Abbreviations

ABCâ Aneurysmal bone cyst

ADCâ Apparent diffusion coefficent

ADEMâ Acute disseminated encephalomyelitis AMLâ Acute myelogenous leukemia

ANAâ Antinuclear antibodies

ANCAâ Anti-neutrophil cytoplasmic antibody APâ Anteroposterior

AQPâ Aquaporin

ASâ Ankylosing spondylitis AVFâ Arteriovenous fistula

AVM â Arteriovenous malformation Caâ Calcium/calcification

CAPNONâ Calcifying pseudoneoplasm of the neuraxis

CIDPâ Chronic inflammatory demyelinating polyneuropathy

CISSâ Constructive interference steady state CLLâ Chronic lymphocytic leukemia

CMLâ Chronic myelogenous leukemia CMPDâ Chronic myeloproliferative disease CMVâ Human cytomegalovirus

CNSâ Central nervous system

CPPDâ Calcium pyrophosphate dihydrate deposition CSFâ Cerebrospinal fluid

CTâ Computed tomography

DISHâ Diffuse idiopathic skeletal hyperostosis DTIâ Diffusion tensor imaging

DWIâ Diffusion weighted imaging EGâ Eosinophilic granuloma

EMA â Epithelial membrane antigen

FIESTAâ Fast imaging employing steady state acquisition FGFRâ Fibroblast growth factor receptor

FLAIRâ Fluid attenuation inversion recovery

FSâ Frequency Selective fat signal suppression FSEâ Fast spin echo

FS-PDWIâ Fat-suppressed proton density weighted imaging

FSPGRâ Fast spoiled gradient echo imaging FS-T1WIâ Fat-suppressed T1-weighted imaging FS-T2WIâ Fat-suppressed T2-weighted imaging GAGâ Glycosaminoglycan

G-CSFâ Granulocyte colony stimulating factor Gd-contrastâ Gadolinium-chelate contrast GREâ Gradient echo imaging

HDâ Hodgkin disease

HIVâ Human immundeficiency virus

HMB-45â Human melanoma black monoclonal antibody HPFâ High power field

HSVâ Herpes simplex virus HUâ Hounsfield unit

ICAâ Internal carotid artery JIAâ Juvenile idiopathic arthritis

LCHâ Langerhans cell histiocytosis MDSâ Myelodysplastic syndromes MFHâ Malignant fibrous histiocytoma MIPâ Maximum intensity projection

MPNSTâ Malignant peripheral nerve sheath tumor MPSâ Mucopolysaccharidosis

MRAâ MR angiography MRVâ MR venography MS â Multiple sclerosis

NF1â Neurofibromatosis type 1 NF2â Neurofibromatosis type 2 NHLâ Non-Hodgkin lymphoma

NSAIDâ Non-steroidal anti-inflammatory drug

NSEâ Neuron specific enloase OIâ Osteogenesis imperfecta PCâ Phase contrast

PDWIâ Proton density weighted imaging PLLâ Posterior longitudinal ligament PNETâ Primitive neuroectodermal tumor RFâ Radiofrequency

SFTâ Solitary fibrous tumor

SLEâ Systemic lupus erythematosus SMAâ Smooth muscle actin antibodies SMDâ Spondylometaphyseal dysplasia STIRâ Short TI inversion recovery imaging SWIâ Susceptibility weighted imaging

S-100â Cellular calcium binding protein in cytoplasm and/or nuceus

T1â Spin-lattice or longitudinal relaxation time (coefficient)

T2â Spin-spin or transverse relaxation time (coefficient)

T2*â Effective spin-spin relaxation time using GRE pulse sequence

T2-PREâ T2-proton relaxation enhancement T1WI â T1-weighted imaging

T2WIâ T2-weighted imaging TEâ Time to echo

TRâ Pulse repetition time interval TOFâ Time of flight

2Dâ 2 dimensional 3Dâ 3 dimensional

UBCâ Unicameral bone cyst WHOâ World Health Organization

Spine

1.1Congenital and developmental abnormalities of the spinal cord

1.2Abnormalities involving the

1.3Intradural intramedullary lesions

1.6Solitary osseous lesions involving

Introduction

Spine and Spinal Cord

Imaging techniques commonly used to evaluate for spinal abnormalities include MRI, MRA, CT, CT myelography, CTA, conventional angiography, and radiographs. MRI is a powerful imaging modality for evaluating normal spinal anatomy and pathologic conditions involving the spine and sacrum. Because of the high soft tissue contrast resolution of MRI and multiplanar imaging capabilities; pathologic disorders of bone marrow (such as neoplasm, infamma- tory diseases, etc.), epidural soft tissues, disks, thecal sac, spinal cord, intradural and extradural nerves, ligaments, facet joints, and paravertebral structures are readily discerned to a much greater degree than with CT.

The normal spine is comprised of seven cervical, twelve thoracic, and fve lumbar vertebrae (Fig.Â1.1). The upper two cervical vertebrae have different confgurations than the other vertebrae. The atlas (C1) has a horizontal ringlike confguration with lateral masses that articulate

with the occipital condyles superiorly and superior facets of C2 inferiorly (Fig.Â1.2). The dorsal margin of the upper dens is secured in position in relation to the anterior arch of C1 by the transverse ligament. Ligaments at the craniovertebral junction include the alar, transverse, and apical ligaments (see Fig.Â1.50 and Fig.Â1.51). The alar ligaments connect the lateral margins of the odontoid process with the lateral masses of C1 and medial margins of the foramen magnum. The alar ligaments limit atlantoaxial rotation. The transverse ligament extends medially from the tubercles at the inner aspects of the lateral articulating masses of C1 behind the dens, stabilizing the dens with the anterior arch of C1. The transverse ligament is the horizon- tal portion of the cruciform ligament, which also has fbers that extend from the transverse ligament superiorly to the

2 clivus, and inferiorly to the posterior surface of the dens.

Fig.Â1.1â Lateral view of the normal osseous anatomy and alignment of the spine. From THIEME Atlas of Anatomy: General Anatomy and Musculoskeletal System, © Thieme 2005, Illustration by Karl Wesker.

Fig.Â1.2â Lateral view of the normal osseous anatomy and alignment of the cervical vertebrae. From THIEME Atlas of Anatomy: General Anatomy and Musculoskeletal System, © Thieme 2005, Illustration by Karl Wesker.

The apical ligament (middle odontoid ligament) extends from the upper margin of the dens to the anterior clival portion of the foramen magnum. The tectorial membrane is an upward extension from the posterior longitudinal ligament that connects with the body of C2 and the occipital bone (jugular tubercle and cranial base). Other ligaments involved with stabilization of the mid and lower cervical spine include the anterior and posterior longitudinal ligaments, ligamenta fava, and nuchal ligament (Fig.Â1.3). Various anomalies occur in this region, such as atlantooccipital assimilation, segmentation (block vertebrae, etc.), basiocciput hypoplasia, condylus tertius, os odontoideum, etc. The lower fve cervical vertebral bodies have more rectangular shapes, with progressive enlargement inferiorly. Superior projections from the cervical vertebral bodies laterally form the uncovertebral joints. The transverse processes are located anterolateral to the vertebral bodies and contain the foramina transversaria, which contain vertebral arteries and veins. The posterior elements consist of paired pedicles, articular pillars, laminae, and spinous processes. The cervical spine has a normal lordosis.

The twelve thoracic vertebral bodies and fve lumbar vertebral bodies progressively increase in size caudally (Fig.Â1.1, Fig.Â1.2, Fig.Â1.4, and Fig.Â1.5).

Fig.Â1.3â Lateral view of the normal osseous and ligamentous anatomy of the cervical spine. From THIEME Atlas of Anatomy: General Anatomy and Musculoskeletal System, © Thieme 2005, Illustration by Karl Wesker.

Fig.Â1.4â Lateral view of the normal osseous anatomy and alignment of the thoracic vertebrae. From THIEME Atlas of Anatomy: General Anatomy and Musculoskeletal System, © Thieme 2005, Illustration by Karl Wesker.

The posterior elements include the pedicles, transverse processes, laminae, and spinous processes. The transverse processes of the thoracic vertebrae also have articulation sites for ribs. The thoracic spine has a normal kyphosis and the lumbar spine a normal lordosis. Anterior and posterior longitudinal ligaments connect the vertebrae, and inter-

spinous ligaments and ligamentum favum provide stabil- ity for the posterior elements (Fig.Â1.6).

The cortical margins of the vertebral bodies have dense compact bone structure that results in low signal on T1and T2-weighted images. The medullary compartments of the vertebrae are comprised of bone marrow and trabecular bone. The signal intensity of the medullary com-

Fig.Â1.5â Lateral view of the normal osseous anatomy and alignment of the lumbar vertebrae. From THIEME Atlas of Anatomy: General Anatomy and Musculoskeletal System, © Thieme 2005, Illustration by Karl Wesker.

partment is primarily due to the proportion of red versus yellow marrow. The proportion of yellow to red marrow progressively increases with age, resulting in increased marrow signal on T1-weighted images. Similar changes are pronounced in patients who have received spinal irradia- tion.Pathologicprocesses(suchastumor,infammation,or infection)causeincreasedT1andT2relaxationcoefficients, which result in decreased signal on T1-weighted images and increased signal on T2-weighted images. MRI with fat-signal suppression techniques (short time to inversion recovery [STIR] sequence, and fat-frequency-saturated T1and T2-weighted sequences) provide optimal contrast between normal and pathologic marrow. Corresponding abnormal gadolinium enhancement is also usually seen at the pathologic sites, which can also be optimized using fat-frequency-saturated T1-weighted sequences. Because it allows direct visualization of these pathologic processes in the marrow, MRI can often detect the abnormalities sooner than CT, which relies on later indirect signs of tra- becular destruction for confrmation of disease.

The intervertebral disks enable fexibility of the spine.

The two major components (nucleus pulposus and annulus fbrosus) of normal disks are usually seen well with MRI. The outer annulus fbrosus is made of dense fbrocartilage and has low signal on T1and T2-weighted images. The central nucleus pulposus is made of gelatinous material and usually has high signal on T2-weighted images. The combination of various factors, such as decreased turgor

of the nucleus pulposus, and loss of elasticity of the annulus, with or without tears, results in degenerative changes in the disks. MRI features of disk degeneration include decreased disk height, decreased signal of nucleus pulposus on T2-weighted images, disk bulging, and associated posterior vertebral body osteophytes. Tears of the annulus fbrosus often have high signal on T2-weighted images at the site of injury. Annular tears can be transverse, which are oriented parallel to the outer annular fbers, and are sometimesreferredtoasannularfssures.Annualtearscan also be radial, extending from the central portion of the disk to the periphery. Radial tears are often clinically sig- nifcant,andareassociatedwithdiskherniations.Theterm disk herniation usually refers to extension of the nucleus

pulposus through an annular tear beyond the margins of the adjacent vertebral body end plates. Disk herniations can be further subdivided into protrusions (when the head of the herniation equals the neck in size), extrusions (when the head of the herniation is larger than the neck), or extruded fragments (when there is separation of the herniated disk fragment from the disk of origin). Disk herniations can occur in any portion of the disk. Posterior and posterolateral herniations can cause compression of the thecal sac and contents, as well as compression of epidural nerve roots in the lateral recesses or within the intervertebral foramina. Lateral and anterior disk herniations are less common but can cause hematomas in adjacent structures. Disk herniations that occur superiorly or inferiorly

result in focal depressions of the end plates, i.e., Schmorl’s nodes. Recurrent disk herniations can be delineated from scar or granulation tissue because herniated disks do not typically enhance after gadolinium contrast administration, whereas scar/granulation tissue typically enhances.

The thecal sac is a meningeal covered compartment that contains cerebrospinal fuid (CSF), which is contigu- ous with the basal subarachnoid cisterns. The thecal sac extends from the upper cervical level to the level of the sacrum, and it contains the spinal cord and exiting nerve roots. The distal end of the conus medullaris is normally located at the T12–L1 level in adults. Lesions within the thecal sac are categorized as intradural and intraor extramedullary. Intramedullary lesions directly involve the spinal cord, whereas extramedullary lesions do not primarily involve the spinal cord. Extradural or epidural lesions refer to spinal lesions outside of the thecal sac.

The high soft tissue contrast resolution of MRI enables evaluation of various intradural pathologic conditions, such as congenital malformations, neoplasms, benign mass lesions (dermoid, arachnoid cyst, etc.), infamma- tory/infectious processes, traumatic injuries (spinal cord, contusions, hematomas), vascular malformations, and spinal cord ischemia/infarction, as well as the adjacent CSF and nerve roots. With the intravenous administration of gadolinium contrast agents, MRI is useful for evaluating lesions within the spinal cord as well as neoplastic or infammatory diseases within the thecal sac.

The normal blood supply to the spinal cord consists of seven or eight arteries that enter the spinal canal through the intervertebral foramina, which divide into anterior and posterior segmental medullary arteries to supply the three main vascular territories of the spinal cord (cervicotho- racic—cervical and upper three thoracic levels; mid tho- racic—T4 level to T7 level; and thoracolumbar—T8 level to lumbosacral plexus) (Fig.Â1.7 and Fig.Â1.8). The cervicotho-

racic vascular distribution is supplied by radicular branches arising from the vertebral arteries and costocervical trunk. The midthoracic territory is often supplied by a radicular branch at the T7 level. The thoracolumbar territory is supplied by a single artery arising from the ninth, tenth, elev- enth, or twelfth intercostal arteries (75%); the ffth, sixth, seventh, or eighth intercostal arteries (15%); or the frst or second lumbar arteries (10%). The artery is referred to as the artery of Adamkiewicz. The anterior segmental medullary arteries supply the longitudinally oriented anterior spinal artery, which is located in the midline anteriorly adjacent to the spinal cord and supplies the gray matter and central white matter of the spinal cord. The posterior segmental medullary arteries also supply the two major longitudinally oriented posterior spinal arteries, which course along the posterolateral sulci of the spinal cord and supply one-third to one-half of the outer rim of the spinal cord via a peripheral anastomotic plexus. Ischemia or infarcts involving the spinal cord are rare disorders associated with atherosclerosis, diabetes, hypertension, abdominal aortic aneurysms, and abdominal aortic surgery. Venous blood from the spinal cord drains into the anterior and posterior venous plexuses, which connect to the azygos and hemiazygos veins via the intervertebral foramina (Fig.Â1.9). Vascular malformations can be seen within the thecal sac, with or without involvement of the spinal cord.

Epidural structures of clinical importance include the lateral recesses (anterolateral portions of the spinal canal located between the thecal sac and pedicles and that contain nerve roots, vessels, and fat), the dorsal epidural fat pad, the posterior elements and facet joints, and the pos- terior longitudinal ligament and ligamentum favum. The intervertebral foramina are bony channels between the pedicles through which the nerves traverse.

Narrowing of the thecal sac, lateral recesses, and intervertebral foramina can result in clinical signs and

Fig. 1.7â Axial view of the arterial supply to the vertebrae and spinal canal. From THIEME Atlas of Anatomy: General Anatomy and Musculoskeletal System, © Thieme 2005, Illustration by Karl Wesker.

symptoms. Narrowing can be caused by disk herniations, posterior vertebral body osteophytes, hypertrophy of the ligamentum favum and facet joints, synovial cysts, excessive epidural fat, epidural neoplasms, abscesses, hematomas, spinal fractures, and spondylolisthesis or spondylolysis. MRI is useful for evaluating these disorders and for categorizing the degree of narrowing of the thecal sac, as well as compression of nerve roots in the lateral recesses and intervertebral foramina.

Spinal Development

During the second week of gestation, the developing embryo consists of a layer of cells adjacent to the yolk sac referred to as the hypoblast, and a layer of cells adjacent to the amnion referred to as the epiblast. Cells in the midline of the embryo form the primitive knot (Hensen’s node) and adjacent primitive streak posteriorly. At the beginning of the third week, cells from the rostral portion of the primitive streak (Hensen’s node) extend between the epiblast and hypoblast to eventually form the notochord. The gastrulation stage of development of the spine begins during the third week of gestation, when the bilaminar embryonic disk differentiates into a trilaminar disk con- sisting of endoderm, mesoderm, and ectoderm (Fig.Â1.10). During the third week of gestation, the notochord induces the overlying ectoderm to form the neural plate, which thickens and folds to form the neural tube (this process

is referred to as primary neurulation) (Fig. 1.10). After 5 weeks, the embryonic caudal cell mass forms the secondary neural tube, which will form the tip of the conus medullaris and flum terminale in a process referred to as secondary neurulation.

Between the fourth and ffth weeks of gestation, the notochord also induces adjacent paraxial mesoderm (derived from the primitive streak) to form bilateral somites, which form the myotomes that will eventually develop into the paraspinal muscles and skin and the sclerotomes that will develop into the bones, cartilage, and ligaments of the spinal column (Fig.Â1.10 and Fig.Â1.11). At 5 weeks, each sclerotome separates into superior and inferior halves, which fuse with corresponding halves of the adjacent sclerotomes to form the vertebral bodies (this process is referred to as resegmentation). Portions of the notochord between the newly formed vertebral bodies evolve into the nucleus pulposus of each disk. Chondrif- cation of the vertebrae occurs after 6 weeks, followed by ossifcationafter9weeks.ExceptforC1andC2,eachverte- bra has two ossifcation centers in the vertebral body that merge, and single ossifcation centers in each side of the vertebral arch (Fig.Â1.12). In C1, a single ossifcation center or two or more ossifcation centers can occur in the ante- rior arch. Six ossifcation centers and four synchondroses typically occur in C2 (Fig.Â1.13).

Disruption of any of these developmental processes can lead to the various anomalies of the spinal cord or vertebrae.

Cerebellar tonsillar ectopia. Most common anomaly of CNS. Not associated with myelomeningocele.

Complex anomaly involving the cerebrum, cerebellum, brainstem, spinal cord, ventricles, skull, and dura. Failure of fetal neural folds to develop properly results in altered development affecting multiple sites of the

CNS.

Intradural lipoma (Fig.Â1.20, Fig.Â1.21, and Fig.Â1.22)

Focal dorsal dysraphic spinal cord attached to a lipoma, which has high signal on T1-weighted imaging. The lipoma often extends from the central canal of the spinal cord to the dorsal pial surface, +Âintact dorsal dural margins, and posterior vertebral elements.

Intradural lipomas usually occur in the cervical or thoracic region. Can result in fixation of the upper and mid portions of the spinal cord, or tethering of the lower spinal cord.

Abnormal thickening of the filum terminale can limit the normal developmental ascent of the conus medullaris, resulting in a tethered spinal cord.

Presenting symptoms include leg weakness, back and/ or leg pain, scoliosis, gait problems, and bowel and/or bladder symptoms. Occurs in 0.1% of young children.

Traction on the spinal cord results in decreased blood flow, causing abnormal metabolic changes and neurologic dysfunction. For symptomatic patients, transection of the filum can lead to resolution of symptoms.

Fig.Â1.23â Sagittal T2-weighted imaging shows a dorsal dermal sinus (lower arrow) that extends into the spinal canal through dysraphic posterior elements at the L4–L5 level. There is tethering of the spinal cord, which is attached to a dorsal lipoma (upper arrow).

Fig. 1.24â Sagittal T2-weighted imaging of a 2-year-old male withatetheredlow-lyingspinalcordfromathickenedfilumtermi- nale (arrow) in association with caudal regression and formation of only three sacral segments.

Fig.Â1.25â (a,b)SagittalT2-weighted imaging of a 76-year-old man shows a tethered spinal cord with the conus medullaris at the L4 level (arrow in a) attached to a thickened filum terminale (arrow in b).

Acquired meningoceles are more common than meningoceles resulting from congenital dorsal bony dysraphism or localized weakening of the dura. Anterior sacral meningoceles can result from trauma or be associated with mesenchymal dysplasias

(neurofibromatosis type 1, Marfan syndrome, or syndrome of caudal regression). Multiple lateral meningoceles involving the spine can be seen with a rare hereditary connective tissue disorder (lateral meningocele syndrome), which is often associated

with facial dysmorphism, hypotonia, muscle weakness, scoliosis, abdominal hernias, and cryptorchidism.

a

Fig.Â1.31â (a) Lateral radiograph of a 7-year-old female shows multiple segmentation anomalies of the cervical vertebrae. (b) Sagittal

T1-weightedimagingshowsacircumscribed,intraduralextramedul- lary lesion with high signal anterior to the spinal cord (arrows) representing a neurenteric cyst. (c) Sagittal fat-suppressed T1-weighted imaging shows persistent high signal related to the elevated protein content within the lesion (arrows). (d) The lesion (arrow) has low signal on sagittal fat-suppressed T2-weighted imaging.

b

c

d

Most common congenital anomaly of the craniovertebral junction. Failure of segmentation of the occipital condyles (fourth occipital sclerotome) and the C1 vertebra (first cervical sclerotome). Can be associated with C1–C2 instability.

Atlas anomalies (See Fig. 1.57 and Fig. 1.58)

Unilateral or bilateral hypoplasia/aplasia of the posterior arch of C1. Clefts can also be seen in C1, most commonly at the posterior arch in the midline.

The first spinal sclerotome forms the atlas vertebra, while caudal portions of the proatlas form the lateral masses and upper portions of the posterior arch. Anomalies include aplasia of C1 or partial aplasia/hypoplasia of the posterior arch, ±Âatlanto-axial subluxation. Another, more common type of anomaly involving C1 is clefts in the atlas arches (rachischisis) from developmentally defective cartilage formation. Clefts most commonly occur in the posterior arch in the midline (>Â90%), followed by lateral clefts and anterior clefts.

Os odontoideum (See Fig. 1.59 and Fig. 1.60)

Separate, corticated, bony structure positioned below the basion and superior to the C2 body at the normally expected site of the dens, often associated with enlargement of the anterior arch of C1 (which may sometimes be larger than the adjacent os odontoideum). Instability can result when the gap between the os and the body of C2 is above the plane of the superior articular facets and below the transverse ligament.

Independent bony structure positioned superior to the C2 body and lower dens at the normally expected site of the mid to upper dens, often associated with hypertrophy of the anterior arch of C1, ±Âcruciate ligament incompetence/instability (±Âzone of high signal on T2-weighted imaging in spinal cord). Os odontoideum can be associated with Klippel-Feil anomaly, spondyloepiphyseal dysplasia, Down syndrome, and Morquio syndrome. Possibly a normal variant or due to childhood injury (between 1 and 4 years), with fracture/separation of the cartilaginous plate between the dens and body of axis.

Represents congenital partial or complete fusion of two or more adjacent vertebrae resulting from failure of segmentation of somites (third to eighth weeks

of gestation). Occurs in 1/40,000 births. Can be asymptomatic or result in limitations in range of neck motion. Can be associated with Chiari I malformation, syringohydromyelia, diastematomyelia, anterior meningocele, or neurenteric cyst.

Dysmorphic high-positioned scapula at birth that results from lack of normal caudal migration of the scapula during embryogenesis. During the fifth week of gestation, the scapula develops as a mesenchymal structure adjacent to the C4 or C5 vertebra. From the fifth to twelfth weeks of gestation, the fetal scapula normally migrates inferiorly to its normal position, where the inferior angle is located at the T6–T8 levels. In up to 50% of cases, a fibrous, cartilaginous, and/ or osseous (omovertebral bone) structure is present between the cervical vertebrae and scapula. Surgical resection of the interposed structure between

the scapula and spine can be beneficial. Sprengel deformity can occur in association with Klippel-Feil anomaly, hemivertebrae, diastematomyelia, spina bifida occulta, and morphologic rib and clavicular abnormalities.

Disordered embryogenesis in which the paramedian centers of chondrification fail to merge, resulting in failure of formation of the ossification center on one side of the vertebral body. May be associated with scoliosis.

Disordered embryogenesis in which there is persistence of separate ossification centers in each side of the vertebral body (failure of fusion).

Mild anomaly with failure of fusion of dorsal vertebral arches (lamina) in midline. Usually a benign normal variation.

Usually associated with significant clinical findings related to the severity and type of neural tube defect.

Fig. 1.38â Axial CT shows spina bifida occulta with a midline defect where the lamina do not fuse (arrow).

Fig.Â1.39â Axial CT in a patient with a surgically repaired myeloceleshowsspinabifidaapertawithawidedefectwherelaminaare unfused (arrow).

Developmental variation with potential predisposition to spinal cord injury from traumatic injuries or disk herniations, as well as early symptomatic spinal stenosis from degenerative changes.

Fig.Â1.40â Sagittal T2-weighted imaging of a neonate shows severe caudal regression with agenesis of the lumbar spine, sacrum, and coccyx (arrow). Prominent narrowing of the thecal sac and spinal canal is seen below the lowest normal vertebral level.

Fig.Â1.41â SagittalT1-weightedimagingofaneonatewithcaudal regression syndrome shows agenesis of the lower sacral segments and coccyx, and tethering of the spinal cord containing a distal syrinx from a thickened lipomatous filum terminale (arrows).

Autosomal dominant rhizomelic dwarfism with abnormally reduced endochondral bone formation. Most common nonlethal bone dysplasia and shortlimbed dwarfism, with an incidence of 1/15,000 live births. More than 80–90% of cases are caused by spontaneous mutations involving the gene

that encodes the fibroblast growth factor receptor 3 (FGFR3) on chromosome 4p16.3. Mutations typically occur on the paternal chromosome and are associated with increased paternal age. The mutated gene impairs endochondral bone formation and longitudinal lengthening of long bones.

Neurofibromatosis type 1 CT: Neurofibromas are ovoid or fusiform lesions with

(Fig.Â1.45) low-intermediate attenuation. Lesions can show contrast enhancement. Often erode adjacent bone. Dural dysplasia/ectasia, often with scalloping of the dorsal aspects of vertebral bodies, dilatation of

intervertebral and sacral foraminal nerve sheaths, and lateral meningoceles.

MRI: Neurofibromas are circumscribed or lobulated extra-, intra-, or both intraand extradural lesions, with low-intermediate signal on T1-weighted imaging, intermediate-high signal on T2-weighted imaging (T2WI), +Âprominent gadolinium (Gd) contrast enhancement. High signal on T2WI and Gd contrast enhancement can be heterogeneous in large lesions. Findings with dural dysplasia include erosions of adjacent vertebral bone by dilated dura containing CSF, ±Âlateral meningoceles.

Autosomal dominant disorder (1/2,500 births) caused by mutations of the neurofibromin gene on chromosome 17q11.2. Represents the most common type of neurocutaneous syndrome, and is associated with neoplasms of the central and peripheral nervous systems (optic gliomas, astrocytomas, plexiform

and solitary neurofibromas) and skin lesions (café- au-lait spots, axillary and inguinal freckling). Also associated with meningeal and skull dysplasias, as well as hamartomas of the iris (Lisch nodules). Dural dysplasia/ectasia can involve multiple spinal levels and can also occur with Marfan syndrome.

SMD is a heterogeneous group of bone dysplasias involving vertebrae and metaphyses of appendicular bones. Most common type is the Kozlowski type, SMD-K, which usually has an autosomal dominant inheritance pattern involving mutations of the TRPV4 gene. The TRPV4 gene normally encodes a calcium-permeable cation channel in osteoblasts and

osteoclasts. Other mutations involving the TRPV4 gene are associated with other skeletal dysplasias, such

as brachyolmia and metatropic dysplasia, as well as parastremmatic dysplasia, SMD Maroteaux type, and familial digital arthropathy. SMD-K has a prevalence of 1/100,000. Results in dwarfism (adult height <Â140 cm). Patients appear normal at birth, but present with a waddling gait at 1 to 4 years. Clinical findings include short stature, short trunk, bowlegs, and a short and broad thorax.

Table 1.2â Abnormalities involving the craniovertebral junction

•Congenital and Developmental –â Basiocciput hypoplasia

–â Chiari I malformation –â Chiari II malformation –â Chiari III malformation –â Condylus tertius

–â Atlanto-occipital assimilation/nonsegmentation –â Atlas anomalies

–â Os odontoideum –â Achondroplasia

–â Down syndrome (Trisomy 21) –â Ehlers-Danlos syndrome

–â Mucopolysaccharidosis (MPS) –â Osteogenesis imperfecta (OI) –â Neurenteric cyst

–â Ecchordosis physaliphora

•Osteomalacia

–â Renal osteodystrophy/secondary hyperparathyroidism

–â Paget disease

–â Fibrous dysplasia

–â Hematopoietic disorders

•Traumatic Lesions

–â Fracture of skull base

–â Atlanto-occipital dislocation –â Jefferson fracture (C1)

–â Hangman’s fracture (C2) –â Odontoid fracture (C2)

•Infammation

–â Osteomyelitis/epidural abscess –â Langerhans’ cell histiocytosis –â Rheumatoid arthritis

–â Calcium pyrophosphate dihydrate (CPPD) deposition

•Malignant Neoplasms –â Metastatic disease –â Myeloma

–â Chordoma

–â Chondrosarcoma

–â Squamous cell carcinoma –â Nasopharyngeal carcinoma –â Adenoid cystic carcinoma –â Invasive pituitary tumor

•Benign Neoplasms –â Meningioma –â Schwannoma –â Neurofbroma

•Tumorlike Lesions –â Epidermoid

–â Arachnoid cyst

–â Mega cisterna magna

The lower clivus is a portion of the occipital bone (basiocciput), which is composed of four fused sclerotomes. Failure of formation of one or more of the sclerotomes results in a shortened clivus and primary basilar invagination (dens extending > 5 mm above Chamberlain’s line). Can be associated with hypoplasia of the occipital condyles. The occipital condyles develop from the ventral segment of the proatlas derived from the fourth occipital sclerotome.

Cerebellar tonsillar ectopia. Most common anomaly of CNS. Not associated with myelomeningocele.

Condylus tertius, or third occipital condyle, results from lack of fusion of the lowermost fourth sclerotome (proatlas) with the adjacent portions of the clivus. The third occipital condyle can form a pseudojoint with the anterior arch of C1 and/or

dens and can be associated with decreased range of movement.

Fig.Â1.52â SagittalT1-weightedimagingshowsbasiocciputhypo- plasia, with the dens extending intracranially above Chamberlain’s line by more than 5 mm.

Fig.Â1.53â Sagittal T1-weighted imaging in a 19-year-old woman shows a Chiari I malformation, with the cerebellar tonsils (arrow) extending below the foramen magnum to the level of the posterior arch of the C1 vertebra. The fourth ventricle has a normal appearance.

The first spinal sclerotome forms the atlas, while caudal portions of the proatlas form the lateral masses and upper portions of the posterior arch. Anomalies include aplasia of C1, or partial aplasia/hypoplasia of the posterior arch, ± atlanto-axial subluxation. Another more common anomaly involving C1 is rachischisis, clefts in the altas arches caused by developmentally defective cartilage formation. Clefts most commonly occur in the posterior arch in the midline (> 90%), followed by lateral clefts, and anterior clefts.

Independent bony structure positioned superior to the C2 body and lower dens at site of normally expected mid to upper dens, often associated with hypertrophy of the anterior arch of C1, ± cruciate ligament incompetence/instability (± zone of high signal on T2-weighted imaging in spinal cord). Os odontoideum can be associated with Klippel-Feil anomaly, spondyloepiphyseal dysplasia, Down

syndrome, and Morquio syndrome. Os odontoideum is considered to be a normal variant or arising from a childhood injury (between 1 and 4 years), with

fracture/separation of the cartilaginous plate between the dens and body of axis.

Ehlers-Danlos syndrome Separation between the anterior arch of C1 and the anterior margin of the upper dens by more than 5 mm and narrowing of the spinal canal, ± indentation on the spinal cord.

Mutation involving genes involved with the formation or processing of collagen, which results in ligamentous laxity at the atlanto-axial joint.

Osteogenesis imperfecta (OI) Diffuse osteopenia, decreased ossification of skull

(Fig.Â1.64) base with microfractures, infolding of the occipital condyles, elevation of the posterior cranial fossa and posterior cranial fossa, and upward migration of the dens into the foramen magnum, resulting in basilar impression (secondary basilar invagination).

Also known as brittle bone disease, OI has four to seven types. OI is a hereditary disorder with abnormal type I fibrillar collagen production and osteoporosis resulting from mutations involving the COL1A1

gene on chromosome 17q21.31-q22.05 and the COL1A2 gene on chromosome 7q22.1. OI results in fragile bone prone to repetitive microfractures and remodeling. Type IV is most commonly associated with abnormalities at the craniovertebral junction.

Neurenteric cysts are malformations in which there is a persistent communication between the ventrally located endoderm and the dorsally located ectoderm secondary to developmental failure of separation of the notochord and foregut. Obliteration of portions of a dorsal enteric sinus can result in cysts lined by endothelium, fibrous cords, or sinuses. Observed in patients < 40 years old. Location: thoracic > cervical > posterior cranial fossa > craniovertebral junction > lumbar. Usually midline in position and often ventral to the spinal cord or brainstem. Associated with anomalies of the adjacent vertebrae and clivus.

Ecchordosis physaliphora MRI: Circumscribed lesion ranging in size from 1 to 3 cm, with low signal on T1-weighted imaging, intermediate signal on FLAIR, and high signal on T2weighted imaging. Typically shows no gadolinium contrast enhancement.

CT: Lesions typically have low attenuation,

±remodeling/erosion of adjacent bone,

±small calcified bone stalk.

Congenital benign hamartoma composed of gelatinous tissue with physaliphorous cell nests derived from ectopic vestigial notochord. Incidence at autopsy ranges from 0.5 to 5%. Usually located intradurally, dorsal to the clivus and dorsum sella within the prepontine cistern, and rarely dorsal to the upper cervical spine or sacrum. Rarely occurs as an

extradural lesion. Derived from an ectopic notochordal remnant or from extension of extradural notochord at the dorsal wall of the clivus through the adjacent dura into the subarachnoid space. Typically is asymptomatic and is observed as an incidental finding in patients between the ages of 20 and 60 years.

Paget disease (Fig.Â1.66)

Expansile sclerotic/lytic process involving the skull.

CT: Lesions often have mixed intermediate and high attenuation. Irregular/indistinct borders between marrow and inner margins of the outer and inner tables of the skull.

MRI: MRI features vary based on the phases of the disease. Most cases involving the skull and vertebrae are the late or inactive phases. Findings include osseous expansion and cortical thickening with low signal on

T1and T2-weighted imaging. The inner margins of the thickened cortex can be irregular and indistinct. Zones of low signal on T1and T2-weighted imaging can be seen in the diploic marrow secondary to thickened bony trabeculae. Marrow in late or inactive phases of Paget disease can have signal similar to normal marrow, contain focal areas of fat signal, have low signal on

T1and T2-weighted imaging secondary to regions of sclerosis, have areas of high signal on fat-suppressed T2-weighted imaging caused by edema or persistent fibrovascular tissue, or have various combinations of the aforementioned.

Paget disease is a chronic skeletal disease in which there is disordered bone resorption and woven bone formation, resulting in osseous deformity. A paramyxovirus may be the etiologic agent. Paget disease is polyostotic in up to 66% of patients. Paget

disease is associated with a risk of < 1% for developing secondary sarcomatous changes. Occurs in 2.5 to 5% of Caucasians more than 55 years old, and in 10% of those more than 85 years old. Can result in narrowing of neuroforamina, with cranial nerve compression and basilar impression, ± compression of brainstem.

Benign medullary fibro-osseous lesion of bone, most often sporadic. Fibrous dysplasia involving a single site is referred to as monostotic (80–85%) and that involving multiple locations is known as polyostotic fibrous dysplasia. Results from developmental failure in the normal process of remodeling primitive bone to mature lamellar bone, with resultant zone or zones of immature trabeculae within dysplastic fibrous tissue.

The lesions do not mineralize normally and can result in cranial neuropathies caused by neuroforaminal narrowing, facial deformities, sinonasal drainage disorders, and sinusitis. Age at presentation is < 1 year to 76 years; 75% of cases occur before the age of 30 years. Median age for monostotic fibrous dysplasia

= 21 years; mean and median ages for polyostotic fibrous dysplasia are between 8 and 17 years. Most cases are diagnosed in patients between the ages of 3 and 20 years.

Thickening of diploic space related to erythroid hyperplasia caused by inherited anemias, such as sickle-cell disease, thalassemia major, and hereditary spherocytosis. Sickle-cell disease is the most common hemoglobinopathy, in which abnormal hemoglobin S is combined with itself, or other hemoglobin

types such as C, D, E, or thalassemia. Hemoglobin SS, SC, and S-thalassemia have the most sickling of erythrocytes. In addition to marrow hyperplasia seen

in sickle-cell disease, bone infarcts and extramedullary hematopoeisis can also occur. Beta-thalassemia is

a disorder in which there is deficient synthesis of β chains of hemoglobin, resulting in excess α chains in erythrocytes, causing dysfunctional hematopoiesis and hemolysis. The decrease in β chains can be severe in the major type (homozygous), moderate in the intermediate type (heterozygous), or mild in the minor type (heterozygous).

Traumatic fractures of the skull (calvarium and/or skull base), occipital condyles, C1, and/or C2 can be associated with traumatic injury of brainstem and upper spinal cord, epidural hematoma, subdural hematoma, subarachnoid hemorrhage, and CSF leakage (rhinorrhea, otorrhea).

Hangman’s fracture (C2) Disrupted ring of C2 caused by bilateral pedicle (Fig.Â1.71) fractures separating the C2 body from the posterior

arch of C2. Skull, C1, and C2 body are displaced anterior with respect to C3.

Unstable injury due to traumatic bilateral pedicle fractures caused by hyperextension and distraction mechanisms, with separation of the C2 body from the posterior arch of C2. Fractures can extend into the C2 body and/or through the foramen transversarium, with injury/occlusion of the vertebral artery. Often associated with spinal cord injury.

Osteomyelitis (bone infection) of the skull base and upper cervical vertebrae can result from surgery, trauma, hematogenous dissemination from another source of infection, or direct extension of infection from an adjacent site, such as the sphenoid sinus, nasopharynx, oropharynx, petrous apex air cells, and/ or mastoid air cells.

Multiple myeloma are malignant tumors composed of proliferating antibody-secreting plasma cells derived from single clones. Multiple myeloma primarily involves bone marrow. A solitary myeloma or plasmacytoma is an infrequent variant in which a neoplastic mass of plasma cells occurs at a single site of bone or soft tissues. In the United States,

14,600 new cases occur each year. Multiple myeloma is the most common primary neoplasm of bone in adults. Median age at presentation = 60 years. Most patients are more than 40 years old. Tumors occur in the vertebrae > ribs > femur > iliac bone > humerus > craniofacial bones > sacrum > clavicle > sternum > pubic bone > tibia.

Chordomas are rare, locally aggressive, slowgrowing, low to intermediate grade malignant tumors derived from ectopic notochordal remnants along the axial skeleton. Chondroid chondromas

(5–15% of all chordomas) have both chordomatous and chondromatous differentiation. Chordomas that contain sarcomatous components are referred to as dedifferentiated chordomas or sarcomatoid

chordomas (5% of all chordomas). Chordomas account for 2–4% of primary malignant bone tumors, 1–3% of all primary bone tumors, and < 1% of intracranial tumors. The annual incidence has been reported to be

0.18 to 0.3 per million. Dedifferentiated chordomas or sarcomatoid chordomas account for less than 5% of all chordomas. For cranial chordomas, patients’ mean age = 37 to 40 years.

Chondrosarcomas are malignant tumors containing cartilage formed within sarcomatous stroma.

Chondrosarcomas can contain areas of calcification/ mineralization, myxoid material. and/or ossification.

Chondrosarcomas rarely arise within synovium.

Chondrosarcomas represent 12–21% of malignant bone lesions, 21–26% of primary sarcomas of bone, 9–14% of all bone tumors, 6% of skull base tumors, and 0.15% of all intracranial tumors.

Squamous cell carcinoma MRI: Destructive lesions in the nasal cavity, paranasal sinuses, and nasopharynx, ± intracranial extension via bone destruction or perineural spread. Intermediate signal on T1-weighted imaging, intermediate-slightly high signal on T2-weighted imaging, and mild gadolinium contrast enhancement. Can be large lesions (± necrosis and/or hemorrhage).

CT: Tumors have intermediate attenuation and mild contrast enhancement. Can be large lesions

(± necrosis and/or hemorrhage).

Malignant epithelial tumors originating from the mucosal epithelium of the paranasal sinuses (maxillary sinus, 60%; ethmoid sinus, 14%; sphenoid and frontal sinuses, 1%) and nasal cavity (25%). Includes both keratinizing and nonkeratinizing types. Accounts for

3% of malignant tumors of the head and neck. Occurs in adults, usually > 55 years old, and in males more than in females. Associated with occupational or other exposure to tobacco smoke, nickel, chlorophenols, chromium, mustard gas, radium, and material in the manufacture of wood products.

Nasopharyngeal carcinoma CT: Tumors have intermediate attenuation and mild contrast enhancement. Can be large lesions (± necrosis and/or hemorrhage).

MRI: Invasive lesions in the nasopharynx (lateral wall/ fossa of Rosenmüller, and posterior upper wall),

± intracranial extension via bone destruction or perineural spread. Lesions have intermediate signal on T1-weighted imaging, intermediate-slightly high signal on T2-weighted imaging, and often gadolinium contrast enhancement. Can be large lesions

(± necrosis and/or hemorrhage).

Carcinomas arising from the nasopharyngeal mucosa with varying degrees of squamous differentiation.

Subtypes include squamous cell carcinoma, nonkeratinizing carcinoma (differentiated and undifferentiated), and basaloid squamous cell carcinoma. Occur at higher frequency in Southern Asia and Africa than in Europe and the Americas.

Peak ages: 40–60 years. Nasopharyngeal carcinoma occurs two to three times more frequently in men than in women. Associated with Epstein-Barr virus, diets containing nitrosamines, and chronic exposure to tobacco smoke, formaldehyde, chemical fumes, and dust.

Adenoid cystic carcinoma MRI: Destructive lesions with intracranial extension via bone destruction or perineural spread, with intermediate signal on T1-weighted imaging, intermediate-high signal on T2-weighted imaging, and variable mild, moderate, or prominent gadolinium contrast enhancement.

CT: Tumors have intermediate attenuation and variable mild, moderate, or prominent contrast enhancement.

Basaloid tumor comprised of neoplastic epithelial and myoepithelial cells. Morphologic tumor patterns include tubular, cribriform, and solid. Accounts for

10% of epithelial salivary neoplasms. Most commonly involves the parotid, submandibular, and minor salivary glands (palate, tongue, buccal mucosa,

and floor of the mouth, as well as other locations).

Perineural tumor spread is common, ± facial nerve paralysis. Usually occurs in adults > 30 years old. Solid type has the worst prognosis. Up to 90% of patients die within 10–15 years of diagnosis.

Benign slow-growing tumors involving cranial and/ or spinal dura that are composed of neoplastic meningothelial (arachnoidal or arachnoid cap) cells. Usually solitary and sporadic but can also occur as multiple lesions in patients with neurofibromatosis type 2. Most are benign, although ~Â5% have atypical histologic features. Anaplastic meningiomas are rare and account for less than 3% of meningiomas.

Meningiomas account for up to 26% of primary intracranial tumors. Annual incidence is 6 per 100,000.

Typically occur in adults (> 40 years old), and in women more than in men. Can result in compression of adjacent brain parenchyma, encasement of arteries, and compression of dural venous sinuses.

Schwannomas are benign encapsulated tumors that contain differentiated neoplastic Schwann cells.

Multiple schwannomas are often associated with neurofibromatosis type 2 (NF2), which is an autosomal dominant disease involving a gene mutation at chromosome 22q12. In addition to schwannomas, patients with NF2 can also have multiple meningiomas and ependymomas.

Schwannomas represent 8% of primary intracranial tumors and 29% or primary spinal tumors. The incidence of NF2 is 1/37,000 to 1/50,000 newborns. Age at presentation is 22 to 72 years (mean age = 46 years). Peak incidence is in the fourth to sixth decades. Many patients with NF2 present in the third decade with bilateral vestibular schwannomas.

Benign nerve sheath tumors that contain mixtures of Schwann cells, perineural-like cells, and interlacing fascicles of fibroblasts associated with abundant collagen. Unlike schwannomas, neurofibromas lack

Antoni A and B regions and cannot be separated pathologically from the underlying nerve. Most frequently occur as sporadic, localized, solitary lesions, less frequently as diffuse or plexiform lesions. Multiple neurofibromas are typically seen with neurofibromatosis type 1, which is an autosomal dominant disorder (1/2,500 births) caused by mutations of the neurofibromin gene on chromosome 17q11.2.

Epidermoid cysts are ectoderm-lined inclusion cysts that contain only squamous epithelium, desquamated skin epithelial cells, and keratin. Result from persistence of ectodermal elements at sites of neural tube closure and suture closure. Can occur within bone or as an extra-axial lesion.

Fig.Â1.84â Sagittal T1-weighted imaging shows a large arachnoid cyst with CSF signal in the posterior cranial fossa associated with anterior displacement of the vermis and erosion of the inner table of the occipital bone.

Fig.Â1.85â Sagittal T2-weighted imaging shows a slightly enlarged posterior cranial fossa with prominent cisterna magna filled with

CSF located below the cerebellum and cerebellar tonsils.