Student Corner: How to Read a Head CT

Head imaging is both a crucial tool in acute medical care, particularly in the setting of trauma, and a very daunting aspect of learning radiology for students. However, as is the case with many clinical skills, a “systematic approach” goes a long way in helping ease the initial challenge of learning how to read and understand head imaging. For this post, we will focus primarily on head CTs because they are more commonly used in emergency departments due to the fact that they are fast, readily available, and highly informative in trauma.

A head CT presents a few unique challenges. The anatomy is subtle and nuanced. The area has numerous pathological possibilities. The pathologies themselves can change over short time periods. There are different types of fluids and soft tissues. In short, the brain is kind of scary.

But, the best way to get over your fears is to face them. And therefore the best way to look at a head CT is to look at it with a plan. The plan in this case is a (surprise!) mnemonic: Blood Can Be Very Bad” and it is detailed below.

Blood

Hemorrhage of blood into the cranial vault is one of the easier things to identify on head CT. Acute hemorrhage is hyperdense (bright) and becomes hypodense (dark) as time goes on. Two of the most commonly encountered types are subdural hematoma and epidural hematoma. Subdural hematomas arise from the bridging veins and are seen as crescent shaped anomalies at the periphery of the cranial vault. Epidural hematomas arise from the middle meningeal artery and are lentiform or lens-shaped because their expansion in limited by suture lines (the dura attaches to the cranium at the suture lines).

Other types of hemorrhage include:

Interparenchymal hemorrhage–can either be traumatic or non-traumatic, occur in the brain matter itself

Interventricular hemorrhage–seen as hyperdense fluid in the ventricles, which are usually black because they are filled with hypodense CSF, can be secondary to other types of hemorrhage or trauma

Subarachnoid hemorrhage–most often due to aneurysm rupture and presents with very acute headache (thunderclap headache), seen as fluid in the subarachnoid spaces.  Subarachnoid is also very common in trauma.

The image below is an example of subdural hemorrhage. The left side of the cranial vault is filled with hyperdense fluid, indicating that this process is acute. Also, note the midline shift that occurs, which is shown by the compression of the ventricles more so on the patient’s left than the right and the movement of brain tissue over to the patient’s right. There is also some extracranial soft tissue swelling on the patient’s left, indicating a possible traumatic process. Extracranial soft tissue swelling can help guide your eyes, so to speak, when looking for pathology.

SDH with midline shift 1

Cisterns

Cisterns are spaces between the pia and subarachnoid meningeal layers that can be filled with CSF. There are numerous cisterns that can be identified on a head CT, but the major ones that you should be familiar with are outlined here on Radiopaedia.

These cisterns can be used to identify increased intracranial pressure or subarachnoid hemorrhage (detailed above). In the setting of increased ICP, these spaces become compressed. In subarachnoid hemorrhage, there is hyperdense blood inside them instead of hypodense CSF.

Brain

The brain tissue itself is composed primarily of grey matter and white matter. You can see the difference between these two types of tissue because grey matter is more dense and therefore appears more bright on CT. The gyri and sulci can also be visualized and they should be generally symmetric.

The pathologies that can be identified in the brain parenchyma include:

Abscesses–areas of focal infection from bacteria or fungi, often seen as round areas of ring-enhancing hypodensity with associated edema; midline shift is also a possible finding depending on the size of the lesion.

Tumors–areas of abnormal growth whose particular appearance is variable depending on type and location; midline shift is also a possible finding depending on the size of the lesion; particularly well visualized on contrast-enhanced CT because the blood-brain barrier is disrupted during tumor development and growth, which allows the contrast to leak into the tumor and make it bright.

Infarction–when the blood supply is cut off from brain tissue it causes swelling (which can result in midline shift) and the area becomes hypodense and loses grey-white differentiation.

The CT image below shows a few interesting things. The most obvious one is the multiple hyperdensities seen in the brain matter. These lesions are most likely calcified and can represent anything from inflammatory reactions to infections to tumors. The other finding is that the gyri are thin and the space between them is much more evident than normal, which represents atrophy of the brain due to old age, dementia or both.

Multiple calcifications 1

Ventricles

For the sake of brevity, we will not go over the normal anatomy of the ventricular system. The key radiological aspects of the ventricles in the brain are their size and symmetry. They are filled with hypodense CSF and their size can increase due to hydrocephalus, or increased accumulation of CSF. Hydrocephalus is either communicating (obstruction at the arachnoid granulations which function to resorb the CSF) or non-communicating (obstruction at any point in the ventricular system, usually at the foramina which connect the different ventricles.

Symmetry comes into play when there is a mass lesion on one side of the brain, which can cause compression of one of the lateral ventricles with or without midline shift.

One other aspect to keep in mind is that enlargement of the ventricles can be due to atrophy of the brain parenchyma itself, a condition known as “hydrocephalus ex-vacuo”. Therefore if the ventricles do indeed look large, the brain parenchyma should be examined, paying close attention to signs of atrophy. If the ventricles are enlarged and the brain matter looks compressed and the sulci lose their normal wavy pattern (a process called “effacement”), hydrocephalus is more likely.

Bone

Skull fractures are a common finding in head trauma and they can be seen on head CT. Fractures are seen as dark lines in the usually bright bones. They must be distinguished from suture lines, which are seen as symmetrical wavy lines across bones. Basilar skull fractures are harder to identify, as the base of the skull has multiple different areas and bones. Radiopaedia has a great example of this here.

One of the things to keep in mind with fractures of the skull is to follow the fracture lines. Fractures often cross into different bones and, especially when looking at the base of the skull, fracture lines can extend much further than you would expect.

The image below shows a painfully obvious frontal sinus fracture, where the the bone fragments actually protrudes back into the brain tissue itself. This view is slightly different from the other images on this post because it is shown in the “bone window”, which is a type of image processing that highlights the hyperdense bones on a CT. It makes fractures much easier to identify (although I’m not quite sure you needed the special window to see this one).

CT head trauma2

 

 

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All in all, it is also helpful to keep a few other concepts in mind.

Symmetry is key in identifying pathologies, since irregularities in the tissues or fluids are almost never symmetrical.

Utilize the bone window, even if you don’t suspect a fracture.

Soft tissue swelling on the outside of the cranial cavity itself can help you identify the principal point of impact in traumatic injuries and help you find underlying pathologies.

Always use a systematic approach because otherwise it is pretty easy to miss subtle pathology.

Hope this was helpful to you all, but don’t take this as a complete manual of how to read a head CT. Always corroborate your reads with a more experienced physician and always attempt to read the image on your own before looking at any published interpretations. Ask other people about tips and tricks that they might have. And finally, read as many as you can!

Author: Jaymin Patel

References/Resources:

University of Virginia tutorialhttp://www.med-ed.virginia.edu/courses/rad/headct/

Elsevier Health, How to Read a CT Scan- http://www.elsevierhealth.com.au/media/us/samplechapters/9781416028727/Chapter%2069.pdf

Agrawal A. How to read a CT scan of a patient with traumatic brain injury?. NMJ. 2013; 2(1): 02-11.


Filed under: CT, Head, Head, How To's, Student Corner, Trauma Tagged: blood can be very bad, bone window, computed tomography, ct, Head, head ct, head trauma, how to, midline shift, student corner

Massive splenomegaly…Answer

Last week I showed you this CT showing massive splenomegaly:

Splenomegally + Masses

 

The abdominal CT above shows massive splenomegaly with various areas of hypo attenuation throughout the spleen.  Massive splenomegaly is a term used when the volume of the spleen is expected or calculated to be >1000 grams or clinically extends well into the left lower quadrant or past midline.

A short differential diagnosis for massive splenomegaly includes (1):

  • Malaria
  • Myelofibrosis
  • Leukemia (especially CML)
  • Polycythemia Vera
  • Lymphoma (several types)
  • Lieshmaniasis
  • Thalessemia

The ill-defined hypo attenuated lesions in this spleen raise a high concern for lymphoma.

Author:  Russell Jones, MD

References

1.  Luo EJ, Levitt L.  Massive Splenomegaly.  Hospital Physician, 5/2008.  Accessed 11/2014 at: http://www.turner-white.com/memberfile.php?PubCode=hp_may08_spelnomegaly.pdf


Filed under: Abdomen/Pelvis, Abdomen/Pelvis, CT, Non-Trauma

Massive splenomegaly…

This patient presented with left upper quadrant abdominal pain:

Splenomegally + Masses

 

The abdominal CT above shows massive splenomegaly with various areas of hypo attenuation throughout the spleen.

In the ED, the spleen is not often the organ responsible for non-traumatic pain in the left upper quadrant.  Gastric, colonic, and kidney disorders are much more predominant.  In this example however the spleen is definitively causing the patient’s discomfort.

What is your differential diagnosis for massive splenomegally?

Answer to follow

Author:  Russell Jones, MD


Filed under: Abdomen/Pelvis, Abdomen/Pelvis, CT, Non-Trauma

WWWTP #21… Answer

This is an interesting X-ray of a newborn with respiratory distress:

WWWTP 21

WWWTP 20

 

The upper Chest X-ray has an endotracheal tube near the carina (probably should be pulled back a bit).  It also has cardiomegally with vascular congestion.  The line coming up from below is an umbilical venous catheter in the inferior vena cava.

The “baby gram” below shows the same.  This image gives a better view of the umbilical line.

An umbilical venous catheter should traverse as this one does.  It comes straight up from the umbilicus to just above the diaphragm near the right atrium and inferior vena cava junction.  If the catheter does not go straight up and veers to the left side of the patient, it may have erroneously entered the hepatic vasculature.  This can result in hepatic complications.

The patient ended up having a double outlet right ventricle (both the aorta and main pulmonary artery are attached to the right ventricle) which is one of many anatomic heart abnormalities that can lead to congestive heart failure.  There was also a patent ductus arteriosus and a large ventral septal defect (VSD) that allowed for mixing of deoxygenated and oxygenated blood.  Without the large VSD the patient would not have been able to survive.

Author:  Russell Jones, MD

 


Filed under: WWWTP Tagged: Cardiomegally, CHF, Dyspnea, Endotracheal Tube, Umbilical Line

Student Corner: Ottawa Ankle Rules

The Ottawa Ankle Rules are a set of criteria that are designed to help clinicians identify which patients that present with acute ankle injuries require imaging. The 1992 paper which outlined the criteria (PMID:1554175) consisted of a prospective study of 750 patients who came into the Ottawa Civic and Ottawa General hospitals with acute ankle injuries. The study was designed to record each patient’s particular presentation (area of tenderness, amount of swelling, ecchymoses, etc) and see if any aspect of their presentation correlated with a fracture identified on subsequent imaging (i.e. if a patient has pain over the medial malleolus, how likely are images of that ankle to show a fracture?).

MD Calc has a good summary picture of the criteria here. I’ll summarize it below as well:

A series of ankle x-rays is necessary if:

There is tenderness in the malleolar zone (lateral or medial) AND bony tenderness at the posterior edge of the medial malleolus OR bony tenderness at the posterior edge of the lateral malleolus OR an inability to bear weight immediately and in the ED

OR

There is tenderness in the midfoot zone AND bony tenderness at the base of the 5th metatarsal OR bony tenderness at the navicular OR an inability to bear weight immediately and in the ED

The picture on the link above is probably more helpful to visualize the algorithm. They note that 102 patients out of the 750 cohort had “significant” fractures and these criteria would have led to imaging on all of those cases. Also, they report that this criteria would have led to a 32.3% decrease in the number of radiographs ordered. The algorithm’s sensitivity was 100% and specificity was 40% for identifying fractures that were later confirmed by imaging. In other words, it was touted as a great screening tool since it was highly sensitive in picking up an ankle fracture.

(Note: The original criteria included an age stipulation, so that every patient with ankle pain [but not midfoot pain] over the age of 55 was recommended to get imaging. Additional research and subsequent modification of the algorithm proved that age was actually not a predictive variable. [PMID: 8433468])

Now on to a case:

Homeless male, in his 50’s, with ankle and foot pain after falling 10 feet. Walked into the E.D. with some pain, but had the ability to bear weight. Pt had swelling on exam, but no tenderness at the lateral malleolus, medial malleolus, mid foot or lateral foot.

The question is, do you get imaging on this patient?

Oh, look, it turns out we have criteria for that! And, in short, if you follow the Ottawa Ankle Criteria, the answer is no. The patient can bear weight and has no tenderness at any of the 4 areas that the criteria specifies, therefore according to the algorithm, imaging should not be ordered.

But we have a twist! This patient did indeed get ankle x-rays.

Ottawa Ankle 1

Why did this patient end up getting ankle x-rays despite not having met the Ottowa Ankle criteria?

Dr. Jones plays “devil’s advocate” in arguing against the use of the Ottowa Ankle Rules:

“Despite high negative likelihood ratio’s found on creation and validation of the Ottowa Ankle Rules, ED physicians are still ordering x-rays for most traumatic ankle complaints.  Why?  Because they are immediately available, low cost, and low radiation.  Many of our radiology decision rules pertain to expensive tests that are 10-100 times the amount of radiation (CT head, CT c-spine) and/or may not be readily available.  It is less practical to try and decrease a test that has little downside…such as an ankle radiograph.  

There is usually significant comorbidity associated with many different types of ankle fractures including calcaneal and talar fractures (I mention these because in my experience these are the two fracture patterns that are missed by the Ottowa Ankle Rules despite their reported 100% sensitivity…see the case above).  In our medicolegal environment in the United States, it is very difficult to defend missing an ankle fracture when you have a low cost, low radiation, readily available test at your disposal.  One must take into account that it is nearly impossible to recreate an exam with our current medical documentation.  A radiograph is an objective picture of a non-fractured ankle while a nicely worded exam is not so defendable in the eyes of a layman jury.  You open yourself up to legal problems if you miss a high-morbitidy injury because you used a rule that “decreases medical costs and increases efficiency” (these are the main benefits of the Ottowa Ankle Rules).  Courts are more patient-centered, they don’t care about our waiting room times!

We practice medicine taking into account more than just evidence-based medicine.  Until the “standard of care” we are held up to in court is in line with evidence-based medicine, we will always have to take into account the burden of the medicolegal consequences.  Be careful utilizing any clinical decision rules until they are universally accepted as standard of care among all ED physicians.  

I personally use “shared decision making” with most of my decision rule utilization.  My practice pattern using Ottowa Ankle Rules involves (1) A medical record documenting negative Ottowa Ankle Rules AND (2) a patient that understands the decision not to x-ray AND (3) the patient agrees.  This situation is rare but I will sometimes not x-ray if all the above parameters are met.  This is easier to defend if you happen to miss something by not getting an x-ray.  

The above statement is of course my own opinion and practice pattern.  Please utilize the Ottowa Ankle Rules as you feel fit and I appreciate any comments for and against their use in the ED.    

-Russell Jones, MD”

So, there you have it. As is the case with many different areas of medicine, real-life practice varies from guidelines, rules and algorithms (even if they are backed up by multiple research studies) for various different reasons which include, but are not limited to differences in: availability of testing methods, medical setting, hospital policies, patient needs, legal considerations and the physician’s own interpretation of all of the above factors and the medical research/literature.

For students, this means that you’ll have to soon adapt yourself to an environment and way of thinking that takes multiple variables into account when it comes to decision making. Almost every patient is a different shade of grey, not black and white. After all, medicine is both art and science.

But, I digress from the patient. Can you spot the fracture in the above image? Answer below:

Calcaneal fracture with arrow

 

There is indeed a fracture of the calcaneus right around the inferior edge of the bone. Good thing this patient got imaging, right?

Author: Jaymin Patel

References:

Stiell IG, Greenberg GH, McKnight RD, Nair RC, McDowell I, Worthington JR. A study to develop clinical decision rules for the use of radiography in acute ankle injuries. Ann Emerg Med. 1992 Apr;21(4):384-90. PubMed PMID: 1554175

Stiell IG, Greenberg GH, McKnight RD, Nair RC, McDowell I, Reardon M, Stewart JP, Maloney J. Decision rules for the use of radiography in acute ankle injuries. Refinement and prospective validation. JAMA. 1993 Mar 3;269(9):1127-32. PubMed PMID: 8433468.


Filed under: Ankle XR, Articles, Radiology Rules, Student Corner, XR Tagged: Ankle Criteria, ankle XR, Ottawa, Ottawa ankle criteria, ottawa ankle rules, student corner