5 ways to improve your brain aneurysm search pattern

In this video, I walk you through 5 quick tips that you might use to improve your brain aneurysm search pattern on CT angiograms of the brain. This is a longer version of a lecture I put together with Everlight Radiology, so be sure to check them out.

Have a standard search pattern. When I’m looking at a CTA of the head, I do the anterior circulation first and then move from right to left, then over to the posterior circulation.

Know the common aneurysm locations. The most common aneurysm location is the anterior communicating artery (35%) followed by the carotid terminus (30%) and middle cerebral artery (20%). Posterior circulation aneurysms are relatively uncommon (10%) but it’s important to look there as well. Try to use these tips on the sample case.

Use reformats and 3-D imaging. These supplemental tools can help you improve your sensitivity. Multiplanar reformats are thin slices that are displayed in the other planes, while maximum intensity projections (or MIPs) show you the brightest pixel in a thicker slice. Volume renderings are a nice way to make measurements and increase your sensitivity.

Using the MIPs can definitely make you more sensitive. The axial MIPS are great to see the MCAs, the sagittal MIPs are great to see the carotid terminus and ACAs, and the coronal MIPs are great to see the posterior circulation and MCAs again.

Follow the blood. This is my favorite tip. The location of the blood on the non-contrast CT is one of the best clues about where your aneurysm is going to be. You need to check that area very closely.

 

 

 

Recognize the mimics. There are some things which can mimic aneurysmal subarachnoid hemorrhage, but some features may help you know that it is less likely to be from an aneurysm. Atypical location, an unusual history, or unusual patient demographics can clue you in that it might be a different cause. Be sure to think about hypertensive hemorrhage, venous infarct, tumor (glioma, metastasis, or cavernous malformation), and benign perimesencephalic hemorrhage.

Summary. These 5 quick tips can help you be better at understanding aneurysms and being better and finding them.

If you haven’t already, be sure to check out the vascular imaging course and sample cases that you can scroll through.

See all of the search pattern videos on the Search Pattern Playlist.

Neuroradiology Board Review – Brain Tumors – Case 20 – Summary

Neuroradiology brain tumor board review. This lecture is geared towards the ABR core exam for residents, but it would be useful for review for the ABR certifying exam or certificate of added qualification (CAQ) exam for neuroradiology.

This video has both the final case of the series and a quick review summary!

Case 20

In this case, you are starting with an immunocompromised patient with HIV. Initial CT images show a hyperdense mass in the left basal ganglia with a lot of surrounding edema. This is helpful, because a few things are known for being hyperdense on CT.

MRI images confirm a mass in the basal ganglia. It is somewhat T2 hypointense with well-defined margins and surrounding edema. On postcontrast images, it has peripheral enhancement but central non-enhancement compatible with necrosis.

The differential diagnosis for a solitary enhancing parenchymal mass is different in an immunocompromised patient (or someone on immune suppressing agents. In an immune normal patient, the top diagnoses are

  • metastatic disease
  • high grade glioma
  • lymphoma

On the other hand in an immunocompromised patient the order of these diagnoses shifts to include:

  • lymphoma
  • infection
  • metastatic disease
  • high grade glioma

As you can see, lymphoma and infection jump to the top in an immunocompromised patient.

The diagnosis is: CNS lymphoma

CNS lymphoma can occur when associated with systemic lymphoma or primarily in the CNS, as in this case. This is most commonly a diffuse large B-cell lymphoma. It is more common in immune compromised patients. It often occurs in the basal ganglia and periventricular white matter and can often be multifocal. Lymphoma is one of the rare diseases which is T2 hypointense, so you should think about it if you see a T2 hypointense mass.

In immunocompetent patients, lymphoma most commonly has solid enhancement. However, in immunocompromised patients it is much more likely to show central necrosis, as in this case. Also, in an immunocompromised patient, it can be hard to differentiate lymphoma from infection, particularly toxoplasmosis. The two most common ways to try to differentiate this are to start a trial of toxoplasmosis therapy for a few weeks and see if the lesions improve and to perform a thallium-201 chloride nuclear medicine scan. Lymphoma has thallium uptake, while toxoplasmosis does not.

Summary

In this board review lecture, you’ve seen a lot of different tumors and how they manifest in different situations. In many cases, you can’t make a definitive diagnosis but you should always be able to come up with a reasonable differential diagnosis. It’s also helpful to know some of the basics about treatment and prognostic factors.

There are two key strategies that I hope can help you get a few additional points, the approach to CP angle masses and the approach to cortical tumors.

Cerebellopontine angle masses

As we’ve seen in some of the other cases, cerebellopontine angle masses can be solid or cystic. Solid masses that involve the IAC and expand it are likely schwannomas, while others outside the IAC are likely meningiomas. Arachnoid cysts and epidermoids are the most common cystic masses which are differentiated by DWI (which is bright in ependymomas.

Cortical tumors

Several of the cases in this series dealt with cortical temporal tumors. Ill-defined masses that are larger are more likely to be low grade gliomas (oligodendrogliomas and astrocytomas). Completely non-enhancing bubbly masses favor DNET. A little nodular enhancement favors ganglioglioma, while pleomorphic xanthoastrocytoma (PXA) can be more avidly enhancing and irregular.

Neuroradiology Board Review – Brain Tumors – Case 19

Neuroradiology brain tumor board review. This lecture is geared towards the ABR core exam for residents, but it would be useful for review for the ABR certifying exam or certificate of added qualification (CAQ) exam for neuroradiology.

More description and the answer (spoiler!) are seen below the video.

This case of a patient with diplopia (double vision) starts with a CT through the orbits. You can see there is a well-defined mass at the right orbital apex.

On MRI, you can see the lesion again is well-defined with well defined margins and is hyperintense on T2. On T1, the lesion is isointense to muscle on pre-contrast and then demonstrates heterogeneous enhancement on postcontrast. It looks like the lesion is enhancing more on the coronal image compared to the axial image.

The diagnosis is: orbital venous vascular malformation

Orbital venous vascular malformations are sometimes referred to as hemangiomas, although this term is falling out of favor because it is not neoplastic (unlike the neoplastic infantile and neonatal orbital hemangiomas). These are relatively benign lesions that can cause visual problems secondary to mass effect, but it’s relatively uncommon for them to enlarge.

One characteristic finding of orbital venous malformations is progressive enhancement on delayed images. On early images, it might be enhancing a little bit but if you have more delayed images, you might see more enhancement. If you don’t have more than one plane of contrast, you can bring them back and image them again 15-30 minutes later and it should fill in.

The primary differential considerations for orbital masses are sarcoidosis, idiopathic or IgG4 related orbital disease, metastatic disease, and lymphoma. When it is this well defined and has the characteristic delayed enhancement, the diagnosis is relatively certain.

Neuroradiology Board Review – Brain Tumors – Case 18

Neuroradiology brain tumor board review. This lecture is geared towards the ABR core exam for residents, but it would be useful for review for the ABR certifying exam or certificate of added qualification (CAQ) exam for neuroradiology.

More description and the answer (spoiler!) are seen below the video.

This case starts with 2 axial images from a CT through the posterior fossa followed by MRI images through the same region. There is a heterogeneous lesion to the left of the midline along the left foramen of Lushka. On postcontrast images, it is pretty avidly enhancing. The enhancing margins are pretty well defined and it looks like it is wholly in the ventricle.

The diagnosis is: ependymoma

Ependymomas are enhancing intraventricular tumors arising from the ependymal lining. They are commonly enhancing and conform to the ventricles and the ventricular outflow tract, which results in their description of “toothpaste” like lesions. In adults, they most commonly occur in the 4th ventricle although in pediatric patients they can occur elsewhere.

When in the posterior fossa, your main differential is choroid plexus papilloma/tumor. If you can’t tell that it’s an intraventricular lesion it can be harder because the differential diagnosis also include metastatic disease and possibly medulloblastoma. If you see a lesion that looks similar but doesn’t enhance very much, think about it’s sister lesion subependymoma.

Neuroradiology Board Review – Brain Tumors – Case 17

Neuroradiology brain tumor board review. This lecture is geared towards the ABR core exam for residents, but it would be useful for review for the ABR certifying exam or certificate of added qualification (CAQ) exam for neuroradiology.

More description and the answer (spoiler!) are seen below the video.

In this case, we have an MRI showing a FLAIR and T2 hyperintense mass in the left insula with relatively ill-defined margins. On SWI, there are some areas of susceptibility that probably represent calcification, although blood products could look similar. Postcontrast images demonstrate little or no contrast enhancement.

1:33 The diagnosis is: oligodendroglioma

Oligodendrogliomas are gliomas which are now defined by the characteristic genetic features of IDH mutation and 1p19q codeletion (loss of portions of both chromosomes 1 and 19). They can be WHO grade 2 (as in this case) or grade 3 (anaplastic oligodendroglioma). Theoretically, these lesions never degrade into WHO grade 4 lesions although the grade 3 lesions can be quite aggressive. In general, oligodendrogliomas have a better prognosis than their sister gliomas, astrocytomas. They respond better to radiation and have better overall survival.

Oligodendrogliomas are treated with a combination of resection and chemoradiotherapy.

The susceptibility seen within the tumor on this case represents areas of calcification. Oligodendrogliomas are one of the main considerations if you see an expansile tumor with calcification.

 

Neuroradiology Board Review – Brain Tumors – Case 16

Neuroradiology brain tumor board review. This lecture is geared towards the ABR core exam for residents, but it would be useful for review for the ABR certifying exam or certificate of added qualification (CAQ) exam for neuroradiology.

More description and the answer (spoiler!) are seen below the video.

This case shows a 20 year-old with seizures. MRI shows a lesion in the medial temporal lobe along the tentorium. It is relatively well circumscribed with a cystic portion as well as an enhancing nodule. There is not much mass effect.

The diagnosis is: ganglioglioma

Gangliogliomas are low grade tumors often found in the temporal lobes of patients with seizures. They are mixed in their cell origin, containing both components of glial and neuronal cells. Along with pilocytic astroctyoma, PXA, and hemangioblastoma, they are one of the tumors in the differential for a tumor with a cyst and a nodule. They can be impossible to differentiate from DNET, but if you see enhancement it is more likely to be a ganglioglioma. Gangliogliomas are the most common neoplastic cause of epilepsy.

When you see a minimally enhancing cortical tumor, you should have a relatively short differential which includes:

First consider whether they are ill-defined or well-marginated. If ill-defined, the differential includes astrocytoma or oligodendroglioma. If well-marginated, then consider whether there is enhancement. If no enhancement, DNET is most likely. If there is a small amount of nodular enhancement, favor ganglioglioma, as in this case.

 

In a testing situation, if a small and minimally enhancing cortical tumor enhances a little bit, choose ganglioglioma. If you don’t seen enhancement, choose DNET. PXAs tend to be much more heterogeneous and irregular.

If you use a structured approach to these tumors, you can fall back on it if you aren’t really sure what you are looking at. With these relatively simple rules, you can be sure to get the most points on your exams AND give the most meaningful differential diagnosis.

Full Brain Tumor Board Review Playlist on Youtube

Neuroradiology Board Review – Brain Tumors – Case 15

Neuroradiology brain tumor board review. This lecture is geared towards the ABR core exam for residents, but it would be useful for review for the ABR certifying exam or certificate of added qualification (CAQ) exam for neuroradiology.

More description and the answer (spoiler!) are seen below the video.

As we start this case, we see a brain and a bone window from a CT through the posterior fossa. It is a little bit hard to see because it is a midline abnormality. The sagittal and coronal reformats are helpful in identifying where the lesion is located.

MRI is a little bit easier to see the lesion, but only a little. There is a well-demarcated lesion along the inferior aspect of the 4th ventricle. There is calfication, which you could see both on CT and GRE sequences from MRI. On post-contrast imaging, there is little, if any enhancement.

The diagnosis is: subependymoma

Subependymomas are relatively benign tumors arising from the walls of the ventricles. In contrast to most other intraventricular tumors, they often do not have much enhancement. The most common locations are in the 4th ventricle and lateral ventricles. Many times they are incidental but they can cause symptoms related to hydrocephalus.

Your differential diagnosis for intraventricular lesions includes meningioma, ependymoma (more enhancing), choroid plexus tumors (also more enhancing), and other tumors such as subependymal giant cell tumors (SEGT, often seen in patients with tuberous sclerosi).

Some tumor types have characteristic histologies that you should be familiar with for the test. Ependymomas are associated with perivascular pseudorosettes, while other tumors such as glioblastoma have their own histologic keywords (pseudopallisading necrosis, microvascular proliferation). These are pretty low yield to study but if you see them it’s good to be familiar with them.

Neuroradiology Board Review – Brain Tumors – Case 14

Neuroradiology brain tumor board review. This lecture is geared towards the ABR core exam for residents, but it would be useful for review for the ABR certifying exam or certificate of added qualification (CAQ) exam for neuroradiology.

More description and the answer (spoiler!) are seen below the video.

This case shows an MRI with a mass in the left parietal region near the midline. It is pretty well circumscribed and is probably extra-axial. It is homogeneously enhancing on postcontrast, and both T2 and T1 images demonstrate significant vascular flow voids suggesting that this is a very vascular lesion.

The diagnosis is: solitary fibrous tumor

Solitary fibrous tumors of the CNS (previously known as hemangiopericytomas) are similar in histology to fibrous tumors elsewhere in the body, such as the pleura. These were originally thought to be related to meningiomas, but their genetics has proven this to be false. However, the imaging features are similar to aggressive meningiomas. They are most often extra-axial, have avid enhancement, and broad dural attachments. It is common to have flow voids showing a high degree of vascularity.

Like meningiomas, these can be highly vascular lesions with much of their blood supply coming from external carotid branches. This angiogram shows the high degree of vascularity. It can be favorable to embolize as many of these vessels as possible prior to surgical resection to minimize bleeding.

Remember that the nomenclature has changed but you still may run into the term hemangiopericytoma. It’s something that should be on your differential if you see something that looks like an aggressive meningioma.

Neuroradiology Board Review – Brain Tumors – Case 13

Neuroradiology brain tumor board review. This lecture is geared towards the ABR core exam for residents, but it would be useful for review for the ABR certifying exam or certificate of added qualification (CAQ) exam for neuroradiology.

More description and the answer (spoiler!) are seen below the video.

This case presents an MRI in a patient with symptoms that sound like partial seizures. There is a pretty subtle abnormality in the medial right temporal lobe. The abnormality is a little bit hard to see, but there is some FLAIR and T2 hyperintensity in the right medial temporal lobe and amygdala. You see it best on the coronal images.

The diagnosis is: dysembryoplastic neuroepithelial tumor, or DNET

DNETs are benign and relatively slow growing tumors often in the gray matter of the medial temporal lobe. They rarely have much enhancement or hemorrhage. They are often described as “bubbly” or “soap bubble” lesions. They are often associated with seizures. Resection or ablation can be curative.

When you see a minimally enhancing cortical tumor, you should have a relatively short differential which includes:

First consider whether they are ill-defined or well-marginated. If ill-defined, the differential includes astrocytoma or oligodendroglioma. If well-marginated, then consider whether there is enhancement. If no enhancement, DNET is most likely. If there is a small amount of nodular enhancement, favor ganglioglioma. As in this case, PXAs tend to have more enhancement in a more irregular pattern.

 

In a testing situation, if a small and minimally enhancing cortical tumor enhances a little bit, choose ganglioglioma. If you don’t seen enhancement, choose DNET. PXAs tend to be much more heterogeneous and irregular.

If you use a structured approach to these tumors, you can fall back on it if you aren’t really sure what you are looking at. With these relatively simple rules, you can be sure to get the most points on your exams AND give the most meaningful differential diagnosis.

Full Brain Tumor Board Review Playlist on Youtube

Neuroradiology Board Review – Brain Tumors – Case 12

Neuroradiology brain tumor board review. This lecture is geared towards the ABR core exam for residents, but it would be useful for review for the ABR certifying exam or certificate of added qualification (CAQ) exam for neuroradiology.

More description and the answer (spoiler!) are seen below the video.

In this case, you first see a CT with a hyperdense mass anterior to the frontal horn of the left lateral ventricle. On MRI, you see a somewhat nodular appearing mass with a rim of hypointensity on T2. Centrally, there are areas of T1 and T2 hyperintensity. On postcontrast, there is minimal if any enhancement, best seen on the 3D postcontrast images.

The diagnosis is: cavernous malformation

Cavernous malformations are benign collections of disorganized blood vessels. They have previous names, including cavernoma and cavernous hemangioma, but these have fallen out of favor because these lesions do not have a proliferative component.

On imaging, these are characterized as “popcorn” like masses with a rim of hemosiderin. They usually have areas of T1 and T2 hyperintensity centrally. Classically they are described as non-enhancing, but in my experience it is relatively common (maybe 25-30% of the time), probably because of the increase in thin-slice 3D imaging. Cavernous malformations can be isolated (about 2/3 of cases) or familial (the remaining 1/3). Familial cavernous malformation are associated with mutations in the KRIT or CCM genes. There is a relatively low annual risk of hemorrhage from these lesions (about 0.25-0.75% per year for single lesions or 1% per year per lesion for familial cavernous malformations).

Cavernous malformations can mimic hemorrhage, particularly if the history is trauma. CT sometimes has calcification, which can be a nice clue. Otherwise, the lack of symptoms and lack of edema can help you. Sometimes, you may need an MRI or a delayed CT follow-up (24-48 hours later) to show that it is stable and prove it is not a hemorrhage.

Often cavernous malformations have an associated developmental venous anomaly adjacent to them. This is a venous structure which has a tree-like branching pattern and otherwise resembles a normal vein. These can sometimes be large and confuse people into thinking it is an arteriovenous malformation, but there is no shunting.

 

Full Brain Tumor Board Review Playlist on Youtube