How to read a brain CT

[00:00:00]Okay, this video is how to read a head CT or a brain CT.

[00:00:05]Um here is a CT scanner.

[00:00:08]And the patient lays on this table, then the table moves into the scanner. So, let's say we're doing a CT brain, and then a radiation beam passes from one side of the scanner through the patient's brain and then into a detector camera detector on the other side. So, from right here, passes through the brain into a detector on the other side.

[00:00:26]Here's the standard densities on a head CT. Um air is -1,000.

[00:00:31]Cortical bone is about +1,000. Water is zero. You need to know that. Water is zero. These are called Hounsfield units.

[00:00:39]Godfrey Hounsfield, a guy from England, was one of the co-discoverers of CAT scan. Actually, um the Beatles helped found fund the initial funding to make the CAT scanner, like EMI Electrical Musical Instruments.

[00:00:53]And um they um helped fund it. So, anyways, water is always going to be zero, and fluid in the body that's similar to water, like CSF, cerebral spinal fluid, is going to be close to water. We often think of zero to 20 as being water. Um the white matter of the brain has a lot of fat in it from myelin, so it's relatively low in density at +30.

[00:01:15]The gray matter, where the cell bodies are of the neurons, the brain cells, um is denser. It's about +45 because it has a lot more blood flow, about four times as much blood flow to it. And blood's a little denser. Blood's usually about 70 Hounsfield units.

[00:01:30]Okay, and all these things are going to be helpful when we start looking at these pictures.

[00:01:36]Okay, so the first thing is how do I read a normal head CT? Brain CT, head CT means the same thing. I usually start at the axials. Axials are transverse images. Imagine you are slicing the body like um like [clears throat] a loaf of bread. Okay, these are transverse images. The slice would be from side to side.

[00:01:54]Okay, this is at the level of the basal ganglia. So, this would be the thalamus.

[00:01:57]This would be the posterior internal capsule, the lentiform nucleus.

[00:02:02]Uh the insula in here. This would be the caudate nucleus. Here's the frontal horns of the lateral ventricle. These are the occipital horns of the lateral ventricle actually extending more posteriorly.

[00:02:11]Uh you can see this is the white matter.

[00:02:13]It's less dense than the gray matter ribbon which traces the outline of the of the brain. Cortex means bark like the bark of a tree. Okay, so the cortex is a little bit denser than is the white matter again cuz the cortex has more blood flow. That's where the cell bodies are. There's more metabolic activity.

[00:02:28]So, there has to be more blood flow. You can see the the cortex is denser here than the the white matter, the deep white matter. This is called Um the main levels of the brain looking at axial images would be basal ganglia level here where you can see things like the thalamus and the lentiform nucleus versus here you're at the level of what's called a corona radiata. It looks like a crown and radiates around the ventricles. This is the caudate nucleus little dense adjacent to the lateral ventricles. Okay, the caudate corona radiata is especially the white matter, the periventricular white matter. The white matter adjacent to the cortex, the cortical ribbon is called the subcortical white matter. Okay, so I go through the axials real fast. Just make sure there's no big bleed or any surprise. I look at the size of the ventricles. I check a couple key spots and I make a prelim read. And I seldom I hardly ever change my read from that prelim read. But then just to be thorough, I go through [clears throat] the um the uh coronal images. Okay, this were as it were cut from front to back. And I look real carefully at the midline interhemispheric fissure. Make sure there's no bleeds in there. So, I go all the way to the back then I come all the way forward. Now, when I'm coming forward, I'm looking along the convexities of the brain. The outer surface of the brain is convex. Um and I look for subtle bleeds along there.

[00:03:41]Um after I've gone through the coronals, then I look at the sagittals. When I'm looking at the sagittals, um that's the cuts from side to side vertically from side to side cuts. I will especially look at these midline structures. I make sure that the cerebellar tonsils are where they should be above the foramen here above the what's called the basion-opisthion line.

[00:04:00]Uh the back of the clivus right here is called the basion. This is called the opisthion. And I make sure the tonsils are not below there. Okay? That could be a tonsillar herniation with mass effect or could be something called a Chiari malformation. I take a close look at the pituitary. Make sure there's no pituitary tumor. The only real difference I can see between the brain of a man and a woman that's obviously visible is that premenopausal females got big pituitaries. It has a convex, you know, upward projecting margin on the top. Men have smaller pituitaries, often a flat top, so to speak, or even a concave top. Okay? And I think that's why, you know, a premenopausal woman, her mood can vary uh more than a man does. You know, you talk to a guy, it's the same guy every day. Talk to a woman, you got to look her in the eye first.

[00:04:44]See if she, you know, if she has if there's anything going on in terms of her mood. How she looks at you tells you a lot about her mood.

[00:04:51]Um this is the fourth ventricle right here, the fastigium in the back of it, uh its little tail part right there.

[00:04:59]Um you also need to look right here at the tectum, uh superior and inferior colliculus.

[00:05:04]Make sure there's nothing going on there, pineal gland. You know, there almost never is, but you got to look, okay? And it's kind of a rather aesthetically beautiful. I think it's the most aesthetically beautiful thing in all of medicine is a midline sagittal brain MRI. Actually, a brain MRI is prettier than a than a CT. CT's nice. I mean, it's kind of cool that we can look at the brain at all, but when I'm looking at a head CT, I'm mostly trying to answer a couple of questions. Number one, is there a bleed? Yes or no? Cuz with an acute stroke, they may or may not give uh clot-dissolving medicine, you know, TPA, um so thrombolytic therapy. So, first question is always is, is there a bleed?

[00:05:41]Yes or no? The second question is, is there a stroke? Yes or no? Is there a tumor? Yes or no?

[00:05:48]Um, so anyways, so I go through the axials, I go through the coronals, and I go through the sagittal brain, and then I look at the bone window. The bone window is windowed differently to emphasize the bones themselves. It's also good sequence to look at the paranasal sinuses in here. Is there evidence of sinusitis with a fluid level or bubbly secretions? Is there evidence of fluid accumulating in the mastoids? Mastoid fluid is usually irrelevant, but we look at it. It's usually incidental trapped fluid. Um, if there were complete opacification of the mastoid on one side, then I would check the nasopharynx to see if there's obstruction of the Eustachian tube.

[00:06:22]That's a typical boards question, by the way. Okay, so here's some subdural fluid collections. This subdural fluid collection is the same density as a cerebral spinal fluid. Well, it's almost the same density. It's actually a touch more dense. This is looks like a chronic subdural hematoma. If it was isodense, meaning same density as the lateral ventricular cerebral spinal fluid, then it would probably be, you know, like maybe a hygroma, which isn't exactly the same thing as a subdural.

[00:06:46]Okay, so this is a chronic subdural hematoma, and um this is a more sort of subacute subdural hematoma. It's not quite as dense. The typical dense bleeds more dense like this. This is little sort of intermediate density. You can see the mass effect. I drop a plumb line from the falx in front to the falx in back, and see if this is called the septum pellucidum. Normally, it should be right in the midline. This is quite a bit displaced. That looks like it's displaced over a centimeter. So, this would be a candidate to be taken to the operating room to drain this subdural hematoma here. Okay, when patients are demented, we get head CTs to see if they've got something like a subdural hematoma that can be drained or a meningioma tumor that can be drained.

[00:07:24]But, I can tell you that's super, super rare. Almost always, I I I don't see anything significant. You know, the vast majority of head CTs have no significant findings on them. You know, maybe as many as like 29 out of 30, okay? It's like more than 95% of them. They're usually nothing but chronic atherosclerotic disease, okay? So, anyways, here's also midline shift with this one. It's a sort of milder midline shift, meaning we might not take this patient to the operating room. Here's the interpeduncular cistern in the midbrain, and this is too dense this material here. So, this is a bleed.

[00:07:55]Subarachnoid hemorrhage in the uh interpeduncular cistern.

[00:07:59]And there's also a little bit of blood here extending along the side of the midbrain, okay? Uh you always got to look here cuz smaller bleeds can be this tiny, and they can be missed. You always got to look at the occipital horns of the lateral ventricles for blood layering in that location.

[00:08:14]I see a bleed missed here once every 10 years. I see a bleed missed over here, also about once every 10 years, maybe once every 5 years.

[00:08:25]Okay, um here is an interpeduncular I'm sorry, here is an intraparenchymal hemorrhage in the basal gang. This is typical appearance of a hypertensive intraparenchymal hemorrhage. These are rare. I hardly ever see them, okay? They do happen, of course. You'll see them in all the books. Everybody talks about them all the time, but they're not that common. This is incidental calcification of the basal ganglia, and here's an incidental incidental calcification of the pineal gland, which is so common we don't even you know, a lot of docs don't even include that in the report. They just consider it normal variation. I don't think it is normal, but it's so common.

[00:08:55]It's like um you know, not far away from being like fatty liver. So many people have it that people almost ignore it. Okay, here is a basal ganglia hemorrhage, intraparenchymal hemorrhage that has ruptured into the lateral ventricle. So, this significantly worsens the prognosis. I mean, this is a bad prognosis to begin with, but this makes it even worse when the blood's gone into the ventricles, then you're prone to getting vasospasm, enlargement of the ventricles, hydrocephalus, and all that.

[00:09:23]Okay, here's a big stroke. So, this would be there Always imagine that the patient's feet are towards you. So, this is the patient's right side. Here's the patient's left side. So, this is in the right middle cerebral artery along the convexities, and this is a large uh we call it an MCA infarct. So, this is a very poor prognosis. Patient will get weakness on the other side of the body, the left side of their body.

[00:09:42]Um they'll often have significant cognitive impairment, of course, from such a big stroke.

[00:09:47]Okay, now here's something. These are relatively uncommon. Yeah, I see them, but I don't see them that often. This is what we see every day.

[00:09:54]Um there is a lot of periventricular lucency, you can call it hypodensity.

[00:09:59]Shouldn't be It should be more like about like this. And this is all markedly lucent, and that is all damaged brain uh from a lack of blood flow, either from overtreated hypertension, or from microvascular disease, from hypertension and diabetes.

[00:10:13]And there's some other things that can do it as well, but this is a lousy-looking brain. And we'll even call these coalescent. The way I'd probably dictate this is extensive hypodensities, most likely due to chronic small vessel cerebrovascular ischemic disease. Okay?

[00:10:32]Um so, this is super common. And I often see this with cognitive impairment, but the next slide I'll show you what I see most often.

[00:10:40]This is what I usually see. Typical patient, memory loss, cognitive impairment, dementia.

[00:10:46]All of this is cerebrospinal fluid anteriorly and in the interhemispheric fissure here. It's isodense with this uh intraventricular cerebrospinal fluid, CSF. And the point I'm making is an atrophic shrunken brain is the most common thing seen on uh cat scan of the brain when looking for um a cause of dementia. So, basically, 99% of the time, the horse is out of the barn, okay? The patient's already corked. Their brain is severely dysfunctional. And it's kind of late to do just about anything, okay?

[00:11:22]And what I'm trying to say is, you know, we see macroscopic things on CT. We're much better at seeing things on MRI, but still, even MRI, this is usually all I see, just an atrophic shrunken brain due to chronic loss of cells like from apoptosis, okay? Apoptosis meaning that Remember we talked about Delatorre's theory of um of dementia, the vascular hypothesis of dementia, lack of blood supply to the brain either due to small vessel atherosclerosis from hypertension and diabetes typically or from uh overtreated hypertension. And of course, there's the micro uh vascular game going on. We talked about that, hypertension diabetes. And then there's the I talked about the challenge between oxygen and glucose delivery versus metabolic rate of those neurons, okay? So, anyways, the point I'm saying is it comes down to this.

[00:12:09]Health is really determined largely at a cellular level. Is that cell getting enough blood supply? That's why every cell functions better when it has good blood supply. Is that cell being overworked due to psychological stress, due to caffeine, due to MSG, due to toxins, okay? So, anyways, that's a quick overview of how to read a head CT.

[00:12:31]Uh I hope that was helpful.