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TRAUMA RADIOLOGY
VASCULAR TRAUMA

 

 

Radiology Variants, Over-reads & Misreads
VOMIT Protection

Traumatic Aortic Injury

Case 1
Andrew Bowman
27.09.2004

PULSATION ARTEFACT

[...] attached are GE Lightspeed CT Scanner images of a blunt chest trauma patient (motorcycle vs. car). Tachy in ED but BP good with strong pulses x 4 extremities

Based on these images the radiologist, surgeon and cardiothoracic surgeon all agreed that patient needed a thoracotomy.[...] and off patient went for mid-line sternotomy.

Operative finding = Normal Aorta

I think they thought there was an intimal flap. In retrospect it was agreed that they were looking at the dye column in the ascending aorta averaged over 2 points in time of the ejection phase, rendering a "false flap"

The Panel's Read:

3.10.2004
Sal Sclafani

that CT does not look like an aortic injury to me. looks more like artefacts. Absence of hematoma in mediastinum clinches it for me I would not consider this a CT angiogram since there is no reformations, 3D or other volume rendered processing. Axial images just dont cut it any more

another contributor said: "I have seen 5 - 10 aortic tears in my life. I have read about hundreds but what is the experience of your hospital? How many CT angio's have your radiologists, CT surgeons, etc. really seen? If you are in a low volume hospital then you haven't seen that many. You need to go with the gold standard."

I would suggest that if the hospital is a low volume one, then the risks of angio would be higher, the lilkelihood of errors on angiography would be higher and it would probably take much longer to obtain an angio.

I find it interesting that people consider angiography the gold standard although the modern version it has also never undergone rigorous testing and comparison to cut films. The best assessment of aortography was obtained during analog cut film angiography days. Frankly i find DSA not as well suited as cut film; detection of some of the subtle findings like flaps and intramural hematomas are surely not going to be identified..Some hospitals have suboptimal DSA equipment, they include 512 matrix, poor subtraction algorithms, inadequate postprocessing, etc.

Ken complains about the inadequacy of CTA to show all these anomalies. For the life of me, i dont think angiography is going to identify all of them either.

7.10.2004
Bertil Leidner

Any imaging will have artifacts, including multi-slice or multidetector-row CT (MDCT) - a 16-row multidetector CT gives less pulsation artifacts then a 4-row, but they still do exist! Adding new equipment/new CT will generate artifacts that may be different from earlier generation CTs, which may take some time to learn. Always, but especially in such situations, the radiological findings must be judged together with clinical data before a definte diagnosis is made!

I acknowledge Ken´s fact that trauma rarely makes a tear in the ascending aorta and very seldom a dissection, so this knowledge should raise the suspicion that the finding could be an artifact. So then you must know your artifacts and know when a "finding" could be artifactual. There is obviously a learning curve - we have also had a similar case at Karolinska that lead to an unnecessary thoracotomy! If you have the suspiscion of ascending aortic dissection before the scanning, you should use ecg-gating to avoid the pulsation artifact.

Othervise to deal with this type of artifact, it is essential to have some understanding of CT-technique. The pulsation artifact is generated when the pulse rate coincides with the rate at which images are made, so that the artifact is generated at the same position in every image - when this is projected inside the aortic lumen it may simulate a "membrane". If you "rescan" the patient in some way, for example with a different table speed the artifact will be generated at different position and you have proved it to be an artifact. A true dissection will be consistant.

With modern CT you can "rescan" virtually knowing the following: 1 MDCT generates a volume of raw data from which you reconstruct images. 2. From one scanning you may choose to generate several image sets with different slice thicknesses. 3. You have also to choose at what interval the images are made (called increment) - for example you may do 3 mm thick images at an interval of 3 mm (no overlap) as was the case with non-helical CT or you may do images with overlap, ie 3 mm thick with an interval (increment) of 1 mm or 2mm. 4. Changing the increment between image sets, means that you get images with a time difference from the original raw data (scanning) and thus a new image set will give you a scan with images with a changed time interval - which changes the position of the artifact. 5. To change the starting position with say 1-2 mm for the second reconstruction may give the same result.

11.10.2004
Ken Mattox

Submitted are two cuts of CTs of the chest without accompanying plain chest x-rays. The ascending aorta demonstrates flow artifact and NO evidence of aortic tear or extra aortic hematoma. Such artifacts are well documented in the radiologic literature, and are often seen in patients who have chest and mediastinal CT scans for other reasons, (i.e. staging for lung cancer). Should there be any concern, this inmage should be followed by aortography. No operation is indicated. This is NOT a dissection.

Other Views:

27.09.2004
Karim Brohi

This is not a CT of aortic injury. There is no mediastinal haematoma, and the appearances are not characteristic of an intimal flap. If concern existed then, as you say, further investigation is required (angio) - not operation.

27.09.2004
Gervais Wansecheong

this is in the ascending aorta. Again, not the typical site for a dissection unless it progressed proximally from the usual site near the ligamentum. The thing to remember is that a flap will not just be seen on 1 or 2 slices alone. Also, flaps cannot jump from one site to another. As tempting as it is to just do the expedient, being careful and meticulous is worthwhile. I would not been particularly satisfied with the quality of this scan if the questions is ? dissection. There is too much movement for an accurate call and in this case, turned out to be a bad one.

22.10.04
Mats Beckman

Re the discussion on VOMIT and aortic injury my esteemed collegue Dr
Leidner is referring to a case that occured at my department. This was not
a trauma case, but the principles discussed are the same.

An elderly lady presented with intense chest pain, ECG, enzymes etc were
negative so an aortic CT was obtained, see below. As the attending junior
radiologist was suspicious of dissection at the aortic root, reformats were
obtained to "confirm" the findings, and an anterior low attenuating
structure reaching up from the aortic root to the arch was identified. At operation the aorta was found to be normal. Subsequent reconstructions using only part of the detector arch reveal this
as an artifact, and the case indeed a VOMIT one. Observe also a tendency of
artifact adjacent to the left wall of the pulmonary artery.

This illustrates painfully the truth that NO medical method can ever be full proof, but enhanced knowledge of the methods used can keep the number of misses as low as possible. At the introduction of new machinery extra care should be taken, and this was an early case after the introduction of 16 slices. Still, in all the routine PE cases we do we have not come across anything quite similar. ECG gating, (which we did not have), rescan at different pitch, reconstrucion using part of the detector arch could help resolve problems, but first you need to have " a high index of suspicion" as the saying goes...

22.10.04
Lauri Handolin

My traumaradiologist colleague Mika Koivikko [has commented], and he [notes] that one must always make sagittal CT reformats to get more accurate assessment of aorta. There are two attached scans: in the axial scan there is obvious artefacial finding on the anterior part of ascending aorta, that pulsation artefact is nicely seen on the sagittal reformat (see the steps with regular intervals on the anterior figure of the aorta). [...].




TRAUMA RADIOLOGY

VOMIT CASES:
AORTA
PANCREAS

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THE ANTIEMETIC PANEL

Sal Sclafani
Trauma radiologist
New York

Bertil Leidner
Trauma Radiologist
Karolinska, Stockholm

Ken Mattox
Trauma & Thoracic Surgeon
Houston

WHAT IS VOMIT?

VOMIT is 'Victim of Medical Imaging Technology'. A term used collectively to describe misuse or misreading of imaging studies. Often associated with VOMIT is BARF: Brainless Application of Radiologic Findings.

The term is clearly biased and overused, yet hass a sound principle - that inappropriate radiology may be worse than no radiology at all.

These pages will present these cases (usually discussed by the Trauma-list, and have the films reviewed by a select panel, as well as reads by other physicians).

If you have a case that you think classifies as a potential VOMIT, please email a brief outline and the images to 'antiemetic@trauma.org'.

If you would like to add your read of these images, please email 'antiemetic@trauma.org'.

 

trauma.org 9:10, October 2004