Module 8, Year 1 - Radiology Flashcards
1
Q
What is the anode heel effect?
A
Greater x-ray absorption occurs at the anode (+) side, thin part toward anode and and atlas at anode
2
Q
What primarily controls density on a x-ray?
A
mAs - increasing mAs increases quantity of photons reaching film, increasing density
3
Q
What makes a x-ray appear darker?
A
Increasing mAs
4
Q
If a x-ray film is too light or too dark, what is the rule to change it?
A
Change mAs by a factor of 2
5
Q
Inverse square law
A
The intensity of the x-ray beam is inversely proportional to the square of the distance of the object from the source. In other words, there is a rapid decrease in intensity as the beam spreads out over an increasingly larger area
6
Q
T or F: KVP fine-tunes the density of the x-ray film.
A
False, KVP does NOT change the density of the x-ray film.
7
Q
How does KVP affect the x-ray film?
A
Increases the contrast, short scaling, or creating more black and white (less detail)
OR
Decreases contrast, long scaling, or creating more grey (more detail)
8
Q
What is the 15% rule?
A
If you want to double density, 2x mAs and increase kvp by 15%. If you want to half density, 1/2 mAs and decrease kvp by 15%.
9
Q
How would you adapt a film for children or the elderly?
A
Decrease exposure by 30%
10
Q
Why collimate?
A
Decreases radiation dose, scatter and density; while increasing the contrast
11
Q
What does ALARA mean?
A
Keep radiation “as low as reasonably possible”
12
Q
Do x-rays accumulate in the body?
A
No, x-rays do not make you radioactive, but the effects of exposure can accumulate.
13
Q
What is OID?
A
The object to image receptor distance (OID) is the distance between the object to the detector.
OID is directly proportional to size distortion.
14
Q
What is SID?
A
The source image receptor distance (SID), is the distance of the tube from the image receptor, affecting magnification. The greater the SID, the less magnification the image will suffer.
The SID is inversely proportional to size distortion.
15
Q
What is the best way to avoid shape distortion?
A
Proper equipment alignment and patient positioning
16
Q
What is dynamic range?
A
The ability of the detector to respond to change in exposure.
17
Q
What is basilar invagination? What are some ways to determine if someone has this?
A
Upward displacement of the vertebral elements into the normal foramen magnum with normal bone - upward migration of the upper cervical spine.
McRae's Line McGregor's Line Chamberlain's Line Digastric Line Bimastoid Line
18
Q
What are common causes of invagination?
A
Deformity (whether genetic or acquired) or softening of the bone at either the occipital bone or upper neck, esp. the dens.
19
Q
Describe Chamberlain’s Line
A
Line joining the back of the hard palate with the opisthion
If dens is more than 3mm above this line, basilar invagination is suspect
20
Q
Describe McRae’s Line
A
Line joining opisthion and basion
If dens is less than 5mm away from this line, basilar invagination is suspect
21
Q
Describe McGregor’s Line
A
Line between hard palate and the most caudal point of outer table of occiput - only used when the opisthion is not available
If the tip of dens lies more than 4.5mm above this line, basilar invagination is suspect
22
Q
Describe digastric line
A
Line drawn between right and left digastric grooves.
Tip of dens and atlanto-occipital joint normally project 11mm and 12mm below this line.
Basilar invagination is suspect when the dens is at or above this line.
23
Q
Describe bimastoid line
A
Line between tips of the mastoid processes
Basilar invagination is suspect if the tip of dens projects above 10mm
24
Q
What is Platybasia/Flat Skull Base/Martin’s Anomaly?
A
Developmental anomaly (or acquired deformity) of the skull in which the base of the posterior cranial fossa bulges upward; seen as flattening angle between clivus and body of sphenoid.
Determined by basilar angle, measuring greater than 143 degrees.
25
Describe the basilar angle
Angle from lines connecting nasion to mid-sella, and mid-sella to basion
Normal: 125-143 degrees
Platybasia: >143 degrees
Basilar kyphosis: <125 degrees
Modified MRI technique for the basilar angle extends line across the anterior cranial fossa to the tip to the dorsum sella and line along posterior of clivus
Adult normal: 116-118
Children normal: 113-115
26
What congenital conditions predispose someone to platybasia?
```
Achondroplasia
Down Syndrome
Chiari malformations
Craniocleidodysostosis
Craniofacial anomalies
Osteogenesis imperfecta
```
27
What conditions may lead to acquiring platybasia?
```
Paget Disease
Osteomalacia
Rickets
Trauma
Fribrous Dysplasia
Hypoparathyroidism
```
28
Describe a normal sella turcica
No more than 12mm craniocaudal and 16mm anterior-posterior
29
ADI normals
<3mm adults
| <5mm children
30
A practice member's x-ray shows a "V-shaped" atlantodental interval space. She states she was in a car accident a few months ago and had a concussion. What may be suspect?
Transverse ligament instability
31
Describe the cervical gravity line
Line drawn vertically from tip of dens should intersect C7 vertebral body
32
Describe horizontal and angular instability
Difference in the angles formed by the intersection of lines extended from the endplates of two contiguous vertebrae
Each segment should NOT be greater than 11 degrees
33
The accumulated measurement between C3-C4 and C4-C5 parallel endplate lines is 29 degrees. What does this suggest?
Horizontal and angular instability
34
Describe Clinical Instability
Pathological state of motion at an intervertebral level in the cervical spine that results in clinically intolerable symptoms (like root and cord damage) requiring prolonged bracing or surgery
35
What better shows instability Flex/Ext x-rays or CT/MRI?
CT/MRI
36
Describe the cervical lordosis depth method
Line from tip of odontoid to posterior surface of C7
Average: 12mm
Negative value: kyphosis
Larger value: hyperlordosis
Smaller value: hypolordosis
37
Describe cervical lordosis angle (Cobb)
Angle between lines centered through anterior and posterior tubercles of C1 ad across the inferior endplate of C7
Normal: 40 degrees
38
Describe Harrison posterior tangent method
Angle measurement between intersection of C2 posterior body line and C7 posterior body line
Smaller standard of error measurement than Cobb angle
Normal range: 31-40 degrees
39
Describe healthy prevertebral soft tissue thickness on x-ray
Adults only: 6mm at C2 and 22mm and C6
Kids: 7mm at C2 and 14mm at C7
Adults: 7mm at C2 and 21mm at C7
Generally, the prevertebral soft tissue increases with flexion and decreases with extension.
40
Normal spinal canal measurements on x-ray
```
C2: 16mm
C3: 14mm
C4: 13mm
C5: 12mm
C6: 12mm
C7: 12mm
```
41
What is a significant finding on George's Line?
Anything greater than 3mm, 3.5mm or more is permanent damage
42
Describe Grabb-Oakes Line
Tip of basion to posterior inferior C2 vertebra
Normal: 9mm or less
Anything higher than 9mm suggests ventral brainstem compression
43
Describe the clivoaxial angle
Clivus to basion and another line drawn long the posterior margin of the dens
Normal: 150-180
< 135 degrees is "potentially pathological"
44
What measurement assesses the degree of basilar invagination?
Clivoaxial angle
45
Describe Harris Measurement
Measurement from the tip of the clivus to either the tip of the dens or 90 intersect with posterior axial line
12mm or greater indicates occipitoatlantal disassociation
46
Describe Power Ratio
Calculated by dividing the distance between the tip of the basion to the spinolaminar line by the distance from the tip of the opisthion to the midpoint of the posterior aspect of the anterior arch of C1
>1 = vertical distraction
<0.55 = posterior disassociation
47
Describe condyle-C1 interval
Interval between Condyle and C1 at 4-equidistant points on the joint surface in sagittal and coronal reconstructions of computed tomography
*Been shown to provide the highest diagnostic accuracy for pediatric patients
48
Describe Lee x-line
The first line connects the basion to the midpoint on the C2 spinolaminar line (the anterior aspect of the posterior ring of C2) - should tangentially intersect across the superior posterior aspect of dens
The second line connects the opisthion to the posteroinferior edge of the body of C2 - should tangentially intersect just anterior the posterior ring of C1 (the highest edge of the C1 spinolaminar line)
49
What would indicate a significant finding when evaluating the APOM lateral masses?
2mm or greater overhang of atlas over axis superior articular facet.
This could indicate Jefferson fracture, odontoid fracture, alar ligament instability, rotatory atlantoaxial subluxation (and possibly spondyloschisis)
Generally, <2mm is okay
50
Describe a child's psuedo-jefferson fracture
Children up to 4 years old may have an overhang of the atlas over the axis superior articular facet and it be a normal variant due to accelerated growth of atlas (pseudo-spread)
51
Describe Swischuck line and child's psuedo-anterolisthesis
Anterior aspect of posterior arch of C1 –to- anterior aspect of posterior arch of C3
The anterior aspect of posterior arch of C2 should be within 1-2mm of this line. <2mm is a pseudosubluxation, but this does not rule out a hangman fracture
>2mm indicates a true subluxation
52
When is it appropriate to take an image?
When the data gained from the test will influence patient care. (All or nothing approach is NOT advisable)
53
A practice member has has acute rheumatoid arthritis. Adjust?
No dynamic thrust
54
A practice member was in a car wreck. The x-ray makes you suspect of instability. Adjust?
No dynamic thrust
55
A practice member has sacral ankylosing spondylitis. He states he has been adjusted manually before. Adjust?
No dynamic thrust
56
There is excessive movement on the flexion/extension film. The practice member states he had a fracture in his neck years ago, but it has healed. Adjust?
No dynamic thrust
57
A tilted APOM shows movement of the os odontoideum. The practice member states she has never had any heavy trauma to the head. Adjust?
No dynamic thrust
58
Metastasis is see on the x-ray. Adjust?
No dynamic thrust
59
A practice member has suspected Paget's disease. Adjust?
No dynamic thrust on the suspected segment.
60
Practice member states she has had tingling bilaterally in her arms and legs. Adjust?
No dynamic thrust in either the cervical or lumbar regions.
61
A practice member is suspect of vertebrobasilar insufficiency syndrome. Adjust?
No dynamic thrust.
62
Practice member has an MRI showing pooling of the jugular vein bulb. Adjust?
No dynamic thrust to the atlas bone.
63
What are some relative contraindications of adjusting with a dynamic thrust?
Articular hypermobility (when stability of joint is uncertein)
Severe demineralized bone
Benign bone tumors
Bleeding disorders and anticoagulant therapy
Radiculopathy with progressive neurological signs
64
A practice member was in a car wreck. The x-ray makes you suspect of instability. Adjust?
No dynamic thrust
65
Name any of the spine trauma and x-ray criteria
Back pain
Midline tenderness on palpation
Distracting injury or other high risk mechanism
Neurological deficits
Altered consciousness: head trauma, ethanol/intoxication, drugs
66
When should you get new films on a practice member?
At least at the year mark
If there is any change in history
Symptoms persist or worsen
There is doubt that the patient in the old images is the "same patient"
67
A tilted APOM shows movement of the os odontoideum. The practice member states she has never had any heavy trauma to the head. Adjust?
No dynamic thrust
68
Metastasis is see on the x-ray. Adjust?
No dynamic thrust
69
A practice member has suspected Paget's disease. Adjust?
No dynamic thrust on the suspected segment.
70
Practice member states she has had tingling bilaterally in her arms and legs. Adjust?
No dynamic thrust in either the cervical or lumbar regions.
71
A practice member is suspect of vertebrobasilar insufficiency syndrome. Adjust?
No dynamic thrust.
72
Practice member has an MRI showing pooling of the jugular vein bulb. Adjust?
No dynamic thrust to the atlas bone.
73
What are some relative contraindications of adjusting with a dynamic thrust?
Articular hypermobility (when stability of joint is uncertein)
Severe demineralized bone
Benign bone tumors
Bleeding disorders and anticoagulant therapy
Radiculopathy with progressive neurological signs
74
Name some "red flags" in non-traumatic practice members where radiographs are indicated
Patient <20 or >50
No response to care after 4 weeks
Significant activity restriction > 4 weeks
Nonmechanical pain - like unrelenting pain at rest or constant or progressive signs or symptoms
Suspected inflammatory joint disease
Suspected compression fracture
Suspected neoplasm
Suspected infection
Suspected failed surgical fusion
Progressive or painful structural deformity/scoliosis
Elevated laboratory evaluation and positive signs of disease
75
Name any of the spine trauma and x-ray criteria
Back pain
Midline tenderness on palpation
Distracting injury or other high risk mechanism
Neurological deficits
Altered consciousness: head trauma, ethanol/intoxication, drugs
76
When should you get new films on a practice member?
At least at the year mark
If there is any change in history
Symptoms persist or worsen
There is doubt that the patient in the old images is the "same patient"
77
T or F: Doses normally delivered from diagnostic radiographic procedures (less than 50 mGy) have not been associated with pregnancy termination.
True
78
Specs for T2 MRI
```
Long TR (>2000ms)
Long TE (>80ms)
Flip angle 90 degrees
```
79
T or F: The lifetime attributed cancer incidence for a fetal dose is 50 mGy in the gestational period, but estimated at 2% occurrence. Thus, there is a 98% likelihood a child will be unaffected by radiation.
True. While this is the estimate, knowing for certain is impossible.
80
T or F: Most diagnostic examinations result in much less dose to the conceptus/fetus.
On the higher end, abdominal/pelvic CT imaging typically delivers 10 to 25 mGy. Even this is no where close to the 50mGy fatal requirement.
True
81
What is cord myelomalcia?
"Softening of the spinal cord"
Hemorrhagic infarction of the spinal cord can occur as a sequela to acute injury (such as a car accident).
If C3 - C5 motor nuclei of the phrenic nerves are affected by an ascending lesion, this could result in respiratory paralysis.
82
On MRI, if it is high signal, the image is...
White/bright
83
On MRI, if it is a low signal, the image is...
Black
84
On MRI, T1 has water as the...
Low signal (black)
85
On MRI, T2 has water as the...
High signal (white)
86
Why is having a T1 and T2 MRI important?
To be able to compare the tissues
87
Specs for a T1 MRI
```
Short TR (<800ms)
Short TE (<30ms)
Flip angle 90 degrees
```
88
Specs for T2 MRI
```
Long TR (>2000ms)
Long TE (>80ms)
Flip angle 90 degrees
```
89
Specs on PD MRI
```
Mid TR (<1000ms)
Short TE (<30ms)
Flip angle 90 degrees
```
90
How does natural history and imaging share importance with a chiropractor?
Natural history is the course of a process over time without external influence (like HIV exposure affecting T-cells then leaving the body susceptible to immune deficiency). A subluxation unaddressed leads to joint dysfunction, then degeneration, then fusion, etc. Chiropractic aims to prevent this.
91
What is cord myelomalcia?
"Softening of the spinal cord"
Hemorrhagic infarction of the spinal cord can occur as a sequela to acute injury (such as a car accident).
If C3 - C5 motor nuclei of the phrenic nerves are affected by an ascending lesion, this could result in respiratory paralysis.
92
Best image for brain
MRI
93
Best image for trauma to the head
CT
94
Best image for bleeding in the head
CT
95
Best image for genitourinary investigation
Ultrasound
96
Best image for the spinal cord
MRI
97
Associated CT imaging presents at above _____ for white images and ______ for black
```
+240 = white
-160 = black
```
98
What is a contrast CT?
Iodine is administered into the practice member orally, intravenously, rectally or insubarachnoid (for a myelogram), emphasizing regions of the body to accentuate differences between tissues.
Good kidney function is required to do this test.
Typically minor side effects.
99
What is an arthrography?
Visualizes soft tissue structures such as cartilage and capsules. This allows the surface of soft tissue linings in the joint and bones to be seen.
This is done with contrast injected into the region of interest. This is typically performed on hips, knees, ankles, shoulders, elbows, and wrists.
100
Best image for chest investigation
CT
101
What imaging would you order for someone who is having "the worst headache of my life"?
CT
No contrast
(MRI with no contrast would be a secondary option)
102
Best image for mediastinum
MRI
103
Best image when metal is in the field of view
MRI
104
When should you NOT order a MRI?
Patient is claustrophobic, pacemaker, or obese
Metal can be limiting... always let the imaging center know if there is metal involved - certain aneurysm clips in the brain are wearisome although most surgical clips are fine. Healed joint replacements and orthopedic implants are well anchored and generally okay.
If metal is in the eye, absolutely NO MRI.
105
Best image for facial trauma and fractures is suspect
CT
Without contrast
Conventional radiographic exam can only see so much (nasal spine)
106
What imaging technique should you use when acquiring a CT?
Volume spiral acquisition perpendicular to tabletop. Each axial slice should be 1 to 3mm thick.
107
Associated CT imaging presents at above _____ for white images and ______ for black
```
+240 = white
-160 = black
```
108
What is a contrast CT?
Iodine is administered into the practice member orally, intravenously, rectally or insubarachnoid (for a myelogram), emphasizing regions of the body for a more appropriate viewing.
Good kidney function is required to do this test.
Typically minor side effects.
109
What is an myelography?
Evaluates the fluid-filled subarachnoid space in spinal canal by x-ray with contrast injected in the subarachnoid space to get view of neurological tissues.
This is performed to evaluate a tumor, infection, herniated dis, or stenosis.
110
Best image for someone with acute head trauma but shows no evidence of concussion.
CT
| No contrast
111
Best image for someone with acute trauma and shows evidence of a concussion.
MRI
| With and without contrast
112
Best image for seeing cranial neuropathy causes by a suspected mass
MRI
| With and without contrast
113
*What do you suspect with a misalignment in the facet joints on lateral, flexion, and extension with a prominent anterolisthesis?
Bilateral facet fracture
114
Best image for TMJ pain
MRI
Without contrast
Looking for the dysfunctional disc between the mandibular condyle and temporal bone
X-ray not helpful
CT minimally helpful... shows joint narrowing, sclerosis, and osteophytes
115
Best image for carotid or vertebral artery stenosis
CTA of neck
With contrast
MRA
With and without contrast
Ultrasound does not evaluate the vertebral artery because it cannot image through the transverse process
116
Best image for neurological deficit in the brachial plexus
MRI
| With and without contrast
117
Best image for spine trauma
Start with x-ray: AP, APOM, lateral (and possibly obliques)
Then CT without contrast, and if there is neurological deficit, follow up with MRI without contrast
118
*How can you tell image quality?
You can see trabeculae
119
*What is quantum mottle?
Pixelated effect, not enough photons, need to increase mAs
120
*90% of tear drop fractures have...
Neurological issues
121
*Normal marrow signal on a T1 image...
High signal, higher than IVD
122
*What is natural history?
The course of a process over time without outside influences
123
*What effect can atlas instability have?
Guillotine effect
124
*What is the best scan for bone metastasis?
Pet scan or bone scan
125
*What percentage of the population will have pillar instability up to 3mm?
30-40%
126
*Indications for contrast in advance imaging...
Hint: "Mi Mi VS"
```
Mass
Infection
Malignancy
Inflammatory disease
Vascular injury
Scars
Disc herniation
(with contrast)
```
127
*What is the job of the alar ligaments?
Limit rotational and lateral bending to the contralateral side when relating C2 to the skull
128
What is the Gold Standard for cervical spine injury?
MDCT/MSCT/HRCT
129
Describe CCJ range of motion
During flexion-extension, both C0-C1 and C1-C2 participate equally combining for about 25 degrees
Cranio vertebral rotation occurs mostly at C1-C2 with 41.5 degrees of rotation to each side and 4.3 degrees at C0-C1, according to Dvorak
130
What is considered hypermobile ROM in the CCJ?
>8 rotation at C0-C1
>56 rotation at C1-C2
Differences of >5 degrees between sides at C0-C1
Differences of >8 degrees between sides at C1-C2
131
Can the CCJ ligaments be seen reliably on routine MRI?
No, it is a suboptimal technique with a suboptimal field of view, excluding CCJ on axial sequences
132
What is a protocol for viewing ligaments and membranes of the upper cervical spine?
Krakenes protocol: 2mm slice thickness, interleaved, contiguous proton-density-weighted sections in 3 planes
With the head in neutral position: axial includes foramen magnum to base of dens, coronal from anterior arch of atlas 1/2 way through spinal canal, and sagittal from right to left occipital condyle
133
Head trauma mechanism
Flexion, extension, lateral flexion combination
134
Best time for MRI for potentially injured CCJ ligaments
Best within 72 hours of injury, but should be performed as soon as possible as the edema is most prominent at the beginning of the acute damage. With time, edema starts to reabsorb, thus sensitivity of detection drops
135
CCJ ligaments can be injured without fracture present leading to...
Loss of normal osseous anatomic relationships under normal physiologic stress, leading to ongoing pain and making on more susceptible to further injury
136
Describe CCJ range of motion
During flexion-extension, both C0-C1 and C1-C2 participate equally combining for about 25 degrees
Cranio vertebral rotation occurs mostly at C1-C2 with 41.5 degrees of rotation to each side and 4.3 degrees at C0-C1, according to Dvorak
137
What is considered hypermobile ROM in the CCJ?
>8 rotation at C0-C1
>56 rotation at C1-C2
Differences of >5 degrees between sides at C0-C1
Differences of >8 degrees between sides at C1-C2
138
Ligamanet attaching lower anterior arch of atlas to the front of axis body, continuation of the anterior longitudinal ligament
Anterior atlanto-axial ligament
139
Ligament that originates on the posterior upper dens and insert into the fovea on medial occipital condyles, stabilizes structures of the atlantoaxial joint and act to limit axial rotation (primarily) and lateral bending (secondary) on the contralateral side
Alar ligaments
140
Thin ligament that attaches the anterior atlas to the anterior rim of the foramen magnum
Anterior atlanto-occipital membrane
141
Thin, broad ligament that attaches the posterior arch of atlas inferiorly to the posterior rim of the foramen magnum superiorly
Posterior atlanto-occipital membrane
142
Continuation of the ligamentum flavum cephalically...
Posterior antlanto-occipital membrane
143
Houses alar, apical, and barkow ligaments...
Anterior atlanto-occipital membrane
144
Both the vertebral artery and suboccipital nerve pass through this ligament
Posterior atlanto-occipital membrane
145
Ligamanet attaching lower anterior arch of atlas to the front of axis body, continuation of the anterior longitudinal ligament
Anterior atlanto-axial ligament
146
Ligament that is an extension of the posterior longitudinal ligament, extends from the base of axis to basilar groove of occiput and along the dura of the upper canal
Tectoral membrane
147
What clinical diagnoses often follow whiplash?
Neck pain immediately after 24 hours of injury, may radiate to head, shoulders, arm, or interscapular regions. It is worse with movement and associated with stiffness
Headaches in the suboccipital region - tension, migrane, cervicogenic or unspecified, may cause dizziness with vertigo or auditory symptoms
Visual Disturbances - accommodation errors and diverging eye movements and oculomotor dysfunction
Weakness and/or fatigue
Paresthesia/ numbness/ tingling in the arms and hands
148
Ligament stabilizers for the C0-C1 and C1-C2 articulations
Capsular ligaments
149
What is the best view for seeing a capsular tear?
Coronal or sagittal planes on T2 or proton density imaging
150
T or F: Rarely are the capsular ligaments injured by themselves.
True
151
What is the indicator that a capsular ligament is injured?
Fluid in the joint seen on MRI
152
The shape of the capsular ligaments allow for what kind of movement in the CCJ?
C0-C1 flexion/extension
| C1-C2 transverse rotation
153
Ligament that runs from C7 spinous process to external occipital prominence, cephalic extension of the supraspinous ligament, restricts hyperflexion of the cervical spine
Nuchal ligament
154
What clinical diagnoses often follow whiplash?
Neck pain immediately after 24 hours of injury, may radiate to head, shoulders, arm, or interscapular regions. It is worse with movement and associated with stiffness
Headaches in the suboccipital region - tension, migrane, cervicogenic or unspecified, may cause dizziness with vertigo or auditory symptoms
Visual Disturbances - accommodation errors and diverging eye movements and oculomotor dysfunction
Weakness and/or fatigue
Paresthesia/ numbness/ tingling in the arms and hands
155
Quebec Task Force whiplash grading system:
0 - no complaint
1 - neck complaint, stiff or tender only
2 - neck complaint, musculoskeletal signs
3 - neck complaint with neurological signs
4. neck complaint and fracture or gross dislocation
156
Segment angulation beyond ______ degrees in the cervical spine is considered impairment by the AMA.
11.5 degrees, but Dr. Richardson argues 10 degrees
157
Segment translation _____ mm is considered unstable.
>3.5mm
158
Fanning ______ mm between the spinous processes is evidence of whiplash and instability
>12mm
159
T or F: 10% of normal x-rays in acute phase develop new degenerative changes at 32 month follow-up.
True
160
T or F: Degenerative changes has occurred in 68% of whiplash-injured patient, 87% of which were symptomatic.
True
161
Classification for structural changes in the ligament (Krakenes)
```
0 - low signal throughout
1 - high signal 1/3 or less
2 - high signal 1/3 to 2/3
3 - high signal 2/3 or more
Intermediate signal - scarring or fibrous changes
```
162
On DMX, lateral slip of axis to atlas is normally 2mm max. If >4.5mm, ________ is often seen in patients.
Intractable migraine headaches
163
What notable feature is seen on a posterior atlanto-occipital membrane tear?
Dural hump
