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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_6034_Библиотеки_им_академика_М_И_Перельмана.pdf
penetrate the PLL and migrates beneath the PLL cranially or caudally as a fragment and is separated from
the remaining portion intervertebral disc.
The schema proposed by Herzog (57) is more related
to practical experience concerning protrusion and extrusion.
Protrusion is a herniation of disc material and not only
nuclear material. It results in a focal contour abnormality
of the disc margin (Fig. 42-6).
Extrusion means penetration of the outer annulus of
any disc material, including possible bony fragments
(Figs. 42-10, 42-11). This material may remain beneath
the PLL and is called subligamentous extrusion. If it penetrates through the PLL it is called transligamentous
extrusion. Once the extruded material looses contact with
the parent disc, it is called a sequestered disc fragment,
which can be transligamentous or subligamentous.
Because CT examination cannot discriminate between
nuclear and disc material or outer annular fibers and PLL
(Fig. 42-10), the pathomorphologic schema should be
used only with restrictions.
Bulging occurs when the disc symmetrically and uniformly exceeds the contour of the margin of the vertebra
(Fig. 42-9) (22,58,59). The differentiation between protrusion and extrusion as well as subligamentous and
transligamentous extrusion is uncertain (Fig. 42-10). A
distinct focal extension of disc material of remarkable
volume and clear lateral position is probably an extrusion. A protrusion normally has a broader base with
regard to its extension (Fig. 42-12) (60). A sequester has
to be assumed when there is clear loss of continuity of
extruded disc material in successive slices. Reformatting
of the axial slices into sagittal orientated views are helpful in demonstrating a sequestered extrusion. Therefore, a
CT description of herniation is mainly restricted to the
localization of the herniated material. This may be central, lateral, intraforaminal, and extraforaminal and can
extend into cranial and caudal direction. The extent of
herniated disc material is better visualized by CT discography (Fig. 42-13).The relation of disc herniation contact
and displacement to the nerve root can be depicted.
COMPUTED TOMOGRAPHY DISCOGRAPHY
CHAPTER 42/DISC HERNIATION: IMAGING / 413
Diffuse enhancement of
the contrast media .
FIG. 42-14. CT-discography of L4-5. Patches of enhancement of contrast media in internal disc disruption. No herniation.
of the disc; (b) the unstained annulus amount is still one
third of the disc radius; and (c) the contrast medium
extends to the outer fibers of the annulus (Fig. 42-14).
Leakage is possible in this case (Fig. 42-15). Type 5 is
also subdivided into a, b, and c groups, where (a) means
protrusion (Fig. 42-16); (b) subligamentous extrusion
(Fig. 42-17); and (c) transligamentous extrusion (Fig. 42-
18). Types 5 b and c include sequestration (63,65). Small
and broad-based disc herniation can be defined (66). The
amount of contrast-medium uptake in the herniated portion can be evaluated (67). Because of the high information value, CT discography is regarded as golden standard in evaluating disc degeneration and herniation for
other imaging procedures.
Leakage of contrast media into the
epidural space
To get more information about the pathoanatomy of
the degenerative disc, discography may be followed by
CT examination (12,61–64). When performing a CT
immediately after discal injection, the annular fissures
are mainly filled with contrast media. When a CT 4 to 6
hours after the injection is performed, mainly the nuclear
material is stained. On the base of the discography grading (13,14), it may be useful for CT discography-staging
to subdivide type 4 into a, b, and c, where in (a) the
derangement extends to less than half of the cross-section
Disc disruption
leakage
FIG. 42-15. CT-discography of the level L5-S1. Axial view in
the upper part of the image and sagittal reconstruction in the
lower part. The leakage may mimicry straining of sequestrated disc herniation.
414 /SECTION V/SPECIFIC CLINICAL ENTITIES
Outer border of the
annulus
Contrast media
extends to the
outer fibers of the
annulus
FIG. 42-16. CT-discography of the level L4-5. The intradiscal
applied contrast media extends with a broad base to the dorsal border of the disc according to type Va.
Herniation with
uncertain defined
limits
A
stained extruded
disc material
C
FIG. 42-17. A: Computed tomography of the level
L5-S1. The herniation has uncer tain defined limits.
Distinction from nerve root is not possible. B: CTdiscography of the le vel L5-S1 displayed in the softtissue window defines clearly the border of the
extruded disc material. C: CT-discography of the
level L5-S1 displayed in the bony window.The bony
structures are better defined CT-discography.
nerve root
small based
extrusion of disc
material stained
with contrast
media
B
Transligamentous
extrusion
Extruded annulus
material
FIG. 42-18. CT-discography L4-5 displayed with soft-tissue
window shows a transligamentous extrusion with staining of
the disc material. The extruded annulus material has less
uptake of contrast media.
CHAPTER 42/DISC HERNIATION: IMAGING / 415
MAGNETIC RESONANCE IMAGING
Up to now, MRI has become the most frequently used
method to depict disc herniation. In contrast to CT, MRI
can directly produce slices in every chosen plane. In CT
as in all X-ray modalities, the electron density is the contrast-determining parameter. In MRI there are at least
three intrinsic parameters (proton density, spin-spin, and
spin-lattice relaxation) with a multitude of extrinsic
parameters (echo-time (TE), repetition-time (TR), inversion-time (TI), flip angle, field-strength, receiver-coils, etc.).
This allows to show the different spinal tissues with
remarkable different signal intensities and results in high
contrasts (Fig. 42-19). The nucleus, which is indistinguishable from the annulus in T1-weighted images,
becomes very bright in strongly T2-w eighted images. The
annulus, ligaments, and nerve roots with f iberlike structures are bright in gradient-echo sequences, out of phase,
and T1-weighted and dark in T1- and T2-weighted SEimages. Epidural and intraforaminal fat appears very
bright in T1-weighted images and less bright in T2weighted images. It is dark with fat-suppression techniques. Cerebrospinal fluid has very low signal intensity
on T1-weighted images and gets higher signal intensity
with more T2 weighting. Because of identical values for
T1 and T2 relaxation as for proton density, it is impossible to differentiate the outer annulus PLL complex. The
resolution is equal to high-resolution CT. Inherent artifacts, mainly chemical shift (68) and pulsation, hav e to be
considered because they can affect morphometric and
signal intensity analysis. For signal intensities are no
absolute values, ratios of the signal intensity of interest-
A,B
C,D
FIG. 42-19. Appearance of disc,
vertebrae, and neuronal structures
in differently weighted sequences.A
slight protrusion exists in L4-5 and
L5-S1. A: T1-weighted image. B:
Enhanced vascular structures after
intravenous (i.v.) application of
gadolinium (Gd) contrast medium.
C: T1-weighted opposed phased
image. D: Better delineation of the
vascular structures after i.v. application of Gd contrast medium. E: Pro-
ton density weighted image. F: T2-
weighted image.G: Fat suppression
with appearance of heavily T2
weighting.
E,F,G
416 /SECTION V/SPECIFIC CLINICAL ENTITIES
ing tissue to the signal intensity of a reference tissue, are
used to describe physiologic or pathologic changes; for
example, the change of signal intensity of the aging or
degenerated disc. Cerebrospinal fluid, adjacent vertebral
marrow, or intensity of the nucleus of obviously normal
disc segments mostly are taken as reference tissues
(69–73). Because of the multitude of parameters that
influence tissue contrast, there is no commonly accepted
protocol for image-based investigation of the lumbar
spine. T1- and T2-weighted images are included in most
studies. The guidelines for quality control of the German
Board of Medicine (Bundesärztekammer) list the spinal
structures that have to be delineated and require in-plane
resolution of 1 × 1.5 mm with a slice thickness less than
4 mm (74).
Different classification systems are used to describe
the degeneration process of the disc. The used parameters
are the signal intensity of the nucleus, which decreases
with growing age and degeneration, and the height of the
intervertebral interspace. There is no commonly accepted
procedure to determine stages of the intervertebral disc
degeneration. Classification schemata, as proposed by
Battié (69) and Pfir rmann (72), include the signal intensity of the nucleus, disc height, and morphologic description of the nucleus, and seem to be most appropriate to
evaluate the degree of degeneration.
Herniated material may contain nuclear, annular, and
end plate tissues. The classification schema of BrantZawadzki (60) for herniation, which is purely based on
morphologic criteria, is widely accepted. These authors
give the following def initions:
Normal: No disc extension beyond the interspace
Bulge: Circumferential extension beyond the interspace
(Fig. 42-20). If a spondylolisthesis occurs, the axial
images can lead to misinterpretation of the disc f ixed
on the upper end plate, and the adjacent non-dislocated
vertebra as protrusion (pseudoprotrusion) (Fig. 42-21).
Herniation: Any focal extension beyond the interspace.
Subdivisions:
(a) Protrusion: Focal or asymmetric extension beyond
interspace into the canal, base is broader than any other
diameter of the protrusion (Fig. 42-22);
(b) Extrusion: Focal, obvious extension beyond interspace; the base against the parent disc is narrower than
the diameter of the extruding material itself, or there is
no connection to parent disc at all (Fig. 42-23).
To eliminate a false-positive diagnosis it seems important not to use the global term “herniation,” but rather its
subgroups.
The subdivisions of extrusion in transligamentous
and subligamentous herniation as described by Herzog
(57) are not included in the preceding schema, probably
because of the difficulty of depicting the outer annulus
PLL complex. An exact differentiation between these
two subgroups can only be done when the rupture of
this complex is clearly demonstrated (75,76). For the
same reason, differentiation between protrusion and
extension of disc
material beyond the
interspace
A
circumferential extension
of disc material
B C
FIG. 42-20. A: The bulging disc slightly dents the dural sac
(sagittal image, STIR 2000/150/20). B: The convex shape of
the disc is characteristic for bulging disc (transverse image,
GRE 500/7 out of phase). C: We report the enhancement of
the outer annulus fibers to the elevated tension of the ann ulus (transverse image, GRE 500/7 out of phase after intravenous administration of gadolinium contrast medium).
slight enhancement of
outer annulus fibres
CHAPTER 42/DISC HERNIATION: IMAGING / 417
disc
bone
annulus
A
enhancement of
outer annulus
fibers
C
FIG. 42-21. A: The spondylolisthesis mimicries a bulging disc
(sagittal image, GRE 500/7 out of phase). B: The axial slice
position in spondylolisthesis exhibits the total posterior annulus as in bulging conditions (pseudo bulge) (transverse image,
GRE 500/7 out of phase). C: The enhancement of the outer
annulus in pseudo bulge conditions may be caused by stress
to the rim (transverse image, GRE 500/7 out of phase after
intravenous administration of gadolinium contrast medium).
extrusion may be difficult (60). Extrusion is more
likely if the herniated material contains nuclear fragments with high signal intensity on T2-weighted
images (Fig. 42-23). With older extrusions, the nuclear
fragment tends to become dark by resorption and des-
impression of the
dural sac
low signal intensity
of the disc L4/5
B
iccation (76,77). There may be different opinions when
defining a bulge or protruded disc (77). The divergence
from the concentric contour cannot be clearly identified in every case. Foraminal and extraforaminal herniations are difficult to classify into protrusion and extru-
disc material extending beyond
the interspace
epidural tissue (plexus, PLL) and
dura)
A
focal extension of
disc material
nerve root
C
FIG. 42-22. A: Water loss of the degenerated disc leads to
signal loss in the T2-weighted image.The cerebrospinal fluid
of the dural sac appears very bright. The dural sac is
indented by the protruded disc (sagittal image, STIR
2000/150/20). B: In T1-weighted opposed phased image, the
whole disc appears bright, posterior longitudinal ligament,
parts of the plexus, and the dura have intermediate signal
intensities, and the vertebrae appear dark. Therefore, the
extension beyond the interspace is well delineated (sagittal
image, GRE 500/7 out of phase). C: Broad-based asymmetric extension of disc material beyond the interspace (protrusion) (transverse image, GRE 500/7 out of phase).
B
418 /SECTION V/SPECIFIC CLINICAL ENTITIES
herniated disc material
extruded nuclear
material
herniated disc
material
dural poach of S1 nerve
A
C D
FIG. 42-23. A: Obvious compression of the dural poach of the nerve root S1 by herniated disc material. The herniated nuclear material has penetrated the outer fibers of the annulus (sagittal image, STIR
2000/150/20). B: The herniated disc obstructs the recessus S1 on the right side and displaces the nerve
root (transverse image, GRE 500/7 out of phase). C: The uptake of contrast medium in the tissue adjacent to the herniation is caused by edema or hypervascularization (transverse image, GRE 500/7 out
of phase after intravenous administration of gadolinium contrast medium). D: Coronal image may be
helpful in delineating extension and position of the herniation with regard to the neuronal and bony
structures (coronal image, GRE 500/7 out of phase after intravenous administration of gadolinium contrast medium).
root
herniated disc
material
enhancing tissue
arround the herniation
displaced nerve
root S1 right side
B
perifocal enhancement
herniated disc
material
ganglion of the nerve
root S1
sion, especially when nuclear material inside the herniation cannot be depicted (Figs. 42-24, 42-25).
Sequestered intervertebral discs are well delineated by
sagittal images (Fig. 42-26)(78).
The relationship of herniation and the neurovascular
structures is of major clinical importance. The contact of
disc material
extending into
the neuroforamen L4
A
FIG. 42-24. A: The degenerated disc L4-5 extends laterally into the neuroforamina. Ner ve root, intervertebral vessels, and intraforaminal fat cannot be differentiated by this sequence (sagittal image, GRE
500/7 out of phase). B: The coronal image after intravenous application of gadolinium (Gd)-contrast
medium differentiates better between the affected nerve root and the intraforaminal herniation (coronal
image, GRE 500/7 out of phase after intravenous administration of Gd contrast medium).
the herniation with the nerve root and its possible deviation, mostly posteriorly, is well visualized in T1- and T2weighted axial images. The term “nerve root compression” (79–81) does not seem to be adequate for these two
conditions and is not convincingl y presented in pub lished
images.
nerve root L 4 with
high uptake of contrast medium
degenerated disc
herniated into the
neuroforamen
B
CHAPTER 42/DISC HERNIATION: IMAGING / 419
-
extraforaminal herniated disc material
A
intravertebral
vessel
displaced nerve
root
herniated disc
material
C
The effect of disc herniation on neurovascular structures may be visualized as sw elling of the nerve root, possibly caused by edema. This effect is better demonstrated
by enhancement after i.v. administration of gadolinium
(Gd) contrast media (82–89). Enhancement is nearly
always seen at the rim of the herniation (90,91). This is
extraforaminal her
niated disc material with a rim of
high contrast
medium uptake
B
FIG. 42-25. A: There is a large space occupying lesion with
disclike signal intensity (transverse image, GRE 500/7 out of
phase). B: The enhancing rim better delineates the border of
the herniation (transverse image, GRE 500/7 out of phase
after intravenous [i.v.] administration of gadolinium [Gd] contrast medium). C: The parasagittal image after i.v.administration of contrast medium demonstrates the relationship of the
herniation with the adjacent tissues (sagittal image, GRE
500/7 out of phase after i.v. administration of Gd contrast
medium).
caused by neurovascularization. Together with dynamic
examination, MR angiography allows the separation of
vascularization from edema (Fig. 42-27) (92–94). Also,
the venous stasis of the anterior venous plexus caused by
the herniation that obstructs the spinal canal can be visualized (83,95).
herniated nucleous material
A
herniated disc
l4/5
sequestered
nucleus material
C
FIG. 42-26. A: Migrated nucleus material with questionable origin (sagittal
image, STIR 2000/150/20). B: Migrated
disc material (sagittal image, GRE 500/7
out of phase). C: Obvious discontinuity
of the migrated nucleus material with the
herniated disc L4-5 (sagittal image, GRE
500/7 out of phase after intravenous
administration of gadolinium contrast
medium).
herniated disc
material
B
420 /SECTION V/SPECIFIC CLINICAL ENTITIES
nerve root S1
rim enhancement
herniated disc
material
A
intervertebral vessels
anterior branches of segmental
vein and artery
segmental anastomosis
perifocal hypervascularization
herniated disc material
B
unaffected nerve root
with perineural fat tissue
affected nerve root within
scar tissue
scar tissue
A
FIG. 42-27. A: The enhanced rim represents
perifocal edema or vascularization (coronal
image, GRE 500/7 out of phase after intravenous administration of gadolinium contrast
medium). B: The ar terial phase of angiography
demonstrates the hypercapillarization of the perifocal tissue.
nerve root S1 surrounded by enhanced
scar tissue
enhanced scar tissue
B
FIG. 42-28. A: Scar tissue appears with lower signal
intensity than the normal ligamentum flavum at the opposite side (transverse image, GRE 500/7 out of phase).B:
Scar tissue has high uptake of contrast medium and better delineation of the affected nerve root.
scar tissue
CHAPTER 42/DISC HERNIATION: IMAGING / 421
space occupying
lesion
scar tissue
A
herniation
C
FIG. 42-29. A: Recurrent low back pain 9 months after discectomy. Epidural scar tissue with suspicion
of reherniation (sagittal image, GRE 500/7 out of phase). B: The reherniated nucleus appears very
bright in T2-weighted images, indicating recent herniation (sagittal image, STIR 2000/150/20). C: For-
eign mass on the left side compressing dural sac (transverse image, GRE 500/7 out of phase).D: After
intravenous (i.v.) administration of gadolinium (Gd) contrast medium, the reherniation is demarked by a
rim of high enhancement (transverse image, GRE 500/7 out of phase after i.v. administration of Gd contrast medium).
Shortly after discectomy, scar tissue appears dark in
T1- and bright in T2-weighted images because of its high
water content. It appears enhanced after i.v. administration of Gd-contrast media (Fig. 42-28) (96,97). Gradually, scar tissue becomes brighter in T1- and darker in T2weighted images. The enhancement of contrast does not
change much. Differentiation of recurrent herniation and
scar tissue can be difficult when the herniated disc material also enhances by ingrowth of vascular structures.
Normally, the herniated material does not enhance (Fig.
42-29). The usefulness of Gd-contrast media is doubtful
when the high resolution fast spin-echo sequences are
used along with proton density–weighted images (98).
T1-weighted images before and after Gd-contrast
application are not sufficient to investigate the origin of
reappearing pain in the early postoperative period. In
such cases, retrodiscal infection has to be taken into
account. T1-weighted out-of-phase sequences before and
after Gd administration show the inflammatory tissue
with high enhancement (Fig. 42-30). Possibly re-herni-
B
herniation with
surrounding
enhancement
enhancing scar
tissue
D
ated disc material appears brighter than any possible
abscess (Fig. 42-31) (99).
Perineural or neurogenic tumors, which might be confounded with lateral herniation in native MR images, are
identified by their high uptake of contrast medium, which
may be homogeneous, heterogeneous, or annular (Fig.
42-32) (100–102).
Synovial cysts and ganglia can be recognized easily by
their high homogeneous signal intensity in T2-weighted
images and various signal intensities on T1-weighted
images. The signal intensity depends on the fluid composition ranging from serous to proteinaceous to hemorrhagic (Fig. 42-33). In most cases, the synovial tissue is
enhanced after i.v. application of Gd-contrast media
(42,103,104).
Hematomas may be confounded with herniation in T1and T2-weighted images (34,76,105). Better differentiation is possible with T1-weighted GE out-of-phase
sequences where hematomas appear very bright because
of susceptibility effects.
422 /SECTION V/SPECIFIC CLINICAL ENTITIES
e
retrodiscal space
occupying mass
A
FIG. 42-30. A: Five days after surgical intervention, the patient
presented with acute low back pain. A bend-shaped retrodiscal
the enhancing mass
contains multiple spots
of minor signal intensity
C
space occupying
mass
structure can be seen with nearly disclike signal intensity (sagittal
image, GRE 500/7 out of phase). B: The throughout enhanced
mass after i.v. application of Gd-contrast media exclude a disc
herniation (transverse image, GRE 500/7 out of phase after intravenous [i.v.] administration of gadolinium [Gd] contrast medium).
C: At reoperation, the mass reveals to be infectious tissue with
pus accumulation (coronal image, GRE 500/7 out of phase after
intravenous administration of Gd contrast medium).
nearly complete enhancement of the
mass
B
fluid containing mass
surrounding en-
Scar tissue
A
FIG. 42-31. A: The unenhanced T1-weighted opposed phased image shows a mass of uncertain origin (transverse image, GRE 500/7 out of phase). B: After intravenous (i.v.) application of gadolinium
(Gd) contrast medium, an enhancing rim appears. The center has slightly lower signal intensity than
disc material. At operation, the mass is revealed to be an abscess (transverse image, GRE 500/7 out
of phase after i.v. administration of Gd contrast medium).
foraminal
obstruction L1/2
right
nerve root L 3
A B
FIG. 42-32. A: The foramen is obstructed by a mass of high-signal intensity equal to the intensity of the
disc (sagittal image, GRE 500/7 out of phase). B: The homogenous high uptake of contrast media is
characteristic for neurinomas (transverse image, GRE 500/7 out of phase after intravenous administration of gadolinium contrast medium).
hanced scar tissue
mass in the right
foramen with high
homogenous uptak
of contrast media
B