Cervical Spine

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The cervical spine consists of two "special" vertebrae - the atlas and axis - connecting the spine with the cranium in a complex set of joints and ligaments, and five "ordinary" vertebrae in a slightly lordotic curve (Figs. 2.1-2.3). In young adults, the average length of the cervical spine measures 12.5 cm from the lower border of C7 to the tip of the dens axis. In retroflexion, the average length is 11.5 cm, compared to 12.69 cm in anteflexion [9, 10]. This needs to be considered for correct intraoperative localization of intradural tumors; radiological examinations are performed in a different neckposition than the operative one!

The atlas is formed like a ring with small lateral masses, which articulate with the occipital condyles of the cranium above and the lateral masses of the axis underneath. A fifth joint provides the rotation of the head and is formed between the atlas and the dens axis (i.e., the odontoid process). The axis articulates with the lateral masses of C1 above and supports the dens axis in the midline (Figs. 2.2 and 2.3). The re maining vertebral bodies are rectangular in shape, with a slight depression of the superior surface, giving rise to bony edges on either side (i.e., the uncinate processes). Thus, the intervertebral discs rest on a cup-like surface of the lower vertebra, whereas the lower surface of a cervical vertebra (i.e., the upper surface of the intervertebral space) is flat (Fig. 2.2).

The posterior elements of the second to seventh vertebra form the neural arches consisting ofpedicles, the lamina, and spinous processes. The short pedicles connect the vertebral body with the facetjoints, which are formed by articular processes above and below. These processes are named according to their orientation: the articular of the inferior vertebra projecting upward is called the superior articular process, and vice versa for articular process from the superior vertebra facing downward (Fig. 2.1). In axial sections through the facet joints, the posterior facet belongs to the superior neural arch representing the inferior articular process and vice versa for the anterior facet (Fig. 2.3). A neuroforamen is formed by pedicles above and below the vertebral body and uncinate process medially, the transverse process laterally, and the articular processes posteriorly. The cervical forami-nae are oriented about 30° anterolaterally. The neural arches project posteriorly to meet at the base of the spinous process. On cross section, they are ovoid in shape, with a flattened anterior surface. The spinous processes point downward in the midline (Fig. 2.1). There is no spinous process at C1, but there are particularly large processes at C2 and C7. The average anterior-posterior diameter of the bony spinal canal measures 18-20 mm at C1 and C2, and 15-17 mm between C3 and C7. The thecal sac measures 10-14 mm throughout the cervical spine, and the spinal cord 6-9 mm. In other words, the spinal cord normally occupies about 40-50% of the spinal canal.

As far as ligamentous structures are concerned, the atlantoaxial ligaments, anterior and posterior longitudinal ligaments, the yellow ligament, the interspi-nous ligament, and the supraspinous ligament should

Basivertebral Veins Mri

YL yellow ligament, BVV basivertebral vein. b Sagittal paramedian T2-weighted MRI scan of the cervical spine. OC Occipital condyle, AOJ atlantooccipital joint, VA vertebral artery, SAP superior articular process, IAP inferior articular process, FJfacet joint

Occipital Condyle Mri
Fig. 2.1. a Sagittal T2-weighted magnetic resonance imaging (MRI) scan of the cervical spine in the midline: CL Cli-vus, PFM posterior rim of the foramen magnum, TM tectorial membrane, AOM atlantooccipital membrane, TL transverse ligament, LN ligamentum nuchae, SL supraspinous ligament,

YL yellow ligament, BVV basivertebral vein. b Sagittal paramedian T2-weighted MRI scan of the cervical spine. OC Occipital condyle, AOJ atlantooccipital joint, VA vertebral artery, SAP superior articular process, IAP inferior articular process, FJfacet joint be mentioned. The medial atlantoaxial joint is stabilized by a complex set ofligaments. The most important of these is the cruciform ligament, which lies immediately behind the dens in the coronal plane (Fig. 2.3). The vertical and horizontal arms of this ligament explain its name. The horizontal arms form the so-called transverse ligament between the lateral masses of C1 and the posterior surface of the dens to hold it firmly against the anterior arch of C1 (Fig. 2.1). The vertical arms run between the anterior rim of the foramen magnum and the body of C2. The dens is linked to the skull base by the apical ligament extending from its tip to the anterior foramen magnum and the alar ligaments laterally toward the occipital condyles. The vertebral bodies are connected by anterior and posterior longitudinal ligaments from C1 right down to the sacrum along their anterior and posterior surfaces, respectively. The anterior longitu dinal ligament ends in the anterior atlantooccipital membrane at the level of the foramen magnum. The posterior longitudinal ligament is connected with the posterior foramen magnum via the tectorial membrane (Fig. 2.1). The posterior vertebral elements are stabilized by yellow, interspinous, and supraspinous ligaments. The yellow ligament links the vertebral laminae and, thus, forms the posterior border of the spinal canal in the interlaminar space and is connected to the posterior atlantooccipital membrane crani-ally. The interspinous ligament serves as an important posterior anchor and runs between spinous processes, whereas the supraspinous ligament extends between the tips of the spinous processes (Fig. 2.1).

The vascular anatomy consists of the vertebral arteries and a venous plexus. This plexus runs along the posterior surface of the vertebral bodies mainly in the midline, where it elevates the posterior longitudinal

b ligament. The vertebral arteries arise from the subclavian arteries in 90% of patients. In rare instances, the left vertebral artery may arise from the aortic arch. Other unusual origins such as the inferior thyroid and the common carotid artery have been described. The arteries travel anterolaterally of the neuroforami-nae between C6 and C1 through foraminae in the transverse processes. However, the vertebral artery may enter the spine at other levels such as C3, C4, C5, and C7 [10]. In about 89% of cases the artery arises in a straight line through these transverse foraminae.

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Fig. 2.2. a Anterior coronal T1-weightedMRI scan of the craniocervical junction and upper cervical spine: D Dens axis, UP uncinate process. b Coronal Tl-weighted MRI scan of the craniocervical junction and upper cervical spine in the midline. c Posterior coronal Tl-weighted MRI scan of the craniocervical junction and upper cervical spine. OB Occipital bone, IOM inferior oblique muscle, MM multi-fidus muscle, SM semispinal muscle

However, medial loops at C4, C5, and C6 may occur in rare cases [10]. Above C2, the artery turns posteriorly and superiorly, traverses the transverse foramen of C1 and continues medially along the superior margin of the atlas in a sulcus to form a loop toward the dura of the foramen magnum. In some cases, a foramen is formed in this area (i.e., the arcuate foramen). The vertebral artery is surrounded by a venous plexus, which is particularly prominent between C2 and its intracranial section (Figs. 2.1-2.3).

Arcuate ForamenDentate Ligament Spine Mri Spine Tumors

Fig. 2.3. a Axial T2-weighted MRI scan at C1. CRL Cruciate ligament, SC spinal cord. b Axial T2-weighted MRI scan at C1/2. c Axial T2-weighted MRI scan atC2. d Axial T2-weight-

ed MRI scan at C7. IJV Internal jugular vein, CCA common carotid artery, AR anterior root, DL dentate ligament, PR posterior root, PS posterior septum, SP spinous process

Fig. 2.3. a Axial T2-weighted MRI scan at C1. CRL Cruciate ligament, SC spinal cord. b Axial T2-weighted MRI scan at C1/2. c Axial T2-weighted MRI scan atC2. d Axial T2-weight-

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