Книги по МРТ КТ на английском языке / MRI for Orthopaedic Surgeons Khanna ed 2010
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Fig. 10.24 Degenerative upon congenital ste- |
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nosis. (A) A sagittal T1-weighted image shows a |
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developmentally shortened AP dimension of the |
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spinal canal. (B) A sagittal T2-weighted image |
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shows a small disc bulge at the C4-C5 level that |
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causes spinal cord signal abnormality, represent- |
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ing spondylotic myelomalacia (arrow). (C) An axial |
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T2-weighted image shows the moderate to severe |
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central canal stenosis. |
Given that the great majority of cervical spine MRI stud- |
of the CSF column and spinal cord compression, whereas the |
ies are obtained to evaluate for the presence, location, and |
parasagittal images allow for visualization of lateral recess |
degree of degenerative cervical spinal stenosis, one should |
and foraminal stenosis (Fig. 10.27). The information from |
have a systematic approach to the evaluation of these stud- |
these images should be correlated with that from the axial |
ies. The authors’ suggested approach for the evaluation of |
images, which show the same pathology in an orthogonal |
a cervical spine MRI study (see Chapter 3) includes a criti- |
plane. |
cal evaluation of the degree of spinal cord and nerve root |
There are several objective measures of cervical spinal |
compression on the sagittal, parasagittal, and axial T2- |
stenosis. Relative stenosis is defined as an AP canal diameter |
weighted images. The midline sagittal T2-weighted images |
of <13 mm, and absolute stenosis is defined as an AP canal |
provide a global view of the levels and degree of e acement |
diameter of <10 mm. The Torg or Pavlov ratio is calculated |
254 IV Spine
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Fig. 10.26 Spinal cord atrophy. (A) A sagittal T2-weighted |
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image showing moderate-severe stenosis at C4-C6, with |
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resultant atrophy of the spinal cord at the level of C5 and |
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regions of cord edema proximal and distal to the region of |
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atrophy. (B) A sagittal T1-weighted image showing a seg- |
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ment of low signal intensity within the spinal cord from |
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C4-C5 to C6-C7. (C) An axial T2-weighted image at the C4-C5 |
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A, B |
level showing atrophy of the spinal cord and indistinct mar- |
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gins between the spinal cord and the surrounding CSF. |
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relationships and lines have now been extrapolated for use |
○ Associated with spina bifida aperta and myelome- |
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with MR and CT imaging and can be used to diagnose and |
ningocele |
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quantify the degree of basilar invagination and cranial set- |
○ Not usually associated with atlantooccipital assim- |
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tling (Table 10.4; Fig. 10.30). |
ilation or basilar invagination60 |
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• Type III |
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Chiari Malformations |
○ Defined as herniation of the hindbrain into a high |
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cervical encephalocele |
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Chiari malformations result in a caudal migration of the cer- |
○ Occurs rarely60,61 |
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ebellar tonsils to and through the foramen magnum with |
RA |
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resultant occipitocervical stenosis. Although many such |
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malformations are minor, incidentally noted findings, ad- |
RA is a systemic disease that causes inflammation of syno- |
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vanced lesions can produce symptoms, and thus may benefit |
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vial joints. The synovial joints develop pannus secondary to |
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from a neurosurgical evaluation and eventual suboccipital |
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erosion of supporting ligamentous structures and the asso- |
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decompression. Three types of Chiari malformations have |
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ciated instability.60,62,63 In the cervical spine, this condition |
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been described56,57: |
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may a ect the craniocervical junction as well as the subaxial |
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• Type I (Fig. 10.31) |
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cervical spine, as described below.60,62–65 Most commonly, |
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○ Defined as a defect in the cerebellum with a down- |
atlantoaxial instability develops secondary to erosion of the |
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ward displacement of the tonsils >5 mm below the |
ligaments at the occipitocervical junction.62,63 As the disease |
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plane of the foramen magnum58,59 |
progresses, erosion of the lateral masses of C1, the occipital |
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○ Associated with basilar invagination in 50%, atlan- |
condyles, and facets of C2 occurs, resulting in cranial set- |
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tooccipital assimilation in 10%, and Klippel-Feil |
tling.60,62,63 As the odontoid process begins to occupy a rela- |
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syndrome in 5%58,59 |
tively more rostral position, it compresses the brainstem and |
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• Type II |
vertebrobasilar system. This pathologic process is postulated |
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○ Results from dysgenesis of the hindbrain60 |
by some as the etiology of sudden death in those with ad- |
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○ Involves herniation of the inferior cerebellar ver- |
vanced RA.60,62,63,66 It is important to note that in contrast |
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mis, fourth ventricle, and medulla |
to other disorders, the C1 arch migrates with the skull base |
258 |
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Table 10.4 Occipitocervical Junction: Anatomic Relationships, and |
nuclear scintigraphy in identifying vertebral osteomyelitis.71 |
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Lines for Use with MRI, CT, and Conventional Radiographs |
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Infectious spondylitis may present with findings such as |
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Eponym |
Parameters |
Pathology |
low T1-weighted signal with or without high T2-weighted |
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signal (high signal is often more evident on fat-suppressed |
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Wackenheim’s |
Tangent drawn along |
Dens should be |
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T2-weighted or STIR images); increased T2-weighted signal |
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clivus |
the superior surface |
below the line. |
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baseline |
of the clivus |
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within the intervertebral disc; contrast enhancement in the |
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Clivus canal |
Angle formed between |
Normal ranges are |
disc, subchondral marrow, and epidural space; erosion of |
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angle |
Wackenheim’s line |
180 degrees in |
end plates; epidural fluid collections; paraspinous soft-tissue |
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and the posterior |
extension to |
abnormalities; and posterior element involvement17,71,73,75 |
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vertebral body line |
150 degrees in |
(Fig. 10.33). Unfortunately, these imaging characteristics |
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flexion; an angle |
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are the same as those of many spine pathologies, includ- |
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of <150 degrees |
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is considered |
ing neoplastic disease. One can di erentiate infection from |
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abnormal. |
other processes a ecting the vertebral body bone marrow by |
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Chamberlain’s |
Between the hard |
Protrusion of the |
noting that the epicenter of the former pathology tends to be |
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line |
palate and the |
dens >3 mm |
at the intervertebral disc. Conversely, neoplastic processes |
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opisthion |
above this line |
tend to have their epicenters within the vertebral body, and |
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is considered |
the edema tends not to cross the intervertebral disc. In |
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abnormal. |
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addition, the vertebral end plate may have an irregular ap- |
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McRae’s line |
Basion to the opisthion |
Protrusion of the |
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pearance because of infectious destruction, and disc height |
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dens above this |
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loss or collapse may occur with progressive infection. On |
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line is abnormal. |
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McGregor’s |
From the hard palate |
Odontoid process |
gadolinium-enhanced images, disc enhancement is an es- |
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sential factor for the diagnosis of discitis, and enhancement |
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line |
to the most caudal |
rising >4.5 mm |
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point on the midline |
above this line |
of the vertebral subchondral bone may indicate a well- |
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occipital curve |
is considered |
established and chronic infection.17,71,73 |
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abnormal. |
In comparison with other bacterial infections, Mycobac- |
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Ranawat |
Distance between |
Measurement of <15 |
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terium tuberculosis infection of the spine has some distinct |
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criterion |
the center of the |
mm in males and |
di erences: |
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pedicle of C2 and |
<13 mm in females |
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the transverse axis |
is abnormal. |
• Intervertebral discs are damaged less or completely |
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of C1 |
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spared and may not show signal enhancement on T2- |
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Welcher’s |
Tangent to the clivus |
The normal range |
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weighted images.71 |
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basal angle |
as it intersects a |
is 125 to 143 |
• Tuberculous spondylodiscitis is a slow-growing pro- |
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tangent to the |
degrees; platybasia |
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cess that often results in marked collapse of the verte- |
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sphenoid bone |
exists when the |
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basal angle is >143 |
bral bodies. |
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degrees. |
• Subligamentous spread of infection is often observed. |
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• Telescoping of one vertebral body disc into an adjacent |
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bacteria, such as Aspergillus, Candida, Nocardia asteroides, |
level may be seen. |
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Gadolinium-enhanced MRI also is essential for monitor- |
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and Mycobacterium. Pseudomonas infections may occur in |
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intravenous drug abusers. Children with sickle cell disease |
ing the e cacy of treatment of vertebral infection.76 With |
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may develop spine infections secondary to Salmonella. |
appropriate treatment of the infection, a regression of the |
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Isolated discitis is common in the pediatric population be- |
T2-weighted signal hyperintensity is observed.73 Scar for- |
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cause vascularity extends through the cartilaginous growth |
mation within the intervertebral disc is seen as a region |
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plate into the nucleus pulposus, allowing direct deposition |
of low signal intensity. A region of mottled signal inten- |
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of bacteria into the disc center. In adults, blood vessels reach |
sity may also develop within the area of previous infection |
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only the annulus fibrosus, limiting bacterial deposition to |
with associated contrast enhancement. Over time, osteo- |
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the vertebral body metaphysis and end plate. In adult in- |
phytic bridging may occur, followed by segmental fusion.73 |
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fections, intervertebral disc destruction may occur through |
It should be noted, however, that a lack of improvement on |
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bacterial proteolytic enzyme infiltration. |
MRI and even deterioration of MRI features in the setting of |
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MRI is the imaging modality of choice for the diagnosis |
clinical improvement do not necessarily indicate failure of |
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and evaluation of spinal infections and for monitoring the |
treatment.77,78 |
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response to treatment.71 High sensitivity (96%), specificity |
In the postoperative patient, evaluation for cervical spine |
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(93%), and accuracy (94%) have been reported for the MRI |
infection may be complicated by the normal enhancement of |
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diagnosis of vertebral osteomyelitis.51 MRI is more sensitive |
the uninfected disc. MRI findings of infection in a postopera- |
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than conventional radiographs or CT and more specific than |
tive patient include contrast enhancement of the subchon- |