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Subdural Hygroma

Definition – What is Subdural Hygroma?

A general hygroma is a capsule that is filled with fluid and is surrounded by a layer of fibrous tissue. Some medical personnel refer to them as hydromas. Not only can people have hygromas but also animals. They can be associated with other medical problems or benign in nature. It all depends on what the underlying reason was for the sac to develop to begin with.

In a subdural hygroma it is a subdural body of cerebrospinal fluid without blood. Cerebrospinal fluid is a colorless, clear body fluid that is found in your spine and brain and acts like a cushion for your brain’s cortex, which is your brain’s outer layer of neural tissue. This fluid provides protection to your brain inside your skull. This type of hygroma is often seen in elderly patients but can also be seen in children. Most of these types of hygromas are small but there are some larger ones that can cause a secondary localized mass.

Subdural Hygroma in Infants

When a subdural hygroma is seen in infants and children it is often after they have had an infection but it could also be from a minor head injury from falling, hitting their head, or even child abuse.


What symptoms a person has with a general hygroma depends on the cause.

Trauma – there is usually localized swelling that over time will normally increase as the hygroma grows and starts to become more prominent.

When a person has a subdural hygroma some of the symptoms that can be seen include:

  • Headache
  • Confusion
  • Mild fever
  • Drowsiness


There are some general hygromas that develop over time, normally in response to a trauma while others are congenital in nature, which means it was present at birth.

  • Trauma causes – this type will normally develop at your joints like your elbows and knees. They are sometimes referred to as false bursae. The reason is because they mimic the structure of a bursa. A bursa is a tough capsule that surrounds your joints and is designed to reduce friction so your joint can move freely with only minimal resistance, like your shoulder, knee, or elbow. Bursa is also small-fluid sacs.
  • Congenital causes – during the development of the fetus errors occur that can lead to the formation of a cyst that is normally around the neck or head. At birth these fluid-filled sacs may be visible but at other times it may not become apparent until the infant has gotten older along with the growth aging. With congenital hydromas they are not usually inherited because there are conditions in the womb that has lead to their development. This growth could sometimes be associated with chromosomal anomalies that could be spontaneous in nature or inherited. In this case the patient may have other medical problems.

With subdural hygromas it is thought that they are caused from:

  • Chronic subdural hematomas, which is a localized collection of blood outside of your blood vessels that gathers between your brain and dura mater, which is the thick membrane of the outermost of the three layers of the membranes that surround your spinal cord and brain. With a chronic subdural hematoma they usually develop over a period of days to often weeks after a minor head trauma.
  • A sudden decrease in pressure from ventricular shunting, which is a surgical procedure to put a tube in one of the fluid-filled chambers inside your brain. With this procedure there could be a leakage of your cerebrospinal fluid into your subdural space. This is especially true in cases with moderate to severe brain atrophy, which is a loss of neurons and the connections between the two.

If it is an acute subdural hygroma they can be caused by head trauma but can also happen after a neurosurgical procedure. They have also been associated with different other conditions such as:

  • Lymphoma, which is a group of blood cell tumors and often refers to just the ones that are cancerous
  • Dehydration in the elderly
  • Connective tissue diseases


When a person displays the symptoms of a subdural hygroma they can be relieved by draining the subdural fluid. If a person is suffering from an acute subdural hygroma they can be a possible neurosurgical emergency that requires decompression.

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