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 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. Infants, too, have larger subdural spaces and are more predisposed to subdural bleeds than are young adults. 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.

Other risk factors for subdural bleeds include taking blood thinners (anticoagulants), long-term alcohol abuse, dementia, and the presence of a cerebrospinal fluid leak.

Subdural hematomas are most often caused by head injury, when rapidly 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. 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 or antiplatelet drugs, such as warfarin and aspirin. Patients on these medications can have a subdural hematoma after a relatively minor traumatic event.

A further cause can be a reduction in cerebral spinal fluid pressure which can create a low pressure in the subarachnoid space, pulling the arachnoid away from the dura mater and leading to a rupture of the blood vessels.

A hematoma (US spelling) or haematoma (UK spelling) is a localized collection of blood outside the blood vessels, due to either disease or trauma including injury or surgery and may involve blood continuing to seep from broken capillaries. A hematoma is initially in liquid form spread among the tissues including in sacs between tissues where it may coagulate and solidify before blood is reabsorbed into blood vessels. An ecchymosis is a hematoma of the skin larger than 10mm.

They may occur among/within many areas such as skin and other organs, connective tissues, bone, joints and muscle.

A collection of blood (or even a hemorrhage) may be aggravated by anticoagulant medication (blood thinner). Blood seepage and collection of blood may occur if heparin is given via an intramuscular route; to avoid this, heparin must be given intravenously or subcutaneously.

It is not to be confused with hemangioma, which is an abnormal buildup/growth of blood vessels in the skin or internal organs.

Some hematomas are visible under the surface of the skin (commonly called bruises) or possibly felt as masses/lumps. Lumps may be caused by the limitation of the blood to a sac, subcutaneous or intramuscular tissue space isolated by fascial planes. This is a key anatomical feature that helps prevent injuries from causing massive blood loss. In most cases the hematoma such as a sac of blood eventually dissolves; however, in some cases they may continue to grow such as due to blood seepage or show no change. If the sac of blood does not disappear, then it may need to be surgically cleaned out/repaired.

The slow process of reabsorption of hematomas can allow the broken down blood cells and hemoglobin pigment to move in the connective tissue. For example, a patient who injures the base of his thumb might cause a hematoma, which will slowly move all through the finger within a week. Gravity is the main determinant of this process.

Hematomas on articulations can reduce mobility of a member and present roughly the same symptoms as a fracture.

In most cases, movement and exercise of the affected muscle is the best way to introduce the collection back into the blood stream.

A mis-diagnosis of a hematoma in the vertebra can sometimes occur; this is correctly called a hemangioma (buildup of cells) or a benign tumor.

A breast hematoma may appear due to direct trauma to the breast, for example from a sports injury or a road accident, for example a vehicle collision in which a seat belt injury occurs.

Hematoma can also be a consequence of breast surgery, usually due to post-operative bleeding. Bleeding may occur shortly after the intervention or a number of days later and can occur for cosmetic surgery (for example breast reduction or breast enhancement) and for non-cosmetic surgery (for example lymph node removal, lumpectomy, or mastectomy). More rarely, hematoma can result from breast biopsy.

Rarely, a breast hematoma can also occur spontaneously due to a rupture of blood vessels in the breast, especially in persons with coagulopathy or after long-term use of blood-thinning drugs such as aspirin or ibuprofen.

Small breast hematomas often resolve on their own within several days or weeks by means of reabsorption of the blood. Larger hematomas are more likely to lead to inflammation or fibrosis.

Breast hematomas can sometimes lead to skin discoloration, inflammation, or fever. When a hematoma resolves, it may become fibrotic, leaving behind scar tissue. A resolving hematoma may liquify to form a seroma.

Post-surgical breast hematomas can also impede wound healing and therefore impact the cosmetic outcome. Hematomas are furthermore one of the risk factors for breast surgical site infections. There is preliminary evidence that, after breast implant surgery, the presence of hematoma increases the risk of developing capsular contracture.

In mammography screening, scar tissue resulting from a breast hematoma can easily be confused with tumor tissue, especially in the first years following surgery. Ultimately, fat necrosis may occur in the concerned region of the breast.

There are many causes of subcutaneous hematomas including ecchymoses. Coagulopathies such as Hemophilia A may cause ecchymosis formation in children. The medication betamethasone can have the adverse effect of causing echhymosis.

Intracranial hemorrhage is a serious medical emergency because the buildup of blood within the skull can lead to increases in intracranial pressure, which can crush delicate brain tissue or limit its blood supply. Severe increases in intracranial pressure (ICP) can cause brain herniation, in which parts of the brain are squeezed past structures in the skull.

The anatomy of the epidural space is such that spinal epidural hematoma has a different presentation from intracranial epidural hematoma. In the spine, the epidural space contains loose fatty tissue and a network of large, thin-walled veins, referred to as the epidural venous plexus. The source of bleeding in spinal epidural hematoma is likely to be this venous plexus.

Intracranial bleeding occurs when a blood vessel within the skull is ruptured or leaks. It can result from physical trauma (as occurs in head injury) or nontraumatic causes (as occurs in hemorrhagic stroke) such as a ruptured aneurysm. Anticoagulant therapy, as well as disorders with blood clotting can heighten the risk that an intracranial hemorrhage will occur.

If diagnosed within the first few hours of presentation, the pooling blood may be evacuated using a syringe. Once the blood has clotted, removal by this method is no longer possible and the clot can be removed via an incision over the lump under local anesthetic. The incision is not stitched, but will heal very well. Care needs to be taken in regard to bleeding from the wound and possible infection with fecal bacteria. If left alone it will usually heal within a few days or weeks. The topical application of a cream containing a Heparinoid is often advised to clear the clot .

The risk of the development of a lymphocele is positively correlated to the extent of the removal of lymphatic tissue during surgery (lymphadenectomy). Surgery destroys and disrupts the normal channels of lymph flow. If the injury is minor, collateral channels will transport lymph fluid, but with extensive damage, fluid may accumulate in an anatomic space resulting in a lymphocele. Typical operations leading to lymphocysts are renal transplantation and radical pelvic surgery with lymph node removal because of prostatic or gynecologic cancer. Other factors that may predispose of lymphocele development are preoperative radiation therapy, heparin prophylaxis (used to prevent deep vein thrombosis), and tumor characteristics. After radical surgery for cervical and ovarian cancer studies with follow-up CT found lymphoceles in 20% and 32%, respectively. Typically they develop within 4 months after surgery.

Hematomas can be subdivided by size. By definition, ecchymoses are 1 centimeter in size or larger, and are therefore larger than petechiae ( less than 2 millimeters in diameter) or purpura (2 millimeters to 1 centimeter in diameter). Ecchymoses also have a more diffuse border than other purpura.

Blunt splenic trauma most often occurs in automobile accident victims, in which it is a leading cause of internal bleeding. However, any type of major impact directed to the spleen may cause splenic trauma. This can happen in bicycling accidents, when the handlebar is forced into the left subcostal margin, and into the spleen. The degree of injury ranges from subcapsular hematoma, to splenic rupture.

The most common cause of intracranial epidural hematoma is traumatic, although spontaneous hemorrhage is known to occur. Hemorrhages commonly result from acceleration-deceleration trauma and transverse forces. The majority of bleeds originate from meningeal arteries, particularly in the temporal region. 10% of epidural bleeds may be venous, due to shearing injury from rotational forces. Epidural hematoma commonly results from a blow to the side of the head. The pterion region which overlies the middle meningeal artery is relatively weak and prone to injury. Thus only 20 to 30% of epidural hematomas occur outside the region of the temporal bone. The brain may be injured by prominences on the inside of the skull as it scrapes past them. Epidural hematoma is usually found on the same side of the brain that was impacted by the blow, but on very rare occasions it can be due to a contrecoup injury.

Blunt splenic trauma occurs when a significant impact to the spleen from some outside source (i.e. automobile accident) damages or ruptures the spleen. Treatment varies depending on severity, but often consists of embolism or splenectomy.

It may cause seizures but cephalohematoma and caput will not cause seizure

Epidural hematoma is when bleeding occurs between the tough outer membrane covering the brain and the skull. Often there is loss of consciousness following a head injury, a brief regaining of consciousness, and then loss of consciousness again. Other symptoms may include headache, confusion, vomiting, and an inability to move parts of the body. Complications may include seizures.

The cause is typically head injury that results in a break of the temporal bone and bleeding from the middle meningeal artery. Occasionally it can occur as a result of a bleeding disorder or blood vessel malformation. Diagnosis is typically by a CT scan or MRI. When this condition occurs in the spine it is known as a spinal epidural hematoma.

Treatment in generally by urgent surgery in the form of a craniotomy or burr hole. Without treatment death typically results. The condition occurs in one to four percent of head injuries. Typically it occurs in young adults. Males are more often affected than females.

The majority (90%) result from applying a vacuum to the head at delivery (Ventouse assisted delivery). The vacuum assist ruptures the emissary veins (connections between dural sinus and scalp veins) leading to accumulation of blood under the aponeurosis of the scalp muscle and superficial to the periosteum. Subgaleal hematoma has a high frequency of occurrence of associated head trauma (40%), such as intracranial hemorrhage or skull fracture. The occurrence of these features does not correlate significantly with the severity of subgaleal hemorrhage.

Perianal hematoma are caused by the rupture of a small vein that drains blood from the anus. This rupture may be the result of forceful or strained bowel movement or caused by heavy lifting, coughing or straining. Once the rupture has formed, blood quickly pools within a few hours and, if left untreated, forms a clot.

Spinal epidural hematoma is bleeding into the epidural space in the spine. These may arise spontaneously (e.g. during childbirth), or as a rare complication of epiduralanaesthesia or of surgery (such as laminectomy). Symptoms usually include back pain which radiates to the arms or the legs. They may cause pressure on the spinal cord or cauda equina, which may present as pain, muscle weakness, or dysfunction of the bladder and bowel.

The best way to confirm the diagnosis is MRI. Risk factors include anatomical abnormalities and bleeding disorders.

Treatment is generally with emergency surgery. The risk following epidural anaesthesia is difficult to quantify; estimates vary from 1 per 10,000 to 1 per 100,000 epidural anaesthetics.

It has been suggested that suction drains placed during surgery and non-peritonisation (not closing the posterior peritoneum) may reduce the possibility of lymphocele development.

Smaller lymphoceles can be managed expectantly, and many lesions will regress over time. For symptomatic lesions a number of approaches are available and include fine needle aspiration with US or CT guidance, catheter insertion and drainage (with possible use of sclerosants), and surgical drainage. Sex and masturbation may cause the lymphocele to grow if it is in the genital area. It is suggested to avoid these activities for around one to one and a half months. Some exercises may also help to shrink it.

Intracerebral bleeds are the second most common cause of stroke, accounting for 10% of hospital admissions for stroke. High blood pressure raises the risks of spontaneous intracerebral hemorrhage by two to six times. More common in adults than in children, intraparenchymal bleeds are usually due to penetrating head trauma, but can also be due to depressed skull fractures. Acceleration-deceleration trauma, rupture of an aneurysm or arteriovenous malformation (AVM), and bleeding within a tumor are additional causes. Amyloid angiopathy is a not uncommon cause of intracerebral hemorrhage in patients over the age of 55. A very small proportion is due to cerebral venous sinus thrombosis.

Risk factors for ICH include:

- Hypertension (high blood pressure)

- Diabetes mellitus

- Menopause

- Cigarette smoking

- Excessive alcohol consumption

- Severe migraine

Traumautic intracerebral hematomas are divided into acute and delayed. Acute intracerebral hematomas occur at the time of the injury while delayed intracerebral hematomas have been reported from as early as 6 hours post injury to as long as several weeks.

Arachnoid cysts are seen in up to 1.1% of the population with a gender distribution of 2:1 male:female Only 20% of these have symptoms, usually from secondary hydrocephalus.

A study that looked at 2,536 healthy young males found a prevalence of 1.7% (95% CI 1.2 to 2.3%). Only a small percentage of the detected abnormalities require urgent medical attention.

The risk of death from an intraparenchymal bleed in traumatic brain injury is especially high when the injury occurs in the brain stem. Intraparenchymal bleeds within the medulla oblongata are almost always fatal, because they cause damage to cranial nerve X, the vagus nerve, which plays an important role in blood circulation and breathing. This kind of hemorrhage can also occur in the cortex or subcortical areas, usually in the frontal or temporal lobes when due to head injury, and sometimes in the cerebellum.

For spontaneous ICH seen on CT scan, the death rate (mortality) is 34–50% by 30 days after the insult, and half of the deaths occur in the first 2 days. Even though the majority of deaths occurs in the first days after ICH, survivors have a long term excess mortality of 27% compared to the general population.