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Hi, I'm Jim Smirniotopoulos
and today's MedPix video is on imaging
brain hemorrhage. We have no significant financial disclosures
and the opinions expressed herein are those of the author and should not be
construed as being
official. Hemorrhage can have a very complex appearance on
MR and CT. The appearance on MR
is especially going to change based on the scan pulse sequence
and the time after the hemorrhage has occurred. We have MR scan here showing
micro hemorrhages from amyloid angiopathy ...
a blood fluid level from pituitary apoplexy ...
multiple hemorrhagic Mets on a CT scan ...
hemorrhagic transformation of a cerebral infarction ...
and two extra axial blood collections: an epidural hematoma; and, a sub-dural hematoma.
Let's think more closely about how blood should appear
on imaging. What is blood? Blood is a mixture of fluid (plasma) and cells -
approximately 35 to 45 percent red cells -
that is your hematocrit. If we think about flowing whole blood, the red cells
and the fluid are
intermixed. But, if we allow blood to clot or to settle out
by sedimentation
or by gravity, we can separate the serum (plasma) -
which has a very low attenuation like water, of 0 to 10 Hounsfield units -
from the red cell mass - which is going to have a high attenuation of 60
to 90 Hounsfield units. Of course,
the low attenuation of the serum will be dark on the CT scan;
and, the high attenuation or the red cells will be white.
On a CT scan, if we think about the normal density of the brain,
it falls between about 20 and forty Hounsfield units.
An acute extra axial subdural hematoma is going to be hyper attenuating (white)
in a patient with a normal hematocrit - hyperdense
with a Hounsfield values 60 to 90 units
If the patient is untreated, after several weeks - in the chronic time frame -
the blood will be digested and break-down. It will become liquefied;
and, we will have a low attenuation or a hypoattenuating collection about 0 to 10
Hounsfield units.
Of course if blood starts white (dense) ends up being black (lucent)
it must pass through a phase where it will have nearly the same
attenuation or density as the adjacent brain - the "isodense" or "iso-attenuating" phase.
This is the subacute appearance up a subdural hematoma
where it is nearly isodense to brain at about twenty
to 40 Hounsfield units. Now the appearance on MR is much more complex. Blood is
like a chemistry experiment; and, we have to think about the
oxidative state of the iron in the hemoglobin molecule
will change the signal intensity. We also talk about the susceptibility
and paramagnetic effects of the iron moiety in the various hemoglobin products.
At the RSNA 2011 there was a wonderful graphical
representation of how blood products
change the signal intensity on MR. The vertical axis is the signal intensity on T1
the horizontal axis is T2 signal. A hyper acute hemorrhage will have
intracellular oxyhemoglobin - which may be bright
on the T2 weighted image, yet isointense to brain on T1.
After several hours, we will have the conversion oxyhemoglobin to
de-oxyhemoglobin - which is going to be quite dark on T2-weighted
images.
After several days the intracellular de-oxyhemoglobin
is converted to met-hemoglobin. Intracellular met-hemoglobin is going to be bright
on the T1-weighted image but remains dark on the T2 sequences.
Wait several days more, and we will see the breakdown of the red cell membrane
and the release of methemoglobin into the aqueous solution of the liquefied hematoma.
In solution, the now extra-cellular methemoglobin is bright on both the T1
and the T2-weighted images. Wait days, to several weeks later
and macrophages - scavenger cells will come in
to clean up the blood products. Within macrophages (and also in astrocytes) methemoglobin is converted to ferritin and hemosiderin.
Now, in the late phase, we once again we have been intracellular blood
products - protein with iron.
The intracellular ferritin and/or hemosiderin
are both going to be dark on T2-weighted images.
In this phase, the old blood may be slightly hypointinse or isointense
on the T1-weighted image. Wo we have this very complex progression that we show on a
two column multiple three row chart showing the pattern of
changes of the signal intensity over time on T1 and T2 -weighted images.
Some people have summarized whether the blood product is
isointense, bright (hyperintense)
or dark (hypointense) by this mnemonic: I:B (iso on T1: bright on T2)
I:I iso on both T1&Tw I:D for T1-iso and T2-dark
BD for bright (T1) and dark (T2) BB for bright (T1) and bright (T2)
and, finally - DD for dark (T1) & dark (T2). Describing the transformation of blood products over time.
But, even this is hard to remember, so
a good mnemonic tool is to remember this:
I Be Iddy Biddy BaBy Do-Do or
Iso bright then Iso dark then bright dark
then bright bright and finally dark dark for chronic
hemorrhage (ferritin and hemosiderin).
This has been Jim Smirniotopoulos, and I approve this message.
Thank you very much for your kind attention.