| 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).
[...].
|
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'.
|
