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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_6022_Библиотеки_им_академика_М_И_Перельмана
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FIGURE6.9DWIdistinguishesbetweenpostoperativearachnoidcyst
and recurrent epidermoid neoplasm. Sagittal (A) fat-saturated
postcontrast T1 and (B) FSE-T2 images show a rounded, large,
nonenhancing intradural lesion at the L3 level with signal
characteristicssimilartoCSFnearlyfillingthespinalcanal.Extending
anteriorto the cauda equina fromL4to mid L5, and downtoS2,is
subtlyenhancingintraduraltissue,slightlyhypointensetoCSFonT2.
OldL1throughS2laminectomiesareevident.(C)SagittalDWIwith
corresponding (D) apparent diffusion coefficient (ADC) map shows
markedrestricteddiffusionoftheL3intraduralmass(brightonDWI,
dark on ADC) and mild restricted diffusion of the lower intradural
component from L4 through S2. DWI findings are consistent with
recurrentepidermoid tumor rather than postoperative arachnoid cyst,
andthiswasconfirmedatsurgery.
ADC, apparent diffusion coefficient; CSF, cerebrospinal fluid; DWI, diffusion-weighted
image;FSE,fastspin-echo.
Source:CasecourtesyofDr.S.Imbesi;TangL,CianfoniA,Imbesi SG.Diffusion-weighted
imagingdistinguishesrecurrentepidermoidneoplasmfrompostoperativearachnoidcystinthe
lumbosacral spine. J Comput Assist Tomogr. 2006;30:507–509. doi:10.1097/00004728-
200605000-00026
AsdiscussedintheSectiononFastSpin-Echo,thisFSEsequenceshouldbe
used in concert with titanium instrumentation to minimize the metal
susceptibilityartifact.
Summary
Therehave beenmanyrecent developmentsinthe fast-growing fieldof spinal
imaging. Some (fast MRI, especially FSE, multichannelMRI coilsemploying
parallelimagingtechniques,andmultisliceCT)resultinfasterintrinsicimaging
times, which can be exploited to yield improved S/N and spatial resolution.
Other advances (e.g., variable bandwidth, phased-array coils, or increasing
magnetfieldstrengthto3Tesla(47))yieldimprovedS/Nandsecondarilyresult
infasterimagingandimprovedpatientcomfort.Stillothers(fatsaturation,DWI,
and use of titanium instrumentation) improve contrast resolution or otherwise
improveimagequality.
Allthese developments are undergoingcontinual refinement,andadvances
in the future will continue to improve image quality, imaging speed, and
ultimately,thequalityofpatientcare.
CONGENITALABNORMALITIES
With the exception of early infancy, when ultrasound of the spine can be
successfullyperformedbecauseofthelimitedvertebralossificationatthisage,
MRI is the test of choice for imaging spinal malformations. In early infancy,
sonographycanvisualizethespinalcordbetweentheareasofearlyossification.
Tetheringofthespinalcordcanbedemonstratednotonlybyalowpositionof
theconusmedullarisbutbythefailureofthespinalcordtomovewithpositional
changesandwithcardiacandrespiratorymovement.
FIGURE 6.10 (A) Axial CTimage through a lumbar vertebra with
stainless steel pedicle screws and vertebral body screw shows
extensive beam-hardening artifact from the hardware, completely
precludingevaluationofthespinalcanalorthebonystructuresatthis
level. (B) Sagittal T1-weighted MR image of the same patient with
stainless steel pedicle screws shows severe metallic susceptibility
artifact,renderingthislumbarMRIcompletelyuninterpretable.
FIGURE6.11TitaniumhardwareminimizesartifactonCT.(A)Axial
CT-myelogramimageatlevelofleft-sidedtitaniumlaminarhookand
right-sided rod shows only minimal artifact. Posterior elements and
contents of the spinal canal including cord and contrast-filled thecal
sacareclearlydiscernable. Steel hardware would have rendered this
level uninterpretable. (B) Sagittal reconstruction from the axial CT
data again clearly demonstrates the titanium hardware and the spine
withonlyminimalbeam-hardeningartifact.
Source: From Lee RR. Recent advances in spinal MRI. In: Lee RR, ed. Spinal Imaging.
Philadelphia,PA:Hanley&Belfus;1995:45–60.
Plainradiographsareoftenveryhelpfultoevaluatethebonystructuresofthe
spine. Spina bifida occulta is a common finding that may be seen withmany
differenttypes of congenital malformations, but it is not specificinpredicting
congenitalabnormalities.Ararebutfairlyspecificplain-filmfindingiscrossed
laminarfusionordiagonalfusionoflaminaeofadjacentvertebrae,which,when
seen, is strongly associated with diastematomyelia, a malformation resulting
from a split notochord. CT can be helpful to delineate bone abnormalities,
identify bony or cartilaginous septa, and identify fat within the spinal canal.
MyelographyandpostmyelographyCThavealimitedroleintheevaluationof
congenitalabnormalities.Foralmostallcongenitalspinemalformations,MRIis
byfarthebestwaytoevaluatethespinalcord(48).
Myelomeningocele (Figure 6.12), which is an open neural tube defect, is
obviousatbirth,andtheroleofimagingissupplemental.Evaluationofthedistal
spinal cord for tethering is a common problem at later ages. Because a high
percentageofpatientswithChiariIImalformationandmyelomeningocelehave
hydrocephalus,CTorMRIofthehead(orsonographyininfancy)iscommonly
used to help evaluate the need for shunt catheter placement and to monitor
functionofashuntcatheterlater.SyrinxcanoccurinChiariII.Cervicalspinal
cord atrophy is occasionally seen, probably caused by compression from the
downwardly displaced cerebellum in the upper cervical spinal canal (Figure
6.13).
Lipomyelomeningocele,despiteitssimilarname, is a quite differententity
than myelomeningocele. It results from the premature dysjunction of the skin
from the neural tube before completeclosure, thus exposing mesoderm to the
developing CNS and inducing the formation of fat. Thus, the spinal cord is
intimately associated with fat that is continuous with subcutaneous fat and
thereforetethered. Because the overlying skin is intact, the malformation may
not present for years or even for several decades. The lipoma can be
demonstratedbyCTbut is especially well shown by MRI (Figure6.14). Low
attenuation on CT and similar signal intensity to fat elsewhere on MRI are
specificforlipomasinthespinalcanal.Thepositionofthedistalspinalcordis
best demonstrated by MRI. Spina bifida occulta is seen at the site of
communicationwithsubcutaneousfat.Lipomyelomeningoceleisnotassociated
with the Chiari II malformation, and the incidence of hydrocephalus in these
patientsissimilartothatofthegeneralpopulation.
FIGURE6.12Myelomeningocele.SagittalT1-weightedMRimageof
6-year-oldchildwithsymptomsoftetheredcordandprevioussurgery
for myelomeningocele. The spinal cord extends inferiorly into the
meningoceleatthelevelofthesacrum.
FIGURE6.13ChiariIIandspinalcordatrophy.SagittalT1-weighted
MR image of a 6-year-old child with myelomeningocele shows
downwarddisplacementofthe cerebellumfar downinto thecervical
spinalcanal.Thecervicalspinalcordisatrophied.
A lipoma of the filum terminale may be associated with a tethered cord
(Figure 6.15). Very small amounts of fat within the filum terminale are
commonlyseenandareofdoubtfulsignificance.Thelipomaofthespinalcordis
theleastcommonofthespinallipomas.Itisactuallyasubpialcollectionoffat,
nearlyalwaysalongthedorsalsurfaceofthespinalcord(Figure6.16).
Afocalfailureofdisjunctionofthespinalcordfromtheoverlyingectoderm
leadstothe formation of a dorsal dermal sinus tract lined by epithelial tissue.
When a dimple, patch of hair,orpigmentedskin leads to suspicion of such a
tract,MRIcandemonstratethetract.Suchtractsoftenextendobliquelythrough
thesubcutaneoustissue.Theymayterminateanywherefromsubcutaneoustissue
toepiduralspace,todura,tothespinalcorditself.Inabouthalfofdorsaldermal
sinustracts,adermoidorepidermoidcystispresent.MRIshowssuchtumorsor
cystsasroundorovalmassesinthespinalcanalandcanshowtheirrelationship
tothespinalcord.
FIGURE6.14Lipomyelomeningocele.Twelve-year-oldboywithlifelong urinary incontinence and no previous surgery. (A) Sagittal T1weightedMRimageshowslargelipomawithinthedistalspinalcanal.
(B)AxialT2-weightedMRimagedisclosesasyrinx(hydromyelia)of
thedistalspinalcord.
FIGURE6.15Tetheredcordandfilum lipoma.SagittalT1-weighted
MRimageofayoungadultwithbackpainshowshighsignalintensity
(arrow)inalipomaofthefilumterminale.
Thespinalcordcanbetetheredfromavarietyofcauses.Myelomeningocele
andlipomyelomeningocelebothimplythatthespinalcordistethered.However,
errorsinalaterstageofdevelopmentrelatingtothecaudalcellmasscanleadto
atethered cord without the moreobviousabnormalities of the spinalcordand
vertebra.ThetipoftheconusmedullarisliesattheL2levelorabovein98%of
people,andthepositionoftheconusmedullarisatorbelowtheL2–L3levelis
generally considered abnormally low (49). Sagittal MR images alone can
sometimes be confusing, because the nerve roots in the cauda equina may
simulate the conus medullaris; additional coronal or axial images are often
necessary to accurately image the distal spinal cord. T1-weighted images are
often the most reliable way to identify the conus medullaris. As mentioned
earlier, sonography is only possible early in life, but has the advantage of
providingdynamicinformation.
FIGURE 6.16 Intradural lipoma. Axial T1-weighted MR image of
adultman withscoliosis showshighsignal intensityfat dorsaltothe
spinalcordintheupperthoracicspine.
Diastematomyelia is a rare congenital malformation resulting from a split
notochord.Thespinalcordissegmentallydividedinthesagittalplane,andthe
duralsacmaybeintactormayalsobedivided.Inabouthalfofthesecases,there
isabony orcartilaginousseptum throughthespinal canal.Suchseptaarebest
demonstrated by CT but may be shown by MRI, especially with GRE
techniques.Thesplitspinalcordandthelengthofthedivisionarebestshownby
MRI.
TRAUMA
Imaging plays a key role in the evaluation of spine trauma, both in the acute
situationandinthelaterimagingofcomplications.Thecomplementarynatureof
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