Brain imaging course – 4 – Reviewing a normal case

This video is the fourth in a series from brain imaging course. In this video, we go through a normal brain imaging case in a patient who is normal. We first go through a head CT and then the patient’s brain MRI.

Check out the entire course if you haven’t already.

Introduction

In this video, we are going to go through a normal case together. I’ll show you how to apply what you’ve learned in the other videos on your own. Be aware of the strength of having a structured pattern when looking at the images so you can use them effectively.

Normal Head CT

A normal head CT search pattern begins on the brain images. I go from top to bottom, looking for symmetry, gray-white differentiation, and normal underlying structures. I also first review the brain window, then the bone window, then any reformats.

Click here to get the Head CT

On the brain window, I start at the bottom, reviewing normal structures for symmetry, including normal CSF structures. White matter should be a little less dense than gray matter because it has higher fat/myelin content. You should see some gray-white differentiation in the basal ganglia structures. As you reach the vertex, you should see symmetric sulcation, and the brain should be coated with gray matter in all locations. If you lose gray-white differentiation, that can be a sign of stroke.

CT bone window

On the bone window, I also start at the bottom, looking for any fractures in the skull base, any destructive lesions, and that the cortex is maintained everywhere. I will often come back and look at soft tissues using a soft tissue window, including the orbits, sinuses, and facial soft tissues.

CT reformats

There are two reformats provided with this case. The coronal reformat is great to look at the convexity, the floor of the anterior and middle cranial fossa, and the posterior fossa (cerebellum). The sagittal reformat is similar with the additional advantage of being able to see some midline structures like the corpus callosum really well.

Normal Brain MRI

Reviewing a normal MRI is similar, but you need to make multiple passes because of the different information that is found on different sequences. Each sequence has its own advantages, so use them to your benefit.

Click here to get the Brain MRI

Diffusion weighted imaging

DWI is great for seeing restricted water movement. Strokes and abscesses are usually hyperintense. You can use the ADC (not shown) just to make sure it is not bright from T2 effects only (“T2 shine through”).

FLAIR

FLAIR is a real workhorse of clinical imaging. You can recognize FLAIR because the white matter is darker than gray matter. Pathology will be bright because it has excess water. CSF is suppressed on FLAIR imaging, which makes pathology easier to see.

GRE

Gradient recalled echo (GRE) T2 imaging is a blood sensitive sequence which is good to see iron, hemosiderin, blood, and air. These things will be dark on GRE. Some normal structures like blood vessels and iron containing nuclei can be darker normally.

T2

T2 is like FLAIR in that pathology tends to be bright (hyperintense). However, the fluid is not suppressed. This gives you a little bit better view of fluid filled structures like the ventricles but you see pathology in the brain parenchyma worse.

Pre-contrast T1

T1 has the opposite contrast of T2, in that white matter is hyperintense to gray matter. This is a key trick for identifying what kind of imaging you are looking at. T1 precontrast images are great for seeing normal anatomical structures as well as the normal marrow. They are also important to compare pre-contrast

Post-contrast T1

The post-contrast T1 is a key sequence because it will identify areas of breakdown of the blood brain barrier. Pathology like tumors, infection, and demyelination, will often enhance. Some normal structures like vessels, the pituitary, and choroid plexus enhance normally.

Conclusion and recap

Thanks for tuning in to the video. Hopefully now you have developed your own basic approach to brain imaging that you can use on the test cases. On the next video, we’ll review some of the most common brain pathology. The final videos will provide some individual cases you can go through on your own.

See all of the brain course videos on the brain course playlist, or go back to the brain capstone course page.

Brain imaging course – 3 – How to review brain cases

Introduction

This video is the third in a series of a brain imaging course. In this video, we talk about basics of how to review brain cases on your own, including some tips for how to get effective at finding abnormalities and learning your on your own.

Check out the entire course if you haven’t already.

Basics, slice thickness and reformats

When you are reviewing brain cases, you need a structured way of looking at each case to make yourself a sensitive and effective radiologist. This is called a search pattern. You also need to know the ways in which the different images you are provided are different. For example, images can be provided at different thicknesses. In general, thinner images have sharper edges but more noise. Thicker images are better for looking at the bones.

We also have different reformats. On CT, that is usually from one set of data that is displayed in a different plane. The most conventional is perpendicular to the long axis of the body, or axial. Coronal is parallel to the face. Sagittal is parallel to the long axis of the nose. Each of these views has relative strengths and weaknesses.

CT density, window, and level

CT images are standardized for the degree of x-ray absorption, which is closely tied to the density of the material. Each type of tissue has a typical expected density that will be roughly the same on different scanners.

The window and level of a set of images control what is shown on the screen at one given time. The window is the size of the range, or width of the range, of data shown. The level is the center of the range being shown, sometimes referred to as the center. These values are akin to brightness and contrast, although somewhat more exact.

Brain window is structured to see the difference between gray matter and white matter, which is very small, but is poor at seeing very dense structures like bone. For that, a much wider window, the bone window is used.

Basic search pattern

When you are looking at a CT, you need a pattern for looking at each feature in the images. I usually start from the bottom, looking at the brain and focusing on symmetry. Then I move to the bone windows, checking the calvarium, temporal bone, orbits, and sinuses. I may spend an extra minute or two looking at the orbits and soft tissues. To learn more in detail about a head CT search pattern, check out the video.

When reviewing an MRI, you have a similar strategy, but given the different strengths and weaknesses of each sequence, you use each one with a slightly different emphasis. To learn more in detail about how to review a brain MRI, check out the video overviewing MRI sequences and how to review them.

Conclusion

Thanks for tuning into the video about general approaches to brain imaging. On the next video, we’ll have a structured review of a normal case that you can follow along with on your own.

See all of the brain course videos on the brain course playlist, or go back to the brain capstone course page.

Stroke vascular distributions – Imaging Case Review

Dr. Bailey is back for a case-based review of stroke and the vascular distributions commonly seen in stroke.

Introduction

In this video, we’ll review vascular territories in the brain as well as typical appearance of acute infarcts. This covers the distribution of the anterior cerebral artery (ACA), middle cerebral artery (MCA), posterior cerebral artery (PCA), cerebellar arteries, and basilar artery.

Case 1 – ACA infarct

This case shows an infarct in the right anterior cerebral artery distribution. There is loss of gray white differentiation on the CT. On MRI, it is even more apparent, with DWI abnormality which is dark on ADC. There is a corresponding abrupt occlusion of the ACA.

Case 2 – MCA infarct

In this case, there is hypoattenuation in the left posterior temporal lobe and inferior parietal lobe and posterior insular cortex. The MRI confirms that there is a stroke in this region. This is the posterior MCA distribution, with a posterior M2 branch occlusion

Case 3 – PCA infarct

There is subtle hypodensity in the left occipital lobe seen both on axial and sagittal CT. This is again confirmed on MRI, where there is T2 hyperintensity and diffusion abnormality. The MRA shows an abrupt cutoff of the left PCA.

Case 4 – Cerebellar infarct

This case shows a small, wedge shaped hypodensity in the left inferior cerebellum. MRI confirms abnormal diffusion in the left inferior cerebellum. In this case, the neck MRA shows

Case 5 – Multiple infarcts

This case shows multiple infarcts, including a right occipital and a left frontal infarct. When you have infarcts in multiple vascular territories, you should consider the possibility of a central source of thrombi, such as atrial fibrillation or cardiac disease, or vasculitis.

Case 6 – PCA plus

This case has an infarct in the left occipital lobe, but there is also hypoattenuation in the left midbrain and cerebral peduncle. MRI reveals even more areas of ischemia, including a small area in the right occipital lobe and multiple areas in the left thalamus. This indicates that the occlusion is more proximal and likely includes the basilar artery.

Case 7 – Medulla

This is a specific location which is frequently involved in infarcts, the lateral medulla. There is associated severe stenosis of the right vertebral artery.

Case 8 – Border zone

These are often seen as linear low attenuation along the border between vascular territories. In this case, it is the border between the ACA and MCA territories.

Special bonus case – artery of Percheron

This bonus case shows bilateral thalamic infarcts from an artery of percheron, a variant where the arterial supply for both thalami comes from a perforating branch on one PCA. This can also come from central venous thrombosis, so that is the other consideration

Special bonus case – venous infarct

If you have an infarction in an unusual location, particularly if associated with hemorrhage, then think about the possibility of sinus thrombosis. In this case, the straight sinus is dense and occluded on an MRV.

Summary

Hopefully these cases taught you something about the common locations of infarcts and their typical appearance on CT. Please check out the rest of the vascular and stroke content on the site.

See this and other videos on our Youtube channel

Brain imaging course – 2 – Choosing brain imaging

Introduction

This video is the second in a series of a brain imaging course. In this video, we talk about when to order different types of imaging and the relative advantages of each type of imaging. This includes head CT, brain MRI, and the different types of vascular imaging like CT angiography and MR angiography.

Check out the entire course if you haven’t already.

Head CT

Head CT is one of the most commonly performed neuroradiology exams. It’s a common screening exam that is performed for indications like trauma, new neurologic symptoms (such as weakness or sensory symptoms), or the worst headache of someone’s life. Head CT is also very commonly performed on patients with known brain abnormalities to investigate whether they are changing.

CT vessel imaging

CT can be performed with timing to evaluate arteries (angiography) or veins (venography). CT angiography (CTA) is frequently performed for acute stroke, trauma, or if the patient has a hemorrhage.

CT venography (CTV) is done to evaluate the veins. This is most commonly done if a patient has elevated intracranial pressure (or papilledema), an atypical hemorrhage that could be due to venous thrombosis, or if there is trauma near a dural sinus.

MRI brain

MRI of the brain is the workhorse of neuroradiology. You would want to order an MRI of the brain if a patient had a known abnormality that was found on a head CT. An MRI can give you much more information about the underlying abnormality.

If the patient has continued symptoms but a normal head CT, that is another reason to get an MRI. It is much better at seeing small or subtle abnormalities in the brain. In general MRI is a better exam for indications with it is not time-sensitive.

When do MRIs need contrast?

It’s a constant question of when patients should get contrast on MRI of the brain. For low probability screening exams for conditions like headache, stroke, or dizziness, an MRI without contrast is usually adequate. For higher probability of a significant abnormality, you may need contrast. For example, if a patient has concern for meningitis or intracranial abscess, contrast is helpful. Contrast is also usually used when patients have tumors or possible metastatic disease.

In general contrast is needed when there is a higher suspicion of an acute abnormality.

MR vessel imaging

MR angiography (MRA) and venography (MRV) is most commonly used when vascular abnormalities need to be evaluated, but time is not a major concern. This is often done in cases of strokes when the patient has had symptoms for a while (often more than 24 hours). MRA is great for evaluating aneurysm and vascular malformations. MRV can see venous thrombosis and other abnormalities.

Summary

Thanks for tuning in to the video. Hopefully you learned a lot about how to choose the best brain imaging for your patients. The next video will cover basic concepts about reviewing brain imaging on your own.

See all of the search pattern videos on the brain course playlist.

Brain imaging course – 1 – Imaging Modalities

Introduction

This video is the first in a series of a brain imaging capstone course to learn some of the basics about brain imaging. The overall series will cover the range of imaging used to investigate the brain, information about how to choose what type of study will help your patient, teach you how to review images on your own, review some common pathology, and then provide some interactive courses that you can review on your own.

Check out the entire course if you haven’t already.

Modalities used

The main types of imaging, or modalities, used in brain imaging, are computed tomography (CT) and magnetic resonance imaging (MRI). Each of these can be tailored in specific ways to look at vessels, including arteries or veins.

CT head without contrast

CT head is the main screening exam used in neuroradiology. This is commonly done any time a patient has new neurologic symptoms and can see common pathologies such as stroke, hemorrhage, fracture, edema, and hydrocephalus. Once patients are in the hospital, it may be used to follow up their pathology.

CT head with contrast

While possible, we almost never perform CT of the head with contrast because MRI is a much better examination and will almost always be done anyway.

CT angiogram

CT angiogram, or CTA, is an arterial timed exam to look at the arteries of the brain. This is very commonly done in evaluation of stroke, intracranial hemorrhage, and trauma. Aneurysm and vascular malformations are very well evaluated by CTA.

CT venogram

A CT venogram, or CTV, is very similar to a CTA, but the timing is a little later. This is optimal for evaluating the veins of the brain for thrombosis or trauma.

X-rays

We don’t use many x-rays in neuroradiology, but you may see a few to evaluate for shunts and hardware. CT is almost always better, particularly in trauma.

MRI brain

MRI of the brain is a workhorse of neuroradiology. It has great tissue contrast and is excellent for finding diseases of the brain. Some limitations include availability/expense, limitations in patients who have devices, and the time that it takes. There are a variety of sequences that we use in MRI of the brain, and each tells us a little bit of something different about the brain.

T1 precontrast

The T1 precontrast images are useful for evaluating the overall brain structure and alignment. It is also useful for comparing to postcontrast imaging to see how much enhancement there may be.

T2/FLAIR

T2 images are water-sensitive images on which most pathology will show up as bright. It is great for looking at edema, swelling, and fluid-filled structures. FLAIR images are very similar to T2, but the fluid has been suppressed. This helps pathology be more obvious and easier to detect.

Diffusion (DWI)

This is a measure of how well water moves through tissue. In stroke, water moves into cells and can’t move as freely, resulting in areas of stroke being bright on DWI.

Blood sensitive imaging

Gradient imaging (GRE) or susceptibility weighted imaging (SWI) provide a chance to better detect calcium and blood, which will appear dark.

T1 postcontrast

These T1 images are obtained after an intravenous contrast agent has been administered. Things that enhance, or are bright on these images but not the precontrast images, accumulate contrast. This often occurs in pathologies like tumors because the blood-brain barrier has become leaky.

MRA head

MRA of the head is (most frequently) a noncontrast technique to evaluate the vessels of the brain. This is a great technique to see the vessels of the brain if you are not in a rush, particularly to see aneurysms and vascular malformations.

MRA neck

Similar to MRA of the head, this is vessel imaging of the neck. You can do it without contrast or with contrast, but contrast often helps see the vessels at the thoracic outlet better.

MR venogram

Like a CT venogram, an MR venogram is a dedicated exam to look at veins to look for venous thrombosis or venous injury.

Summary

Thanks for tuning in to the video. Hopefully you learned a lot about the types of imaging used to evaluate the brain.

See all of the search pattern videos on the brain course playlist.

Vascular Imaging – Playlist

This playlist covers a range of topics in vascular imaging including general concepts about how to approach brain and neck vascular imaging, what intracranial aneurysms, are, and how to improve your aneurysm search pattern.

You can learn more about other concepts in vessel imaging and other abnormalities on the vascular imaging page. If you haven’t already, you might consider taking a look at the vascular imaging capstone course. Also, please check out our full channel on Youtube.

Fast 10: Neuroradiology high speed case review part 6 – Cases 51-60

In this 6th video, we present 10 more neuroradiology high speed review cases so you can review them quickly before your exams. If you want to see more information about these cases, you can find longer versions on the channel under the Board review playlist

Cases included in this set:
Neurocysticercosis
Sarcoidosis
Subdural hematoma
Limbic encephalitis
Arteriovenous malformation (AVM)
Traumatic shear injury/Diffuse axonal injury (DAI)
Frontal sinus osteomyelitis (Pott’s puffy tumor)
Carotid artery dissection
Tuberculosis lymphadenopathy (Scrofula)
Cauda equina syndrome imaging

Be sure to check back in for the remainder of the high speed cases.

Fast 10: Neuroradiology high speed case review part 5 – Cases 41-50

In this 5th video, we present 10 more neuroradiology high speed review cases so you can review them quickly before your exams. If you want to see more information about these cases, you can find longer versions on the channel under the Board review playlist

Cases included in this set:
Subependymoma
CNS lymphoma
Metastatic disease to calvarium
Meningioma
Metastatic melanoma
Hypothalamic hamartoma
Pituitary adenoma (with hemorrhage/apoplexy)
Pilocytic astrocytoma
Cerebellopontine angle meningioma
Glioblastoma

Be sure to check back in for the remainder of the high speed cases.

Fast 10: Neuroradiology high speed case review part 4 – Cases 31-40

In this fourth video, we present 10 more neuroradiology high speed review cases so you can review them quickly before your exams. If you want to see more information about these cases, you can find longer versions on the channel under the Board review playlist

Cases included in this set:
Renal cell carcinoma
Tuberculosis discitis osteomyelitis
Osteosarcoma of the spine
Ischemia with penumbra (tissue at risk)
Traumatic spine epidural hematoma
Thoracic spine meningioma
Benign perimesencephalic subarachnoid hemorrhage
Chiari malformation
Traumatic vertebral artery injury
Temporal lobe anatomy – fusiform gyrus

Be sure to check back in for the remainder of the high speed cases.

Fast 10: Neuroradiology high speed case review part 3 – Cases 21-30

In this third video, we present some 10 more neuroradiology high speed review cases so you can review them quickly before your exams. If you want to see more information about these cases, you can find longer versions on the channel under the Board review playlist

Cases included in this set:
Vestibular schwannoma
Surfer’s ear (external auditory canal exostosis)
Dural sinus thrombosis
Idiopathic basal ganglia calcification (Fahr disease)
Subclavian steal
Hypertensive hemorrhage
Craniopharyngioma
Ganglioglioma
Synovial cyst
Spinal lymphoma

Be sure to check back in for the remainder of the high speed cases.