Bookmarks
Imaging Anatomy
- There are 33 spinal vertebrae, which comprise 2 components: A cylindrical ventral bone mass, which is the vertebral body, and the dorsal arch.
- 7 cervical, 12 thoracic, 5 lumbar bodies
- Arch
- The 2 articular processes (zygapophyses) are diarthrodial joints.
- Pars interarticularis is the part of the arch that lies between the superior and inferior articular facets of all subatlantal movable elements. The pars are positioned to receive biomechanical stresses of translational forces displacing superior facets ventrally, whereas inferior facets remain attached to dorsal arch (spondylolysis). C2 exhibits a unique anterior relation between the superior facet and the posteriorly placed inferior facet. This relationship leads to an elongated C2 pars interarticularis, which is the site of the hangman's fracture.
- Cervical
- The cervical bodies are small and thin relative to the size of the arch and foramen with the transverse diameter greater than the AP diameter. The lateral edges of the superior surface of the body are turned upward into the uncinate processes. The transverse foramen perforates the transverse processes. The vertebra artery resides within the transverse foramen, most commonly starting at the C6 level.
- C1 has no body and forms a circular bony mass. The superior facets of C1 are large ovals that face upward, and the inferior facets are circular in shape. Large transverse processes are present on C1 with fused anterior and posterior tubercles.
- The C2 complex consists of the axis body with dens/odontoid process. The odontoid embryologically arises from the centrum of the 1st cervical vertebrae.
- The C7 vertebral body shows a transitional morphology with a prominent spinous process.
- Thoracic
- Lumbar
- The lumbar vertebral bodies are large, wide, and thick and lack a transverse foramen or costal articular facets. The pedicles are strong and directed posteriorly. The superior articular processes are directed dorsomedially and almost face each other. The inferior articular processes are directed anteriorly and laterally.
- Joints
- Synarthrosis is an immovable joint of cartilage and occurs during development and in the 1st decade of life. The neurocentral joint occurs at the union point of 2 centers of ossification for 2 halves of the vertebral arch and centrum.
- Diarthrosis is a true synovial joint that occurs in the articular processes, costovertebral joints, and atlantoaxial and sacroiliac articulations. The pivot-type joint occurs at the median atlantoaxial articulation. All others are gliding joints.
- Amphiarthroses are nonsynovial, movable connective tissue joints. Symphysis is a fibrocartilage fusion between 2 bones, as in the intervertebral disc. Syndesmosis is a ligamentous connection common in the spine, such as the paired ligamenta flava, intertransverse ligaments, and interspinous ligaments. An unpaired syndesmosis is present in the supraspinous ligament.
- Atlantooccipital (AO) articulation is composed of a diarthrosis between the lateral mass of atlas and occipital condyles and the syndesmoses of the AO membranes. Anterior AO membrane is the extension of the anterior longitudinal ligament (ALL). The posterior AO membrane is homologous to the ligamenta flava.
- Atlantoaxial articulation is a pivot joint. The transverse ligament maintains the relationship of the odontoid to the anterior arch of atlas. Synovial cavities are present between the transverse ligament/odontoid and the atlas/odontoid junctions.
- Disc
- The intervertebral disc is composed of 3 parts: The cartilaginous endplate, the anulus fibrosis, and the nucleus pulposus. The height of the lumbar disc space generally increases as one progresses caudally. The anulus consists of concentrically oriented collagenous fibers, which serve to contain the central nucleus pulposus. These fibers insert into the vertebral cortex via Sharpey fibers and also attach to the anterior and posterior longitudinal ligaments (PLLs). Type I collagen predominates at the periphery of the anulus, while type II collagen predominates in the inner anulus. The normal contour of the posterior aspect of the anulus is dependent upon the contour of its adjacent endplate. Typically, this is slightly concave in the axial plane, although commonly at L4-L5 and L5-S1, these posterior margins will be flat or even convex. A convex shape on the axial images alone should not be interpreted as degenerative bulging.
- The nucleus pulposus is a remnant of the embryonal notochord and consists of a well-hydrated, noncompressible proteoglycan matrix with scattered chondrocytes. Proteoglycans form a major macromolecular component, including chondroitin 6-sulfate, keratan sulfate, and hyaluronic acid. Proteoglycans consist of protein core with multiple attached glycosaminoglycan chains. The nucleus occupies an eccentric position within the confines of anulus and is more dorsal with respect to the center of the vertebral body. At birth, ~ 85-90% of the nucleus is water. This water content gradually decreases with advancing age. Within the nucleus pulposus on T2-weighted sagittal images, there is often a linear hypointensity coursing in an anteroposterior direction, the intranuclear cleft. This region of more prominent fibrous tissue should not be interpreted as intradiscal air or calcification.
- Anterior Longitudinal Ligament
- The ALL runs along the ventral surface of the spine from the skull to the sacrum. The ALL is narrowest in the cervical spine and is firmly attached at the ends of each vertebral body. It is loosely attached at the midsection of the disc.
- Posterior Longitudinal Ligament
- The PLL runs on the dorsal surface of bodies from the skull to the sacrum. The PLL has a segmental denticulate configuration and is wider at the disc space but narrows and becomes thicker at the vertebral body level.
- Craniocervical Ligaments
- The craniocervical ligaments are located anteriorly to the spinal cord and occur in 3 layers: Anterior, middle, and posterior. Anterior ligaments consist of the odontoid ligaments (apical and alar). The apical ligament is a small, fibrous band extending from dens tip to basion. Alar ligaments are thick, horizontally directed ligaments extending from the lateral surface of dens tip to anteromedial occipital condyles. The middle layer consists of the cruciate ligament. The transverse ligament is a strong horizontal component of the cruciate ligament extending from behind the dens to the medial aspect of C1 lateral masses. The craniocaudal component consists of a fibrous band running from the transverse ligament superiorly to the foramen magnum and inferiorly to C2. Posteriorly, the tectorial membrane is the continuation of PLL and attaches to the anterior rim of the foramen magnum.
- Vertebral Artery
- The vertebral artery arises as the 1st branch of the subclavian artery on both sides. The vertebral artery travels cephalad within the foramen transversarium (transverse foramen) within the transverse processes. The 1st segment of the vertebral artery extends from its origin to the entrance into the foramen of the transverse process of the cervical vertebrae, usually the 6th. The most common variation is the origin of the left vertebral artery from the arch, between the left common carotid and the left subclavian arteries (2-6%). The vertebral artery in these variant cases almost always enters the foramen of the transverse process of C5. The 2nd segment runs within the transverse foramen to the C2 level. Nerve roots pass posterior to the vertebral artery. The 3rd segment starts at the C2 level where the artery loops and turns lateral to ascend in the C1 transverse foramen. It then turns medial, crossing on top of C1 in a groove. The 4th segment starts where the artery perforates the dura and arachnoid at the lateral edge of the posterior occipitoatlantal membrane, coursing ventrally on the medulla to join with the other vertebral artery to make the basilar artery.
- Vertebral Column Blood Supply
- Paired segmental arteries (intercostals, lumbar arteries) arise from the aorta and extend dorsolaterally around the middle of the vertebral body. Near the transverse process, the segmental artery divides into lateral and dorsal branches. The lateral branch supplies dorsal musculature, and the dorsal branch passes lateral to the foramen, giving off branch(es) and providing major vascular supply to bone and vertebral canal contents. The posterior central branch supplies disc and vertebral body, while the prelaminal branch supplies the inner surface of the arch, ligamenta flava, and regional epidural tissue. The neural branch entering the neural foramen supplies pia, arachnoid, and cord. The postlaminar branch supplies musculature overlying lamina and branches to bone.
- Nerves
- Meninges are divided into dura, arachnoid, and pia.
- Dura is a dense, tough covering corresponding to the meningeal layer of the cranial dura. The epidural space is filled with fat, loose connective tissue, and veins. The dura continues with spinal nerves through the foramen to fuse with the epineurium. Cephalic attachment of the dura is at the foramen magnum and the caudal attachment at the back of the coccyx.
- Arachnoid is the middle covering, which is thin, delicate, and continuous with cranial arachnoid. The arachnoid is separated from the dura by the potential subdural space.
- Pia is the inner covering of delicate connective tissue closely applied to the cord. Longitudinal fibers are laterally concentrated as denticulate ligaments lying between posterior and anterior roots and attach at 21 points to dura. Longitudinal fibers are concentrated dorsally as the septum posticum, attaching the dorsal cord to the dorsal midline dura.
Selected References
- Gailloud P: Spinal vascular anatomy. Neuroimaging Clin N Am. 29(4):615-33, 2019
- Shanechi AM et al: Spine anatomy imaging: an update. Neuroimaging Clin N Am. 29(4):461-80, 2019
- Griessenauer CJ et al: Venous drainage of the spine and spinal cord: a comprehensive review of its history, embryology, anatomy, physiology, and pathology. Clin Anat. 28(1):75-87, 2015
- Fardon DF et al: Lumbar disc nomenclature: version 2.0: recommendations of the combined task forces of the north american spine society, the american society of spine radiology, and the american society of neuroradiology. Spine (Phila Pa 1976). 39(24):E1448-65, 2014
- Santillan A et al: Vascular anatomy of the spinal cord. J Neurointerv Surg. 4(1):67-74, 2012
- Modic MT et al: Lumbar degenerative disk disease. Radiology. 245(1):43-61, 2007
- Battie MC et al: Lumbar disc degeneration: epidemiology and genetics. J Bone Joint Surg Am. 88 Suppl 2:3-9, 2006
- Grunhagen T et al: Nutrient supply and intervertebral disc metabolism. J Bone Joint Surg Am. 88 Suppl 2:30-5, 2006
- Haughton V: Imaging intervertebral disc degeneration. J Bone Joint Surg Am. 88 Suppl 2:15-20, 2006
- Roh JS et al: Degenerative disorders of the lumbar and cervical spine. Orthop Clin North Am. 36(3):255-62, 2005
Related Anatomy
Loading...
Related Differential Diagnoses
Loading...
References
Tables
Tables
Imaging Anatomy
- There are 33 spinal vertebrae, which comprise 2 components: A cylindrical ventral bone mass, which is the vertebral body, and the dorsal arch.
- 7 cervical, 12 thoracic, 5 lumbar bodies
- Arch
- The 2 articular processes (zygapophyses) are diarthrodial joints.
- Pars interarticularis is the part of the arch that lies between the superior and inferior articular facets of all subatlantal movable elements. The pars are positioned to receive biomechanical stresses of translational forces displacing superior facets ventrally, whereas inferior facets remain attached to dorsal arch (spondylolysis). C2 exhibits a unique anterior relation between the superior facet and the posteriorly placed inferior facet. This relationship leads to an elongated C2 pars interarticularis, which is the site of the hangman's fracture.
- Cervical
- The cervical bodies are small and thin relative to the size of the arch and foramen with the transverse diameter greater than the AP diameter. The lateral edges of the superior surface of the body are turned upward into the uncinate processes. The transverse foramen perforates the transverse processes. The vertebra artery resides within the transverse foramen, most commonly starting at the C6 level.
- C1 has no body and forms a circular bony mass. The superior facets of C1 are large ovals that face upward, and the inferior facets are circular in shape. Large transverse processes are present on C1 with fused anterior and posterior tubercles.
- The C2 complex consists of the axis body with dens/odontoid process. The odontoid embryologically arises from the centrum of the 1st cervical vertebrae.
- The C7 vertebral body shows a transitional morphology with a prominent spinous process.
- Thoracic
- Lumbar
- The lumbar vertebral bodies are large, wide, and thick and lack a transverse foramen or costal articular facets. The pedicles are strong and directed posteriorly. The superior articular processes are directed dorsomedially and almost face each other. The inferior articular processes are directed anteriorly and laterally.
- Joints
- Synarthrosis is an immovable joint of cartilage and occurs during development and in the 1st decade of life. The neurocentral joint occurs at the union point of 2 centers of ossification for 2 halves of the vertebral arch and centrum.
- Diarthrosis is a true synovial joint that occurs in the articular processes, costovertebral joints, and atlantoaxial and sacroiliac articulations. The pivot-type joint occurs at the median atlantoaxial articulation. All others are gliding joints.
- Amphiarthroses are nonsynovial, movable connective tissue joints. Symphysis is a fibrocartilage fusion between 2 bones, as in the intervertebral disc. Syndesmosis is a ligamentous connection common in the spine, such as the paired ligamenta flava, intertransverse ligaments, and interspinous ligaments. An unpaired syndesmosis is present in the supraspinous ligament.
- Atlantooccipital (AO) articulation is composed of a diarthrosis between the lateral mass of atlas and occipital condyles and the syndesmoses of the AO membranes. Anterior AO membrane is the extension of the anterior longitudinal ligament (ALL). The posterior AO membrane is homologous to the ligamenta flava.
- Atlantoaxial articulation is a pivot joint. The transverse ligament maintains the relationship of the odontoid to the anterior arch of atlas. Synovial cavities are present between the transverse ligament/odontoid and the atlas/odontoid junctions.
- Disc
- The intervertebral disc is composed of 3 parts: The cartilaginous endplate, the anulus fibrosis, and the nucleus pulposus. The height of the lumbar disc space generally increases as one progresses caudally. The anulus consists of concentrically oriented collagenous fibers, which serve to contain the central nucleus pulposus. These fibers insert into the vertebral cortex via Sharpey fibers and also attach to the anterior and posterior longitudinal ligaments (PLLs). Type I collagen predominates at the periphery of the anulus, while type II collagen predominates in the inner anulus. The normal contour of the posterior aspect of the anulus is dependent upon the contour of its adjacent endplate. Typically, this is slightly concave in the axial plane, although commonly at L4-L5 and L5-S1, these posterior margins will be flat or even convex. A convex shape on the axial images alone should not be interpreted as degenerative bulging.
- The nucleus pulposus is a remnant of the embryonal notochord and consists of a well-hydrated, noncompressible proteoglycan matrix with scattered chondrocytes. Proteoglycans form a major macromolecular component, including chondroitin 6-sulfate, keratan sulfate, and hyaluronic acid. Proteoglycans consist of protein core with multiple attached glycosaminoglycan chains. The nucleus occupies an eccentric position within the confines of anulus and is more dorsal with respect to the center of the vertebral body. At birth, ~ 85-90% of the nucleus is water. This water content gradually decreases with advancing age. Within the nucleus pulposus on T2-weighted sagittal images, there is often a linear hypointensity coursing in an anteroposterior direction, the intranuclear cleft. This region of more prominent fibrous tissue should not be interpreted as intradiscal air or calcification.
- Anterior Longitudinal Ligament
- The ALL runs along the ventral surface of the spine from the skull to the sacrum. The ALL is narrowest in the cervical spine and is firmly attached at the ends of each vertebral body. It is loosely attached at the midsection of the disc.
- Posterior Longitudinal Ligament
- The PLL runs on the dorsal surface of bodies from the skull to the sacrum. The PLL has a segmental denticulate configuration and is wider at the disc space but narrows and becomes thicker at the vertebral body level.
- Craniocervical Ligaments
- The craniocervical ligaments are located anteriorly to the spinal cord and occur in 3 layers: Anterior, middle, and posterior. Anterior ligaments consist of the odontoid ligaments (apical and alar). The apical ligament is a small, fibrous band extending from dens tip to basion. Alar ligaments are thick, horizontally directed ligaments extending from the lateral surface of dens tip to anteromedial occipital condyles. The middle layer consists of the cruciate ligament. The transverse ligament is a strong horizontal component of the cruciate ligament extending from behind the dens to the medial aspect of C1 lateral masses. The craniocaudal component consists of a fibrous band running from the transverse ligament superiorly to the foramen magnum and inferiorly to C2. Posteriorly, the tectorial membrane is the continuation of PLL and attaches to the anterior rim of the foramen magnum.
- Vertebral Artery
- The vertebral artery arises as the 1st branch of the subclavian artery on both sides. The vertebral artery travels cephalad within the foramen transversarium (transverse foramen) within the transverse processes. The 1st segment of the vertebral artery extends from its origin to the entrance into the foramen of the transverse process of the cervical vertebrae, usually the 6th. The most common variation is the origin of the left vertebral artery from the arch, between the left common carotid and the left subclavian arteries (2-6%). The vertebral artery in these variant cases almost always enters the foramen of the transverse process of C5. The 2nd segment runs within the transverse foramen to the C2 level. Nerve roots pass posterior to the vertebral artery. The 3rd segment starts at the C2 level where the artery loops and turns lateral to ascend in the C1 transverse foramen. It then turns medial, crossing on top of C1 in a groove. The 4th segment starts where the artery perforates the dura and arachnoid at the lateral edge of the posterior occipitoatlantal membrane, coursing ventrally on the medulla to join with the other vertebral artery to make the basilar artery.
- Vertebral Column Blood Supply
- Paired segmental arteries (intercostals, lumbar arteries) arise from the aorta and extend dorsolaterally around the middle of the vertebral body. Near the transverse process, the segmental artery divides into lateral and dorsal branches. The lateral branch supplies dorsal musculature, and the dorsal branch passes lateral to the foramen, giving off branch(es) and providing major vascular supply to bone and vertebral canal contents. The posterior central branch supplies disc and vertebral body, while the prelaminal branch supplies the inner surface of the arch, ligamenta flava, and regional epidural tissue. The neural branch entering the neural foramen supplies pia, arachnoid, and cord. The postlaminar branch supplies musculature overlying lamina and branches to bone.
- Nerves
- Meninges are divided into dura, arachnoid, and pia.
- Dura is a dense, tough covering corresponding to the meningeal layer of the cranial dura. The epidural space is filled with fat, loose connective tissue, and veins. The dura continues with spinal nerves through the foramen to fuse with the epineurium. Cephalic attachment of the dura is at the foramen magnum and the caudal attachment at the back of the coccyx.
- Arachnoid is the middle covering, which is thin, delicate, and continuous with cranial arachnoid. The arachnoid is separated from the dura by the potential subdural space.
- Pia is the inner covering of delicate connective tissue closely applied to the cord. Longitudinal fibers are laterally concentrated as denticulate ligaments lying between posterior and anterior roots and attach at 21 points to dura. Longitudinal fibers are concentrated dorsally as the septum posticum, attaching the dorsal cord to the dorsal midline dura.
Selected References
- Gailloud P: Spinal vascular anatomy. Neuroimaging Clin N Am. 29(4):615-33, 2019
- Shanechi AM et al: Spine anatomy imaging: an update. Neuroimaging Clin N Am. 29(4):461-80, 2019
- Griessenauer CJ et al: Venous drainage of the spine and spinal cord: a comprehensive review of its history, embryology, anatomy, physiology, and pathology. Clin Anat. 28(1):75-87, 2015
- Fardon DF et al: Lumbar disc nomenclature: version 2.0: recommendations of the combined task forces of the north american spine society, the american society of spine radiology, and the american society of neuroradiology. Spine (Phila Pa 1976). 39(24):E1448-65, 2014
- Santillan A et al: Vascular anatomy of the spinal cord. J Neurointerv Surg. 4(1):67-74, 2012
- Modic MT et al: Lumbar degenerative disk disease. Radiology. 245(1):43-61, 2007
- Battie MC et al: Lumbar disc degeneration: epidemiology and genetics. J Bone Joint Surg Am. 88 Suppl 2:3-9, 2006
- Grunhagen T et al: Nutrient supply and intervertebral disc metabolism. J Bone Joint Surg Am. 88 Suppl 2:30-5, 2006
- Haughton V: Imaging intervertebral disc degeneration. J Bone Joint Surg Am. 88 Suppl 2:15-20, 2006
- Roh JS et al: Degenerative disorders of the lumbar and cervical spine. Orthop Clin North Am. 36(3):255-62, 2005
