The suprahyoid neck is divided into several important spaces. These spaces are divided by layers of the deep cervical fascia. Some of these spaces span both the suprahyoid and infrahyoid neck but are primarily discussed here. Placing pathology to a space is extremely useful since the differential diagnosis is highly dependent on the space of origin.

Centrally on each side, there is the 'prestyloid' parapharyngeal space (PPS), which primarily contains fat (but also small vessels, nerves, and ectopic salivary tissue). The PPS extends from the skull base to the cricoid. It is surrounded circumferentially in the axial plane by other spaces. The primary importance of the PPS in most cases is that the direction of displacement from the central location can be an important clue to the space of origin of mass. Primary PPS masses are uncommon but include salivary gland tumors arising from the ectopic tissue.

The visceral space encompasses the nasopharynx and oropharynx in the suprahyoid neck and hypopharynx (along with the thyroid gland and larynx in the infrahyoid neck. The most common tumor categories to arise in this space reflects the major tissues contained: lymphoma (lymphoid tissue (Waldeyer's ring)), epithelial tumors such as squamous cell carcinoma (epithelial tissues) and salivary gland tumors (minor salivary glands). Masses within the visceral space displace the PPS laterally.

Key components of the nasopharynx are the nasopharyngeal tonsil, torus tubarius, the posterolateral pharyngeal recess (fossa of Rosenmuller), and Eustachian tube orifice. The posterolateral pharyngeal recess is a common location for nasopharyngeal carcinoma. Such carcinoma can obstruct the Eustachian tube orifice, resulting in ipsilateral mastoid/middle ear effusion, or spread laterally through the sinus of Morgagni (a defect in the pharyngobasilar fascia around the Eustachian tube) to the PPS.

The carotid space (a.k.a. post-styloid PPS) is located posterior to the PPS and lateral to the retropharyngeal/prevertebral spaces. This extends from the skull base to the aortic arch. The main contents include the carotid arteries, jugular vein, sympathetic nerves along the ICA, vagus nerve posterior to the vessels, and lymph nodes. Primary masses displace the PPS anteriorly and can be further differentiated based on location relative to the vessels. For example, carotid bulb tumors splay the proximal ICA and ECA; glomus vagale tumors typically displace all vessels anteriorly.

The masticator space contains the muscles of mastication, the mandible, and trigeminal nerve V3 branches. The most common pathologies include infection (spread of dental infection), rhabdomyosarcoma (in children), and perineural spread along V3 branches. Masses displace the PPS posteromedially. The region superior to the zygomatic arch may be referred to as the suprazygomatic masticator space.

The parotid space contains the parotid gland, retromandibular vein, ECA branches, lymph nodes, the facial nerve which exits the stylomastoid foramen, and the auriculotemporal branch of V3. The facial nerve is positioned just lateral to the retromandibular vein and divides the parotid gland into so-called superficial and deep lobes. Deep parotid lobe masses can be difficult to localize, but will often widen the stylomandibular distance (notch). Key pathology includes parotitis, lymphadenopathy, and parotid gland tumors. In parotitis, it is critical to search for a sialolith in the parotid duct (Stensen duct), which pierces the buccinator. Evaluation for perineural spread along the facial and/or auriculotemporal nerve in the setting of tumor is crucial. The auriculotemporal nerve is one area that perineural spread can occur between cranial nerve V and VII branches.

Other important spaces posterior to the pharynx and anterior to the spine include the retropharyngeal space, danger space, and the prevertebral space. The retropharyngeal space and danger space are difficult to distinguish on imaging, but separated by the thin alar fascia. The 'danger' space is located posterior to the alar fascia and forms a connection with the mediastinum (and potential conduit of spread of pathology). Common pathology of these two related spaces include bland effusion, phlegmon, abscesses, and lymphadenopathy. If restricted to the retropharyngeal/danger space, these will be located anterior to the longus coli/capitus complex.

In distinction, primary pathology of the prevertebral space often arises from the vertebral column and involves or is deep to the longus coli/capitus complex. Invasion of the prevertebral space is one feature that typically upgrade head and neck cancers to T stage pT4b (very advanced local disease) and cancer stage to at least Stage IVB.

Spaces related to the mouth include the oral cavity, submandibular space, and sublingual space. The oral cavity extends from the lips anteriorly to the anterior arch of the palatine tonsils and circumvallate papillae posteriorly; the superior border is the hard palate; the inferior border is the tongue and floor, and lateral border is the buccal mucosa/cheeks. The oral cavity contains the oral (mobile) tongue. Recall the base of tongue is located posteriorly and is part of the oropharynx. The oral tongue has intrinsic and extrinsic muscles. Two extrinsic muscles, the hyoglossus/genioglossus complex, form the root of tongue.

retromolar trigone, floor of mouth.

Calcific tendinitis of the longus coli, abscess, bland effusion (e.g. thrombophlebitis or radiation), phlegmon.

References

Meesa IR et al. A simplified approach to the spaces of the suprahyoid neck. Appl Radiol 2017;46(4):6-14