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Magnetic Resonance Imaging

Part 31 HOUR

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Course

objectives

• Contraindications for MRI

• Reading the MRI report

• The MRI appearance of:

• Degenerative Disc Disease

• Annular Tears

• Disc Herniations

• Ligamentum Flavum Hypertrophy

• Post-disc Surgery

• A Case Review of MRI Confirmed Spontaneous Regression of Lumbar Disc Herniations

CONTRAINDICATIONS

FOR MRI

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THE NUMBER 1

CONTRAINDICATION

FERROUS METAL

Cochlear implants are tiny, intricate electronic devices that help provide a sense of sound to severely deaf individuals.

They not absolute contraindications but there have been reports of problems

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DENTAL

IMPLANTS

Pacemakers

and Cardiac Defibrillators

are an Absolute

Contraindication to MRI –

Or Are They?

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MOST SURGICAL

INSTRUMENTATION AND

PROSTHETIC DEVICES ARE OK!

VASCULAR CLIPS IN BRAIN

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BODY PIERCINGS AND TATTOOS

OTHER

CONSIDERATIONS

• Bullets and Shrapnel may be a contraindication depending on the location of the foreign body

• Pregnancy is not an absolute contraindication for MRI, however if the MRI can be delayed until after delivery, that would be preferable

• Gadolinium studies on lactating mothers is not known to be harmful however as a precautionary measure the milk should be pumped and discarded.

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READING THE MRI

REPORT

THE

DIFFERENCES

BETWEEN

READING AN

MR IMAGE

AND

READING AN

X RAY IMAGE

Axial Plane Anatomy

Shades of Gray

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AXIAL PLANE

ANATOMY

MAGNETIC RESONANCE

IMAGING

The Scout Image

• Without the "scout image", it will be near impossible to distinguish the difference between any of the 5 discs of the lumbar spine.

• The scout image is like a road map that tells you which slice is what and is almost mandatory for even the most experience doctor to have.

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• 20 'cuts' or slices through the sagittal lumbar spine

• Each number is assigned to the MRI axial image that was taken along that plane

MAGNETIC RESONANCE

IMAGING

The Scout Image

• Slice #10 goes right through the L4 disc and is the image to look for if you have a L4 disc problem

• Image 18 (line 18) would correspond with the L3 disc and Image 5 is the best cut through the L5 disc

MAGNETIC RESONANCE

IMAGING

The Scout Image

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BASIC AXIAL ANATOMY

• The key structures of the axial MRI are as follows:

• The Thecal Sac (dura and arachnoid matter)

• The Exiting Spinal Nerve Roots (L5)

• The Traversing Spinal Nerve Roots (S1 )

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Regions of

the Epidural

Space

Central Region

Para-central Region AKA Lateral Recess

Intraforaminal Zone AKA Subarticular Zone

Extra-Foraminal Zone

• BLUE:

• This is the 'Central Region' and is located directly behind the disc

• It encompasses the anterior aspect of the thecal sac. Since the PLL (posterior longitudinal ligament) is at its thickest in this region, the disc usually herniates slightly to the left or right of this central zone.

• A centrally located disc herniation, the chances of a successful discectomy are reduced

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• Purple

• This is the 'Paracentral Region' or 'Lateral Recess' and is located just outside of the Central Region.

• Because the PLL is not as thick in this region, disc herniations are frequently found here; in fact, this is the number one region for disc herniations to occur in.

• The Traversing Nerve Roots, which are the neural structures found in this zone, are frequently contacted, deviated and compressed in this zone.

• GREEN:

• 'Intraforaminal Zone', aka 'Subarticular Zone', and is located within the intervertebral foramen (IVF)

• Only 5% to 10% of all disc herniation occur here

• When herniations do occur in this zone, they can compress the Dorsal Root Ganglion

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• YELLOW:

• Extraforaminal Zone it is just outside of the IVF.

• Again, it is very rare for a disc to herniate into this region, but when it does happen, it is often very troublesome for the patient and surgeon.

•

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SHADES OF GRAYSHADES OF GRAY

BRIGHT WHITE = HIGH SIGNAL INTENSITY

DARK GRAY = LOW SIGNAL INTENSITY

COMPARING

INTENSITIES

• If the signal intensities are the same

Isointense

• If the signal intensity is darker

Hypointense

• If the signal intensity is brighter.

Hyperintense

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HIGH SIGNAL FOR FAT

LOW SIGNAL FOR WATER

HIGH SIGNAL FOR WATER

LOW SIGNAL FOR FAT

DEGENERATIVE DISC

DISEASE

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NUCLEUS PULPOSUS

• Accounts for 40% of the bulk of the healthy disc

• As a disc begins to degenerate it looses it’s water content and begins to desiccate.

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T2 Weighted Image

• The discs should appear as white because, when they are healthy, they have a high water content

• The L3 and L4 discs are white, indicating that they are healthy

• The L5 disc however is dark, indicating that it is undergoing a degenerative process

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ANNULAR TEARS

Rim Lesion

Concentric Lesion

Radial Tear Lesion

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3 TYPES OF TEARS

Rim Lesion

A horizontal tearing of the very outer fibers of the disc

near their attachments into

the ring apophysis

Concentric Tear

A splitting apart of the lamellae of the annulus

in a circumferential direction. These tears

are also known as Circumferential tears

Radial Tear

A horizontal or obliquely horizontal tear which begins within the nucleus pulposus

and progresses outward toward the posterior periphery of the disc.

Rim Lesion aka Peripheral Tear or a Transverse Tear

• Rim lesions are horizontal tears in the very outer fibers of the annulus (Sharpey’sfibers) near their insertion point into the bony 'ring apophysis'.

• These tears are thought to be traumatically induced and often are associated with small osteophytes (bone spurs).

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Concentric Annular Tear or Circumferential Tear

• Separation or splitting apart of the annulus fibrosus, between the lamellae.

• Concentric tears are rarely seen in the inner anulus.

• Since the outer 1/3 of the annulus is well innervated a disruption in this region can be extremely painful!

• It is believed that trauma is the cause of concentric tears, especially from torsion over-load injuries, such as swinging a golf club or throwing a discuss.

Radial Tear

• A radial annular tear is any annular tearing that begins within the nucleus pulposus and progresses in an outward or radial direction.

• Full thickness Radial Tear that extends completely through the posterior annulus.

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• When a Radial Annular Tear enters the outer 1/3 of the annulus and exposes the sinuvertebral nerve-endings to degenerated nuclear material pain may well occur secondary to chemical irritation of these pain-carrying fibers.

• This type of pain is called 'Discogenic Pain,' which means that the pain arises from within the disc and not the adjacent neural tissue.

Radial TearRadial TearRadial TearRadial Tear

ANNULAR TEARS MRI APPEARANCE

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DISC HERNIATIONS AND

MRI

DISC BULGE

• Pre-cursor to a disc herniation.

• This type of disc lesion - that bulges into the anterior epidural space without any area of focal-ness or out-pouching -would be called a 'Disc Bulge' on MRI

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DISC HERNIATION

• The term 'Disc Herniation' (or 'disc prolapse' as they use in Europe) includes three specific types of disc lesions

• Protrusion (aka: contained herniation or sub-ligamentous herniation),

• Extrusion (aka: non-contained herniation, or trans-ligamentous herniation)

• Sequestration (aka: free fragment).

DISC PROTRUSION

• The posterior of the disc is pushing backwards into the anterior epidural space and has contacted, and even somewhat compressed, the traversing nerve root (red arrow) and right front corner of the thecal sac.

• Note that the PLL still has NOT be disrupted and is still "containing" the herniated nuclear material.

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DISC PROTRUSION

• Disc protrusions are seen in about 30% of the normal non-symptomatic population

• This patient may well be suffering right sided radicular pain (sciatica) and/or lower back pain as a result of compression/irritation of the traversing nerve root and/or irritation of the sinuvertebralnerves in the posterior of the disc.

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DISC EXTRUSION

• The PLL has completely ruptured allowing further migration of the nucleus into the anterior epidural space.

• Note the marked displacement of the traversing nerve root AND the exiting nerve root

• This Disc Extrusion is NOT typically seen in the asymptomatic person and is often an indication for surgical decompression; the sooner the better IF you're NOT improving with conservative care.

DISC EXTRUSION• Another interesting

phenomenon about extrusions are the fact that these larger disc lesions have a greater ability to be 'reabsorbed' by the body!

• This 'shrinkage phenomenon' has been demonstrated in the literature

• In fact, you can expect that in 80% of large disc extrusions, there will be at least a 50% 'shrinkage' of size.

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DISC HERNIATION

• T2 Weighted MRI lumbar image, demonstrates two types of disc herniations:

• The L5/S1 disc has suffered a 9mm disc extrusion (red arrow) that is not contained by the PLL.

• The L4/5 disc has suffered a smaller 4mm disc protrusion (green arrow) that is contained by the PLL.

DISC SEQUESTRATION

THE FINAL PHASE• A fragment of nuclear

material has detached itself from the main body of the extrusion is and loose in the epidural space.

• It may be excruciatingly painful and, if centrally located, may occasionally cause the patient to lose control of their bowl and bladder function,

• As with the disc extrusion, the sequestration may also undergo a reduction in size

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THE BOTTOM LINE ON DISC HERNIATIONS AND MRI FALSE POSITIVES

CASE STUDIES

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POST-

OPERATIVE

SPINES

• The T1 and T2 MRI appearance of disc herniation in the postsurgical and nonsurgical back looks the same.

• Surgical cases often cause scar tissue to accumulate within the epidural space adjacent to nerve roots often mimicking disc herniations.

• Gadolinium will help make this differentiation and therefore plays a key role in selecting the appropriate management for the postsurgical back pain patient.

CASE STUDY

40 Year old man who underwent laminectomy and discectomy 1 year prior with recurrent back pain

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Spontaneous Regression of Lumbar Disc

Herniations at Different Levels and Times in

a Patient: A Case Report

Turkish Neurosurgery, 2005, Vol: 15, No: 1, 18-22

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The sagittal and axial T2WI of the

second MRI study in October 2002

revealed an L4-L5 protrusion without

L5-S1 extruded disc fragment.

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The axial T2WI of the third MRI study in

August 2003 revealed a left-sided L4-5

extruded disc herniation.The sagittal T2WI of the third MRI study

in August 2003 revealed an extruded L4-

5 disc herniation with caudal migration.

The sagittal T2WI of the follow-up MRI of

the lumbar region in March 2004 again

showed spontaneous regression.

The axial T2WI of the follow-up MRI of the

lumbar region in March 2004 again showed

spontaneous regression.

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This completes the course material for the

MRI Part 3 course.

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