral fascia). The mucosal space is located on the airway side of the pharynx and therefore is not completely fascia-enclosed. The sublingual and submandibular spaces belong to the oral cavity. The advantage of using this terminology is that it allows describing tumor spread in the deep tissues using precise anatomical landmarks, as well as specific differential diagnoses for each space. Noteworthy is the fact that, in the literature, the term "parapharyngeal space" (or even infratemporal fossa) has been used to describe a large area that includes the carotid space, the masticator space and the small area described by Harnsberger as the parapharyngeal space. This parapharyngeal space is an important landmark with three distinct features: it is central (with respect to the masticator, carotid, and parotid spaces); it is symmetrical, and it is essentially composed of fat, which characteristically exhibits high signal intensity on T1-weighted images and low attenuation on CT. The main characteristic of most of these spaces is their verticality: the carotid, retropharyngeal and perivertebral spaces extend both across the infra and the suprahyoid neck (down to T3 for the retropharyngeal space). The parapharyngeal and masticator spaces are related to the oropharynx and nasopharynx. This substantiates the need to explore any cancer from the skull base to the thoracic inlet. These spaces have been compared to vertical elevator shafts, which represent natural routes for tumor or infectious spread (1). The fascia can be transpierced by malignant tumors; however, these spaces tend, at least initially, to channel tumor growth and to confine even high-grade tumors (4).