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.

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

Posted on by Brent Weinberg, MD

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

Posted on by Brent Weinberg, MD

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

Posted on by Brent Weinberg, MD

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.