eRadiograph Volume 7: Imaging of Oral Cavity | Page 164

Pharyngeal mucosal space The pharyngeal mucosal space represents the mucosal surface of the oropharynx and nasopharynx as well as their muscles, bounded by the buccopharyngeal fascia externally. Extent and Anatomy This space lies anteromedial to the parapharyngeal space, anterior to the retropharyngeal space. Medial to carotid space. It extends from the skull base to the cricoid cartilage. Superiorly it communicates with the foramen lacerum.  This provides a perineural access for nasopharyngeal carcinomas to extend intracranially. Nasopharynx The nasopharynx is the superior most portion of the tubular pharynx located immediately caudal to the central skull base extending inferiorly to the level of the soft palate.  Below this level lies the oropharynx.  Anteriorly the nasopharynx communicates with the nasal cavity via the choanae. The posterior and posteriolateral wall of the nasopharynx and oropharynx are contiguous. Posterior to the nasopharynx lies the clivus. The nasopharynx consists of three layers – an inner mucous lining of ciliated pseudo stratified epithelum. This mucosa has one protrusion known as torus tubaris which is the cartilaginous projection of the Eustachian tube. On either side of this projection are recesses. The anterior recess is for Eustachian tube and the more posterior recess is the lateral pharyngeal recess known as the fossa or Rosenmuller. The Eustachian tube drains and aerates the middle ear.  The fossa of Rosenmuller is a common site for the origin of nasopharyngeal CA. The submucosa contains minor salivary glands, lymphoid tissue of Waldeyer ring (adenoids, palatine and lingual tonsils)  Due to the presence of lymphoid tissue non Hodgkins lymphoma may arise at this site. Lymphoid tissue has a symmetric striated appearance on T2W and contrast MRI due to the presence of lymphoid crypts. The middle layer is a fibrous layer consisting of a tough aponeurosis known as pharyngobasilar fascia which attaches the superior constrictor muscle to the undersurface of the clivus. This may be visualized as a thin dark line on T2 W axial MRI.  There is a small hiatus in the pharyngobasilar fascia at its attachment to the skull base allowing the Eustachian tube and levator veli palatani muscles to pass.  The site of perforation is known as the sinus of morgagni. Since the pharyngobasilar fascia is pierced at this location disease processes can extend to the skull base via this hiatus. These two muscles are identified on the lateral nasopharyngeal wall on MRI. 164 Pharyngeal Mucosal Space Contents The contents of the pharyngeal mucosal space from inner to outer margin are the pharyngeal mucosa, submucosa, pharyngobasilar fascia, muscles and its covering the buccopharyngeal fascia.