Книги по МРТ КТ на английском языке / MRI for Orthopaedic Surgeons Khanna ed 2010

Table 10.3 Acquired and Congenital Factors Associated with Spinal Stenosis

ossification, ossification of the posterior longitudinal ligament, di use idiopathic skeletal hyperostosis)

Spondylosis

Metabolic Postinflammatory Spondylolisthesis Postoperative Neoplastic

Congenital Idiopathic with short pedicles Skeletal growth disorders Down syndrome Achondroplasia Mucopolysaccharidosis Scoliosis

•Ligamentum flavum hypertrophy

•Facet arthrosis

•Thickening, calcification, or ossification of the posterior longitudinal ligament or other structures

On MRI, central canal stenosis is characterized by compression of the thecal sac, best seen on the sagittal and axial T2-weighted images. Such images provide a “myelographic e ect,” in which the CSF is seen as bright signal anterior and posterior to the spinal cord on sagittal images and circumferentially around the spinal cord on axial images. E acement, discontinuity, or displacement of this CSF space is seen in patients with focal and concentric spinal stenosis.

The degree of central canal stenosis can range from mild encroachment on the ventral subarachnoid space to severe compression and flattening of the spinal cord with myelomalacia. MRI findings may correspond to the severity and duration of the compression.45 Early changes of spinal cord compression can be seen as cord edema (high signal areas on T2-weighted images); progressive compression may cause spinal cord necrosis and atrophy (Fig. 10.26), cystic degeneration, and syrinx formation (low signal on T1-weighted and high signal on T2-weighted images).45

Fig. 10.25 Illustrations of various potential contributors to cervical spinal stenosis: central disc bulge, facet joint hypertrophy, and ligamentum flavum hypertrophy. (A) An axial view showing central

by dividing the AP canal diameter by the AP vertebral body diameter, with a ratio <0.8 defined as stenotic.53 This ratio is often used to evaluate for congenital stenosis in athletes. Although such definitions are well known, most clinicians and radiologists tend to grade the degree of spinal stenosis using the terms mild, moderate, and severe, as well as gradations such as moderate–severe. The authors tend to use the following terms and definitions (Figs. 10.28 and 10.29):

•Mild—stenosis occupying less than one third of normal canal dimension in which the ventral and dorsal CSF spaces are partially e aced by disc bulging, ligamentum flavum hypertrophy, and facet arthropathy; no mass e ect on the cord

•Moderate—stenosis occupying between one and two thirds of normal canal dimension; findings similar to those of mild stenosis but with compression and minimal flattening and deformity of the spinal cord

stenosis. (B) An axial view showing foraminal stenosis. (C) A lateral view showing central stenosis with cord compression. (D) A 3D view showing foraminal stenosis.

•Severe—stenosis occupying more than two thirds of normal canal dimension, with advanced stenosis with very pronounced flattening and deformity of the spinal cord that is obvious on both sagittal and axial T2weighted images

Occipitocervical Stenosis

Occipitocervical stenosis is not typically degenerative; it can occur secondary to congenital and developmental processes, such as Arnold Chiari malformation and cranial settling, in patients with RA. Other nontraumatic causes of occipitocervical stenosis and instability include occipital, C1, and C2 dysplasia and anomalies; Down syndrome; and tumors. Because of the complexity of the occipitocervical junction, normal relationships are defined using landmarks originally described on conventional radiography.54,55 Many of these

Fig. 10.27 Cervical stenosis. (A) A midline sagittal T2-weighted image shows multilevel degenerative disc disease with mild spondylolisthesis at C3-C4 and thickening of the posterior longitudinal ligament at multiple levels. There is focal thickening of the ligamentum flavum at the C5-C6 level (arrow). (B) A parasagittal T2-weighted image obtained several millimeters lateral to the midline shows e acement of the ventral CSF space and moderate stenosis at the C4-C5

to lie in a more caudal position.60 In some cases, it has been reported to be as inferior as the C2-C3 disc space.60,62,63,67 Two studies reported on the use of MRI to measure the space available for the cord as a technique for predicting recovery after cervical stabilization for patients with RA and atlantoaxial instability.62,63 A cord space, or space available for the cord, of >14 mm on MRI was associated with better clinical outcomes than was a space of <10 mm, which was associated with a poor prognosis.62,63 Flexion–extension MRI is particularly useful for evaluating patients with RA and specifically those with instability at the occipitocervical junction and suboccipital cervical spine (Fig. 10.32), especially because supine extension MRI does not account for the commonly occurring subluxations in such patients that are exaggerated with movement. Similar information can be obtained by combining the information obtained from a static (conventional) MRI study and flexion–extension cervical spine radiographs (Fig. 10.10).

level (arrow) from osteophyte formation and thickening of the posterior longitudinal ligament. Similar, but less severe, changes are seen at the C5-C6 level (arrowhead). (C) A parasagittal T2-weighted image obtained farther laterally in the plane of the neuroforamina shows severe foraminal stenosis at the C4-C5 level (arrow) and moderate foraminal stenosis at the C5-C6 level (arrowhead).

MRI can detect pannus formation in the cervical spine well before conventional radiographic signs become evident. In addition, involvement of the facet joints (inflammation, edema, and fusion) may be detected on MRI. Patients with RA may also present with a rheumatoid discitis that manifests as increased T2-weighted and decreased T1-weighted signal in the disc. The substantial di erences between imaging and clinical features of RA in the spine have been documented and are well known.68,69

■ Infectious Conditions

The treatment of spinal infections continues to be a challenge despite advances in imaging, diagnostic testing, and antimicrobial therapy. A delay in diagnosis is common because spinal infections often have an early indolent course and early symptoms may be nonspecific (neck pain, muscle

Fig. 10.28 Grading of cervical stenosis: mild to moderate-severe. (A) A sagittal T2-weighted image showing minimal spondylolisthesis at C4-C5 with moderate stenosis at this level. (B) An axial T2-weighted image at the C5-C6 level showing mild stenosis secondary to a central disc bulge (arrow), ligamentum flavum hypertrophy (arrowhead), and facet arthropathy (asterisk). (C) Axial T2-weighted image at the

spasm), leading to a misdiagnosis of more common spinal ailments (e.g., muscle strain, degenerative disease). Spine infections may involve the vertebral body, posterior elements, intervertebral discs, epidural space, subdural space, subarachnoid space, or the spinal cord.

C4-C5 level shows moderate stenosis secondary to more substantial central disc bulge (arrow), ligamentum flavum hypertrophy (arrowhead), and facet arthropathy (asterisk). (D) Axial T2-weighted image (di erent patient) showing moderate-severe stenosis at the C5-C6 level as a result of even greater central disc bulge (arrow) and ligamentum flavum hypertrophy (arrowhead).

Cervical Vertebral Osteomyelitis and Discitis

Infections of the cervical spine account for approximately 10% of spine infections and are less common than thoracic (approximately 40%) or lumbar (approximately 50%) spine

Fig. 10.29 Grading of cervical stenosis: severe. (A) A sagittal T2weighted image showing severe stenosis at the C3-C4 level and moderate to moderate-severe stenosis at the C4-C5, C5-C6, and C6-C7 levels. (B) An axial image at the C3-C4 level shows very severe stenosis with complete obliteration of the CSF space and compression of the spinal cord to an AP diameter of 2 mm secondary to a cen-

infections.70 Anatomic di erences between the cervical and thoracolumbar spine (smaller canal diameter, intervertebral discs, and epidural space, and a vast venous plexus) may allow cervical spine infections to have a more aggressive and rapid progression that requires expedited treatment.71 In general, the clinical presentation of vertebral osteomyelitis and discitis has variable signs and symptoms, including fever (approximately 50% of the time), weight loss, and neck or back pain, that do not vary with activity level. Neurologic symptoms may vary based on the level of spinal involvement, spinal cord compression, spinal instability, or deformity.17,18,70–73 Neurologic deficits secondary to spinal

tral disc bulge and severe ligamentum flavum hypertrophy (arrow).

(C) An axial T2-weighted image at the C4-C5 level showing severe (but less severe than in B) stenosis with compression and deformity of the spinal cord with minimal CSF seen in the lateral recesses bilaterally. (Images courtesy of Mesfin A. Lemma, MD.)

infection are more common in patients more than 50 years old and in those with comorbidities such as diabetes, RA, and immunodeficiency.17,70

Bacterial inoculation of the spine may occur through hematogenous seeding, direct inoculation, or contiguous spread from local infection. Staphylococcus aureus is the most commonly cultured organism causing cervical osteomyelitis and discitis.70,74 It is found in 50% to 65% of culture-positive cases and accounts for >80% of pediatric spinal infections.74 Gramnegative infections (Escherichia coli, Pseudomonas, Proteus) may occur after genitourinary infections. Immunocompromised patients are susceptible to infections with atypical

Fig. 10.31 A sagittal T1-weighted image of the brain and upper cervical spine shows inferior migration of the cerebellar tonsils (arrow) below the level of the foramen magnum compatible with a type 1 Arnold Chiari malformation.

Epidural Abscess

A spinal epidural abscess is a collection of purulent material outside the dura mater. An epidural abscess is usually associated with vertebral osteomyelitis, and direct extension from an adjacent infected vertebral body is the most common source for an epidural abscess.71 Epidural abscesses are less common in the cervical spine than in the thoracic or lumbar spine and may be located anterior or posterior to the spinal cord.71 Multiple spinal segments are usually involved (most commonly, C4 to C7).71