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CHAPTER 41/DISC HERNIATION: DEFINITION AND TYPES / 403
Thus, the “about-average” natural history (described
subsequently) is largel y based on clinical experience, and
a mixture of literature information (28,37,43,45,46). The
onset of dominating leg pain is usually the period with
the most intense pain. Commonly, the pain fades out to
some extent after a few w eeks and then tends to remain at
about the same level for a total of approximately 1 to 3
months. Thereafter, the symptoms generally abate over
another few months, and (almost) disappear in 50% to
70% of nonsurgical cases (28,37,46), and in about the
same number of surgical cases in most reports (5,47,48),
with as many as 80% to 90% in a few reports (28,49) (Fig
41-5). The remaining patients experience:
• long-lasting discogenic pain, which also tends to fade
off, but over a period of some years (50,51)
• peripheral neurogenic leg pain due to root damage (52)
• domination of a central nervous system component of
the pain (53).
Among these, psychosocial factors are associated with
the majority of the pain (37).
Formation of a fibrous layer (54,55) is followed by a
gradual reduction of the scar bulge (56) (Fig. 41-6). The
rate of recurrent LDH is about 3% to 14% (54,57).
History and Physical
Several relevant issues of the clinical examination will
be presented, but not all. For further details on clinical
usefulness of history and physical signs, test repeatability, and so forth see Andersson and Deyo (58), Hunt et al.
(59), or Vroomen et al. (60).
From the history taking, one of the most important
questions is probably whether leg pain or paraesthesia
dominates over back pain or vice versa. The distribution
of the leg pain—radicular or diffuse—does not allow a
clear distinction between disc herniation or other causes
of sciatica to be made, as diffuse sciatica has often been
reported where herniation has subsequently been verified
at surgery.
As paresis in gradual progress is an indication for
acute surgery, this should be explored during history taking, as should possible cauda equina symptoms, where
the sequence of symptoms most often is flatus incontinence, urinary retention, and groin hypoesthesia.
“Bowel strain” is also described to be reasonably indicative for herniation.
Whereas painful forward bending is highly correlated
to herniation, there does not seem to be a consistent correlation with lying or sitting. Especially in the acute stage
night pain is common, probably due to increased temperature and inflammation. Sitting has been thought to
aggravate a herniation due to the increased intradiscal
pressure (IDP), but is not often the most pain-free posture. A possible explanation could be that the advantage
of more space around the herniation due to reduced lor-
dosis—or even kyphosis—caused by sitting (61) exceeds
the disadvantage from a small increase in herniation size
(62) (Fig. 41-8). Moreover, the increase in IDP is probably smaller than previously believed (63), and when sitting backwardly inclined with a backrest, the IDP is at
least not higher than when standing (64).
Conversely, lumbar extension is generally omitted due
to the reduction in the foramen size (65).
Of the physical signs, the sagittal lumbar curve in
standing is also influenced by the same principle: the
lumbar curvature is flattened or even kyphotic, automatically arranged by a posterior rotation of the pelvis. This
is done to enable the described mechanism of optimizing
the space for the nerve root. Such a kyphotic curve might
also be obtained by forward bending of the trunk. However, in that case the addition of static back-muscle activity compresses the herniated disc to an uncomfortable
level. Thus, erect posture with flattened or kyphotic loin,
or a supported (e.g., hands on the thighs) forward bended
posture is characteristic.
A scoliotic list seems only moderately correlated to
operative findings (66–68). In particular, the Finneson
hypothesis that a certain side location of the herniation
and the nerve root should cause a specif ic list direction
does not seem valid (67).
A painful forward bending may distinguish disc herniation from recess stenosis, where leg pain also may dominate over back pain, but where forward bending usually
relieves the sciatica (69). A lateral shift—usually away
from the side of the LDH—during forward bending is
often seen in LDH, but does not provide much help in
distinguishing between herniation or recess stenosis.
Side bending toward the opposite side of the pain usually relieves the pain (Fig. 41-8).
The straight leg-raising (SLR) test with radiating pain
below knee le vel seems reasonab l y associated to disc herniation (38), although the test reliability—like that for the
ranges of motion mentioned earlier—seems lower than
commonly believed (59). With the surgical finding as the
FIG. 41-8. With reduction of the lordotic curvature, and with
lateral bending, the size of the herniation increases, but the
enlargement of the intervertebral foramen is even more pronounced.
404 /SECTION V/SPECIFIC CLINICAL ENTITIES
“gold standard,” and without letting SLR influence the
indication for surgery, the following was registered by
Kosteljanetz et al. (48) (Fig. 41-9): Root compression, if
present, was estimated to be caused by disc herniation in
two-thirds of the patients in this study.This is the case for
those patients with dominating leg pain of more than 6
weeks’ duration. It may be differently distributed in
another group of patients, characterized otherwise.
The literature on SLR is confusing regarding the
degree of leg angle and clinical symptoms. Some authors
report that the smaller the SLR angle, the more intense
the symptoms (70), whereas others do not find such correlation (71).
SLR is not very sensitizing to an extraforaminal herniation (41). The crossed SLR sign (lifting the symptomfree leg, increasing contralateral pain) seems highly correlated to LDH, especially to complete and large
herniations (5,67,72).
For a herniation affecting nerve root L4—or L2-L3,
which are rare—the “femoral-nerve stretch test” may be
valid if carried out correctly: the patient is in a prone
position and the 90° flexed knee is lifted causing hip
extension. To avoid co-movements of the lumbar spine,
the pelvis is fixated by pressing on the lower third of the
sacral bone.
The springing test is a “segmental lordosing” pressure
placed successively on all lumbar segments with the
patient lying prone. If it is painful, it may indicate which
segment of the leg pain originates from, and may also
help to differentiate pain arising in areas such as the
sacroiliac joint.
Obviously neurologic signs—altered sensibility, reflexes, muscle strength, and muscle atrophy—should be
tested (refer to neurologic textbooks for more information).
Consideration of the piriformis muscle may be
worthwhile. In many patients with disc herniation piriformis myosis may contribute to some of the buttock
FIG. 41-9. One indication of sensitivity and specificity for
straight leg raising.
and leg pain, especially for herniation at L5-S1,
because the S1 root innervates this muscle. There has
been some discussion whether leg pain is caused by
“self-strangulation” in the major ischiadicus foramen
where swelling of the muscle causes compression of the
sciatic nerve, or whether it is simply referred pain. Piriformis involvement can be tested with (a) palpating the
muscle for tenderness or (b) placing the ipsilateral foot
on the other knee, fixating the pelvis with the “heel of
the hand” on the anterior superior iliac spine (ASIS),
and then pushing the knee tow ard the contralateral side,
and asking for stretch pain.
Dynamic testing ad modem McKenzie should be per-
formed. With extension, an increase in radicular pain
indicates an active herniation (73). As the herniation
increases, and the foramen decreases (65), possible centralization of the pain with repeated extension indicates
either that the healing has begun, or at least that the prognosis is good (74).
It seems likely that future tests ma y include b lood samples elucidating whether or not an inflammatory process
of the disc is present. Serum tested for glycosphingolipid
is already optional, but its applicability in practice is still
unclear (75).
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406 /SECTION V/SPECIFIC CLINICAL ENTITIES
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CHAPTER 42
Disc Herniation: Imaging
Josef Assheuer and Klaus-Peter Schulitz
PLAIN RADIOGRAPH
Following the Quebec Task Force on Spinal Disorders
(1), a radiograph of the lumbar spine is of limited value
in the first 7 weeks after onset of low back pain. Even
with the pain radiating to the extremities with neurologic
signs, radiography can delineate loss of disc height, vacuum phenomena, and calcification, as well as sclerosis of
the end plates, osteophytes, and focal end plate defects.
Those signs are not specific for herniation; they are
hardly found in acute disc herniation.
A radiographic examination is not recommended when
disc herniation is suspected. It is the main purpose of
radiographic evaluation to exclude low back pain (LBP),
which was specifically caused by tumors, infections,
inflammatory spondylarthropathies, and fractures (2).
Functional radiographs can delineate instability. Some
biomechanical studies (3) showed increased hypermobility after open discectomy at the level of operation. How-
ever, hypermobility can be found preoperatively at the
same rate at the level of herniation as in adjacent levels
(4–7). Postoperatively, no signif icant changes in hypermobility were found. Therefore, hypermobility does not
seem to be a consequence of discectomy. Instability in the
levels above or beneath the level of herniation is caused
by increased stress in the moving segment caused by
changes in motion pattern at these levels (4,5).
MYELOGRAPHY
Myelogram delineates the cerebrospinal fluid (CSF)
space of the thecal sac including the subarachnoidal
space of the nerve roots. An indentation or occlusion of
this space can be regarded as an indirect sign of disc herniation and must be differentiated from other space-occupying lesions (Fig. 42-1).Therefore, it is of minor importance for the diagnosis of herniation.
compression of the dural
poach of the nerve root L5
A
FIG. 42-1. A: The right dural poach of the nerve root L5 is not filled because of compression by a herniation (myelography antero-posterior view). B: The mass compressing the dural sac and poach of the
L5 nerve root can not be identified. It is probably a herniation according to the position of the mass
(myelography, right oblique view).
dural poach of
the nerve root L4
compression of the dural
sac and of the dural poach
of the nerve root L5
B
407
408 /SECTION V/SPECIFIC CLINICAL ENTITIES
radial fissure extending
right side into the
outer annulus
FIG. 42-2. Discography L4-5 antero-posterior view. The
intradiscal injected contrast media extends in both le v els
into the outer annulus according to grade 4.
Nerve root entrapment beyond the termination of the
nerve root sheath caused by lateral or foraminal disc herniation cannot be detected. High radiation exposure and
invasive procedure as well as possible complications also
have to be taken into account.
Myelography may be the only method to evaluate disc
herniation and other stenosing diseases in patients having
metal implants.
Functional myelography may be indicated to evaluate
so-called dynamic entrapment in disc herniation in
patients showing motion-dependent pain patterns. In
future, functional myelography may be replaced by positional magnetic resonance imaging (MRI) (8,9).
DISCOGRAPHY
Discography mainly demonstrates the internal state
of the disc and it is very useful to classify types of
internal derangement. The contrast medium injected
into the center of the disc pushes the disc matrix aside
and forms pools. The locations and patterns of these
pools are the criteria for the staging of disc degenera-
tion (10–12). Five different types of discograms are
distinguished based on consistently identifiable features in the shape and extension of the radiopaque
shadow (13,14). There are different classifications.
According to the pathoanatomic classification of
Adams et al. (13), type 1 does not show any signs of
degeneration (cotton ball), type 2 is a mature disc with
the nucleus starting to coalesce into fibrous lumps (lobular or sandwich), type 3 demonstrates a degenerated
disc with fissures and clefts in the nucleus and inner
annulus (irregular), type 4 is a degenerated disc with
radial fissures extending into the outer edge of the
annulus (fissured) (Fig. 42-2), and type 5 has complete
radial fissures that allow injected fluids to escape (ruptured) (Fig. 42-3). Injection is done into at least two
segments depending on the pain pattern. Herniation
cannot be visualized directly but if type 4 and 5 are
found, herniation is likely, especially if the contrast
medium forms a pool beyond the intervertebral interspace (Figs. 42-3, 42-4). The leakage of the contrast
medium beneath the posterior longitudinal ligament
(PLL) is not a relevant sign for herniation. Therefore,
Leakage of contrast
media into the extradural space
Complete fissure of the
annulus
FIG. 42-3. Discography L4-5 reveals total degeneration
of the disc with rupture of the annulus, allowing the
intradiscal injected contrast media to escape into the
epidural space according to grade 5.
Herniated disc
material
FIG. 42-4. Discography L4-5.The rim of the herniated disc is
marked by contrast media.
discography is not a relevant imaging modality to
demonstrate herniation. Discography is widely used as
a pain reproduction test to identify the segment causing
the low back pain and sciatica. The reliability of this
test is controversial because the referred pain depends
to a high degree on the psychological profile of the
patient (15–21).
CHAPTER 42/DISC HERNIATION: IMAGING / 409
COMPUTED TOMOGRAPHY
Computed tomography discriminates with high contrast between bone structures and soft tissue. High resolution computed tomography (HRCT) visualizes the subarachnoidal sac, nerve root sleeves, and ligamentum
flavum (Fig. 42-5) (22). Disc material can well be
detected inside and outside the spinal canal. How e v er , CT
does not differentiate between nuclear and annular tissue
(Fig. 42-6). There is a high contrast between herniated
disc material and epidural fat tissue (23,24). Contrast
media after intravenous (i.v.) administration enhance vascular structures and delineate tissue with disturbances of
the blood-tissue barrier. This is helpful in the diagnosis of
vascular malformations and certain tumors such as
meningiomas (25,26). Sometimes, after i.v. administration of contrast medium, a rim of enhancement is
observed at the margins of the herniated disc material.
This may be related to epidural veins or edema of the
neighboring tissue (27,28). Swelling and displacement of
ganglia and nerve roots can be visualized as well as the
indentation of the dural sac (Fig. 42-7). Howe ver, swollen
nerve roots and ganglia with high content of water may
have the same Hounsfield Units (HU) as disc material
and it may be diff icult to distinguish one from the other.
disc L4/L5
ligamentum flavum
epidural fat
A
Disc
Endplate
Dural sac
ligamentum flavum
B
FIG. 42-5. A: Computed tomography of the disc level L4-5. B: Computed tomography of the level L4-5
4 mm below Figure 42-5A. C: Computed tomography of the level L4-5 8 mm below Figure 42-5A.
Cranial endplate
of L5 vertebra
nerve root L5
Cranial facet L5
Caudal facet L4
Epidural fat
C
410 /SECTION V/SPECIFIC CLINICAL ENTITIES
focal extension of disc
material
FIG. 42-6. By computed tomography herniation is delineated as focal extension of the disc. Differentiation
between nucleus and annular tissue as well as between
protrusion and extrusion is not possible.
Multiplanar reconstruction is helpful in these cases, especially with foraminal disc herniations (23,29).
Conjoined nerve roots occurring on the L5-S1 level are
likely to have the same attenuation as disc material and
may be misinterpreted as a disc herniation (30,31). An
accurate analysis of successive CT slices demonstrates
this anatomic variant. It can be seen how two nerve roots
outside the dura join the same dural sheath cranially. Both
nerve roots occasionally leave the spinal canal by the
same neuroforamina (32). The process is unilateral. A
rounded lateral recess is always found with it. Intrathecal
administration of contrast media verifies the diagnosis,
Herniation
displaced nerve root S 1
showing the common dural recess (33). This anomaly
was found in 2% of the cases within a CT study, and in
14% within an autopsy series (32).
Most hematomas of the lumbar spine are located
epidurally or subdurally. They may be confounded with
disc herniations. The epidural mass has indistinct margins
and extends over the surface of a vertebral body, being
largest at the mid-vertebral level. The hematomas are isodense with the thecal sac and are indistinguishable from
the nerve root and ganglia. They may arise from a tear of
the fragile epidural veins because of disc disruption.
Computed tomography follow-ups show a regression of
A
epidural fat
displaced nerve root S 1
thecal sac
B
FIG. 42-7. A: Computed tomography of the level L5-S1.
A right side disc herniation displacing the right nerve
root S1 dorsally. The nerve root is nearly indistinguishable from the herniated disc material. B: Computed
tomography of the le v el L5-S1 3 mm beneath the level of
Figure 42-11A.The displaced nerve root is delineated by
the surrounding epidural fat of low density.
CHAPTER 42/DISC HERNIATION: IMAGING / 411
soft tissue mass,
obstructing the
spinal canal
scar tissue
A
FIG. 42-8. A: Differentiation between scar tissue and possible reherniation is not possible (computed
tomography native at the level L4-5). B: The enhancement of the intraspinal mass after intradiscal
administration of contrast medium reveals reher niation and differentiation from scar tissue (computed
tomography discography at the level of L4-5).
hematomas with the underlying disc herniation remaining (34–36). Epidural and subdural hematomas also may
originate from hematologic disorders, hypertension, and
atherosclerotic vascular diseases (36–38).
Because of their location, synovial cysts and synovial
ganglia of degenerated facet joints may mimic disc fragments. They are broad-based to the zygapophyseal joint,
mostly rounded, emerging into the central canal or subarticular recess. The mass may exhibit internal gas or a calcified rim (39–42). The thickened and protruding ligamentum flavum and capsule are isodense with the disc
and may cause diagnostic problems. Injection of contrast
media into the relevant facet joint shows the communication of the cyst with the joint space (43). Occasionally
cysts can also emerge out of a degenerated disc and are
difficult to differentiate from herniation. They may result
from resorption or mucoid degeneration of an already
existing herniation (44).
Perineural cysts (45), occurring beneath the perineurium at the level or beyond the dorsal root ganglion,
and subarachnoidal cysts (cystic nerve root sleeve dilatation or meningeal diverticulum) (46) located proximally
to the nerve root ganglion, should not be misinterpreted
as herniation. They can be distinguished from herniation
when the pressure erosion of the surrounding bone is
regarded and contrast medium is filled in after intrathecal
administration (47,48).
Nerve sheath tumors may be confounded with lateral
herniations and because of their locations are only
Schwannomas (49).
The main question with postoperative backaches
(failed back surgery syndrome) is to find out whether the
nerve root compression results from reherniation or scar
tissue, especially epidural fibrosis. Native CT is not suitable to answer this question (Fig. 42-8) (50). It shows
enhancing mass after
intradiscal application
of contrast medium
scar tissue
B
both scar tissue and reherniated disc material with identical density. The location of both processes does not permit discrimination either, because scar tissue normally
extends epidurally and laterally to the posterior aspect of
the operated disc (51,52). Therefore, CT discography is
necessary to clarify this condition (Fig. 42-8). If postoperative spine hemorrhage and noninfectious inflammatory processes arise, they can be well visualized. Contrast
enhancement of scar tissue depends on the time that
passed between operation and CT examination with older
scar enhancing less. Nevertheless, the diagnosis impro ves
by 20% up to 3 years after operation (53,54).
PATHOMORPHOLOGIC DEFINITIONS AND
NOMENCLATURE OF DISC HERNIATION
The grading of disc herniation mainly depends on the
internal disarrangement of nucleus and annulus; the displacement of nuclear material is the most important feature.
Resnick and Niwayama (55) and other authors (56)
propose the following schema for disc herniation:
Annular bulge: Annular fibers are intact and the disc pro-
trudes beyond the intervertebral interspace around the
end plate (Fig. 42-9).
Protrusion: Nuclear material protrudes through torn
fibers of the annulus, with the outermost fibers
remaining intact (Fig. 42-6).
Extrusion: The nuclear material penetrates all of the
fibers of the annulus f ibrosus and lies under the PLL
(Fig. 42-10).
Discal sequestration:The nucleus material penetrates the
posterior longitudinal ligament (PLL) and lies within
the epidural space or the nucleus material does not
412 /SECTION V/SPECIFIC CLINICAL ENTITIES
bony endplate of the
vertebra L4
bulging disc
thecal sac
lig. flavum
FIG. 42-9. Computed tomography at the border of the disc
L3-4 to the vertebra L4. The disc exceeds symmetrically and
uniformly the contour of the margin of the vertebra.
bony fragment
Extruded disc
material
FIG. 42-10. Computed tomography of the level L5-S1. The
extruded disc material is clearly depicted. Possible rupture of
the posterior longitudinal ligament cannot be visualized.
herniated disc
displaced nerve
root
epidural fat
FIG. 42-11. Computed tomography of the level L4-5 (bony
window). A bony fragment has extruded together with disc
material into the subligamentous space of a 15-year-old
trampoline jumper.
foraminal to extraforaminal extruded
disc material with
calcification
A
FIG. 42-13. A: Computed tomography of the level L3-4.An extruded mass of disc material extends from
foraminal to extraforaminal with calcification. B: CT-discography ascertains extraforaminal herniation
suspected by discography.
FIG. 42-12. Computed tomography of the level L5-S1. The
herniation has displaced the left nerve root S1 dorsally.The
epidural fat on the left side has nearly disappeared.
extraforaminal herniated disc
B