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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_6009_Библиотеки_им_академика_М_И_Перельмана.pdf
Normal Postoperative Change: Disc Space
KEY FACTS
http://pdf-radiology.com
TERMINOLOGY
• Substantial imaging overlap in routine early postoperative
findings vs. surgical complications
○ Early postoperative imaging not routinely obtained
○ Edema, granulation tissue at operative site may simulate
residual/recurrent disc herniation
○ Marrow changes and fluid associated with intervertebral
fusion may simulate appearance of spondylodiscitis
IMAGING
• CT: Evaluation of graft position, hardware, bony integrity,
Normal Anatomy and Techniques
and fractures
○ Graft fusion with bony bridging best evaluated by thin-
section CT
• MR: Evaluation of endplates, paraspinal soft tissues,
epidural space, and intrathecal structures
(Left) Sagittal unenhanced
T1W MR shows prior
laminectomy and fusion with
pedicle screws of the L4-L5
level. Fusion appears solid,
with high signal fatty marrow
conversion of the disc space
and adjacent fatty type II
endplate changes ſt. There is
a disc extrusion at the L5-S1
level st. (Right) Sagittal
reformatted NECT shows
intervertebral fusion of the L5S1 using fusion cages .
Mature bone bridges the
intervertebral space ſt,
demonstrating a good bony
union.
○ Postoperative disc signal dependent on preoperative
degree of degeneration, specific surgery and type of
implant, and presence or absence of biologic modifiers
(i.e., rhBMP-2)
○ May see transient increase in disc height and T2 signal
immediately after discectomy (not related to infection)
○ Discectomy accelerates degenerative appearance of disc
with loss of T2 signal and loss of disc height
○ Solid fusion typically shown by fatty marrow
infiltration/ossification of disc with T1 hyperintensity
○ Typical postoperative discectomy enhancement consists
of smooth linear enhancement of disc paralleling
endplates, with enhancement of dorsal annulus at
curettage site
(Left) Sagittal T1 C+ FS MR
shows marked endplate ſt
and fine linear enhancement
of the intervertebral disc
due to degeneration. There is
no endplate irregularity or
paravertebral mass to suggest
disc space infection. Fine
horizontal linear enhancement
is pronounced but not
necessarily indicative of disc
space infection. (Right)
Sagittal T2WI MR shows early
look of L5-S1 posterior lumbar
invertebral fusion (PLIF) with
low signal graft material
within the disc space ſt and
surrounding hyperintense fluid
.
50
Normal Postoperative Change: Disc Space
http://pdf-radiology.com
TERMINOLOGY
Definitions
• Discectomy or partial discectomy
○ Surgical removal of herniated portion of intervertebral
disc
• Interbody fusion
○ Disc removal by posterior (posterior lumbar
intervertebral fusion) or anterior (anterior lumbar
intervertebral fusion) approach
○ Insertion of bone graft &/or fusion hardware
○ Goal is arthrodesis (fusion) across disc space
• Disc replacement
○ Variety of intervertebral hardware
○ Preserves motion across segment: Arthroplasty rather
than arthrodesis
• Pseudoarthrosis
○ Failure to obtain bony union after fusion
○ Ideally, fused segment will show
– Mature bridging bone on radiographs, CT
– Cold on bone scan 6-12 months postop
– Resolution of type I endplate marrow or conversion to
type II
– No motion on flexion-extension radiographs
○ However
– Geometry of pseudoarthrosis may be complex and
difficult to appreciate on radiographs, CT
– Bone scan performs poorly, with significant false-
negative and false-positive findings
□ Somewhat better performance at 12 months
relative to 6 months postop
– Stability provided by instrumentation may prevent
motion on flexion-extension films, despite
pseudoarthrosis
□ 2-3° motion may be present with fusion due to
compliance of normal bone
– Pedicle screw fracture can be seen with
pseudoarthrosis
□ Instrumentation is temporizing mechanism until
bony union can occur
• Peridural fibrosis
○ Some degree of peridural fibrosis along margin of thecal
sac is typical finding following discectomy
– Edema and tissue disruption at discectomy site
particularly conspicuous in first 6 weeks
postoperatively
• Nerve root clumping, enhancement
○ Transient nerve root clumping can be identified in early
postoperative period, often resolves spontaneously
○ Solitary nerve root enhancement may be seen
perioperatively; inflammation related to compression,
manipulation
○ MR: Evaluation of endplates, paraspinal soft tissues,
epidural space, and intrathecal structures
– Postoperative disc signal dependent on preoperative
degree of degeneration, specific surgery and type of
implant, and presence or absence of biologic
modifiers (i.e., rhBMP-2)
– May see transient increase in disc height and T2 signal
immediately after discectomy (not related to
infection)
– Discectomy accelerates degenerative appearance of
disc with loss of T2 signal and loss of disc height
– Disc space surrounding implants may initially show T2
hyperintensity (1st few weeks) but should disappear
over time
– Solid fusion typically shown by fatty marrow
infiltration/ossification of disc with T1 hyperintensity
– Typical postoperative discectomy enhancement
consists of smooth linear enhancement of disc
paralleling endplates, with enhancement of dorsal
annulus at curettage site
□ No edema or enhancement of paraspinal soft
tissues (this would indicate infection)
SELECTED REFERENCES
1. Yang H et al: MRI manifestations and differentiated diagnosis of
postoperative spinal complications. J Huazhong Univ Sci Technolog Med Sci.
29(4):522-6, 2009
2. Tokuhashi Y et al: Clinical course and significance of the clear zone around
the pedicle screws in the lumbar degenerative disease. Spine (Phila Pa 1976).
33(8):903-8, 2008
3. Rutherford EE et al: Lumbar spine fusion and stabilization: hardware,
techniques, and imaging appearances. Radiographics. 27(6):1737-49, 2007
4. Williams AL et al: CT evaluation of lumbar interbody fusion: current
concepts. AJNR Am J Neuroradiol. 26(8):2057-66, 2005
5. Carmouche JJ et al: Epidural abscess and discitis complicating instrumented
posterior lumbar interbody fusion: a case report. Spine (Phila Pa 1976).
29(23):E542-6, 2004
6. Ross JS: Magnetic resonance imaging of the postoperative spine. Semin
Musculoskelet Radiol. 4(3):281-91, 2000
7. Lonstein JE et al: Complications associated with pedicle screws. J Bone Joint
Surg Am. 81(11):1519-28, 1999
8. Fritsch EW et al: The failed back surgery syndrome: reasons, intraoperative
findings, and long-term results: a report of 182 operative treatments. Spine
(Phila Pa 1976). 21(5):626-33, 1996
9. Larsen JM et al: Assessment of pseudarthrosis in pedicle screw fusion: a
prospective study comparing plain radiographs, flexion/extension
radiographs, CT scanning, and bone scintigraphy with operative findings. J
Spinal Disord. 9(2):117-20, 1996
10. Ross JS: Magnetic resonance assessment of the postoperative spine.
Degenerative disc disease. Radiol Clin North Am. 29(4):793-808, 1991
11. Ross JS et al: Lumbar spine: postoperative assessment with surface-coil MR
imaging. Radiology. 164(3):851-60, 1987
12. Ross JS et al: Postoperative cervical spine: MR assessment. J Comput Assist
Tomogr. 11(6):955-62, 1987
Normal Anatomy and Techniques
IMAGING
Imaging Recommendations
• Best imaging tool
○ CT: Evaluation of graft position, hardware, bony integrity,
and fractures
– Graft fusion with bony bridging best evaluated by
thin-section CT
51
Normal Postoperative Change: Disc Space
http://pdf-radiology.com
(Left) Sagittal T1WI C+ FS MR
shows granulation tissue
enhancement in the dorsal
margin of the L4-5 disc st at
the site of a partial
discectomy. This is a typical
finding following discectomy.
(Right) Axial T1WI C+ FS MR
shows a small amount of
enhancing peridural fibrosis at
the site of a partial discectomy
st. The enhancement
Normal Anatomy and Techniques
differentiates fibrosis from a
recurrent disc herniation.
(Left) Axial T1WI MR through
a level of prior laminectomy
st shows soft tissue flattening
the ventral margin of the
thecal sac, particularly
prominent in the right
anterolateral position ,
where the appearance is
concerning for representing
recurrent disc herniation.
(Right) Axial T1WI C+ MR in
the same patient shows
enhancing peridural fibrosis
and annulus . There is
extensive enhancement of the
disc margin ſt reflecting
diffuse disc degeneration and
annular fissures.
(Left) Preoperative sagittal
T1WI MR shows type I marrow
changes st adjacent to
degenerative spondylolisthesis
of the L4-L5. The L4-5 and L51 discs are collapsed. (Right)
Sagittal T1WI MR in the same
patient demonstrates
conversion of type I to type II
marrow st adjacent to the L4L5 disc space. The patient has
undergone posterior
instrumentation and fusion of
L4-S1. Note the metallic
artifact from a pedicle screw
placement ſt. The L5-S1 disc
shows fatty marrow
conversion .
52
Normal Postoperative Change: Disc Space
http://pdf-radiology.com
Normal Anatomy and Techniques
(Left) Sagittal T2* GRE MR
shows changes of a C4-C5
discectomy. Ventral extradural
defect actually represents
metallic susceptibility artifact
and was not present on T1WI.
(Right) Sagittal T1 MR shows
diffuse hyperintensity within
every lumbar intervertebral
disc ſt, consistent with
calcification &/or fatty
marrow replacement. There is
typical squaring of the lumbar
vertebral bodies of ankylosing
spondylitis.
(Left) Lateral radiograph
shows a 2-level posterior
PLIF with 3 levels of pedicle
screws. Posterior rods show
lucency around 1 of the L4 and
1 of the sacral screws ſt.
(Right) Axial NECT in the same
patient shows the interbody
fusion graft and the
lucency around the left sacral
screw ſt and normal
appearance of the
intervertebral graft. The
degree of the lucency
decreased on 1-year follow-up
films.
(Left) Axial CT following
myelography shows PLIF with
2 intervertebral grafts within
the disc with radiopaque
markers on each end ſt.
(Right) Lateral radiograph of
the cervical spine shows C5-C6
discectomy and solid anterior
fusion ſt (ADCF) with metallic
plate and screw placement
. Hardware is intact and
appears satisfactorily
positioned without evidence of
loosening, fracture, or
subsidence.
53
Normal Postoperative Change: Epidural Space
KEY FACTS
http://pdf-radiology.com
TERMINOLOGY
• Peridural fibrosis
○ Some degree of peridural fibrosis along margin of thecal
sac is typical finding following discectomy
○ Edema and tissue disruption at discectomy site
particularly conspicuous in first 6 weeks postoperatively
○ Can simulate disc residual/recurrent disc herniation
○ Scarring has been implicated with nerve root irritation in
failed back surgery syndrome
• Postoperative fluid collection
Normal Anatomy and Techniques
○ Fluid collection in operative bed is not uncommon in
immediate postoperative setting
○ May have complex signal
○ May have fluid-fluid levels
○ May demonstrate peripheral enhancement
IMAGING
• Utility of MR in postoperative epidural space related to
timing since surgery
(Left) Sagittal T1WI C+ MR
shows L2-L5 laminectomy with
a postoperative fluid
collection within the surgical
bed , effacing the dorsal
thecal sac st. A small amount
of enhancement is seen
superiorly ſt. There was no
clinical suspicion of infection,
and the patient did well
without further intervention.
(Right) Sagittal T2WI MR in
the same patient immediately
following surgery shows
effacement of the thecal sac
ſt and ventral displacement
of the cauda equina from the
laminectomy site fluid
collection.
○ If imaging within 4-6 weeks of surgery, normal
postoperative changes may mimic epidural mass,
residual disc herniation
○ Acute imaging of postoperative spine best when limited
to definition of epidural hemorrhage or CSF leak
(pseudomeningocele)
○ Definition of degree of thecal sac compression limited by
poor correlation to patient's symptomatology
• Metal artifact due to disc space implant, posterior fusion
hardware
○ Usually worth attempt at imaging with MR even in face
of significant metal artifact
• MR: Best for epidural space evaluation
○ Hemorrhage
○ Pseudomeningocele
○ Scar vs. disc material
(Left) Axial T2WI MR shows an
asymptomatic fluid collection
in the laminectomy bed st,
effacing the dorsal thecal sac.
(Right) Axial image from a CT
myelogram shows changes of
a left hemilaminotomy. The
actual bony defect is difficult
to appreciate on this image.
What is apparent is the
absence of the left
ligamentum flavum and
mild distortion of the thecal
sac.
54
Normal Postoperative Change: Epidural Space
http://pdf-radiology.com
TERMINOLOGY
Definitions
• Laminectomy
○ Removal of lamina to decompress spinal canal
– Unilateral (hemilaminectomy) or bilateral
– Partial removal of lamina and ligamentum flavum
technically laminotomy, although terminology
sometimes used interchangeably
• Posterior instrumentation
○ Including pedicle screws, paraspinous rods, transverse
rods, laminar hooks
– Translaminar or facet screws; can be inserted with
minimally invasive techniques
• Posterolateral fusion
○ With severe loss of disc height, in lieu of interbody fusion
○ Lateral bone graft placement, fusion of transverse
processes
○ Usually supplemented by posterior instrumentation
• Peridural fibrosis
○ Some degree of peridural fibrosis along margin of thecal
sac is typical finding following discectomy
– Edema and tissue disruption at discectomy site
particularly conspicuous in first 6 weeks
postoperatively
□ Can simulate disc residual/recurrent disc herniation
○ Scarring has been implicated with nerve root irritation in
failed back surgery syndrome
• Postoperative fluid collection
○ Fluid collection in operative bed is not uncommon in
immediate postoperative setting
– May have complex signal
– May have fluid-fluid levels
– May demonstrate peripheral enhancement
○ Can be difficult to differentiate from postoperative
hematoma, pseudomeningocele, infected collection
• Malpositioned pedicle screw
○ Pedicle screw should traverse pedicle and be securely
positioned within vertebral body
○ Malpositioning includes
– Perforation of anterior cortex of vertebral body
– Perforation of cortex of pedicle
□ ± compromise of intervertebral neural foramen or
spinal canal
• Lucency around pedicle screw
○ Clear zones (≥ 1 mm) around pedicle screws may be
encountered on postoperative radiographs
– Traditionally, concerning for loosening or infection
○ 1 longitudinal series describes majority (2/3) of clear
zones as resolving over several years
– Persistence 2 years postoperatively predictive of
pseudoarthrosis
Normal Anatomy and Techniques
– Little use in evaluation of epidural space, unless in
conjunction with intrathecal contrast for definition of
thecal sac compression
○ MR: Best for epidural space evaluation
– Hemorrhage
– Pseudomeningocele
– Scar vs. disc material
○ Utility of MR in postoperative epidural space related to
timing since surgery
– If imaging within 4-6 weeks of surgery, normal
postoperative changes may mimic epidural mass,
residual disc herniation
– Acute imaging of postoperative spine best when
limited to definition of epidural hemorrhage or CSF
leak (pseudomeningocele)
– Definition of degree of thecal sac compression limited
by poor correlation to patient's symptomatology
– Metal artifact due to disc space implant, posterior
fusion hardware
□ Usually worth attempt at imaging with MR even in
face of significant metal artifact
SELECTED REFERENCES
1. Ghobrial GM et al: Iatrogenic neurologic deficit after lumbar spine surgery: a
review. Clin Neurol Neurosurg. 139:76-80, 2015
2. Walsh KM et al: Spinal cord stimulation: a review of the safety literature and
proposal for perioperative evaluation and management. Spine J. 15(8):18649, 2015
3. Yang H et al: MRI manifestations and differentiated diagnosis of
postoperative spinal complications. J Huazhong Univ Sci Technolog Med Sci.
29(4):522-6, 2009
4. Tokuhashi Y et al: Clinical course and significance of the clear zone around
the pedicle screws in the lumbar degenerative disease. Spine (Phila Pa 1976).
33(8):903-8, 2008
5. Rutherford EE et al: Lumbar spine fusion and stabilization: hardware,
techniques, and imaging appearances. Radiographics. 27(6):1737-49, 2007
6. Williams AL et al: CT evaluation of lumbar interbody fusion: current
concepts. AJNR Am J Neuroradiol. 26(8):2057-66, 2005
7. Carmouche JJ et al: Epidural abscess and discitis complicating instrumented
posterior lumbar interbody fusion: a case report. Spine (Phila Pa 1976).
29(23):E542-6, 2004
8. Ross JS: Magnetic resonance imaging of the postoperative spine. Semin
Musculoskelet Radiol. 4(3):281-91, 2000
9. Lonstein JE et al: Complications associated with pedicle screws. J Bone Joint
Surg Am. 81(11):1519-28, 1999
10. Fritsch EW et al: The failed back surgery syndrome: reasons, intraoperative
findings, and long-term results: a report of 182 operative treatments. Spine
(Phila Pa 1976). 21(5):626-33, 1996
11. Larsen JM et al: Assessment of pseudarthrosis in pedicle screw fusion: a
prospective study comparing plain radiographs, flexion/extension
radiographs, CT scanning, and bone scintigraphy with operative findings. J
Spinal Disord. 9(2):117-20, 1996
12. Ross JS: Magnetic resonance assessment of the postoperative spine.
Degenerative disc disease. Radiol Clin North Am. 29(4):793-808, 1991
13. Ross JS et al: Lumbar spine: postoperative assessment with surface-coil MR
imaging. Radiology. 164(3):851-60, 1987
14. Ross JS et al: Postoperative cervical spine: MR assessment. J Comput Assist
Tomogr. 11(6):955-62, 1987
IMAGING
Imaging Recommendations
• Best imaging tool
○ CT: Best for definition of hardware, posterior element
integrity
55
Normal Postoperative Change: Epidural Space
http://pdf-radiology.com
(Left) Normal epidural space
after laminectomy is shown.
Sagittal T1WI MR shows the
laminectomy site as
intermediate signal at L4 and
L5 levels ſt. There is mild
mass effect on the dorsal
thecal sac . (Right) Sagittal
T2WI FS MR in the same
patient shows fluid within the
L4-L5 laminectomy bed st
effacing the dorsal thecal sac.
Normal Anatomy and Techniques
A small amount of
extraarachnoid fluid tracks
cephalad ſt up to the L1 level.
(Left) Axial T2WI FS MR
following lumbar laminectomy
shows complex fluid collection
in laminectomy bed st as well
as a small amount of subdural
fluid ſt. The patient did well
postoperatively. (Right) Axial
T2WI MR shows a large
posterior fluid collection ſt
following multilevel fixation
and pedicle subtraction
osteotomy. Note that the
posterior rods by metal
artifact st and bone graft
present posteriorly at the level
of rods . This degree of fluid
is not uncommon in the
immediate postoperative
period.
(Left) Axial T1WI C+ FS MR
shows pedicle screws ſt and a
laminectomy defect st.
Diffusely increased signal
probably reflects the effect of
field inhomogeneity generated
by the pedicle screws and
resulting in poor fat saturation
that obscures any potential
enhancement due to
underlying peridural fibrosis.
(Right) Axial T1WI MR shows a
defect in the right lamina and
ligamentum flavum st at the
site of a left L5
hemilaminectomy.
56
Normal Postoperative Change: Epidural Space
http://pdf-radiology.com
(Left) Axial nonenhanced T1WI
at L4-L5 demonstrates
appearance of peridural
fibrosis ſt surrounding the
left lateral aspect of thecal
sac and exiting root. (Right)
Axial T1WI C+ at L4-L5
demonstrates enhancing
epidural fibrotic tissue ventral
to the thecal sac ſt and the
traversing left L5 nerve root.
Enhancing scar tissue is also
present posteriorly at the
laminectomy site . The
enhancing scar shows no mass
effect upon the thecal sac and
smoothly encompasses the
exiting root.
(Left) In this postlaminectomy
patient, peridural fibrosis is
seen as intermediate signal on
a T2-weighted image
surrounding the thecal sac and
exiting roots ſt. (Right)
Postcontrast image in the
same patient shows diffuse
homogeneous enhancement
of the peridural fibrosis.
Rounded areas of no
enhancement are exiting roots
and root sleeves ſt, not to be
confused with nonenhancing
disc herniations.
Normal Anatomy and Techniques
(Left) Typical large extrusion
and free fragment with
peripheral enhancement are
shown. T1WI C+ FS shows
peripheral enhancement of
the residual herniation
within the left side of the
epidural space. (Right) Axial
T1WI C+ MR shows a modestsized posterior fluid collection
along the operative tract ,
which is commonly present in
the immediate postoperative
period. Epidural fibrosis shows
homogeneous enhancement
ſt.
57
Metal Artifact
KEY FACTS
http://pdf-radiology.com
TERMINOLOGY
• CT: Beam-hardening artifact and blooming artifact
• MR: Magnetic susceptibility artifact
• Image degradation related to metal prostheses/implants
IMAGING
• CT: Artifact from metal hardware related to image
reconstruction algorithm, tube current, x-ray kilovolt peak,
pitch, hardware composition, shape, & location
○ Beam-hardening artifact is dark banding between dense
Normal Anatomy and Techniques
objects, such as bone
○ Bloom artifacts result of partial volume effects or areas
of photon starvation propagated by high-density
structures, such as metal, within scanned object
○ Materials with lower x-ray attenuation coefficients
produce less artifactual distortions
– Plastic (best) < titanium < < tantalum < stainless steel
< cobalt chrome (worst)
(Left) Plain film shows right
lateral fusion ſt extending
from the L2-L5 with vertebral
body screws and longitudinal
rods, interbody graft material,
and lower lumbar posterior
pedicle screw fixation from L4S1 . (Right) MR study in the
same patient shows very little
obscuration of the central
canal by artifact, despite the
amount of metal present.
Metal artifact is present from
lateral fusion ſt and posterior
fixation . Solid fusion with
incorporated graft is noted st
by fatty disc space signal.
○ Metal composition, mass, orientation + position of
implant are important factors that determine magnitude
of image artifact
• MR susceptibility artifact due to geometric distortion +
signal loss secondary to dephasing
• MR methods to minimize metal artifact
○ Fast spin-echo > conventional spin-echo > gradient-echo
○ Larger field of view
○ Smaller voxel size
○ Increase transmit and receive bandwidth
○ Frequency encoding direction along long axis of
hardware
○ Lower magnet field strength
○ STIR sequences are alternative method of fat
suppression and less dependent on homogeneity of
main magnetic field
(Left) Coronal CT
reconstruction illustrates
bloom hardening artifact ſt.
Beam artifacts are a result of
partial volume effects or
underranging caused by areas
of photon starvation
propagated by high-density
structures, such as metal,
within the scanned object.
When subtle, these artifacts
appear as shading and, when
severe, as high-intensity
streaks and areas of photon
starvation. (Right) Axial NECT
shows star artifact along the
margins of the right corporal
screw, which has migrated out
st.
58
Metal Artifact
http://pdf-radiology.com
TERMINOLOGY
Definitions
• Magnetic susceptibility
○ Partial magnetization of material in presence of applied
external magnetic field
○ Nonferromagnetic metals may produce local electrical
currents induced by changing scanner magnetic field
○ Tissues with greatly different magnetic susceptibilities in
uniform magnetic field lead to difference of
susceptibilities, causing distortion in magnetic field →
distortion on MR
○ Magnetic susceptibility artifact consists of 2 additive
components
IMAGING
General Features
• Trade-off must occur in choice of metal
○ Titanium wires exhibit least artifact on CT when
compared to cobalt chrome or stainless steel but are
more susceptible to failure
○ Titanium screws + cages produce fewer artifacts than
tantalum but may not have desirable biologic properties
• Use of high peak voltage (kilovolts peak), high tube charge
(milliampere-seconds), narrow collimation, and thin
sections helps reduce metal-related artifacts
○ Caution should always be exercised, particularly in
children, young adults, and patients undergoing multiple
examinations
○ Cone beam artifacts caused by geometry of
multichannel CT scanners ↓ by using narrower x-ray
beam collimation and low-pitch setting
• Reduce metal-related artifacts
○ Thick sections, lower kernel values (similar to standard
reconstruction algorithm), and extended CT scale
• MR: Potential safety and biologic considerations
○ Stainless steel is safe but produces severe artifacts
(especially with low nickel content)
○ Titanium = tantalum implant artifact; much less, relative
to stainless steel
• Location
○ Intervertebral disc level related to fusion cages, anterior
plates + screws, iatrogenic metal
○ Pedicles related to pedicle screws
○ Dorsal elements related to dorsal stabilization rods,
interspinous process wiring
• Size
○ Variable
• Morphology
○ Central low signal, with indistinct margins, spatial
mismapping of signal giving peripheral curvilinear high
signal
Radiographic Findings
• Radiography
○ Visualize hardware malposition and alignment
CT Findings
• NECT
○ Missing data from metal attenuation cause classic
"starburst" or streak artifacts
Normal Anatomy and Techniques
MR Findings
• T1WI
○ Focal central signal loss with peripheral "halo" of ↑ signal
related to spatial mismapping
• T2WI
○ Focal central signal loss with peripheral "halo" of ↑ signal
related to spatial mismapping
○ Artifact minimized with FSE technique
• T2* GRE
○ Blooming of susceptibility artifact with gradient-echo
techniques, worse with increasing echo time
Nonvascular Interventions
• Myelography
○ May be necessary if extensive hardware precludes
adequate MR examination
○ Fluoroscopic positioning will obtain most favorable
projection with overlapping hardware
Imaging Recommendations
• Best imaging tool
○ MR best sequence choice: Fast spin-echo > conventional
spin-echo > gradient-echo
• Protocol advice
○ CT: Thin-section spiral imaging has improved quality
compared to conventional discrete slices
○ MR: Optimum sequence should not contain gradient-
echoes
– Preferably FSE technique
– FSE: Maintain short echo spacing (short echo train less
critical)
– Single shot FSE sequences with half-Fourier (HASTE)
useful
– Hybrid imaging sequences that use both gradient-
echo and spin-echo components should not be used
– Frequency-selective fat saturation yields poor image
quality with metal implants
– Orienting frequency encoding direction along long
axial of pedicle screws minimizes artifact (except in
area just beyond tip of implant)
PATHOLOGY
General Features
• Etiology
○ In anterior cervical discectomies, sufficient metals to
produce artifacts are deposited by contact of metal drill
bits + suction tips
CLINICAL ISSUES
Presentation
• Most common signs/symptoms
○ Typically asymptomatic, ancillary finding of surgical
procedure
DIAGNOSTIC CHECKLIST
Image Interpretation Pearls
• Minimize pedicle screw artifact by orienting frequency
encoding gradient parallel to screw long axis, using FSE
technique; slice thickness 3-4 mm is adequate; thinner
sections yield little artifact reduction
59