Blood clots may form on or within the brain from multiple causes. They are divided into three groups based on temporal relationships: Acute (within 3 days of injury), subacute (between 4 and 20 days), and chronic (21 days or longer).
The major causes of intracranial hematomas may be divided into 5 basic groups:
- Traumatic head injury
- Hypertension
- Anticoagulation
- Vascular Diseases
- Miscellaneous Causes: Connective tissue diseases.
Traumatic head injury is the primary cause of death in 75,000 injuries annually in the Unites States. Fortunately of the 500,000 head injuries requiring hospital admission, 80% sustain minor injuries. Traumatic brain injury is a disease of young adult men in the age range of 15-24 years. Most of these injuries are sustained in a motor vehicle accident where alcohol is a significant aggravating factor.
Hypertension that is chronic can damage arterial vessel walls over many years resulting in a spontaneous hemorrhage. Those people who have incompletely treated hypertension that is severe have an additional risk factor.
Anticoagulation may be required on a long-term basis in patients that have had prior cardiac valve replacement, heart attacks and stroke. Strict management of coagulation times helps to decrease the incidence of complications.
Vascular disease such as cerebral aneurysm remains a problem. Aneurysms are often small and without symptoms until an episode of spontaneous rupture occurs. The typical aneurysm represents a weakening in an arterial wall looking much like a child's balloon. Arterio-venous malformations are abnormal collections of blood vessels where arteries connect to veins without the normal capillary interface. Other vascular abnormalities are less common but are still problematic.
Less common causes of bleeding occur in connective tissue disease where vessel walls may not be normal and are prone to failure.
Intracranial bleeding of different types can occur in the skull where the cerebral hemispheres reside:
- Epidural hematomas lie between the
skull and dura that covers the brain. They are often secondary to
a skull fracture that occurs in the temporal or parietal area of
the skull. In this region an artery lies between the skull and
dura. This artery is cut by the fracture and starts to bleed
forming the "epidural hematoma" (Fig.1). The usual mortality rate
ranges from 5 to 30%. Coexistent brain injury shifts the mortality
rate to the higher end of the spectrum. In patients who are awake
before surgery and without additional brain damage, 90+ % have a
favorable outcome following surgery.
-Fig1.jpg)
Figure
1
- Subdural hematomas are deeper in position situated between the dura and brain. The most common causes of this type of hematoma are trauma and long-term anticoagulation. The highest mortality and morbidity lies in the traumatic acute subdural group (Fig.2) since the hematoma is often associated with severe brain damage. The brain damage occurs at the time of traumatic impact to the head and if severe can cause death by itself. The combination of the subdural
hematoma and brain damage can form a deadly combination. Subdural hematomas associated with long-term anticoagulation represent a problem due to the patient's rapid deterioration and the time needed to reverse the anticoagulated state. Spontaneous chronic subdurals
have the best prognosis because the slow formation of the blood
clot pressing on the brain. The slow accumulation of blood allows
the brain to adapt to the pressure created by the blood clot and
minimizes associated brain damage.
-Fig2.JPG)
Figure
2
- Intracerebral Hematomas are still deeper in position and lie within the brain substance. These hematomas expand by compressing adjacent tissue and damaging neural connections, causing further brain damage. The neurological deficit depends on the location of the intracerebral hematoma. If the hematoma is in a critical motor area paralysis results; if the hematoma lies in a "silent" are of the brain complications may be minimal. The need for surgery depends on
the clinical condition of the patient, enlargement of the hematoma, or increasing intracranial pressure causing a shift or dysfunction of the brain.
- Subarachnoid hemorrhage: This
related condition occurs when a blood vessel bleeds into the
subarachnoid space, which is normally filled with cerebrospinal
fluid. This type of bleeding is associated with head injuries,
vascular malformations or ruptured aneurysms. Surgical treatment
of this condition involves a neurosurgical procedure to eliminate
the aneurysm or vascular malformation before a second or third
bleeding episode occurs. Most traumatic subarachnoid bleeding
clears spontaneously.
Another location of intracranial bleeding lies in the posterior fossa where the cerebellar hemispheres reside:
- Posterior Fossa Hematomas: Like
the hematomas above, these lesions may be epidural, subdural, and
intracerebral. They occur in about equal proportions with most
caused by trauma. Prior to computed tomography diagnosis was
difficult and often made upon autopsy. Computed tomography has
resulted in earlier diagnosis and treatment with improved patient
results.
