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Student Corner: How to Read a Head CT

November 24, 2014

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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.

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Massive splenomegaly…Answer

November 17, 2014

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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

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Massive splenomegaly…

November 12, 2014

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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

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Back pain…

October 7, 2014

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Back pain is one of the most frequent complaints in the ED.  The vast majority of patients do not have a life threatening or highly morbid pathology.  Unfortunately, this patient did:

 

CT LSpine 1 LS spine 2

This is a CT scan under bone windows.  It shows erosive changes based around the L4-L5 disc, eroding into the inferior endplate of L4 and the superior endplate of L5. These findings are concerning for discitis-osteomyelitis. It is favored to have both acute
and chronic components.

Finding this pathology is somewhat like finding a needle in a haystack.  However, pay attention to signs such as fever, repeat ED visits without a firm diagnosis, focal weakness, and predisposing factors such as IV drug abuse, history of endocarditis, or immunosuppression.  Sedimentation rate and C-reactive protein are often elevated in this disorder (among others).

CT is a readily available, quick way to diagnose this pathology but it isn’t as sensitive as MRI.  Plain films are not reliable but may show changes similar to the CT above.  Nuclear medicine bone scans as well as PET scans can be used but are not commonplace in the ED.

Author:  Russell Jones, MD

Image Contributor:  Zachary Skaggs

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WWWTP #20 Answer…

August 7, 2014

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This patient presented to the ED with a headache.

delta-sign

 

This patient has an “Empty delta sign” in the superior sagittal  sinus (blue arrow).  This is indicative of dural venous sinus thrombosis.  There is a clot (dark) among normal blood in the sinus (light).  Remember to look at your sinuses for this rare occurrence.

Image Contributor:  Adriel Watts, MD

Author:  Russell Jones, MD

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WWWTP #20 (What’s Wrong With This Picture?)…

August 4, 2014

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This patient presented to the ED with a headache.  What’s Wrong With This Picture?

WWWTP #20

Image Contributor:  Adriel Watts, MD

Author:  Russell Jones, MD

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Liver mass…differential diagnosis

July 14, 2014

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This patient presented with right upper quadrant pain.  I asked last week what your differential diagnosis would be:

Liver Mass 1

Liver mass 2

The CT above shows a multiloculated, rim-enhancing mass in the liver parenchyma.  This is consistent with an abscess.  The differential diagnosis starts by breaking down the categories into bacterial, fungal, and amebic causes. 

Bacterial:  Abscesses can form from ascending cholangitis, especially in setting of biliary malignancies.   Klebsiella pneumoniae has been reported to cause hepatic abscesses, especially in E. Asia (1).  Patients with recent instrumentation (hepatocellular carcinoma embolization, etc) are at risk for MRSA, streptococcus species.  Tuberculosis has been known to cause hepatic abscesses as well.

Fungal:  Disseminated candidiasis in the immunocompromised host can lead to liver and splenic abscesses

Amebic:   Liver abscess is the most common manifestation of extraintestinal entamoeba histolytica (2).  In endemic areas or travelers to endemic areas are at risk for this occurrance. 

Author:  Russell Jones, MD

References

1.  Davis J, McDonald M.  Pyogenic Liver Abscesses.  www.uptodate.com

2.  Leder K, Weller P.  Extraintestinal Entamoeba Histolytica Amebiasis.  www.uptodate.com

 

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Liver mass…

July 7, 2014

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This patient presented with right upper quadrant pain…

Liver Mass 1

Liver mass 2

The CT above shows a multiloculated, rim-enhancing mass in the liver parenchyma.  What is your differential diagnosis?

Author:  Russell Jones, MD

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Aortic dissection…

June 16, 2014

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This patient presented with chest pain radiating to the back:

AD CXR 1

 

The patient’s initial chest X-ray shows a widened mediastinum and an indistinct aortopulmonary window.  CT showed:

AD CT 1 AD CT 2 AD CT 3

This patient has an aortic dissection.  There are two different classification systems for aortic dissection:  Stanford and DeBakey (1).

Stanford Criteria:

  • Type A:  The dissection flap involves the ascending aorta
  • Type B:  The dissection commences distal to the left sub-clavian artery

DeBakey Criteria

  • Type I: The dissection flap involves the ascending aorta and descending aorta
  • Type II:  The dissection flap involves the ascending aorta only
  • Type III:  The dissection flap involves the descending aorta only

This is a Stanford Type A and a Debakey Type I because it involves the ascending aortic arch all the way to the iliac bifurcation.

What is important to remember (besides the number for a cardiothoracic surgeon)?  If the flap involves the ascending aorta these are usually managed operatively. Descending dissections are many times managed medically (1).

Besides rupture, the main problem with aortic dissection is perfusion to various organs.  Virtually every solid organ can be affected depending on the spacial characteristics of the dissection flap.  In this case the last image clearly shows that the right kidney is not perfused, indicating that the dissection flap has occluded the right renal artery.  The kidneys and bowel are the most common organs to develop ischemia.

Author:  Russell Jones, MD

Image Contributor:  Jay Williams, MD

References

  1. Broder JS.  Diagnostic Imaging for the Emergency Physician.  Elsevier, 2011.
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More colonic dilitation…

June 9, 2014

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This patient presented with abdominal pain, nausea, vomiting, and distention:

Volvulus 1 Volvulus 2 Cecal Volvulus 2 Cecal Volvulus

These films and CT show colonic dilatation similar to last week (sigmoid volvulus).  However, in contrast to last week, this is a cecal volvulus.  In this CT there is marked dilatation of the cecum with a central location in the abdomen.  Usually a cecal volvulus will have visible haustra as opposed to a sigmoid volvulus in which colonic haustra will not be present.  Sometimes, as in the above images, the haustra are difficult to see.  This also looks like it may be a more rare form of cecal volvulus called a cecal bascule.  For more information I will defer to our radiology colleagues at Radiopaedia:

Caecal Volvulus

For all you radiologists out there, do you think this is consistent with a cecal bascule?

Why note the difference between cecal and sigmoid volvulus?  The treatment can be drastically different.  Sigmoid volvuli are many times amenable to acute management non-operatively (sigmoidoscopy) whereas cecal volvuli usually require open laparotomy and have a higher frequency of partial colectomy.

Author:  Russell Jones, MD

References

1.   Gaillard F et al.  Caecal Volvulus. http://radiopaedia.org/articles/caecal_volvulus

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