Facial Views, CT & MRI Flashcards
(101 cards)
1
Q
Why is it difficult to determine whether facial fractures are present?
A
- there is often much bruising and swelling of the face
- this can make it difficult to determine whether fractures are present
2
Q
What are the 5 specific external signs that indicate facial fractures?
A
- facial asymmetry
- flattened cheek
- “dish face”
- deviation of the nose / flattened nasal bridge
- pupils not level
3
Q
What is “dish-face”?
A
- occurs when the midface appears “dished-in”
- this represents posterior and inferior displacement of the maxilla
- the face can appear elongated as a result
4
Q
Why are X-rays not often performed even though fractures of the nose are common?
A
- X-rays are only indicated when there is an obvious deformity, such as deviation
- if there is swelling, but no obvious deformity then the patient is advised to wait until the swelling subsides
- if there is a deformity following disappearance of the swelling then imaging is performed
5
Q
What does the pupils not being equal suggest?
A
- this indicates fracture of the orbital floor and prolapse of orbital contents (such as inferior rectus)
- the patient may have diplopia and impaired movements of the eye
6
Q
When does a patient with facial injuries need a CT head or CT C-spine?
A
- in severe blows to the face, the skull, brain and C-spine may have also sustained injury and a CT should be performed
- an injury to the face is an injury to the head, so if any of the NICE criteria for CT scanning after head injury is met, it should be performed
- bones of the face are sturdy (especially strong bones, such as the frontal bone), so fracture to these requires high force
in these situations, there is a high chance of a corresponding intracranial complication
7
Q
Why can it be difficult to examine the eye and vision after facial injuries involving the orbit?
A
- severe swelling and pain can make this examination impossible
- eyelids and soft tissues can be so swollen that the patient cannot open the lids or withstand a gentle attempt to force them open
- the eyes and the vision cannot be examined
- a CT orbit can be performed in this situation
8
Q
When are facial X-rays requested?
Why can they be difficult to interpret?
A
- they are requested when the patient does not require a CT-head, but there is clinical suspicion of facial fractures
- they are difficult to interpret as the anatomy of the facial skeleton is complex and there is superimposition of the bones of the face and skull upon each other
9
Q
What are the 6 different types of facial fractures that can occur?
A
- simple nasal fractures
- LeFort fractures (“middle-third” fractures)
- zygomatic fractures
- orbital fractures
- frontal sinus fracture
- mandibular fractures + TMJ dislocation
- in the case of mandibular fractures, there is likely to be more than one as the mandible is essentially a “ring structure”
10
Q
What are the 2 views of the facial skeleton that are commonly taken?
A
- occipito-mental (OM)
- occipito-mental 30o (OM 30)
- a standard PA facial view or PA mandible may also be taken
- the patient details, date and technical adequacy must be assessed first
11
Q
Why does a CT head not suffice for facial fractures?
A
- a normal CT head will NOT cover the facial bones
- the orbits and some of the maxillary sinuses may be visible
- if the facial bones are specifically required, then CT facial skeleton must be requested to ensure they are included
12
Q
How is an OM view taken?
What is this good for visualising?
A
- the beam travels from the occiput to the jaw
- this gives a good view of:
- frontal and maxillary bones
- zygomatic bone and zygomatic arch (“elephant trunk”)
- dens of C2
- frontal, ethmoid and maxillary sinuses
13
Q
When is the OM 30 view preferred and how is this performed?
A
- the head is tilted backwards by 30o before a beam is fired from the occiput to the jaw
- this is good for visualising:
- maxillary sinuses
- inferior orbital rims
- features of the mandible
14
Q
What are the features of this PA facial X-ray?
Which part of the temporal bone is visible?
A
- the petrous ridge is the part of the temporal bone that can be seen through the orbits
- this is the dense / “rock-like” part of the temporal bone
15
Q
Why can appearance of the mastoid differ between individuals?
What is the risk associated with the less common presentation?
A
- mastoid aeration / presence of air cells is highly variable
- some people have very dense mastoid processes that do not contain any air cells
- these people cannot equalise the pressure in their ears as easily as those with air cells
- they are more likely to develop retraction pockets in the ear drum and subsequent cholesteatoma
- usually, the mastoid air cells appear “bubbly” as they are filled with air
16
Q
What are the features of this OM view?
What type of fracture is this good for visualising?
A
- the head has been tilted backwards, allowing the floor of the orbit and anterior wall of the maxillary sinus to be seen more clearly
- this view is useful for visualising fractures of the orbital floor
17
Q
Why can suture lines be mistaken for fractures?
How can this be avoided?
A
- sutures are less dense than bone and appear as a small dark line
- the suture between the frontal and zygomatic bone is often mistaken for a fracture
- if in doubt, compare to the other side to see if they are symmetrical
18
Q
What type of fracture seen in the OM view implicates 4 sutures and why?
How can this be recognised?
A
tripod / quadripod fracture
- the zygomatic bone is attached to many other bones:
- temporal bone
- frontal bone
- maxillary bone
- pterygoid region
- a severe fracture to the zygoma can rotate and implicate these 4 structures
- look for the intact “elephant trunk” when assessing whether a zygomatic fracture is present
19
Q
What are McGregor’s lines?
What type of fracture are they important in looking for?
A
- in OM views of the face, it is important to systematically review the 3 sections of the face along 3 lines:
- over the upper orbits
- over the upper surface of the zygomatic arch, lower orbit and nose
- over the lower surface of the zygomatic arch and alveolar process
- these are mainly related to LeFort fractures
20
Q
How is integrity of the zygomatic complex determined in an OM view?
A
- the integrity of the zygomatic complex is determined by tracing around the zygoma and upper and lower zygomatic arches
- this is described as looking like an elephant’s head and trunk
21
Q
Why can some fractures of the zygomatic arch be difficult to spot?
A
- not all fractures appear dark on X-rays
- lucency only appears if the bones are separated from each other in the fracture
- the gap is less dense than the bones on either side
- if the bones are overlapping each other in the fracture, it can appear more dense with no dark region
22
Q
What are the features of the OM 30 view?
A
23
Q
What lines should be traced in an OM 30 view?
A
- lines should be traced over the zygomatic arches, nasal bridge and alveolar process
24
Q
Describe the typical appearance of an orbital blowout fracture on facial X-ray
Why does this occur?
A
- a blow to the orbit causes a transient rise in intra-orbital pressure that causes fracture of the thin orbital floor
- there is a break in the cortex of the corresponding infraorbital rim
- there is a fluid level present in the maxillary sinus on the same side
- there is an opacity below the infraorbital rim, indicating prolapse of orbital contents into the maxillary sinus
25
26
What contents may herniate into the maxillary sinus following an orbital floor fracture?
Why is there a fluid level in the maxillary sinus?
* contents that may herniate are **_periorbital fat_** and the **_inferior rectus muscle_**
* a fluid level in the maxillary sinus suggests **_bleeding_** as a **result of the fracture**
* usually the sinuses should be radiolucent and appear dark as they are filled with air
27
Why might someone with a blowout fracture suffer from diplopia?
* the inferior rectus herniates into the maxillary sinus
* if the **inferior rectus becomes trapped**, this can stop the eye from moving properly
* the individual is unable to look up
28
How can an orbital blowout fracture be recognised on MRI?
**_"teardrop sign"_**
* the prolapse of orbital contents into the maxillary sinus appears as a teardrop on coronal MRI
* this is caused by the **herniation of extraconal fat** into the sinus
29
Do orbital blowout fractures always affect the inferior orbital margin?
* the **lamina papyracea of the medial orbital wall** can also fracture
* this leads to herniation of **orbital fat** and **medial rectus** into the **_ethmoidal air cells_**
* this is much less common
30
Why can a patient with an orbital floor fracture present with a numb cheek?
**_infra-orbital nerve injury_**
* this occurs when there is a fracture of the orbital floor **passing through the infra-orbital canal**
* this results in sensory disturbance in the region of the infra-orbital nerve (V2)
31
How can you look for lucency in the orbits?
What does this indicate?
* an area of radiolucency appears as a **_dark shadow_ in the _upper orbit_**
* this is referred to as the **_"black eyebrow sign"_**
* it indicates **air in the orbit** and the **presence of a fracture** somewhere
* this is most commonly fracture of the **_roof of the frontal sinus_**, as fracture of the medial wall would cause air to be present more medially
32
What is shown in this image?
* there is a **_fluid level_** in the **right maxillary sinus** (compare to left)
* there is an **area of radio-opacity below the right infra-orbital rim**, suggesting blow-out fracture and prolapse of orbital contents
33
What are the 6 steps to interpreting facial X-rays (OM and OM 30)?
* check patient details and projection
* assess the technical adequacy of the film
* describe any **obvious abnormalities** in as much detail as possible:
1. look for **_symmetry / asymmetry_** by comparing left / right sides
2. if one fracture is seen, **look very closely for others**
* **_trace the specific "lines"_** along the facial bones to look for fractures
* identify and **_assess the sinuses_**
* *they are air-filled so should be radiolucent*
* *opacity or fluid-level suggests bleeding, and hence, fracture*
* look for **_signs of air in the orbit_** - "black eyebrow sign"
34
Why might a fluid level in the maxillary sinus not always be seen?
* presence of the fluid level depends on the injury, as well as **_when the patient presents_**
* if they present **slightly later,** the fluid level may not be seen
35
What terms are used to describe lesions within the orbit?
**_Extra-conal lesions:_**
* this is used to describe lesions occurring within the muscle cone
**_Intra-conal lesions:_**
* this is used to describe lesions occurring outside of the muscle cone
36
What is meant by a pre-septal and post-septal lesion in the orbit?
* the septum is a line that runs across the midline of the globe
* a post-septal lesion is more concerning
37
What is concerning in this image?
Why is immediate action required?
* there is a **_retrobulbar soft tissue lesion_** on the right side
* it is an **extraconal lesion** as it is occurring to the right of the lateral rectus
* the lesion appears **quite dense** so it is likely to be **_blood_** (retrobulbar haematoma)
* immediate action is required as the lesion is **_compressing the optic nerve_**
38
From what position are CT and MRI images viewed?
* axial CT and MRI images are viewed from a **_caudal position_**
* you are **looking up from the feet** towards the patient's head
* this means that the patient's left is your right as you look at the image
39
What is attenuation / density in CT?
What unit is used to measure attenuation / density?
* attenuation / density describes **how bright or dark structures appear** on CT
* **high density** tissues / regions appear **_bright_**
* **low density** tissues / regions are **_dark_**
* the **_Hounsfield unit (HU)_** is a "measure" of the densities of different tissues:
1. air is -1000 HU (black)
2. water is 0 HU (grey)
3. bone is +1000 HU (white)
40
Why is CT able to produce more detailed images than X-ray?
* the HU scale is a measure of **tissue density**, represented by a **number** and corresponding **_shade of grey_**
* this allows production of more detailed images and allows for **_tissues with similar densities to be differentiated_** from one another
41
How does a CT scan actually work to produce an image?
* as tissues have **different densities**, they **_attenuate X-ray beams to different degrees_**
* an X-ray tube and multiple detectors **rotate around** the patient
* a **thin "slice"** of body is exposed to the X-ray beam at any one time, and as the scanner rotates, the tissues in that slice can be **viewed from multiple angles**
* the slice thickness is between **1 - 10mm**
* the slice is divided into a **grid of voxels** and the **tissue density of each voxel** is calculated
* this allows for a corresponding grid of pixels and the final image to be constructed
42
What are the 3 main advantages of using CT scans over X-ray?
* CT scanner produces images with a much **greater range of contrast**, allowing **_tissues of similar densities to be distinguished_** from each other
* **3D images** can be produced
* images can be manipulated in several ways after they have been taken to **highlight specific areas of interest**
43
When might a CT thorax be performed in the acute setting?
* to rule out / confirm **pulmonary embolism** (CTPA)
* in **chest trauma**
* in suspected **thoracic aorta aneurysm rupture** or **dissection**
44
What is looked for in a CTPA?
What must be administered beforehand?
* it requires administration of **iodine-based contrast** to the patient
* CTPA does not show a pulmonary embolism directly, but a **_filling defect in the pulmonary vasculature_**
* it can also show complications caused by PE, such as **lung infarction**
45
When is contrast used in a CT thorax?
* contrast involves putting a dye into blood vessels
* it is used the **majority of the time** in CT thorax to look at the blood vessels and see whether structures in the lungs / lymph nodes are enhanced
* contrast makes the vessels **_appear bright_**
* this makes **lesions easier to spot** when they are against a bright background
46
What are the following structures?
How could you use an image like this to look for pulmonary hypertension?
* the diameter of the main pulmonary trunk should be less than the diameter of the aorta
* the **diameter of the pulmonary trunk is increased** in pulmonary hypertension
47
How can you tell that this scan has been taken early on after injection of contrast?
* there is still contrast present in the SVC
* contrast is injected into a vein in the antecubital fossa and then flows around the vascular system in a preditable fashion:
1. pulmonary artery
2. aorta (20 seconds)
3. spleen / portal system (60 seconds)
4. IVC (90 seconds)
* this influences the timing that scans should be performed at
48
What is represented by the coloured circles?
At what vertebral level was this taken?
1. blue = right and left bronchi
2. green = thoracic duct
3. pink = azygos vein
4. orange = oesophagus (contains air)
* this scan is taken at **_around T4_**
* *most things happen at T4 in the thorax, so if in doubt, refer to this level*
* the azygos vein carries deoxygenated blood from the posterior chest/abdominal walls, passes over the top of the bronchus to drain into the SVC
* (this scan later than the previous as contrast is less dense in pulmonary arteries than the aorta)
49
What are the 3 most common reasons for requesting a chest CT?
* if a **_suspicious mass is seen on CXR_** and malignancy investigation is needed
* suspected **_pulmonary embolism_** (CT = gold standard)
* suspected **_aortic dissection_** in patients with a suggestive history
50
What is shown in this image?
What is the major concern with this mass?
* there is a **_solid mass at the periphery of the lung_** on the right side of the chest
* it is a solid mass as it **does _not_ contain air bronchograms**, unlike consolidation
* it is likely to be **_cancer**_ as the lesion is _**spiculated_** (spikes on the outside)
* as it is abutting the chest wall, there is concern that it might be **invading into the chest wall**
51
When is a CTPA performed?
How is this performed and what is looked for on the scan?
* CTPA is the gold standard assessment for imaging the **pulmonary arteries** and looking for **_pulmonary embolism_**
* the patient is given an **IV contrast agent** and images are taken when this enters the pulmonary arteries
* the contrast appears **_hyperdense (white)_** on CT scan
* if there is PE obstructing a vessel, **blood (and contrast) _cannot fill_ this area**
* the **clot is seen as a _hypodense (dark) mass**_ and referred to as a _**"filling defect"_**
52
Other than the filling defect on CT, what are some other signs that are suggestive of pulmonary embolism?
* usually, the **LV is larger than the RV** on CT
**_reversal of the RV:LV ratio_** occurs due to the blockage increasing the pressure in the main pulmonary artery, which is fed back into the right side of the heart, causing dilation
* usually, the interventricular septum is **slightly deviated towards the right** as the pressure in the heart is higher on the left side
as a result of an increase in RV pressure, the **_interventricular septum becomes straightened_**
53
What is meant by a saddle embolus?
* a large PE that occurs at the **bifurcation of the pulmonary trunk** and **_extends into both pulmonary arteries_**
* this appears as a dark band extending across both pulmonary arteries
54
Why is there a dark patch present in the SVC in this image?
* this is **_NOT a thrombus_**!!!
* as one brachiocephalic vein contains contrast and one does not, when they meet at the SVC there is **mixing of opacified and non-opacified blood**
* this is called **ad-mixing** and it results in an **artefact that resembles a thrombus**
55
What is significant about the ascending aorta in this CT scan?
* when compared to the diameter of the descending aorta, it is **_noticeably dilated_**
* it appears to have a **line bisecting it**, with differing tissue densities on either side of the line
56
What condition is shown in this CT scan?
Why does the ascending aorta have this appearance?
**_aortic dissection_**
* the line bissecting the aorta demarcates the **_true lumen**_ from the _**false lumen_**
* the **true lumen** is filled with contrast and appears **_more hyperdense (bright)_**
* the **false lumen** appears **_more hypodense (dark)_**
* the false lumen is a defect in the intima, which blood can penetrate to lift a flap of intima
it can still contain contrast and blood, but the true lumen contains denser, faster-flowing contrast so appears brighter
57
What is shown in this CT scan?
**_aortic dissection in the descending aorta_**
* it is difficult to determine which is the true and false lumen in this image as they appear as similar densities
58
Why is CT abdomen performed in the acute setting?
Is contrast required?
* it can be performed **with or without contrast**
* it is performed in the acute setting to assess for **serious / life-threatening intra-abdominal pathology**, such as:
1. ***ruptured / leaking AAA***
2. ***perforation of a hollow viscus***
3. ***acute pancreatitis***
59
How cna you identify the first lumbar vertebra in a CT abdomen?
* as you scroll down, look for the **ribs articulating with the transverse processes** of the thoracic vertebrae
* the **_first vertebra without a rib is L1_**
* the following vertebral levels can be identified from there on
60
What are the highlighted features on this axial CT abdomen?
1. dark blue = rectus abdominis
2. pink = liver
3. blue dot = gallbladder
4. green = stomach (with fluid level)
5. star = duodenum
6. bright blue = pancreas
7. baby blue = right kidney
8. purple = right crus of diaphragm
9. red = aorta
10. yellow = IVC
11. orange = spleen
61
Why is contrast usually preferred for CT abdomen?
* it allows **pathology to be seen more easily** when structures / vessels are enhancing
* in acute **kidney obstruction / hydronephrosis**, the **affected kidney will not enhance as well** as the healthy one
* lesions within the liver can be seen more easily if the **background liver is enhanced and the lesions do not enhance**
62
How does the gallbladder usually appear on CT?
* it is **low density** as it contains **bile**, so usually appears **_hypodense (dark)_**
* if there are gallstones within the gallbladder, these will appear bright (hyperdense)
63
What structures can be seen at L2?
* a smaller part of the abdomen is filled with the liver
* the **transverse colon, duodenum** and **small intestine** are visible
* the **_superior mesenteric artery and vein_** are visible here
* *at L1, we see the **portal vein** which is formed from the union of the superior mesenteric vein and the splenic vein*
64
What structures can be seen at level L3?
* at this level, abdominal contents comprise **_mostly bowel_**
* this is **below the level of the kidneys**, but the **lower part of the liver** can still be seen
* the **_psoas muscles_** are visible
* the **_ureters_** can be seen **running over the psoas muscles** on their course from the kidneys to the bladder
65
Why does a CT-urogram need to be performed later than other types of CT scan?
* the ureters will not usually appear dense as they contain urine
* a late-phase image is required as the patient needs to have **time to excrete the contrast** in order for the **ureters to appear hyperdense (bright)**
66
What are the 4 most common reasons for requesting a CT abdomen?
* investigation of possible **intra-abdominal malignancy**
* imaging the aorta in **suspected or known AAA**
* *this could be in the context of surgical planning or acute abdominal pain*
* patients presenting with **acute abdominal pain** with a history / examination suggesting **serious intra-abdominal pathology**
* CTKUB is the gold standard for **renal colic**
67
What is shown in this image?
* the liver is taking up most of the space in the abdomen, with the abdominal aorta and spleen visible on the left side
* **_several hypodense lesions_** within the liver are present (not enhanced as well as the rest of the liver)
* they are likely to be **_metastases_**
* they are **low density** and appear to be **infiltrating into the liver tissue**
* they are **_not abscesses**_, as these would form _**ring-enhancing lesions_** with accompanying clinical signs
* *some mets can also be ring-enhancing so rely on clinical features*
68
What is shown in this image?
**_abdominal aortic aneurysm_**
* there is a **_hyperdense lumen_** filled with **contrast** (bright)
* and a **_thrombus_** within the aorta that is **_hypodense_** (dark)
* this is different to a dissection, as it is **crescentic in appearance** rather than a line dissecting the lumen
* contrast is required, as without this, you would not be able to tell apart the lumen from the thrombus
69
When is CT-KUB performed?
What is significant about this type of scan?
* it is the first-line investigation for **_suspected renal calculi_**
* this scan is performed **_WITHOUT contrast_**
* most kidney stones are **radio-opaque** and appear **_hyperdense (bright)_** on CT
* if contrast was used, the ureters would also appear hyperdense and this would **disguise the stone**
70
How does the choice of renal tract imaging change in the acute and non-acute setting?
Why is CT preferred in the acute setting?
* CT is preferred in the acute setting a it can demonstrate other potentially life-threatening causes of acute intra-abdominal pain
* e.g. ruptured / leaking AAA in at-risk groups
* intravenous pyelogram (IVP) tends to be used in the non-acute setting
71
What is shown in this image?
* this is a CT-KUB showing a **large stone in the left ureter**
* the left ureter is **grossly dilated**
* there is also **hydronephrosis** as the left renal collecting system is also dilated
72
What is shown in this image?
How do you know it was an incidental finding and what would the treatment be?
* CT-KUB showing a **_large calculus in the hilum of the left kidney_**
* the left kidney is **_not dilated_** and is comparable to the size of the right kidney
* *this is unlikely to be causing any symptoms currently*
* treatment is required before the stone **enlarges further in situ** and obstructs the flow of urine or **passes into the ureter**
* if it passes into the ureter, this can cause **severe pain and ureteric obstruction**
73
When is CT scanning the first-line imaging modality for the brain and why?
* CT is first-line for imaging the brain and skull in the **_acute setting_**
* it has good anatomical detail and is excellent for revealing:
1. **fresh intracranial bleeding** (better than MRI)
2. **infarction**
3. **skull fractures**
74
Why is non-contrast CT performed in suspected ischaemic stroke or intracranial bleeding?
* contrast within the vascular tree will appear **hyperdense**
* this will make it difficult to differentiate the contrast from the acute intracranial bleeding
75
What is represented by labels A-G?
Has contrast been given for this scan?
* A = falx cerebri
* B = frontal lobe
* C = body of lateral ventricle
* D = splenium of corpus callosum
* E = parietal lobe
* F = occipital lobe
* G = superior sagittal sinus
* this is an example of a **_non-contrast_** axial CT head
76
What is represented by labels A-I in this axial CT head?
* A = anterior horn of lateral ventricle
* B = head of caudate
* C = anterior limb of internal capsule
* D = putamen & globus pallidus
* E = posterior limb of internal capsule
* F = 3rd ventricle
* G = quadrigeminal cistern
* H = vermis of cerebellum
* I = occipital lobe
* mainly the cerebellar hemispheres are seen, but a part of the cerebellar vermis is seen due to the plane the scan is taken in
* *the cerebellum can be recognised by the folia*
77
What appears darker on CT, white or grey matter?
Why?
* grey matter contains few axons and a high density of cell bodies
* white matter contains many myelinated axons
* myelin is a fatty substance, so it is of relatively low density compared to the cellular grey matter
* **_white matter appears darker than grey matter_** as it is **lower density**
78
What is a sign of raised intracranial pressure involving the quadrigeminal cistern?
* **_shrinking of the quadrigeminal cistern_** is a sign of raised intracranial pressure
* this is represented as the "bum moving onto the toilet seat"
* the ambient cisterns form the V-shape adjacent to the quadrigeminal cistern
79
What is the quadrigeminal plate?
* the quadrigeminal plate consists of the **_superior and inferior colliculi_**
* the **_quadrigeminal cistern_** sits **behind** the quadrigeminal plate
* the **_cerebral aqueduct_**, which connects the 3rd to 4th ventricle, sits **in front** of the plate
80
In the acute setting, when might CT of the C-spine be performed?
* if **C-spine fracture** is seen on **plain X-ray**
* if a patient with **history of injury** to the C-spine has **neurological signs/symptoms**
* if an XR is equivocal or normal, but there is **ongoing clinical concern**
* *a normal XR cannot rule out pathology when there are ongoing concerns / symptoms / signs*
* as part of a **trauma series** in major trauma
81
When is MRI usually performed?
What are the 2 exceptions to this?
* MRI is usually performed in the **_non-acute setting_**
* the exceptions are in suspected **spinal cord compression** and **cauda equina syndrome** as these are both surgical emergencies
* these arise as a consequence of compression by a **prolapsed intervertebral disc** or a **SOL**
* urgent imaging reduces the risk of irreversible paralysis of the lower limbs and loss of sphincter control
82
What is the basic principle behind how an MRI image is generated?
* when hydrogen nuclei are all **spinning in synchrony ("phase")**, a **_signal is generated_** and an image can be created
* when the RF pulse is switched off, the hydrogen nuclei **relax and desynchronise**, and the **_strength of the signal decreases_**
* relaxation and desynchronisation **_does not_** happen at the **same rate in all tissues** as **different tissue types have _different densities of nuclei_**
* when the RF pulse is removed, **_different tissue types generate different signals_** as their nuclei relax and desynchronise at different rates
* different signals are represented as **differing shades on a grey scale**
83
How is the appearance of structures on MRI referred to?
* the appearance of structures is referred to in terms of **signal intensity**
* **_bright tissues_** are said to have a **_high signal_**
* **_dark tissues_** are said to have a **_low signal_**
* the appearance can vary depending on whether **T1 or T2 images** are being viewed
84
What is the difference between a T1 and T2 scan?
* the **T1 signal** is a representation of **how quickly hydrogen nuclei in different tissues** **_relax_** after the RF pulse is removed
* the **T2 signal** is a representation of **how quickly the hydrogen nuclei _desynchronise_** when the RF pulse is removed
85
What is the difference in the appearance of CSF in a T1 and T2 scan?
* CSF appears **_dark in a T1 scan**_ and _**bright in a T2 scan_**
86
What is a FLAIR sequence and when might this be used?
* it is similar to a **T2 image**, but the **high signal from tissues with a high water content (e.g. CSF) is _suppressed_**
* this is useful for identifying **_lesions that lie close to CSF spaces_**
* suppression of the signal that would have been generated by CSF allows other lesions (e.g. blood) to stand out more clearly
87
What is meant by diffusion-weighted imaging (DW-MRI) and when might this be used?
* this is used to detect an **_acute from an old infarct_**
* in **acute ischaemia**, the cell membrane of glial cells becomes dysfunctional and allows **sodium and water to move into them** and **_cause oedema_**
* this region will generate a **_high signal on DW-MRI_**
88
What is represented by numbers 1 to 12 in this image?
What type of MRI scan is this?
1. pons
2. corpus callosum
3. pituitary gland
4. thalamus
5. midbrain
6. hypothalamus
7. quadrigeminal plate
8. dens
9. 4th ventricle
10. lateral ventricle
11. tentorium cerebelli
12. sphenoid sinus
* this is a **_para-sagittal MRI_** (not quite in the midline as the turbinates can be seen in place of the nasal septum)
* it is a **_T1 weighted image_** (CSF appears dark)
89
What are the structures on this T2 weighted image?
What is meant by peritrigonal high signal?
* the trigones of the lateral ventricles can be seen in this view
* the occipital and temporal horns emerge from the trigones
* high signal around the trigones suggests white matter changes in small vessel disease
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When is CT better than MRI?
* CT is better than MRI for revealing **_acute / fresh bleeding_**
* CT is usually performed in the **acute setting** as it is **much quicker**, and usually sufficient to give a definitive diagnosis
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What is the most common reason for undertaking CT head in the acute setting?
* to identify whether a patient has had an **_intracranial bleed_** (spontaneous or secondary to head trauma) or **_cerebrovascular accident_** (stroke)
* strokes can be **haemorrhagic or ischaemic**, and these appear **very different** on CT
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What is the difference in the way fresh intracranial bleeding and areas of ischaemia appear on CT?
What is the issue with this?
**_New intracranial bleeding:_**
* appears **_bright white (hyperdense)_** on non-contrast CT
**_Areas of ischaemia:_**
* appear **_hypodense_** and **darker than the surrounding brain tissue** on on-contrast CT
* very soon after a stroke this chance can be **very subtle or not visible at all**
* the **hypodensity** ("low attenuation lesion") **_evolves over time_**
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What type of lesion is shown here?
Why is it likely to be an elderly patient?
* this is an infarct in the territory of the **middle cerebral artery**
* this is **_ischaemic_** as the infarct appears **_hypodense_** and d**arker than the surrounding brain tissue**
* it is likely to be **_chronic_** as it is **not causing much mass effect** relating to its large size
* *if the brain was swollen, there would be pressure on the ventricles and they would change shape*
* it is likely to be an elderly patient as there is **_cerebral atrophy_** anteriorly
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Why does this image represent an example of cystic encephalomalacia?
* the neurones within the infarcted area die, but the support structures are still there
* volume is lost from the infarcted area, but it is replaced with cystic changes and gliosis
* the glial cells form a scar, which can be seen on MRI
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Is this lesion acute or chronic?
Why might their be visual disturbances?
* this is likely to be **acute** as there is some **_mass effect_**, shown through **compression of the ventricles**
* this is a posterior circulation infarct affecting the visual cortex within the occipital lobe
* the lesion is **hypodense**, demonstrating an **_area of ischaemia_**
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Where is the lesion?
Is this acute or chronic and how could you confirm this?
* **focal hypodensity** of the **left thalamus**
* there is not much mass effect, but it is difficult to determine whether it is acute or chronic
* this could be confirmed by performing a **_DW-MRI_**
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How can CT be used in the acute and non-acute setting to investigate if a patient has a space-occupying lesion?
* if a SOL is suspected, a **_non-contrast CT_ is performed first**
* if there is a region of suspicion, a **_CT with contrast_** is then taken
* **contrast enhances SOLs** so they can be assessed more easily
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What is the difference between these images?
* image 2 is a contrast-CT, which allows the metastases to be more easily seen
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What is the difference between these 2 images and what do they show?
* MRI images are used to assess SOLs in the non-acute setting
* the image on the left does not use contrast, whereas the image on the right does
* MRI gives excellent visualisation of SOLs, which is enhanced even further when contrast is used
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