Section 1 Head and Neck

1

Skull, Basal View1

2 Head and Neck

Incisive foramen

Choanae

Foramen ovale

Foramen spinosum

Jugular fossa

Mastoid process

Foramen lacerum

Carotid canal

Clinical Note Maxillofacial three-dimensional (3-D) displays are very helpful in preoperative planning to correct deformities caused by trauma, tumor, or congenital malformations.

Inferior view of the skull showing foramina (Atlas of Human Anatomy, 5th edition, Plate 12)

Skull, Basal View 1

Head and Neck 3

• 3-D volume reconstructions have been shown to be useful for detecting the extent and exact nature of fractures of the skull base.

• The nasopalatine nerve is sensory to the anterior hard palate and may be anesthetized by injection into the incisive foramen.

• The mandibular branch of the trigeminal nerve (V3) passes through the foramen ovale to innervate the muscles of mastication.

Incisive foramen

Hard palate

Choanae

Foramen ovale

Foramen spinosum

Carotid canal

Mastoid process

Jugular fossa

Foramen lacerum

Volume rendered display, maxillofacial computed tomography (CT)

1

4 Head and Neck

Foramen ovale

Groove for middlemeningeal artery

Hypophyseal fossawithin the sella turcica

Cribriform plate

Foramen spinosum

Foramen lacerum

Internal acoustic meatus

Interior of skull showing foramina (Atlas of Human Anatomy, 5th edition, Plate 13)

Clinical Note The groove for the middle meningeal artery runs along the inner margin of the thinnest part of the lateral skull known as pterion; accordingly, a fracture of this region may result in an extradural hematoma.

Skull, Interior View

1

Head and Neck 5

• The middle meningeal artery, a branch of the maxillary artery, enters the skull through the foramen spinosum.

• Foramina tend to be less apparent in radiographic images than in anatomic illustrations because of their obliquity.

• A volume rendered display may be useful in demonstrating tumor erosion of bone in the skull base because the skull base consists of many complex curved contours that are only partially shown in any single cross-sectional image. Scrolling through a series of such images may allow one to create a mental picture of bony involvement by tumor. A three-dimensional reconstruction, however, offers an accurate representation that is immediately comprehended.

Foramen ovale

Groove for middlemeningeal artery

Hypophyseal fossawithin the sella turcica

Cribriform plate

Foramen spinosum

Foramen lacerum

Internal acoustic meatus

Volume rendered display, CT of skull base

Skull, Interior View

1

6 Head and Neck

Upper Neck, Lower Head Osteology

Hyoid bone

Stylohyoid ligament

Styloid process

Mental foramen

External acoustic meatus

Lateral view of the skeletal elements of the head and neck (Atlas of Human Anatomy, 5th edition, Plate 15)

Clinical Note In criminal proceedings, the fi nding of a fractured hyoid bone is considered to be strong evidence of strangulation.

1

Head and Neck 7

• The lesser horn of the hyoid bone is attached to the stylohyoid ligament, which sometimes ossifi es. An elongated styloid process in association with such an ossifi ed ligament (or even without such ossifi cation) can produce neck/swallowing pain and is known as Eagle’s syndrome.

• In elderly patients who are edentulous, resorption of the alveolar process of the mandible exposes the mental nerve to pressure during chewing as it exits the foramen. Mastication then becomes a painful process for these patients.

Upper Neck, Lower Head Osteology

Hyoid bone

Styloid process

Mental foramen

External acoustic meatus

Volume rendered display, maxillofacial CT

1

8 Head and Neck

Axis (C2)

Superior articular facet for atlas

Dens (odontoid process)

Inferior articular facet for C3

Anterior arch

Anterior view of the axis (C2) (Atlas of Human Anatomy, 5th edition, Plate 19)

Clinical Note The dens is susceptible to fracture that is classifi ed by the level of the fracture site. The most common fracture occurs at the base of the dens (type II fracture).

1

Head and Neck 9

• The dens is embryologically the vertebral body of the atlas (C1).

• The articular facet on the dens articulates with the facet on the anterior arch of the atlas.

• In rare cases the dens does not appear on radiographs to be fused with the remainder of the vertebra. This condition, known as os odontoideum, may result in atlantoaxial instability.

Axis (C2)

Superior articular facet for atlas

Dens (odontoid process)

Inferior articular facet for C3

Anterior arch

Volume rendered CT scan, axis

1

10 Head and Neck

Cervical Spine, Posterior View

Facet on atlas for articulationwith occipital condyle

Dens

Lamina of axis

Posterior arch of atlas

Zygapophyseal joint

Bifid spinous process

Posterior view of articulated C1-C4 vertebrae (Atlas of Human Anatomy, 5th edition, Plate 19)

Clinical Note The hangman’s fracture consists of bilateral pedicle or pars interarticularis fractures of the axis. Associated with this fracture is anterior subluxation or dislocation of the C2 vertebral body. It results from a severe extension injury, such as from an automobile accident in which the face forcibly strikes the dashboard, or from hanging.

1

Head and Neck 11

• In the cervical region the articular facets of the zygapophyseal joints are oriented superiorly and inferiorly; thus, this is the only region of the vertebral column in which it is possible for adjoining vertebrae to dislocate (rotary) without fracture.

• The zygapophyseal joints are well innervated by medial branches from dorsal rami associated with both vertebral levels participating in the joint. To denervate a painful arthritic joint, the medial branches from both levels must be ablated.

Cervical Spine, Posterior View

Dens

Lamina of axis

Posterior arch of atlas

Zygapophyseal joint

Bifid spinous process

Volume rendered display, cervical spine CT

1

12 Head and Neck

Cervical Spondylosis

Axis (C2)

Uncinate processeswith loss of joint spacein uncovertebral joint

Spondylophytes (osteophytes)on uncinate processes

Degenerative changes in cervical vertebrae (Atlas of Human Anatomy, 5th edition, Plate 20)

Clinical Note Degenerative changes of the uncovertebral joints (of Luschka) typically occur with other degenerative changes such as the development of spondylophytes and the loss of intervertebral disk space. These changes reduce the size of the intervertebral foramina (neuroforamina) resulting in radiculopathy and associated pain, paresthesia, and numbness in the corresponding dermatomes.

1

Head and Neck 13

• Surgeons may use an anterior or a posterior approach to address cervical spondylosis. A bone graft is inserted into the disk space to restore vertical spacing between segments and a metal plate is attached along the anterior margin of the spine to provide stability during the process of intervertebral bone fusion.

• The uncovertebral joints contribute to cervical spine stability and help to limit extension and lateral bending.

Cervical Spondylosis

Normal uncinateprocess anduncovertebraljoint

Uncovertebraljoint with lossof joint space

Spondylophyte(osteophyte) onbody (lipping)

Spondylophyteon uncinateprocess

Axis

Volume rendered displays, cervical spine CT

1

14 Head and Neck

Vertebral Artery, Neck

Vertebral artery

Posterior arch of atlas (C1)

C5 transverse process

Lateral view of the cervical spine and vertebral artery (Atlas of Human Anatomy, 5th edition, Plate 22)

Clinical Note Vertebral artery dissection, a subintimal hematoma, may cause cerebellar or brain infarction; occurrence may be idiopathic or secondary to trauma.

1

Head and Neck 15

• The intimate association of the vertebral artery to the cervical spine makes it susceptible to injury during cervical spine trauma.

• The vertebral artery is typically the fi rst branch of the subclavian artery, although it can arise directly from the arch of the aorta.

• Most commonly, the vertebral artery enters the foramina of the transverse processes of the cervical vertebrae at C6.

Vertebral Artery, Neck

Vertebral artery

Posterior archof atlas (C1)

C5 transverse process

Volume rendered display, CTA of the neck

1

16 Head and Neck

Vertebral Artery, Atlas

Posterior atlanto-occipital membrane

Mastoid process

Transverse processof atlas (C1)

Posterior tubercleof atlas

Vertebral artery

Vertebral artery on the posterior arch of the atlas (Atlas of Human Anatomy, 5th edition, Plate 22)

Clinical Note This is the most tortuous segment of the vertebral artery; increases in tortuosity are associated with atherosclerotic changes.

1

Head and Neck 17

• The vertebral artery pierces the dura and arachnoid mater and ascends anterior to the medulla to unite with the contralateral vessel to form the basilar artery.

• The vertebral artery supplies the muscles of the suboccipital triangle before entering the cranial cavity.

Vertebral artery

Mastoid process

Transverse processof atlas (C1)

Posterior tubercleof atlas

Volume rendered display, CTA of the neck

Vertebral Artery, Atlas

1

18 Head and Neck

Craniovertebral Ligaments

Alar ligaments

Clivus portionof occipital bone

Dens covered bycruciate ligament

Transverse ligament of atlas

Posterior view of the craniovertebral ligaments after removal of the tectorial membrane (Atlas of Human Anatomy, 5th edition, Plate 23)

Clinical Note Atlanto-occipital dislocation is a rare traumatic injury that is diffi cult to diagnose and is frequently missed on initial lateral cervical x-rays. Patients who survive typically have neurologic impairment such as lower cranial neuropathies, unilateral or bilateral weakness, or quadriplegia. Prevertebral soft tissue swelling on a lateral cervical x-ray and craniocervical subarachnoid hemorrhage on an axial CT have been associated with this injury and thus may aid with diagnosis.

1

Head and Neck 19

• The alar ligaments are pencil-thick ligaments that connect the dens to the rim of the foramen magnum, stabilizing the atlanto-occipital relationship.

• The transverse ligament holds the dens against the anterior arch of the atlas.

• Superior and inferior bands arise from the transverse ligament forming with it the cruciate ligament.

Craniovertebral Ligaments

Alar ligament

Dens

Dens

Transverse ligament of atlas

Superior articular facet of atlas

Spinal cord

Cerebellum

Epiglottis

A

B

A, Oblique coronal CT, cervical spine; B, Axial T2 magnetic resonance (MR) image, cervical spine

1

20 Head and Neck

Neck Muscles, Lateral View

Sternocleidomastoidmuscle

Pectoralis major muscle

Masseter muscle

Mylohyoid muscle

Digastric muscle(anterior belly)

Hyoid bone

Sternohyoid muscle

Scalene muscles

Posterior

MiddleAnterior

Lateral view of the superfi cial muscles of the neck (Atlas of Human Anatomy, 5th edition, Plate 26)

Clinical Note Congenital torticollis (wryneck) is typically associated with a birth injury to the sternocleidomastoid muscle that results in a unilateral shortening of the muscle, and the associated rotated and tilted head position.

1

Head and Neck 21

• The sternocleidomastoid is a large and consistent anatomic structure that is easily identifi able and is used to divide the neck into anterior and posterior triangles.

• The hyoid bone provides an anchor for many neck muscles and is suspended solely by these muscles (it has no bony articulation).

Neck Muscles, Lateral View

Sternocleidomastoidmuscle

Pectoralis major muscle

Masseter muscle

Mylohyoid muscle

Digastric muscle(anterior belly)

Hyoid bone

Sternohyoid muscle

Scalene muscles

Volume rendered display, CT of the neck