A , or a '''subdural
Hemorrhage ''' (SDH), is a form of
Traumatic Brain Injury in which
Blood collects between the
Dura (the outer protective covering of the
Brain ) and the
Arachnoid (the middle layer of the
Meninges ). Unlike in epidural hematomas, which are usually caused by tears in
Arteries , subdural bleeding usually results from tears in veins that cross the
Subdural Space . This bleeding often separates the dura and the arachnoid layers. Subdural hemorrhages may cause an increase in
Intracranial Pressure (ICP), which can cause compression of and damage to delicate brain tissue. Acute subdural hematoma (ASDH) has a high mortality rate and is a severe
Medical Emergency . As such, it has become a recurring plot device on current medical dramas such as the television series
ER .
Subdural hematomas are most often caused by
Head Injury , when rapidly changing
Velocities within the
Skull may stretch and tear small bridging
Vein s. Subdural hematomas due to head injury are described as
Traumatic . Much more common than
Epidural Hemorrhage s, subdural hemorrhages generally result from
Shearing Injuries due to rotational or linear forces (University of Vermont; Wagner, 2004).
Symptoms of subdural hemorrhage have a slower onset than those of
Epidural Hemorrhage s because the lower pressure veins bleed more slowly than arteries. Thus, signs and symptoms may show up within 24 hours but can be delayed as much as 2 weeks (Sanders and McKenna, 2001). If the bleeds are large enough to put pressure on the brain, signs of increased
ICP or damage to part of the brain will be present (Wagner, 2004).
Other
Signs and
Symptom s of subdural hematoma include the following:
Most of the time, subdural hematomas occur around the tops and sides of the
Frontal and
Parietal Lobe s (University of Vermont; Wagner, 2004). They also occur in the posterior
Fossa , and near the
Falx Cerebri and
Tentorium (Wagner, 2004). Unlike
Epidural Hematoma s, which cannot expand past the
Sutures Of The Skull , subdural hematomas can expand along the inside of the skull, creating a convex shape that follows the curve of the brain, stopping only at the
Dural Reflection s like the tentorium and falx cerebri.
On a
CT Scan , subdural hematomas have a crescentic shape, with a concave surface away from the skull. Unlike
Epidural Hematoma s, subdural bleeds can cross
Skull Suture s, so they can spread along the inside of the skull. Subdural blood can also be seen as a layering density along the
Tentorium Cerebelli . This can be a chronic, stable process, since the feeding system is low-pressure. In such cases, subtle signs of bleeding such as effacement of
Sulci or medial displacement of the junction between
Gray Matter and
White Matter may be apparent. A chronic bleed can be the same density as brain tissue (called
Isodense to brain), meaning that it will show up on CT scan as the same shade as brain tissue, potentially obscuring the finding.
Subdural hematomas are divided into
Acute , subacute, and
Chronic , depending on their speed of onset. Acute subdural hematomas that are due to trauma are the most lethal of all head injuries and have a high
Mortality Rate if they are not rapidly treated with surgical decompression.
Acute bleeds develop after high speed acceleration or deceleration injuries and are increasingly severe with larger hematomas. They are most severe if associated with
Cerebral Contusion s (Wagner, 2004). Though much faster than chronic subdural bleeds, acute subdural bleeding is usually venous and therefore slower than the usually arterial bleeding of an
Epidural Hemorrhage . Acute subdural bleeds have a high mortality rate, higher even than epidural hematomas and
Diffuse Brain Injuries , because the velocities necessary to cause them cause other severe injuries as well (Vinas and Pilistis, 2004; National Guideline Clearinghouse, 2005). The mortality rate associated with acute subdural hematoma is around 60 to 80% (Dawodu, 2004).
Chronic subdural bleeds develop over the period of days to weeks, often after minor head trauma, though such a cause is not identifiable in 50% of patients (Downie, 2001). The bleeding from a chronic bleed is slow, probably from repeated minor bleeds, and usually stops by itself (University of Vermont; Graham and Gennareli, 2000). Since these bleeds progress slowly, they present the chance to be stopped before they cause significant damage. Small subdural hematomas, those less than a centimeter wide, have much better outcomes than acute subdural bleeds: in one study, only 22% of patients with chronic subdural bleeds had outcomes worse than "good" or "complete recovery" (Wagner, 2004).
Collected blood from the subdural bleed may draw in water due to
Osmosis , causing it to expand, which may compress brain tissue and cause new bleeds by tearing other blood vessels (Downie, 2001). The collected blood may even develop its own membrane (McCaffrey, 2001).
In some subdural bleeds, the
Arachnoid Layer of the
Meninges is torn, and
Cerebrospinal Fluid (CSF) and blood both expand in the
Intracranial Space , increasing pressure (University of Vermont).
Substances that cause vasoconstriction may be released from the collected material in a subdural hematoma, causing further
Ischemia under the site by restricting blood flow to the brain (Graham and Gennareli, 2000). When the brain is denied adequate blood flow, a
Biochemical Cascade known as the
Ischemic Cascade is unleashed, and may ultimately lead to brain
Cell death.
The body gradually reabsorbs the clot and replaces it with
Granulation Tissue .
It is important that a patient receive medical assessment, including a complete
Neurological examination, after any head trauma. A
CT Scan or
MRI Scan will usually detect significant subdural hematomas.
Treatment of a subdural hematoma depends on its size and rate of growth. Small subdural hematomas can be managed by careful monitoring until the body heals itself. Large or symptomatic hematomas require a
Craniotomy , the surgical opening of the
Skull . A surgeon then opens the
Dura , removes the
Blood Clot with suction or irrigation, and identifies and controls sites of
Bleeding . Postoperative complications include increased
Intracranial Pressure , brain
Edema , new or recurrent
Bleeding ,
Infection , and
Seizure .
Factors increasing the risk of a subdural hematoma include very young or very old
Age . As the brain shrinks with age, the
Subdural Space enlarges and the
Vein s that traverse the space must travel over a wider distance, making them more vulnerable to tears. This and the fact that the elderly have more brittle veins make chronic subdural bleeds more common in older patients (Downie, 2001). Infants, too, have larger subdural spaces and are more predisposed to subdural bleeds than are young adults (Wagner, 2004).
Other risk factors for subdural bleeds include taking blood thinners (
Anticoagulant s), long-term
Alcohol Abuse , and
Dementia .
In addition to avoiding risk factors if possible, following safety precautions and wearing
Hard Hat s,
Helmet s, and
Seat Belt s can prevent serious head injuries.
# Dawodu S. 2004.
"Traumatic brain injury: Definition, epidemiology, pathophysiology" Emedicine.com.
# Downie A. 2001.
"Tutorial: CT in head trauma"
# Graham DI and Gennareli TA. Chapter 5, "Pathology of brain damage after head injury" Cooper P and Golfinos G. 2000. ''Head Injury'', 4th Ed. Morgan Hill, New York.
# McCaffrey P. 2001.
"The neuroscience on the web series: CMSD 336 neuropathologies of language and cognition." California State University, Chico.
#
National Guideline Clearinghouse . 2005. Firstgov.
# Sanders MJ and McKenna K. 2001. ''Mosby’s Paramedic Textbook'', 2nd revised Ed. Chapter 22, "Head and facial trauma." Mosby.
# Surinder KN and Raman K. 2005.
Extracranial redistribution causing rapid spontaneous resolution of acute subdural hematoma . ''Neuroimage,'' 53(1): 124
# University of Vermont College of Medicine.
"Neuropathology: Trauma to the CNS."
# Wagner AL. 2004.
"Subdural hematoma." Emedicine.com.
