Brain Bites – Pilocytic astrocytoma

Posted on May 30, 2025May 29, 2025 by Brent Weinberg, MD

Brain Bites – Pilocytic astrocytoma

Welcome to the latest installment in our series, Brain Bites, where we use short videos featuring other physicians and learners to neuroradiology concepts in short, easily digestible bites. Hopefully these videos will give you some quick points so that you can become more effective at evaluating brain and spine imaging.

Today’s video is focused on pilocytic astrocytoma and is presented by Stefani Yates, a medical student at Morehouse School of Medicine.

Pilocytic astrocytoma, or juvenile pilocytic astroctyoma (JPA), is the most common brain tumor in children. These are grade 1 tumors that usually occur in the first decade of life (70% of the time). Patients are often children who present with nausea, vomiting, headache, or other cerebellar symptoms.

The most common imaging appearance is a cystic and nodular mass found in the posterior fossa and cerebellum. They can occur in adults, but they are much less common. On MRI, they often have a very bright T2 appearance with a mix of cystic and solid components. On post-contrast imaging, there will areas of enhancement along the rim as well as enhancing nodules mixed with areas which do not enhance. High water content is reflected in the T2 hyperintense appearance.

Diffusion weighted imaging, including apparent diffusion coefficient (ADC), can help differentiate from other masses of the posterior fossa, such as medulloblastoma. Pilocytic astrocytomas have very permissive water movement and are very bright on ADC. In contrast, medulloblastomas have more reduced diffusion and are darker on ADC. This also reflects prognosis, as medulloblastomas have a much worse prognosis.

Magnetic resonance spectroscopy (MRS) can be useful in differentiating tumors from normal tissue. In tumors, they typically have elevated choline, a component in cell membrane synthesis and measure of cell turnover. They also have decreased n-acetyl aspartate (NAA), a measure of normal neurons.

The differential diagnosis includes:

Ependymoma – a very enhancing mass often found in the midline in the fourth ventricle. It usually is less cystic
Medulloblastoma – an avidly enhancing mass often found in the midline. It has less cystic components
Meningioma – a ventricular mass most common in the occipital horn which has more homogeneous enhancement. They can be found in the 4^th ventricle but this is more rare.

So, if you see a child or teenager with a brain tumor, particularly if it has a cystic and nodular appearance, be on the lookout for pilocytic astroctyoma

Check out the full Brain Bites page or the Brain Bites YouTube Playlist for more short learning content.

Brain imaging course – Unknown case 7 and conclusion

Posted on February 5, 2025January 27, 2025 by Brent Weinberg, MD

Brain imaging course – Unknown case 7 and conclusion

This video is the 7th and final unknown case that goes with the brain imaging capstone course. At the end, we wrap up what we’ve learned.

If you want to follow along, you can find all the images for the case at the brain capstone website.

Introduction

37 year-old man presenting with the worst headache of his life

Interactive review – noncontrast CT

In this case, there is a noncontrast axial and coronal CT. On the axial images, you see some subarachnoid blood in the prepontine cistern and 4^th ventricle which increases as you go superior. There is subarachnoid blood in the sylvian fissures and interhemispheric fissure. There is also enlargement of the ventricles, or hydrocephalus. The coronal CT confirms these findings.

Interactive review –CT angiogram (CTA)

There is an axial CT angiogram and we need to look for causes of subarachnoid hemorrhage. It’s important to follow a search pattern so you don’t miss important findings or fall victim to satisfaction of search. The identifies a potential aneurysm of the anterior communicating artery (A-comm), where there is a 4 mm rightward directed outpouching. The coronal images confirm the finding. We want to make sure to look at our vertebral and basilar arteries too though so we don’t miss any findings.

Imaging recap

A few key images show the hemorrhage centered in the basal cisterns with anterior involvement. Select images from the CTA show the aneurysm of the ACA.

Your first question is what is the cause of the subarachnoid hemorrhage? In this case it is a cerebral aneurysm rupture.

Angiographic images show the outpouching before and after it is coiled through endovascular treatment.

Your second question is what is a common complication of subarachnoid hemorrhage? Vasospasm is a very common complication which occurs 4-10 days after the onset of hemorrhage and can result in narrowing of vessels and possible ischemia.

Diagnosis – Subarachnoid hemorrhage and aneurysm rupture

This is a case of subarachnoid hemorrhage from aneurysm rupture. Hypertension, drug use, trauma, and family history are all risk factors. The pattern of aneurysm can help you identify where the aneurysm might be. Some locations are more common for aneurysms. 90% of aneurysms are anterior, with common locations being the Acomm, ICA terminus, and MCA. Other common locations are the basilar tip and PICA.

Recap

What have we learned? We learned the value of different imaging modalities, including CT, CTA, and MRI, and when to choose them. CT is a screening exam to identify severe pathology, with MRI used to get a more detailed examination of the brain parenchyma.

Thanks for tuning in to all the cases as part of the brain course. There are a total of 7 cases you can review on your own at the website and explanations will be posted here.

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

Brain imaging course – Unknown case 6

Posted on January 29, 2025January 27, 2025 by Brent Weinberg, MD

Brain imaging course – Unknown case 6

This video is the 6th unknown case that goes with the brain imaging capstone course.

If you want to follow along, you can find all the images for the case at the brain capstone website.

Introduction

69 year-old-female with h/o autoimmune hepatitis on immunosuppression, admitted for hyponatremia. Hospital course complicated by vision changes and leukocytosis.

Interactive review – MRI

This MRI includes diffusion weighted imaging (DWI), apparent diffusion coefficient (ADC), FLAIR, T2, T1 pre-contrast, and T1 postcontrast. The FLAIR image shows a lesion which is isointense to gray matter centrally with hyperintense edema around the margin. The T2 has a unique feature which helps point to this diagnosis, which is a relatively T2 dark surrounding rim. On pre-contrast T1, it is dark in the center with a rim of edema which is not too dark. On postcontrast it is enhancing around the periphery with central necrosis.

On the diffusion images you see a rounded hyperintense structure in the right occipital and parietal lobe. It is extremely bright centrally, and is also quite dark on ADC. This proves that there is low water diffusion in the center of the lesion.

Case summary

This case is summarized by a few key findings: lightbulb bright diffusion, dark ADC, and a central rim of enhancement with central necrosis.

Question 6

How would you describe the restricted diffusion pattern, and what is it concerning for? The pattern is centrally reduced diffusion, which is concerning for pus.

Diagnosis – Cerebral abscess

This is a case of a cerebral abscess, in this case from aspergillus. This patient was immunocompromised and had symptoms of infection. Common symptoms for presentation include seizure, altered mental status, or focal neurologic symptoms. Key imaging features are the central hypodensity on CT, a centrally enhancing region with necrosis centrally, and reduced diffusion in the center. The T2 hypointense rim is a characteristic of abscess which isn’t seen on many other disease.

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

Brain imaging course – Unknown case 5

Posted on January 22, 2025January 21, 2025 by Brent Weinberg, MD

Brain imaging course – Unknown case 5

This video is the 5th unknown case that goes with the brain imaging capstone course.

If you want to follow along, you can find all the images for the case at the brain capstone website.

Introduction

51 year-old-female presents with left sided weakness and numbness

Interactive review – CT

This case features a CT with a brain window on the left and a bone window on the right. As you scroll up, you start to note that the right lateral ventricle is a little compressed and there is loss of the normal sulci on the right. If you window it really tightly, you can start to see the outlines of a mass along the parietal convexity. In this case, we want to get an MRI so we can better evaluate it.

Interactive review – MRI

The MRI includes diffusion weighted imaging, FLAIR, T2, and pre- and post-contrast T1 weighted imaging. On diffusion, the mass is faintly hyperintense but pretty homogeneous with compression of the brain away from the mass. Similarly, on FLAIR, the mass is pretty homogeneous and has a large contact with the dura and adjacent calvarium. The T2 is particularly helpful because you see a thin cleft of CSF around the mass (a CSF cleft). You also see a little bit of a radial spoke type pattern radiating out from the calvarium where the bone is abnormal. On pre-contrast T1, the mass is pretty isointense to slightly hypointense to the adjacent gray matter. On postcontrast, you see homogeneous and avid enhancement and again are able to make out the CSF cleft. The coronal postcontrast images confirm the findings you saw on axial imaging

Interactive question 5

Is this lesion intra-axial or extra-axial? It is extra-axial

How do you know? You have a thin CSF cleft, compression of the brain away from the mass, and a thin dural tail.

CT explanation

Some select images from the CT are shown here, where you can see the subtle mass and bony erosion. There are some examples from a CT angiogram showing displacement of the dural vessels away from the mass. An additional representative example shows vessels radiating out from the central portion of the mass.

MRI explanation

Select images from the MRI show key images highlighting the CSF cleft sign, the dural tails, and the avidly enhancing extra-axial mass.

Diagnosis – Meningioma

This is a case of a meningioma. These usually occur in older patients > 40 years old and present with symptoms of brain compression or increased intracranial pressure. Meningiomas range from grade 1-3. The treatment of meningioma is usually surgical resection, sometimes with radiation afterwards. If they are in delicate locations or the patient has health problems making surgery less desirable, you can treat them with radiation alone.

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

Imaging appearance of odontogenic lesions on CT

Posted on January 17, 2025January 17, 2025 by Brent Weinberg, MD

Imaging appearance of odontogenic lesions on CT

In this video, Dr. Katie Bailey gives us an overview of odontogenic lesions, or those lesions related to the teeth and their imaging appearance on CT. In this talk, we will review some of the most common odotogenic lesions and their imaging appearance so you are familiar with them when you see them.

Introduction

Odontogenic lesions are lesions of the jaw that are associated with a tooth or a component of a tooth. They are usually above the level of the alveolar canal, unlike non-odontogenic lesions. One common strategy for helping make your differential is to divide them into radiolucent lesions and radiopaque lesions

Infection

If you see an infection of the sinuses, you should take a look at the adjacent teeth. Dental and periodontal disease can affect the sinuses, particularly the adjacent maxillary sinus. When there is a connection between lucency around a tooth which is directly connected with the sinus, it is called an oroantral fistula, and can either cause inflammation of the sinus or lead pus directly into the sinus.

Radicular cyst

Radicular cysts are the most common asymptomatic cysts. They are usually less than 1 cm and are associated with the root of a tooth. They have a well defined margin which is sclerotic and larger than the typical circumferential periapical lucency.

Residual cyst

A residual cyst is a cystic lesion that remains at the site of a previously extracted tooth. It also has a thin rim with a sclerotic margin, but the tooth is absent.

Dentigerous cyst

These are usually seen in younger adults and surround the crown of an unerupted tooth. This is most common with more posterior molars, such as the third molar.

Odontogenic keratocyst

These are usually also associated with unerupted teeth, and are most common seen along the posterior body and ramus of the mandible. They are often well-defined and expansile. On MRI, they often have restricted diffusion with a rim of enhancement

Ameloblastoma

Ameloblastoma is the most common odontogenic tumor. They are benign but locally aggressive. They are radiolucent and can have one or more cysts. They can have cortical breakthrough and a soft tissue component. While they look like odontogenic keratocysts, they are usually NOT associated with a tooth.

Odontoma/Supernumerary teeth

This is a sclerotic lesion which has a toothlike resemblance and occur in the posterior maxilla or mandible. They can also be associated with a tooth or residual tooth.

Cemento-osseous dysplasia

This is a replacement of bone into a mix of cementum, bone, and fibrous connective tissue. They can be single or multiple and can be associated with the apex of a tooth (peri-apical), focal, or widespread (florid). In these cases, there is ill-defined hyperdense or ground glass extending through the bone of the mandible.

Cementoblastoma

These are cementum forming tumors associated with the tooth root, most commonly the first molar. There is an area of sclerosis at the rooth of a tooth with a rim of surrounding lucency.

Condensing osteitis

This is local reactive sclerosis from chronic inflammation or infection. This is often associated with a tooth that has caries or periodontal inflammation.

Summary

Thank you for checking out this video and short tour of the range of odontogenic lesions you might see. There is a lot of overlap between these lesions, but hopefully you can start to recognize some of the key features.

Be sure to check out the other videos on other head and neck topics or the head and neck YouTube Playlist

See this and other videos on our Youtube channel

Brain imaging course – Unknown case 4

Posted on December 4, 2024November 25, 2024 by Brent Weinberg, MD

Brain imaging course – Unknown case 4

This video is the 4th unknown case that goes with the brain imaging capstone course. If you want to follow along, you can find all the images for the case at the brain capstone page.

Introduction

65 year-old male with possible ground level fall found to be altered. On Coumadin for DVT.

Interactive review

This case features a CT showing a hyperdense hemorrhage in the extra-axial space. You first see it in the left middle cranial fossa and going along the temporal convexity all the way up to over both cerebral hemispheres. There is significant mass effect with uncal unherniation and complete effacement of the basal cisterns. There complete compression of the left lateral ventricle with entrapment of the right lateral ventricle.

Another finding that you can see is hypodensity in the left PCA distribution, which suggests that there is an infarction. This is from mass effect on or stretching of the PCA.

Interactive question 4a

What additional complications do you see on this case? From the explanation, you can see that you have all the complications, including midline shift, uncal herniation, infarct, and ventricular entrapment.

Interactive question 4b

What territory is the infarct in? The left PCA distribution

Diagnosis and Summary

This is a case of acute subdural hematoma. This can occur in patients who are older, who have falls, or who are on anticoagulation. There are a lot of potential complications that you can see in this case, such as ventricular entrapment and hernation.

You can tell the difference in subdural and epidural hematoma most of the time. Subdural hematomas are crescent shaped, cross sutures, and cross along dural reflections. Epidural hematomas are almost always associated with fractures and high energy traumas.

Thanks for tuning in to this case. There are a total of 7 cases you can review on your own at the website and explanations will be posted here.

See all of the brain course videos on the brain course playlist, or go back to the brain capstone course page. Be sure to check back in for additional videos in the future or check out the website at https://www.learnneuroradiology.com

Brain imaging course – Unknown case 3

Posted on November 25, 2024November 24, 2024 by Brent Weinberg, MD

Brain imaging course – Unknown case 3

This video is the 3rd unknown case that goes with the brain imaging capstone course. If you want to follow along, you can find all the images for the case at the brain capstone page.

Introduction

62 year-old male with new onset of left sided weakness, left facial droop and right eye pain

Interactive review

In this case, there is a CT showing a large hypderdense hemorrhage in the right parietal lobe. There is a lot of surrounding edema and mass effect, with effacement of the sulci, herniation from right to left, and complete effacement of the right lateral ventricle. The coronal and sagittal view confirm these findings.

This hemorrhage appears to be in the brain parenchyma, and the most common cause of a parenchymal hemorrhage is hypertension. You can also get hemorrhages from other causes such as cerebral amyloid angiopathy.

Case findings summary

A summary of the imaging findings is reviewed here.

Interactive question 3a

Vascular imaging in this patient is negative, what is the next step? The next step in this patient is neurosurgical consultation, as the patient is at high risk of herniation and death from the hemorrhage.

Companion case

This shows a similar case of hypertensive hemorrhage, only in this case there is extension of the hemorrhage into the ventricles, or intraventricular extension.

Interactive question 3b

What is the major potential complication in this companion case? Because of the intraventricular extension, the patient is at high risk of hydrocephalus, either from outflow obstruction or communicating hydrocephalus.

Diagnosis and Summary

This is a case of hypertensive hemorrhage. These mostly occur in older patients, with common locations being the thalamus, basal ganglia, pons, and cerebellum. You can get them in the cerebral hemispheres as in this case, although it is less common and you might think of other causes such as venous infarct or cerebral amyloid angiopathy. These cases are extremely common and one of the most common things we see in neuroradiology.

Thanks for tuning in to this case. There are a total of 7 cases you can review on your own at the website and explanations will be posted here.

How to read a 4D parathyroid CT

Posted on October 2, 2024September 27, 2024 by Katie Bailey, MD

How to read a 4D parathyroid CT

In this video, Dr. Katie Bailey describes how to review a 4D parathyroid CT for the presence of a parathyroid adenoma. We cover the features of a multiphase, or 4D, CT of the neck and the imaging characteristics which are typical of parathyroid adenomas.

What is 4D parathyroid CT?

It is a multiphase contrast CT, so you have three dimensions in space, and the 4^th dimension is time. It is often done to evaluate for the possible presence of abnormal parathyroid glands or a parathyroid adenoma. There are usually 4 parathyroid glands along the posterior margin of the gland.

How to find a parathyroid adenoma

If looking for a parathyroid adenoma, you should be looking for a round or oval nodule along the posterior margins of the thyroid. A good way to differentiate between a lymph node and a parathyroid is that the vessel often goes to the pole of a parathyroid but to a hilum of a lymph node. If you don’t find one in the expected location, you can check more distant places in the deep neck.

Appearance of parathyroid adenoma

On a noncontrast image, the nodule should be lower in density than the normal thyroid, which contains more iodine.

On arterial phase imaging, a parathyroid adenoma enhances more than the adjacent thyroid.

On venous phase imaging, the adenoma enhances less than the adjacent thyroid because the contrast washes out faster.

Practice case 1

In this practice case, you can see a nodule along the left inferior tracheoesophageal groove. It enhances avidly on the arterial image and washes out on the more venous phase. The sestamibi scan confirms the finding.

Practice case 2

This case shows a normal thyroid which is displaced anteriorly on the left. There is a heterogenous nodule along the posterior margin and extending along the esophagus. The greater heterogeneity of this lesion is caused by hemorrhage

Summary

4D CT is a focused tool to look for parathyroid adenomas in the setting of a clinically suspected adenoma, usually characterized by hypercalcemia. You can use it in conjunction with clinical features, nuclear medicine

Be sure to check out the other videos on other head and neck topics or the head and neck YouTube Playlist

See this and other videos on our Youtube channel

Brain Bites – Central Neurocytoma

Posted on September 30, 2024May 29, 2025 by Brent Weinberg, MD

Brain Bites – Central Neurocytoma

Welcome to our new series, Brain Bites, where we are going to be making short videos featuring other physicians and learners explaining neuroradiology concepts in short, easily digestible bites. Hopefully these videos will give you some quick points so that you can become more effective at evaluating brain and spine imaging.

Today’s video is focused on central neurocytoma and is presented by Stefani Yates, a medical student at Morehouse School of Medicine.

Central neurocytoma is a heterogeneous mass which usually occurs in the frontal horn of the lateral ventricle along the septum pellucidum, or the then septation that separates the lateral ventricles. These masses are usually heterogeneous on T2, isointense or similar to gray matter on T1, and enhance heterogeneously and avidly. In this case you can see a mass in the left frontal horn along the septum pellucidum.

Patients can be asymptomatic or they may present with nonspecific features such as a headache, as this patient did. Treatment is usually surgical resection, or they can be conservatively managed.

The differential diagnosis includes:

Ependymoma – an enhancing mass more common in the 4th ventricle
Subependymoma – a ventricular mass which usually does not enhance
Meningioma – a ventricular mass most common in the occipital horn which has more homogeneous enhancement.

So, if you see an intraventricular mass along the septum pellucidum, keep in mind central neurocytoma. Thanks for watching today!

Check out the full Brain Bites page or the Brain Bites YouTube Playlist for more short learning content.

Neck Imaging Reporting and Data System (NI-RADS) Introduction

Posted on May 8, 2024September 1, 2024 by Katie Bailey, MD

Neck Imaging Reporting and Data System (NI-RADS) Introduction

In this video, Dr. Katie Bailey walks us through an overview of the Neck Imaging Reporting and Data System (NI-RADS) system, including why it was created and a basic overview of the principles and categorization. You can learn more about the American College of Radiology (ACR) NI-RADS system from the ACR website. In this talk, we will walk through some NI-RADS categories, show examples of each, and go through a practice case.

Introduction

NI-RADS was designed to standardize surveillance and follow-up recommendations for tumors of the head/neck and aerodigestive track, including the oral cavity, nasal cavidy, nasopharynx, oropharynx, hypopharynx, and larynx. Most of these are squamous cell cancers but some, such as salivary gland, orbital, and sinonasal tumors are also included.

NI-RADS categories

NI-RADS categories include the primary tumor site and neck to look for recurrence. There are categories from 0-4 depending on the level of suspicion. Each category has a recommended management decision associated with it. Some of the categories are split into subcategories.

NI-RADS 1

Category 1 includes includes expected post-surgical changes and nothing concerning or masslike. Sometimes you can have linear enhancement or mucosal edema, but you definitely don’t have nodular or masslike disease. If you have PET, there will be minimal or no uptake. These patients can have expected follow-up.

NI-RADS 2a

In category 2a, there can be come focal mucosal enhancement, but it would be unlikely to be masslike. If there is FDG-PET, it would be mild to moderate uptake only. These patients may need direct inspection by scope.

NI-RADS 2b

Category 2b may have some ill-defined enhancement in the deep soft tissues. This distinction is important because any abnormal soft tissue may not be visible along the mucosa, so scoping will not be useful. These patients likely need a short-term follow-up.

NI-RADS 3

NI-RADS 3 has a new or enlarging primary mass or lymph node. These tend to be nodular or masslike and probably have intense focal uptake on PET. These patients probably need a biopsy.

NI-RADS 4

Category 4 is for pathologically proven or definite radiologic and/or clinical progression. Because this is definitive progression, these patients need new clinical management or treatment. On follow-up imaging, you may find new disease in a new or distant location. This would be described separately.

Practice case

This practice case is a maxillary sinus squamous cell carcinoma. The initial tumor is very extensive. The first posttreatment scan shows postsurgical changes, with a very small area of focal FDG uptake posterior to the flap. The MRI is very reassuring with no masslike or suspicious enhancement. However, because of the deep PET uptake, we’ll call this a 2b so that it gets short term follow-up.

On the short-term follow-up, the area of nodular enhancement seen previously has worsened considerably, and there is a great deal more involvement of the skull base and adjacent structures. The FDG-PET is very highly avid. We will call this a category 4.

Summary

In summary, we show a flow-chart with the NI-RADS categories so you can quickly review. Hopefully this helps your review of post-treatment head and neck cases go more smoothly.

Be sure to check out the other videos on other head and neck topics or the head and neck YouTube Playlist

See this and other videos on our Youtube channel