CSF flow imaging in - PowerPoint Presentation

Slide1

CSF flow imaging in Chiari 1 malformation

Wende Gibbs, MD, Department of NeuroradiologyGabriel Zada, MD, Department of NeurosurgeryJohn Liu, MD, Department of NeurosurgeryPatrick Hsieh, MD, Department of NeurosurgeryMeng Law, MD, MBBS, Department of NeuroradiologyUniversity of Southern California, Keck School of Medicine

Control # 1775eEdE-227Slide2

DisclosuresWende Gibbs: none

Gabriel Zada: noneJohn Liu: nonePatrick Hsieh: noneMeng Law: Toshiba Grant Speakers Bureau; Bracco speaker and consultant; Guerbet Medical Advisory Board; Prism Stock; Fuji speaker and consultantSlide3

PurposeChiari

1 malformation (CM1) has traditionally been defined by morphologic criteria: cerebellar tonsil herniation 3-6mm below the foramen magnumIt is increasingly clear that CM1 is a complex disorder resulting from not only abnormal anatomy, but disordered CSF flowThis exhibit will review static and dynamic imaging tools applied to the study of CM1, including new techniques that may improve diagnostic accuracy, patient management and surgical outcomeSlide4

ApproachReview theories of pathogenesis of CM1, focusing on the interplay of anatomy and CSF flow dynamics

Describe established and recently developed neuroimaging tools used to study CM1: traditional MRI sequences and dynamic techniques including phase contrast MR and Time-spatial labeling inversion pulse technique (Time-SLIP) Demonstrate the utility of Time-SLIP in providing a rapid, individualized assessment of CSF flow before and after surgical treatmentSlide5

IntroductionCM1 has historically been described as a change in hindbrain morphology characterized by cerebellar tonsil herniation 3-6mm* below the foramen magnum on sagittal MRI or CT images

1-3However, 30 - 50% of individuals with tonsillar herniation greater than 5mm are asymptomatic4In those individuals with symptoms, the degree of herniation does not correlate well with symptom severity5Further, a subset of patients with CM1 symptoms have no tonsillar herniation, suggesting abnormal morphology alone cannot explain CM1 symptomatology6*The degree of herniation is not universally agreed upon, and depends upon ageSlide6

Introduction

Both abnormal anatomy and aberrant CSF flow dynamics contribute to the pathophysiology of CM1Slide7

IntroductionSuboccipital

decompressive surgery is a standard treatment for CM135-45% of patients have minimal or no relief years after surgery7,8The search for a noninvasive method of selecting patients with CM1 symptoms who will benefit from surgical intervention is an active area of research across many fieldsSlide8

CM1 Imaging

Headache (typically suboccipital)Neck, back, face pain“Cape” pain: neck, upper back, shouldersNonradicular limb painWeaknessDizzinessVertigoSlurred speechSyncopeDifficulty swallowing

Tinnitus

Cranial nerve:DysphagiaDysarthriaHoarseness

Cough

Nystagmus

Cerebellar

A

taxia

Dysmetria

Brainstem

Nystagmus

S

leep apnea

Sensorineural

hearing loss

Hypertension

Sinus

bradycardia

/tachycardia

Syncope

Spinal cordHyperactive reflexesBabinski, Hoffman reflexSpastic gaitUrinary incontinence, frequencyExtremity weakness

Symptoms

Signs

The observation of cerebellar

tonsillar

ectopia

in the absence of

syrinx, hydrocephalus, or suggestive signs and symptoms

has uncertain clinical

significance

When

signs and symptoms are present

,

neuroimaging is vital to diagnosis and managementSlide9

CM1 Imaging

Routine imaging sequences are obtained to evaluate for hydrocephalus, syrinx, or other craniocervical junction (CCJ) pathologyThe midline sagittal image is used to quantify cerebellar tonsillar ectopia in relation to a line connecting the basion and opisthion (McRae’s line, foramen magnum)Slide10

CM1 Imaging: Classification

Chiari 0: Tonsils descend 3mm or less below the foramen magnumSyrinx+/- crowding at foramen magnumChiari 1:Greater than 5mm tonsillar descent in age >15 yearGreater than 6mm tonsillar

descent in age < 15 years3-5 mm is borderline, and abnormal if syrinx or symptoms4th

ventricle remains in normal positionChiari 1.5:Herniation of tonsils Elongation and displacement of 4

th

ventricle and brainstem

Chiari

0 and

Chiari

1.5 are controversial classificationsSlide11

CM1 Imaging

Degree of tonsillar herniationTonsillar shapePosterior fossa volumePosterior fossa crowdednessLinear Posterior Fossa Measures:ClivusSupraocciutTwining lineMcRae Line

CSF velocityCSF stroke volumeTonsil and cord movement

PressureResistance to flowCraniospinal compliance

Static

features of CM1 - anatomy and morphology – are studied with traditional

MRI

and CT sequences

Dynamic

aspects of CM1 are evaluated with CSF flow techniques and computational fluid dynamic simulationsSlide12

CM1 Imaging: Morphology

The morphologic abnormality in CM1 is diverseIn general, CM1 is characterized by:Pointed configuration of the tonsilsMore vertically oriented cerebellar foliaCrowded foramen magnumNarrowed retrocerebellar and premedullary subarachnoid spaceLower limits of normal or small posterior fossaShort clivusInferior elongation of the 4th ventricle with mildly low-lying nucleus

gracilis (the demarcation of obex and central canal)40-80% of symptomatic CM1 h

ave a syrinx4Slide13

CM1 Imaging: MorphologyPosterior cranial fossa (PCF)

volumetry is a potential predictor of surgical outcome9,10Alpern et. al. studied 20 morphologic and physiologic measures, of which 10 were found to discriminate CM1 from healthy controls better than tonsillar herniation aloneThe three parameters that best characerized CM1:Cord displacementPosterior cranial fossa crowdednessNormalized posterior cranial fossa volumeUsing these

three parameters, 37 healthy subjects and 35/36 CM1 subjects were correctly classified10Slide14

CM1 Imaging: Morphology

Complex CMI (cCMI) has recently been described in the neurosurgical literature as a CMI variant with more severe clinical phenotypeRecognition by the radiologist is useful as cCMI may require more extensive or repeat neurosurgical proceduresMoore and Moore evaluated a number of morphologic measures and found that obex level was the most important differentiating factor between CMI and cCMI11Inferior herniation of the obex below the foramen magnum (FM) and a prominent dorsal bump was observed in all patients with cCMI in their study

Typical CMI is characterized by obex above or at the FM

Complex CMI: The obex lies just below the FM (arrow).Slide15

CM1 Imaging: DynamicCSF dynamics in the cranial and spinal subarachnoid space may be equally important to morphology in the pathophysiology of CM1

CSF velocity, resistance to flow, pressure, and craniospinal compliance cannot be measured with static MR techniquesDynamic evaluation of CSF flow has primarily been studied with 2D phase contrast MRINew techniques developed to study flow include 4D PC MRI and Time inversion recovery pulse (Time-SLIP)Slide16

Abnormal morphology of cerebellar tonsils at the FM:

-crowding of neural structures-narrowed subarachnoid spaceObstruction of CSF pulsations

Elevated CSF velocity

Increased resistance to CSF flow

Altered

craniospinal

compliance

Cranial arterial driving pressure forces same volume of CSF against obstruction

Increased pressure

: over time may alter neural elasticity, permeability, water content

Increased pressure

: may further displace or damage neural structures

Morphology

Hydrodynamics

Increased

pressure

gradient

Surgical decompression alleviates crowding, results in decreased

peak

CSF velocity, and alters

craniocervical

CSF complianceSlide17

CM1 Imaging: Phase Contrast2D PC MRI in axial and/or sagittal orientation has been used to quantitatively and qualitatively evaluate dynamic CSF features such as:

Direction of flowPeak CSF velocityPulse wave velocity in the subarachnoid spaceRelative timing of CSF and arterial pulsationsBefore PC MR images are acquired, maximum CSF velocity must be anticipated in order to set the Venc (velocity encoding)To optimize signal, CSF velocity should be the same or slightly below the vencVelocities above the Venc produce aliasing artifactVelocities significantly below the Venc have weak signalSlide18

CM1 Imaging: Phase Contrast

Magnitude and phase images provide information about anatomy and velocityThe phase image, reflecting spin phase shifts, is the most sensitive to flowQuantitative information is acquired with images in the axial plane with through-plane velocity encoding in the craniocaudal directionQualitative features of flow are observed in the sagittal plane with in-plane velocity encodingPeripheral cardiac gating allows for collection of 12-24 phases during the repetition interval, depending on HRBy convention, bright signal reflects caudal motion during systole and dark signal represents cranial motion during diastoleSlide19

CM1 Imaging: Phase Contrast

Phase images in sagittal orientation in cine mode “White” flow is moving caudally during systole“Black” flow is moving cranially during diastoleIn this patient with CMI, there is craniocaudal flow ventral to the brainstem and upper cervical cord Craniocaudal

flow dorsal to the tonsils and cord is minimal.Click to play cine clip.Slide20

CM1 Imaging: Phase ContrastThe majority of studies utilizing 2D PC MRI show that CM1 is characterized by

elevated peak CSF flow velocity at the foramen magnum, and that peak velocity decreases after decompressionHowever, there is not an established correlation between change in velocity and the degree of clinical improvementCM1 is characterized by inhomogeneous flow patterns and simultaneous bidirectional flow: important findings confirmed in subsequent studies using different techniques, including 4D PC MRI and computation flow models5,12,13Slide21

CM1 Imaging: Phase ContrastMcGirt

et al. found that pediatric CM1 patients with normal CSF flow at the FM as assessed by PC MR were 4.8-fold more likely to experience symptom recurrence following surgery regardless of the degree of tonsillar herniation or presence of syrinx8Abnormal ventral and dorsal flow was associated with a 2.6-fold reduction in risk of symptom recurrence after surgeryThese findings support the role of inhomogeneous flow patterns in CM1 pathophysiologySlide22

CM1 Imaging: Phase Contrast

Time-resolved three directional velocity encoded phase contrast MRI (4D PC MRI) is a recent advance that can better assess the three dimensional complexities of the CSF flow fieldUsing 4D PC MRI, Bunck et al. showed that in CM1, the anterior subarachnoid space (SAS) is markedly narrowed, with CSF flow diversion to the anterolateral SASThis results in flow jets with elevated velocities and flow vortices14

Coronal 4D PC MRI images in control (A) and CM1 (B). Compare uniform, homogeneous flow in A, with lateral flow diversion and left sided flow jet in B.

Bunck

et al,

Eur

Radiology (2012) 22:1860-1870.

A

BSlide23

CM1 Imaging: Phase Contrast

Peak CSF velocities were significantly greater at the craniocervical junction in CM1 patients than in controls, a finding in most, but not all prior studies using the 2D PC MR techniqueThe volumetric measurement facilitated by the 4D technique demonstrated variability among patients as to the level where peak systolic flow was foundInconsistent results in prior studies may relate to the inability of the 2D technique to capture the correct level for peak flow measurementSlide24

CM1 Imaging: Time-SLIPAnother recently developed MR technique applied to the study of CSF flow dynamics is Time-spatial labeling inversion pulse (Time-SLIP)

Time-SLIP is based upon the arterial spin labeling conceptIn this case, instead of flowing blood, CSF is used as an endogenous tracerAdvantages over phase contrast include:Superior anatomic detail Shorter acquisition timeImproved evaluation of non periodic or turbulent flowSlide25

CM1 Imaging: Time-SLIPFirst the background signal is suppressed with a non selective inversion recovery pulse

This is followed by a second, spatially selective pulse perpendicular to the direction of flowWhen images are acquired, the labeled CSF flows into regions of suppressed background with high conspicuityCSF bulk flow can be observed for up to 5 seconds before contrast between tagged and non tagged CSF is lostSlide26

Time-SLIP

A nonselective IR pulse is applied, inverting all signal in the field of

view

A second, spatially selective inversion pulse is applied to the region of interest

After a short period of time, tagged CSF is seen moving into the non-tagged background (red arrow)Slide27

CM1 Imaging: Time-SLIP

Time-SLIP in CM1 after surgical decompression. The initial image (A) shows the location of the selective pulse (gold lines). Tagged CSF is bright in this slice. All other CSF is suppressed (dark). After several seconds (B) tagged CSF is seen above and below the slice (gold lines), ventral to the brainstem and cord and dorsal to the cerebellum and cord (orange arrows). *Note the exquisite anatomic detail of the images allowing precise localization of CSF flow, a significant advantage over PC MR images.

A

BSlide28

CM1 imaging: Time-SLIP

In this cine clip, we watch the movement of CSF over 5 seconds. Gold lines mark the selective pulse with tagged (bright)

CSF

Notice the movement of CSF above and below the slice with

time

We observe features of flow not possible by any other technique:

CSF

moves from the 4

th

ventricle superiorly

into

the

aqueduct

Turbulent

flow is seen in the 4

th

ventricle (moving dark lines in the midst of bright CSF

)

CSF

moves within the cervical

syrinx

At the end of 5 seconds, contrast between tagged and untagged CSF is lostClick to play cine clip.Slide29

CM1 Imaging: Time-SLIP

2D Phase Contrast

Time-SLIP

2D PC demonstrates the presence and direction of flow. Time-SLIP allows better visualization of location of flow, as well as periodic and turbulent flow.

Click to play cine clip.

Click to play cine clip.Slide30

A. Initial imaging. Sagittal T1-W image shows ectopic, pointed cerebellar tonsils and crowding at the foramen magnum (FM).

B. The preoperative Time-SLIP image demonstrates flow ventral the cervical cord (blue arrow). No flow is seen dorsal to the cord below the FM (gold arrow). Yellow lines indicate the tagged slice. All bright CSF above and below the lines has flowed from the tagged slice.C. Post decompression sagittal T2-W image reveals relief of crowding at the FM. More CSF is seen dorsal and inferior to the tonsils. A small amount of fluid is seen posterior to the duraplasty.D. Post operative Time-SLIP image again shows CSF flow ventral to cervical cord (blue arrow). There is now flow dorsal to the cord at this level (gold arrow).

Case 1: 35 year-old man with 2 years of worsening headache, facial pain, and developing slurred speech. MRI demonstrated

tonsillar herniation 16mm below the foramen magnum. After decompression with C1 and partial C2 laminectomies and duraplasty, the patient had marked improvement of his headaches and resolution of his facial pain.

A

B

C

DSlide31

The pre-operative Time-SLIP image demonstrates flow ventral to the cord, but only trace flow dorsal to the cord at the tagged level (level marked by gold dots). A small amount of flow is also seen within the syrinx.

A

Click to play cine clip.

B

Click to play cine clip.

The high intrinsic signal to noise and temporal resolution of Time-SLIP

in comparison to 2D PC MRI allows

visualization of CSF movement in response to

respiration. Respiratory motion may have a greater effect on CSF flow than cardiac pulsation

.

15

The post-decompression study reveals

increased

flow dorsal to the cord.

Craniocaudal

flow within the syrinx has also increased. Interestingly, there is a small amount of cranial flow of

fluid

within the

pseudomeningocele

.

This may

relate to respiration.

Case 2: 43-year-old man with 10 year history of upper and lower extremity weakness and numbness, ataxia, increasing difficulty with fine motor control.Slide32

Case 3: 58-year-old man with complicated history of cervical stenosis with myelopathy post C6-T1 laminectomy and fusion one year ago. Increasing difficulty with gait, balance, and left leg weakness prompted imaging. He was found to have an increase in his pre-existing

tonsillar ectopia. He underwent posterior fossa decompression, C1 laminectomy, and duraplasty.8/2014 and 12/2014. The patient had only partial improvement in symptoms. Time-SLIP shows that there is no flow dorsally at the FM. The brisk ventral flow is already apparent on the first image. 4 months later, the pseudomeningocele is noted to be larger. There is no change in CSF flow pattern. There is no cranial flow in the fourth ventricle, an abnormal finding.

5/2014. The preoperative image shows crowding at the FM, increased from prior studies. The focus of abnormal T2 signal in the cord at C7/T1 reflects

myelomalacia. The post decompression image shows relief of crowding. There is a large pseudomeningocele.

Click to play cine clip.

A

B

C

D

Click to play cine clip.Slide33

Case 4. 49-year-old woman with history of

suboccipital headaches.

Note the short clivus

, small posterior fossa, and superiorly oriented straight sinus, typical of CM1. Crowding at the FM is minimal but there is a large cervical syrinx (Chiari 0?)

Note the change in shape of the syrinx in relation to the flow in the ventral and dorsal SAS at that level.

No flow is seen dorsally at the FM.

Note the cranially-directed flow through the

aquaduct

into the third ventricle, a normal finding.

S

elective tagging pulses can be performed at multiple levels and in different orientations, as long as the slice is perpendicular to the flow direction of interest. A coronal orientation can evaluate flow between the lateral and third ventricles.

Click to play cine clip.

Click to play cine clip.Slide34

Time-SLIP

Investigators are currently devising methods to quantify flow velocity on Time-SLIP16PC MR and Time-SLIP provide complementary information for the characterization of pathologies with aberrant CSF flow dynamicsCSF dynamics visualized with Time-SLIP differ from classic CSF circulation theories, and the development of this method has advanced knowledge of CSF physiology A better understanding of CSF dynamics in health and disease may lead to increased diagnostic accuracy and better patient selection for surgical interventionsSlide35

SummaryHistorically and currently, neuroimaging is vital to diagnosis and management of CM1

The search for a noninvasive method of selecting patients with CM1 symptoms who will benefit from surgical intervention is an active area of research across many fieldsEmerging techniques such as 4D PC MRI and Time-SLIP are providing unique insights into CSF flow dynamics in CM1 and other pathologies resulting from disordered CSF flow dynamicsSlide36

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