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Stroke vascular distributions – Imaging Case Review

Posted on by Katie Bailey, MD

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

MRI of the Orbits

Posted on by Katie Bailey, MD

MRI of the Orbits

In this video, Dr. Bailey reviews the orbit on MRI, with a focus on anatomy and a few of the most common pathologies.

Introduction

In this video, we’ll review the normal anatomy of the orbit and its appearance on MRI.

Orbital contents and normal anatomy

The postseptal orbit includes the intraconal (within the extraocular muscles) contents and extraconal contents. The muscles themselves are a muscular compartment, but it is useful to think of them in the extraconal compartment. There are many things you’ll find in the orbit, including the muscles, the optic nerve, arteries and veins, and fat.

On pre- and post-contrast imaging, you can identify which structures enhance. The optic nerves, for example, should not normally enhance. Lacrimal glands, the extraocular muscles, and sinus mucosa enhance normally.

Optic nerve

The optic nerve can be affected by masses, infection and inflammation, demyelination, and other pathologies. Optic neuritis is inflammation of the nerve, which is usually seen by enhancement in the optic nerve itself. Radiation can cause optic neuropathy, which may even be bilateral. Optic gliomas are tumors that affect the optic nerve and are associated with neurofibromatosis. Optic nerve ischemia can also cause optic neuropathy, often in the acute setting. Optic nerve atrophy is chronic volume loss that can occur from prior insult. It can be hard to determine which of the nerves is abnormal when they are asymmetric.

Optic nerve sheath and retroorbital fat

The optic nerve sheath and periorbital fat are subject to different pathologies, including perineuritis, idiopathic orbital inflammation, sarcoid, certain tumors such as meningioma, lymphoma, and metastatic disease, and idiopathic intracranial hypertension.

Globes

The globes can be affected by inflammation, tumors, and degenerative changes. Inflammation can affect the entire globe or only portions, such as the posterior sclera. Phthisis bulbi is a chronic atrophy of a non-functional globe. Melanoma is a relatively common malignancy of the uvea, but can be hard to see. It is sometimes manifested as an intrinsic T1 hyperintense mass. Retinal detachment can often be seen on MRI as well.

Orbital apex

Cranial nerves and vessels are the main things passing through the orbital apex, and pathologies that you see probably arise from one of them. Slow flow venous malformations (previously called hemangiomas) are well circumscribed vascular lesions often occurring in the orbital apex and orbit. Masses such as meningioma also occur at the orbital apex.

Extraconal compartment

The extraconal structures include the muscles, lacrimal ducts, fat, and the periosteum. A common cause of extraocular muscle abnormality is thyroid ophthalmopathy, which causes bilateral symmetric enlargement that spares the myotendinous junction. Lymphoma can cause masses of the extraocular muscles or lacrimal ducts and often restricts diffusion. Infection can extend from the sinuses into the extraconal compartment and even extend intracranially. The lacrimal glands are subject to their own specific pathology. They can get inflammatory changes related to idiopathic orbital inflammation or sarcoidosis. Dermoids are well-defined masses in the orbit, likely near suture lines. Osseous lesions can also extend from the orbits into the orbital walls.

Conclusion

Hopefully you learned a little bit about the anatomy and common pathology of the orbit. Be sure to check out the other videos on search patterns as well as all the other head and neck topics.

See this and other videos on our Youtube channel

Brain imaging course – 2 – Choosing brain imaging

Posted on by Brent Weinberg, MD

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

Posted on by Brent Weinberg, MD

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.

Brain Vascular Malformations

Posted on by Katie Bailey, MD

Brain Vascular Malformations

In this video, Dr. Bailey discusses the most common vascular malformations and reviews the most common grading system for arteriovenous malformations (AVMs), the Spetzler-Martin grading scale.

Introduction to arteriovenous malformations

Arteriovenous malformations are vascular anomalies consisting of feeding arteries, a nidus where the shunt is located, and one or more draining veins. AVMs can be compact or have a diffuse nidus. There can be surrounding gliosis and potentially calcification on CT or calcium sensitive imaging. Imaging will demonstrate flow voids,

Spetzler-Martin grading scale

The Spetzler-Martin scale gives a score between 1-5, with points assigned based on size (< 3 cm, 1 point; 3-6 cm, 2 points, and > 6 cm, 3 points), involvement of eloquent cortex (1 point), and involvement of deep veins (1 point). This score can help predict the potential surgical morbidity and mortality.

Arteriovenous fistulas

Arteriovenous fistulas (AVFs) are abnormal shunts most commonly from dural vessels. These are abnormal connections between these arteries and the dural venous drainage. Often external carotid artery branches will be dilated as they are the abnormal supply. There is arterialization of the dural venous sinuses. These are most common at the transverse-sigmoid sinus junction.

Cavernous malformations

Cavernous malformations are slow flow venous malformations that have well contained abnormal veins and vessels. They have areas of hemosiderin with T1 hyperintensity, T2 hyperintensity centrally and a peripheral hemosiderin rim. They may have an abnormal adjacent vessel or developmental venous anomaly (DVA). On CT, they may be hyperdense and can be confused with hemorrhage, but central calcification is a good clue. Multiple cavernous malformations can occur in familial syndromes.

Developmental venous anomaly (DVA)

DVAs are congenital venous malformations draining normal veins. These are the most common vascular malformation and are benign. They appear as a branching tree of abnormal venous drainage going to normal veins.

Capillary telangiectasia

These are slow flow capillary malformations that are incidentally found. They have stippled enhancement and you may see something on the blood sensitive imaging (GRE or SWI). There is usually no abnormal edema or FLAIR.

Thanks for tuning in to this video about intracranial vascular malformations. Please check out the additional vascular videos on the site.

See this and other videos on our Youtube channel

Circle of Willis

Posted on by Katie Bailey, MD

Circle of Willis

In this video, Dr. Bailey reviews the anatomy of the Circle of Willis, or the confluence of the internal cerebral and basilar arteries within the brain. She reviews the normal anatomy, talks about some common variants you may encounter, and introduces a few less common variants.

Introduction to the Circle of Willis

The Circle of Willis is the circular anatomical construct of vessels made up by the internal carotid arteries, the basilar artery, and their intracranial proximal branches. This includes the anterior and posterior communicating arteries and the anterior, middle, and posterior cerebral arteries.

Posterior circulation

The posterior circulation includes the posterior cerebral arteries, the basilar artery, the superior cerebellar artery, the anterior inferior cerebellar artery (AICA), and the posterior inferior cerebellar artery (PICA). The AICA is particularly variable and may be hard to see, particularly on 3D imaging. The PICA arises from the vertebral artery and may also vary in size from one side to the other.

Common variants

One particularly common variant is a vertebral artery that terminates in PICA. That is, there is either no or a very vertebral artery is seen distal to the PICA origin. Dolichoectasia is a tortuous and prominent basilar artery larger than 4.5 mm in transverse diameter. It is also a common variant to have no posterior communicating arteries (P-comms). A fetal PCA, is vessel that arises from the posterior communicating artery with an absent or very small P1 segment of the PCA. A hypoplastic A1 is a small A1 on one side, with both A2 segments arising from one side. The A1 segments may arise at various levels and be tortuous. An azygous ACA is a single, or unpaired, ACA in the A2 segment where both sides fuse and there is a common ACA. Sometimes you can have the opposite and have 3 A2 segments. Any of the arteries can also be duplicated, or you can have a fenestration, a small wall within the center of the vessel. Fenestrations can mimic thrombus but they are often very linear along the course of the vessel.

Less common variants

The persistent trigeminal artery is a persistent fetal connection between the anterior and posterior circulation at the level of trigeminal artery. It is the most common persistent fetal connection and passes through Meckel’s cave (the trigeminal cistern).  

It’s also possible to see a missing vessel, such as an absent ICA. In these cases, they may be congenitally absent or chronically occluded.

Thanks for tuning in to this video about the normal and variant anatomy of the circle of willis. Please check out the vascular imaging page on the site.

See this and other videos on our Youtube channel.

Intracranial aneurysms

Posted on by Katie Bailey, MD

Intracranial aneurysms

In this video, Dr. Bailey reviews intracranial aneurysms, including an overview of what an aneurysm is, how to find them, and tips for searching for aneurysms. The first part of this video covers general principles of aneurysm evaluation and the second part shows 3 sample cases that you can go through to test your individual skills.

Introduction and definition of aneurysm

An aneurysm is an abnormal outpouching of the intracranial vessel. Intracranial aneurysms are true aneurysms, which typically involve all of the layers of the vessel. To find aneurysms, a type of vascular imaging known as an angiogram (which can also be done with CT or MRI) is done to evaluate the arteries.

How to find aneurysms

To find aneurysms, you should be looking for an abnormal dilation of the vessel. Then you should look at the most common locations, which are the anterior communicating artery, the carotid terminus/posterior communicating artery, the middle cerebral artery, and the posterior circulation/basilar tip.

Saccular versus fusiform aneurysm

Saccular aneurysms are the most common type of aneurysm. They are rounded outpouchings of the vessel. Fusiform aneurysms are circumferential areas of enlargement of the vessel, meaning the whole diameter is increased.

Thrombosed aneurysm

Sometimes aneurysms can be thrombosed, meaning they no longer have blood flow. In these cases, their imaging appearance can change, and they may not show up on angiographic imaging.

Tips for reporting aneurysms

When creating a report about an aneurysm, you should describe where the aneurysm is, which direction it points, and its size. It’s common to measure three sizes, the maximal width, the height, and the width at the neck.

Aneurysm treatment

The two most common treatments for aneurysm are surgical clipping, in which a clamp is placed over the base of the aneurysm, and endovascular coiling, in which small coils are placed within the vessel from inside. It is also possible to use stents to treat aneurysms, either in combination with coils or alone.

Practice cases

Take a crack at 3 practice cases at the end of the video.

Hopefully you learned a little bit about finding and reporting intracranial aneurysms. Please check out the additional vascular videos on the site, including the video on 5 quick ways to improve your aneurysm search pattern.

See this and other videos on our Youtube channel

Vascular Imaging – Playlist

Posted on by Brent Weinberg, MD

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.

Emergency Imaging of Brain Tumors: Complications & Summary

Posted on by Brent Weinberg, MD

Emergency Imaging of Brain Tumors: Complications & Summary

This video is the seventh and final video in an overview about the emergent approach to brain tumor imaging. This video talks about frequent complications you might see in the clinical care and imaging of brain tumor patients. The most important complications you need to be aware of are infarction, herniation, hemorrhage, tumor progression or radiation necrosis, and hydrocephalus.

Post-resection infarct

This patient’s preoperative imaging shows a tumor in the left temporal lobe that you can see on CT and MRI. On post-op imaging, the tumor has been resected, but there is a wedge-shaped periphery of abnormal diffusion posterior to the cavity. Sometimes patients can have a thin rim of DWI abnormality after a resection, but this more than expected. This is a post-operative infarct. Remember, on delayed imaging this can have enhancement, but it will usually have a gyriform pattern which is different from the original tumor.

Tumor progression

This is a patient who is 2 weeks into radiation therapy for a tumor in the right posterior temporal lobe and inferior parietal lobe. Within this time, there is a lot more edema in the tumor bed with small areas of hemorrhage. The differential diagnosis here is acute radiation necrosis or rapidly worsening tumor.  The MRI confirms that there is marked worsening of enhancement, mass effect, and tumor. This was diagnosed as rapid worsening of tumor and the patient was ultimately transferred for palliative care. Remember though that acute radiation necrosis and worsening tumor can have the same appearance.

Post-operative infection and hydrocephalus

This patient had a recent resection of a tumor with implantation of brachytherapy implants. The post-op pneumocephalus has improved, but ge has developed new postdural collections and new hydrocephalus. This was concerning for acute infection, and the patient was also febrile. This patient had an additional surgery to evacuate the fluid collections, wash out the wound, and place a ventricular drain.

Recap of complications

In summary, you can see a number of complications in patients with brain tumors, many of which will be visible on CT. When you have a suspicion for these things, you should communicate with the surgeons and neuro-oncologists as it can precipitate a change in management.

Lecture series summary

In this lecture, we’ve talked about the role of imaging in brain tumor patients, particularly in the emergent settings, including a review of the role of imaging, some common tumors, and common complications to be on the lookout for.

Thanks for tuning in. Be sure to check out the other videos on the brain tumor topic page if you want to learn more about brain tumors. Also check out the Emergency Imaging of Brain Tumors Playlist to see all the videos from this lecture.

 

Emergency Imaging of Brain Tumors: Tumor mimics

Posted on by Brent Weinberg, MD

Emergency Imaging of Brain Tumors: Tumor mimics

This video is the sixth video in an overview about the emergent approach to brain tumor imaging. This video talks about some of the common mimics for things that look like tumors. The most common diagnoses you need to be aware of are infection, abscess, and demyelination.

Herpes encephalitis

This case shows a CT in a patient that has hypodensity in the left medial temporal lobe. It is ill-defined and not well marginated. On CT, the differential is an acute encephalitis and tumor. Stroke is less likely given that it isn’t in a vascular distribution and doesn’t have the right clinical onset. The MRI shows really apparent swelling and edema/hyperintensity on T2 and FLAIR. Diffusion is also hyperintense. On post-contrast imaging, there is avid and solid nodular and ill-defined enhancement.

Herpes encephalitis is a dreaded intracranial infection that requires urgent recognition and treatment. It can be unilateral or bilateral, and is often asymmetric. Red flags include temporal involvement, acute clinical signs of illness, and not following a vascular distribution. These patients may have rapid progression. If no cause is found via clinical workup or lumbar puncture, these patients should get a follow-up in 6-12 weeks to ensure that it is improve and is not a tumor.

Abscess

This case has a CT which shows marked edema in the left frontal lobe with a mass in the left frontal lobe adjacent to the frontal horn. It looks like the mass is peripherally hyperdense but hypodense centrally. It is not following a vascular distribution. Your differential diagnosis includes tumors, both primary tumors and metastatic disease. An MRI and systemic work-up for malignancy are justified. The MRI shows a mass with peripheral T2 hyperintensity and small areas of susceptibility which are probably blood products. On post-contrast imaging, the periphery is avidly enhancing with blurry margins. The DWI images are key and show pretty marked central diffusion hyperintensity which is dark on ADC.

This is a case of intracranial abscess. Brain abscesses are areas of pus and infection within the brain which have central diffusion restriction. Sometimes there are thinner along the ventricular margin. In many ways they can mimic tumors, but the central DWI hyperintensity which is “light-bulb” bright is a huge clue that you should suspect abscess. Red flags that should make you suspect infection are immune compromised patient, systemic signs of infection, rapid onset, and severe symptoms.

Tumefactive demyelination

This patient has a CT which looks somewhat similar to the previous patient. There is a marked area of edema with sparing of the cortex in the left parietal lobe. There is no clear central mass that you see there, but given that it is vasogenic edema and there is mass effect you should be pretty suspicious. Your initial differential includes primary tumor and metastatic disease, but you want to see the MRI. The MRI shows a marked area of FLAIR and T2 hyperintensity. The area is markedly T1 hypointense but has heterogeneous and incomplete enhancement around the rim.

Tumefactive demyelination is associated with patients who have other demyelinating disease. In many cases, it’s going to be indistinguishable from tumor, but clues are sudden onset of symptoms and young age of the patient. Imaging features to look for are that incomplete rim of enhancement around the margin and the leading edge of abnormal diffusion.

Summary

When approaching a case that seems like a tumor, you have to remember that there are lesions that can mimic tumors. Systemic signs or clinical features can help you, but it can be particularly hard on CT alone. The next step is to get an MRI and work the patients up for their systemic features.

Thanks for tuning in. Be sure to check out the other videos on the brain tumor topic page if you want to learn more about brain tumors. Also check out the Emergency Imaging of Brain Tumors Playlist to see all the videos from this lecture.