Head and Neck

8.1 Skull: Anterior View

The prominent bones of the skull in an anterior view are the frontal bone forming the anterior calvarium and roof of each orbit, nasal bones, zygomatic bones of the cheek and lateral wall of the orbit, maxilla, and mandible. The upper part of the nasal septum and middle nasal conchae are parts of the ethmoid bone; the lower part of the septum is the vomer.

8.2 Skull: Anteroposterior X-Ray

The most radiopaque (whitest) parts of the skull in an anterior x-ray are the petrous parts of the temporal bone and the overlap of the molar row of teeth in the maxilla and mandible. The head is positioned to superimpose the petrous temporal on the lower parts of the orbits to better view the inferior parts of the maxillary sinuses for fluid or blood (e.g., from trauma). The most radiolucent (darkest) areas are from air in the mastoid air cells, nasal cavity, and paranasal sinuses (frontal, maxillary, and ethmoid). The ethmoid sinuses appear darker; they are superimposed on the sphenoid sinus behind it. Also note the increase in density where x-rays pass end-on through the flat bones at the periphery of the neurocranium and through the cribriform plate of the ethmoid bone.

8.3 Skull: Anteroposterior Caldwell Projection and Face/Orbit Detail

In an anteroposterior (AP) Caldwell view of the skull, the head is positioned so the petrous parts of the temporal bone are projected through the maxillary sinuses rather than the orbits. Orbital anatomy and pathology are better seen here; maxillary sinuses are better studied (e.g., for “blow-out” fractures) in a conventional film. A dominant feature of the orbit is the superior orbital fissure separating the greater and lesser wings of the sphenoid bone. The lateral surface of the greater wing of the sphenoid bone in the infratemporal fossa behind the orbit is also prominent.

8.4 Skull: Lateral View

The skull consists of a neurocranium surrounding the brain and a viscerocranium consisting of upper and lower jaws and the orbits. The coronal suture separates the frontal and parietal bones, the lambdoidal suture the parietal and occipital bones, and the squamous suture the parietal and temporal bones. Following the contour of the lateral surface of the neurocranium from superficial to deep are three fossae: the temporal fossa for the temporalis muscle; the infratemporal fossa for the pterygoid muscles, mandibular nerve, and maxillary artery; and the pterygopalatine fossa for the maxillary nerve and sphenopalatine artery.

8.5 Skull: Midsagittal Section

The frontal sinus and sphenoidal sinus are cut in section. The sella turcica (“Turkish saddle”) housing the hypophysis of the brain is an important landmark at the junction of the anterior and posterior cranial base between the viscerocranium and neurocranium. The petrous parts of the temporal bone separate the middle and posterior cranial fossae. Grooves on the neurocranial bones contain the middle meningeal vessel branches that supply these bones and the dura mater surrounding the brain.

8.6 Lateral X-Ray

Radiolucent air is apparent as dark areas in the mastoid air cells, paranasal air sinuses, and pharynx. The very dense opacity represents the petrous parts of the temporal bones superimposed on each other. Note the sella turcica, coronal and lambdoidal sutures, and atlas (C1) and axis (C2). The squamosal suture is not visible because the thin bones overlap at their articulation unlike the end-to-end articulations of thicker bone at the other sutures. Also note in the neurocranial bones the outer and inner tables of compact bone and the diploë (trabecular bone) in between.

8.7 Calvaria

The sagittal suture separates the left and right parietal bones. From the frontal bone to the occipital bone is a groove for the superior sagittal sinus, a venous channel in the dura mater that receives blood from the brain. All dural sinuses converge on the internal jugular vein. Depressions on the parietal bone are for arachnoid granulations that penetrate lacunae, lateral extensions of the superior sagittal sinus. This is where cerebrospinal fluid (CSF) reenters the circulation. The parietal foramina and smaller foramina along the midline are for emissary veins that connect the scalp veins to the superior sagittal sinus.

8.8 Cranial Base: Inferior View

The cranial base is the inferior portion of the neurocranium that is the interface with the viscerocranium (facial skeleton) anteriorly. The petrous parts of the temporal bones extend medially between the occipital and sphenoid bones. The inferior extent of the upper jaw is the bony palate consisting of the maxilla and horizontal plate of the palatine bones. Behind the upper jaw are the medial and lateral pterygoid plates of the sphenoid bone. The nasal septum is the vomer posteriorly. Note the mandibular fossa of the temporal bone, the carotid and jugular canals, and the occipital condyles flanking the foramen magnum.

8.9 Cranial Base: Superior View

The lesser wings of the sphenoid divide the anterior and middle cranial fossae, and the petrous parts of the temporal bone separate the middle and posterior cranial fossae. From anterior to posterior along the cranial base are the ethmoid bone (between the orbits), body of the sphenoid bone, and basilar part of the occipital bone. The anterior cranial fossa contains the cribriform plate of the ethmoid bone (for the olfactory nerve). The middle cranial fossa has the three openings for the three divisions of the trigeminal nerve: superior orbital fissure, foramen rotundum, and foramen ovale. Next to the foramen ovale is the foramen spinosum for the middle meningeal artery.

8.10 Skull of the Newborn

A newborn skull has a relatively large neurocranium and a relatively small viscerocranium. The bones of the cranial base develop via endochondral ossification. The flat bones of the neurocranium and the bones of the viscerocranium develop via intramembranous ossification. Unossified portions of the membranes called fontanelles are present anterior and posterior to the sagittal suture to facilitate deformation of the skull passing through the birth canal. The tympanic part of the temporal bone is a ring around the tympanic membrane at birth; there is no external acoustic meatus.

8.11 Mandible

A mandible has a body with dense compact bone, an alveolar part containing the roots of the teeth, and a ramus. Parts of the latter include the angle, condyles for articulation with the temporal bones, and a coronoid process for attachment of the temporalis muscles. With the loss of teeth, the alveolar part of the mandible (and maxilla) is resorbed as a person grows older.

8.12 Cervical Vertebrae and Lateral X-Ray

The seven cervical vertebrae are characterized by transverse foramina in the transverse processes. The first six are for passage of the vertebral arteries; the seventh is vestigial. The articulations between superior and inferior articular processes of adjacent vertebrae (facet joints) are flat and relatively horizontal. In the x-ray note the vertebral canal posterior to the vertebral bodies and the overlap of the dens (odontoid process) of C2 with the occipital condyles of the atlanto-occipital joint. The foramen magnum in this x-ray is obscured by the temporal bones. Its anterior margin can be located by extrapolating the lines of the clivus and the anterior wall of the vertebral canal. The projections of these lines converge on the anterior lip of the foramen magnum.

8.13 Atlas and Axis

With the ability to reconstruct different planes, computed tomography (CT) has largely replaced the open mouth C1/C2 x-rays. The atlas is the widest cervical vertebra, and it lacks a body (centrum). It articulates superiorly with the occipital condyles in a hinge joint for flexion and extension. Together with the skull, it pivots on the dens (odontoid process) of the axis (C2). The dens is the body of C1 that fuses to the axis during development.

8.14 Imaging of Cervical Trauma and Pathology

Part of the systematic search strategy for the study of any image of the spine includes a close inspection of the size, shape, and alignment of the vertebral bodies. The anterior and posterior walls of the vertebral bodies and the posterior wall vertebral canal are known as the anterior spinal line, posterior spinal line, and spinolaminar line, respectively. The patient in A and B was in an automobile accident and has a fracture of the C2 body (hangman’s fracture) and dislocation of the atlantoaxial joint (C1/C2). The dens is below the arch of the atlas, and the vertebral canal and spinal cord are displaced posteriorly below C1. There are also compression fractures of the C5 and C6 vertebral bodies. Note the increased density of bone, the narrow intervertebral space, and the posterior protrusion of bone into the vertebral canal. Other components of a search strategy include the evaluation of vertebral bodies for metastases and lesions (see Chapter 2, p. 27), other components of the vertebrae, plus the soft tissues anterior to the vertebral column (C [a different patient than in A and B]).

8.15 Superficial Vessels, Nerves, and Muscles of the Neck

The large, superficial sternocleidomastoid and trapezius muscles define the contours of the neck. Deep and anterior to the sternocleidomastoid muscle are the thin, infrahyoid “strap” muscles that are named by their attachments: omohyoid (reflected on one side); sternohyoid; and deep to these, the sternothyroid and thyrohyoid muscles. The hyoid bone is at vertebral level C3. At C5 is the thyroid cartilage of the larynx, and at C7 is the thyroid gland anterior to the trachea. The external jugular vein courses superficial to the sternocleidomastoid muscle. Deep to the muscle is the carotid sheath containing the internal jugular vein, common carotid artery, and vagus nerve.

8.16 Arteries of Oral and Pharyngeal Regions

The deeper muscles of the neck are the three scalene muscles (anterior, middle, and posterior) that attach to the first and second ribs and the constrictors of the pharynx. The inferior constrictor muscle attaches anteriorly to the thyroid cartilage of the larynx, the middle constrictor muscle to the hyoid bone (not seen clearly here), and the superior constrictor muscle to the buccinator muscle. The common carotid artery bifurcates in the carotid sheath into the external and internal carotid arteries around the level of C4.

8.17 Axial CT and Cross Section of the Neck through C7 and the Thyroid Gland

The fascias of the neck envelop a visceral unit that includes the trachea/larynx, esophagus, and thyroid gland and a vertebral unit consisting of the vertebral column and surrounding muscles. The carotid sheath contains the common carotid artery, internal jugular vein, and vagus nerve. An axial (transverse) section of the neck at the level of the seventh cervical vertebra (C7) is through the thyroid gland (A and B). CT (A) is used for evaluation of the neck because of rapid scanning that can be obtained during a breath hold. Magnetic resonance imaging (MRI) can be used as well but is often less well tolerated by patients with significant pathologies. In addition, artifact from motion such as breathing and swallowing can degrade images.

8.18 Axial CT Through C5 and the Larynx

The larynx is the most prominent structure at the level of C5. In this axial CT, the section is through the true vocal folds and thyroid cartilage of the larynx. It is above the level of the cricoid cartilage. Between the larynx and C5 vertebra is the carotid sheath containing the internal jugular vein and common carotid artery. Note that the left internal jugular vein is much larger than the right. The sternocleidomastoid and trapezius muscles define the contour of the neck at all levels.

8.19 Axial CT through C3 and the Hyoid Bone

A section at C3 passes through the hyoid bone and epiglottis, just below the mandible in this individual. The projecting contour anteriorly indicates that the plane is close to the mandible, and the mylohyoid and anterior belly of the digastric muscles and the submandibular glands are visible. This is also at the level of the division of the common carotid artery into its internal and external branches.

8.20 Search Strategy: Neck Imaging of Laryngeal Tumor

In addition to an analysis of the vertebral compartment (p. 199), a search strategy for the interpretation of neck images includes careful, systematic study of spaces, blood vessels, lymph nodes, organs of the visceral compartment, and other structures and layers visible in the image. A and B are views of a mass in the larynx on the left. In the axial image (A), the thyroid cartilage of the larynx is pushed laterally on the left. The mass is eroding and displacing inferiorly the cricoid cartilage on the left and compromising the air space in the larynx. The coronal view (B) shows an airway tube in the trachea and the mass filling much of the interior of the larynx.