30
ANATOMY FOR DIAGNOSTIC IMAGING
behind, and communicates with, the nasal and oral cavities, providing a common entrance to the respiratory and gastrointestinal tracts. The pharynx has three coats. Innermost is the mucous coat, which is continuous with the mucosa of the oral and nasal cavities. The submucous layer is the pharyngobasilar fascia and forms a thick fibrous coat, which gives the pharynx its shape. It is attached superiorly to the base of the skull and is continuous with the fibrous material filling the foramen lacerum. It is pierced only by the eustachian tube. The outermost coat is formed by the three constrictor muscles. These fan out laterally from their anterior attachments to insert into a posterior raphe, which is attached superiorly to the base of the skull anterior to the foramen magnum and is continuous with the oesophagus inferiorly. The superior pharyngeal constrictor is attached anteriorly to the inferior extension of the medial pterygoid plate (the pterygoid hamulus), and to a raphe joining this to the inner surface of the mandible. The middle constrictor muscle is attached anteriorly to the hyoid bone and lower part of the stylohyoid ligament. Its upper fibres overlap the superior constrictor muscle superficially. The inferior constrictor muscle attaches anteriorly to cricoid and thyroid cartilages and overlaps the inferior part of the middle constrictor. Its lowermost fibres are horizontally orientated and merge with the circular fibres of the oesophagus. A gap between the oblique and horizontal fibres of the inferior constrictor may become a weak spot known as Killian's dehiscence, through which a pharyngeal pouch may emerge. The constrictor muscles are covered by loose buccopharyngeal fascia, which is continuous with the fascia covering the buccinator muscle.
Fig. 1.35 CT scan of nasopharynx: axial section.
10. Lateral pterygoid plate
2 3 . Nasal bone
The pharynx lies behind the nasal and oral cavities and the larynx and is divided accordingly into the nasopharynx, oropharynx, and hypo- or laryngopharynx. Posteriorly it lies on the upper cervical vertebrae and their prevertebral muscles.
11. Lateral pterygoid muscle
24. Nasal septum
THE NASOPHARYNX AND RELATED SPACES (Figs 1.35-1.37) The nasopharynx The nasopharynx is that part of the pharynx between the posterior choanae and the lower limit of the soft palate. It communicates anteriorly with the nasal cavity and inferiorly with the oropharynx. The roof of the nasopharynx is bound to the inferior surface of the sphenoid and clivus by the pharyngobasilar fascia. It has the parapharyngeal space and the deep soft tissues of the infratemporal space laterally. Posteriorly it lies on the upper cervical vertebrae and longus collis and capitus, and posterolaterally the styloid muscles separate it from the carotid sheath. The eustachian tube opens on to the lateral wall of the nasopharynx on either side, piercing the pharyngobasilar fascia. This opening has a posterior ridge formed by the
1. Nasopharyngeal space
13. Styloid process
2. Prevertebral muscle
14. Internal carotid artery
3. Lateral pharyngeal recess,
15. Internal jugular vein
fossa of Rosenmueller
16. Parotid gland
4. Cartilaginous end of
17. Ramus of mandible
eustachian tube
18. Infratemporal space
5. Opening of eustachian tube 6. Torus tubarius
19. Coronoid process of mandible and masseter muscle
7. Pterygoid bone
20. Zygoma
8. Medial pterygoid plate
21. Maxillary sinus
9. Medial pterygoid muscle
2 2 . Polyp in left maxillary sinus
12. Parapharyngeal space
cartilaginous end of the tube known as the torus tubarious. Behind these ridges are the paired lateral pharyngeal recesses, also known as the fossae of Rosenmueller. The muscular layer of the nasopharynx is formed by the superior pharyngeal constrictor. The palatal muscles arise from the base of the skull on either side of the eustachian tube. The levator veli palatini accompanies the eustachian tube, piercing the pharyngobasilar fascia before inserting into the posterior part of the soft palate. The tensor veli palatini runs around the nasopharynx and hooks around the pterygoid hamulus before inserting into the membranous part of the soft palate. These muscles, along with those in the palatopharyngeal arch, elevate the soft palate, closing it against a muscular ridge in the superior constrictor muscle (known as the Passavant ridge) during deglutition, thereby isolating the nasopharynx from the oropharynx. Lymphoid tissue lines the nasopharynx, and this is prominent superiorly where it forms the adenoids. The lymphatic drainage of the nasopharynx and related spaces is to the jugular chain of lymph nodes, especially the jugulodigastric node, which lies at the angle of the mandible.
