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Epidural And Subdural Hematomas Dangerous Blood Clots On The Brain Article
Epidural and Subdural Hematomas: Dangerous Blood Clots on the Brain
from: Gary CordingleyTo understand epidural and subdural hematomas -- two serious
consequences of head injuries -- we need to know the basic
anatomy of the brain and its coverings. Imagine an evil
carpenter with an electric drill intent on drilling into a
person's brain. What layers would the drill encounter in its
passage from the outside of the head to its destination?
The drill would pass through the skin and then the skull
(braincase) before penetrating a series of three membranes
comprising the meninges. In sequence, the three membranes are
the dura mater (Latin for "tough mother"), the arachnoid mater
(cobwebby mother) and the pia mater (tender mother) and then
finally the brain itself.
Epidural and subdural hematomas are alike in that they are
masses of clotted blood (hematomas) caused by head trauma and
deposited outside the brain but inside the skull. However, they
differ in their locations relative to the dura mater. An
epidural hematoma lies outside (on top of) the dura mater, while
a subdural hematoma lies inside (beneath) the dura mater and
outside the arachnoid mater. Thus, the locations of the two
kinds of hematoma are encoded in their names -- "epi" is Greek
for "upon" and "sub" is Latin for "below." A third kind of
hematoma caused by head injuries is traumatic intracerebral
hemorrhage. These occur within the brain tissue itself and are
no less serious than those outside the brain, but are not the
subject of the current essay.
Epidural and subdural hematomas are produced by ruptures of
different blood vessels. Epidural hematomas are usually caused
by bleeding from an artery that nourishes the meninges known as
the middle meningeal artery, while subdural hematomas are
usually due to bleeding from veins that drain blood away from
the surface of the brain.
Yet another difference between epidural and subdural hematomas
is what they look like on computed tomographic (CT) scans. When
the bleeding was recent, both show up as intensely bright
objects on the scan, but the shapes of the blood clots are
different. In epidural hematomas the blood is more limited in
its spread because it has to push harder to move outward in the
tight space between the inner surface of the skull and the outer
surface of the dura mater. In contrast, the bleeding that
produces subdural hematomas is more free to spread in the looser
space beneath the dura mater and typically runs from the front
of the head to the rear.
One issue that applies to both kinds of hematomas is that they
occupy space -- sometimes a lot of it -- within the braincase
where there isn't a lot of extra space to go around. As they
expand they compress the brain tissue next to them and
additionally raise the pressure within the skull which can
damage the rest of the brain. Moreover, the hematoma is not
necessarily the only problem caused by the head injury. The blow
to the head that caused the bleed can also damage the brain
tissue directly.
Who gets epidural hematomas? They usually occur in people with
obvious and significant blows to the head, as from motor vehicle
accidents. In one study they were present in 10% of head-injured
patients who arrived at an emergency department in coma, but
they can also be seen in conscious patients. Epidural hematomas
usually occur in conjunction with skull fractures, and this is
no coincidence, as the ruptured blood vessel often lies beneath
the fracture. The presence of an epidural hematoma signifies a
highly dangerous condition. Between 5 and 43% of people who have
them die. Emergency surgery to remove the clot is the usual
treatment.
When considering subdural hematomas, it is useful to divide them
into acute and chronic varieties, with "acute" meaning the
hematoma is new, and "chronic" meaning it has been present for
at least three weeks. (The hematoma can also pass through a
"subacute" phase, meaning that it has been present for 3 days to
3 weeks.) By the time an acute subdural hematoma has become
chronic, it is a thick liquid instead of a solid blood clot, and
also appear darker on CT scans.
Acute subdural hematomas usually occur in people with obvious
and significant blows to the head. In one study they were
present in 24% of the patients who arrived at an emergency
department in coma, but can be present in non-comatose patients
as well. Acute subdural hematomas are associated with a death
rate between 30 and 90%, with a figure of 60% typically cited.
Emergency surgery is the usual treatment, though studies have
shown that alert patients with small subdural hematomas can do
as well without surgery if monitored closely for signs of
worsening.
Infants are also vulnerable to acute subdural hematomas.
Neurosurgeons at the Kaohsiung Medical University in Taiwan
reviewed records on 21 children, ages 6 days to 12 months, who
had acute subdural hematomas. In this case series, "shaken baby
syndrome" was the most common cause. Eight of the infants
underwent an immediate operation, and another 11 required
delayed surgery. While most of the children did well, one baby
died and another 7 sustained moderate to severe disabilities
from their injuries.
Chronic subdural hematomas often show up in patients over 60
years of age in whom the head injuries that caused them might
have seemed trivial when they occurred, or might even have been
forgotten. Older people are especially vulnerable due to the
fact that their brains have atrophied (shrunk) and the veins
draining the surface of the brain are stretched and fragile,
easily disrupted by glancing blows. Risk of subdural hematoma
rises still higher if the individual falls a lot, drinks alcohol
a lot or takes blood-thinning medication.
Subdural hematomas can expand progressively to the point of
causing symptoms like headache, slurred speech, confusion,
lethargy, unsteadiness or even a seizure. Surgery to remove the
hematoma and stop the bleeding is the typical treatment, and 93
to 97% of patients survive to 30 days after surgery. Most regain
their pre-injury level of function. Milder cases of chronic
subdural hematoma can be monitored without surgery.
(C) 2006 by Gary Cordingley
About the author:
Gary Cordingley, MD, PhD, is a clinical neurologist, teacher and
researcher who works in Athens, Ohio. For more health-related
articles see his websites at:
href="http://www.cordingleyneurology.com">http://www.cordingleyne
urology.com and
href="http://www.neurologyarticles.com">http://www.neurologyartic
les.com