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Subdural hematoma adam.about.com | LearningRadiology - Subdural Hematoma learningradiology.com | Subdural Hematoma Recovery brainandspinalcord.org | : Chronic Subdural Hematoma (Hemorrhage) : theneuromedicalcenter.com |
 A subdural haematoma (subdural hematoma) or subdural hemorrhage (SDH) is a form of traumatic brain injury in which blood gathers within the inner meningeal layer of the dura matter (the outer protective covering of the brain). Usually resulting from tears in veins that cross the subdural space, 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. In contrast, epidural hematomas are usually caused by tears in arteries, resulting in a buildup of blood between the dura and the skull.
[edit] CausesSubdural hematomas are most often caused by head injury, when fast changing velocities within the skull may stretch and tear small bridging veins. Subdural hematomas due to head injury are described as traumatic. Much more common than epidural hemorrhages, subdural hemorrhages generally result from shearing injuries due to various rotational or linear forces.[1][2] Subdural hemorrhage is a classic finding in shaken baby syndrome, in which similar shearing forces classically cause intra- and pre-retinal hemorrhages. Subdural hematoma is also commonly seen in the elderly and in alcoholics, who have evidence of cerebral atrophy. Cerebral atrophy increases the length the bridging veins have to traverse between the two meningeal layers, hence increasing the likelihood of shearing forces causing a tear. It is also more common in patients on anticoagulants, especially aspirin and warfarin. Patients on these medications can have a subdural hematoma with a minor injury. [edit] Signs and symptomsSymptoms of subdural hemorrhage have a slower onset than those of epidural hemorrhages 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.[3] 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.[2] Other signs and symptoms of subdural hematoma can include any combination of the following:
[edit] FeaturesSubdural hematomas occur most often around the tops and sides of the frontal and parietal lobes.[1][2] They also occur in the posterior cranial fossa, and near the falx cerebri and tentorium cerebelli.[2] Unlike epidural hematomas, which cannot expand past the sutures of the skull, subdural hematomas can expand along the inside of the skull, creating a concave shape that follows the curve of the brain, stopping only at the dural reflections like the tentorium cerebelli and falx cerebri. On a CT scan, subdural hematomas are classically crescent-shaped, with a concave surface away from the skull. However, they can have a convex appearance, especially in the early stage of bleeding. This may cause difficulty in distinguishing between subdural and epidural hemorrhages. A more reliable indicator of subdural hemorrhage is its involvement of a larger portion of the cerebral hemisphere since it can cross suture lines, unlike an epidural hemorrhage. 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. [edit] SubtypesSubdural 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 contusions.[2] 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 force (acceleration/deceleration) required to cause them cause other severe injuries as well.[4] The mortality rate associated with acute subdural hematoma is around 60 to 80%.[5] 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.[6] They may not be discovered until they present clinically months or years after a head injury.[7] The bleeding from a chronic bleed is slow, probably from repeated minor bleeds, and usually stops by itself.[1][8] Since these bleeds progress slowly, they present the chance to be stopped before they cause significant damage. Small chronic 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".[2] Chronic subdural hematomas are common in the elderly.[7] [edit] PathophysiologyCollected 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.[6] The collected blood may even develop its own membrane.[9] 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.[1] 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.[8] 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. [edit] TreatmentIt 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. Some small subdural hematomas can be managed by careful monitoring until the body heals itself. Other small subdural hematomas can be managed by inserting a temporary small catheter through a hole drilled through the skull and sucking out the hematoma; this procedure can be done at the bedside. 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.[10][11] Postoperative complications include increased intracranial pressure, brain edema, new or recurrent bleeding, infection, and seizure. The injured vessels must be repaired. [edit] Risk factorsFactors 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 veins 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.[6] Infants, too, have larger subdural spaces and are more predisposed to subdural bleeds than are young adults.[2] For this reason, subdural hematoma is a common finding in shaken baby syndrome. In juveniles, an arachnoid cyst is a risk factor for a subdural hematoma.[12] Other risk factors for subdural bleeds include taking blood thinners (anticoagulants), long-term alcohol abuse, and dementia. [edit] External links
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