This is part of our House MD Project series.

Click here to read the connection to the episode (spoiler alert!)


On episode 2 of season 2, named “Autopsy”, a 9 year old girl named Andie with terminal cancer (rhabdomyosarcoma) is suffering from hallucinations. Since her cancer was improving, it wasn’t the cause of her hallucinations. Deducing that her cancer has caused a blood clot in her brain, the team do a sort of autopsy while she is living to find out if she indeed has a blood clot in her brain which doesn’t show up on MRI, which she did.

First of all – what are blood clots?

Blood is the red liquid we all know that flows throughout our body in our blood vessels.

When a blood vessel gets injured, the body does all it can to repair the damage. It does this by forming a blood clot (which, in medicine, is called a thrombus). Remember when you were a kid and got wounded? Most of us find out then that the body forms this hardened “plug” on the wound, which stops it from bleeding. That’s the blood clot.

If the lining of a blood vessel becomes damaged, cells called platelets are recruited to the injured area to form an initial plug. The platelets, in turn, release chemicals that start a cascade of events called the clotting cascade. In the end, a protein called fibrin crosslinks with itself to form a mesh that makes up the final blood clot.

This video makes it easier to understand:

Where can a blood clot form?

Anywhere there is a blood vessel:

1. On arteries – These are the vessels that carry blood from the heart to our organs.
2. On veins – These carry blood back from the organs to the heart.
3. In the heart itself

When do they happen?

1. On veins: Vein clots usually occur when a person becomes immobilized. Usually our muscles help pump blood back to the heart from the veins. When we don’t move, this doesn’t happen, causing blood to stagnant in the area and causing a tendency towards blood clot formation.
   Examples of such situations include being hospitalized or bedridden after illness or surgery. Also with long trips in a car or a plane, with orthopedic injuries and casting, and also in pregnancy. One other important reason is cancer, which raises your chance of having blood clots formed (which is probably why the girl on the House episode had a blood clot).

   Some people also have a genetic tendency towards clotting, putting them at much higher risk than the rest of the population for vein clotting.

   You can read about a condition that forms when clots form in your leg veins here:
   Deep vein thrombosis – Clots in Your veins which can travel to your heart and lungs

   
   Being immobile for a long time can lead to clots in your veins. Photo by Patrick Powers.

2. On arteries:
   Here the mechanism is different. A disease process causes plaques to accumulate along the lining of the artery. They grow and occlude the blood vessel, causing diseases like a heart attack and stroke. You can read further about this process here:
   Understanding heart attacks part 1 – Atherosclerosis
3. In the heart:
   When a condition called atrial fibrillation occurs (it’s a condition in which the heart beats and pumps blood in an irregular fashion) blood tends to become stagnant along the walls of the heart. This may lead to clot formation. Also when there is damage to the heart, such as after a heart attack, clots can form.

What can they cause?

The list is long. Blood clots can cause all sorts of conditions. Those in the veins can cause deep vein thrombosis (see the article linked above) and clots that prevent your lungs from doing their job (a condition called pulmonary embolism).

Those in the arteries can lead to heart attacks, strokes, and peripheral arterial disease.

Clots can be sent from the heart when they occur there. They can then block blood supply to all sorts of organs in the body, causing problems there: from damage to your intestines, kidneys, or even the brain (as was seen on the House episode).

How are clots discovered?

Besides symptoms caused by each of the conditions listed above, which doctors can identify, other means can help as well.

For example, a clot in the leg can be discovered using ultrasound. When it reaches the lung, methods like a CT scan of the chest can discover it. When a clot blocks blood supply to the heart, an EKG can discover that.

There are also blood tests which show that a clot was formed.

There are as many methods of detecting a clot as there are diseases caused by excessive clotting.

How are they treated?

That really depends on the condition they caused. For example, if a clot was formed in the lungs or legs, a blood thinner is used. If it was formed in the heart, a procedure called cardiac catheterization may be needed.

You can read about the various treatments for each condition in the links around this article leading to the condition’s page.

How can blood clots be prevented?

1. Arterial clots: To prevent those you have to minimize your risk factors (an explanation about each is given in our atherosclerosis article) – this means lowering your blood pressure and cholesterol, taking care of diabetes, and quitting smoking. Exercising regularly can also help a lot.
2. Vein clots: It’s important to move around to avoid being immobile and letting the clots happen. You can read the whole list of preventative measures in our article. They include, among others, walking while on a plane, moving as much as you can after a surgery, etc.

Related posts:

1. Deep Vein Thrombosis – Clots in Your Veins Which Can Travel To Your Heart and Lungs
2. Are Obese Kids at Risk for Heart Disease?
3. Lung Cancer – Why You May Be at Risk (As Seen on House MD)