The nasopharynx and related spaces

behind, and communicates w i t h, 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 w i th 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 w i th 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 w i th 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 w i th 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 w i th the fascia covering the buccinator muscle.

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.

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 w i th the nasal cavity and inferiorly w i th 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

Fig. 1.35 CT scan of nasopharynx: axial section.

1. Nasopharyngeal space 2. Prevertebral muscle 3. Lateral pharyngeal recess, fossa of Rosenmueller 4. Cartilaginous end of eustachian tube 5. Opening of eustachian tube 6. Torus tubarius 7. Pterygoid bone 8. Medial pterygoid plate 9. Medial pterygoid muscle 10. Lateral pterygoid plate 11. Lateral pterygoid muscle 12. Parapharyngeal space 13. Styloid process 14. Internal carotid artery 15. Internal jugular vein 16. Parotid gland 17. Ramus of mandible 18. Infratemporal space 19. Coronoid process of mandible and masseter muscle 20. Zygoma 21. Maxillary sinus 22. Polyp in left maxillary sinus 23. Nasal bone 24. Nasal septum

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 w i th 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.

Fig. 1. 36 Nasopharynx: axial section.

Fig. 1. 37 Infratemporal fossa: axial section.

Spaces related to the nasopharynx

The parapharyngeal space is a slit-like space just lateral to the nasopharynx extending down from the base of the skull. The space is bounded by the buccopharyngeal fascia. This fascial plane separates the pharyngeal muscles from the muscles of mastication (the pterygoids and the deep part of the temporalis muscle). It is loosely applied to allow movement and contains branches of the external carotid artery, pharyngeal veins and mandibular nerve. Posteriorly; it is separated from the carotid sheath by the styloid process and its muscles, and the deep part of the parotid gland lies laterally.

The infratemporal space (Fig. 1. 37) lies lateral to the nasopharynx and paranasopharyngeal space behind the posterior wall of the maxilla. It extends from the base of

the skull to the hyoid bone, and contains the pterygoid muscles. It is continuous superiorly w i th the temporal fossa through the gap between the zygomatic arch and the side of the skull. Medial to this, the roof is formed by the inferior surface of the middle cranial fossa and is pierced by the foramen ovale and foramen spinosum. Laterally, the space is bounded by the zygomatic arch, temporalis muscle, ascending ramus of mandible and its coronoid process. Medially, the space is limited by the lateral pterygoid plate and nasopharynx. The space lies anterior to the deep part of the parotid, the styloid process and its muscles, and the carotid artery and jugular vein.

The anteromedial limit of the infratemporal space is formed by the junction of the lateral pterygoid plate w i th the posteromedial limit of the maxilla superiorly and the posterior border of the perpendicular plate of the palate inferiorly. The anterior and medial walls of the space meet inferiorly but are separated superiorly by the pterygo¬ maxillary fissure, where the pterygoid plates diverge from the posterior wall of the maxilla.

The pterygopalatine fossa is a medial depression of the pterygomaxillary fissure lying just below the apex of the orbit between the pterygoid process and the posterior maxilla. Its medial margin is the perpendicular plate of the palatine bone. It is important as it connects several spaces and may facilitate the spread of pathology between them. It communicates superiorly w i th the orbit through the posterior part of the inferior orbital fissure. The foramen rotundum opens into it superiorly, connecting it w i th the middle cranial fossa. Laterally it communicates freely w i th the infratemporal fossa. Medially the space communicates w i th the nasal cavity via the sphenopalatine foramen in the perpendicular plate of the palatine bone, and with the oral cavity through the greater palatine canal, which runs inferiorly between the palatine bone and the maxilla. The fossa contains the maxillary division of the fifth cranial nerve, which runs through the foramen rotundum and into the orbit via the inferior orbital fissure. It also contains the pterygopalatine segment of the maxillary artery, which makes a characteristic loop and gives off branches to the middle cranial and infratemporal fossae and to the nasal cavity, palate and pharynx.

The oropharynx and laryngopharynx

The oropharynx is the part of the pharynx that extends from the lower part of the soft palate to the epiglottis. It is continuous through the posterior fauces w i th the oral cavity and w i th the laryngopharynx below. It is lined by mucosa which is continuous w i th that of the oral cavity and nasopharynx. Its submucosal layer is continuous with the pharyngobasilar fascia above, and its muscular layer has contributions from the superior constrictor, some of the tongue muscles, and levator and tensor veli palatini.

The laryngopharynx is the part of the pharynx that lies behind the larynx. It extends from the level of the epiglottis to the level of C6, where it continues as the oesophagus. The upper laryngopharynx is moulded around the proximal part of the larynx, forming two deep recesses on either side known as the p i r i f o rm fossae. During deglutition the epiglottis stands erect and conducts fluid and solid boluses along the piriform fossae from the oropharynx to the oesophagus, avoiding the entrance to the larynx.

Cross-sectional anatomy of the nasopharynx

(see Figs 1. 34-1. 36) At the level of the upper nasopharynx, the paired lateral pharyngeal recesses or fossae of Rosenmueller are posterolateral with the torus tubarius anteriorly. The entrance to the eustachian tube forms a recess anterior to the torus on either side. The medial and lateral pterygoid plates and their muscles are anterolateral to the nasopharynx. The lateral pterygoid muscle extends across the infratemporal space to the condyle and neck of the mandible. The parapharyngeal space is posterior to the infratemporal space, lying anterior to the carotid vessels and the styloid process and its muscles. The deep part of the parotid gland is lateral to the parapharyngeal space. The prevertebral muscles and upper cervical spine are posterior. Anteriorly are seen the maxillary antra, w i th the nasal cavity between.

Radiology of the pharynx (Figs 1. 34-1. 38)

Plain films (Fig. 1. 38) Lateral views of the skull and neck demonstrate the softtissue outlines of the pharynx and lateral tomography gives improved separation of the soft-tissue planes.

The posterior wall of the pharynx forms a soft-tissue shadow curving posteroinferiorly below the body of the sphenoid and anterior to the cervical vertebrae. This shadow thins as it passes down anterior to the upper cervical vertebrae, measuring 3 mm anterior to C4. Below this the wall is thicker but should not exceed the AP diameter of the cervical vertebrae. In children, lymphoid tissue results in a relatively thicker posterior wall, measuring up to 5 mm anterior to C4 and up to 12 mm anterior to C6. The lymphoid tissue in the upper posterior part of the nasopharynx (adenoids) may cause a large soft-tissue shadow. It tends to swell down towards the soft palate in young children and may be continuous w i th the pharyngeal tonsils on the lateral walls of the oropharynx and the lingual tonsils on the posterior surface of the tongue, forming a ring of lymphoid tissue known as Waldeyer's ring.

The base of the tongue and the epiglottis, forming the anterior surface of the oropharynx, are also identifiable on lateral radiographs.

The posterior and lateral walls of the nasopharynx may be identified on the basal skull projection and the piriform fossae of the laryngopharynx are seen on AP views of the neck.