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What is an Aneurysm?

The kids took out a hose to wash our cars. We have several hoses, but the kids like the cheap nylon hose for most of the jobs around the house because it is light and easy to move around. They used the cheap nylon hose to fill up a bucket with some soap and water, got some sponges, and had a lot of fun cleaning the cars.

Then they put a spray nozzle on the hose to rinse the cars off. That’s when my daughter came into the house dripping wet to give me some bad news.

“Dad … there’s something wrong with the hose.”Aneurysm Wide View

I went outside and the hose was in bad shape.

“The hose has an aneurysm. Not going to last much longer.”

“What’s an ann-you-rism?” My youngest daughter asked.
Light bulb! What a perfect idea for a blog post!
I went to get my camera.

At this point, you’re probably asking yourself what a garden hose has to do with a discussion of aneurysms on a medical blog.
The simple answer is that the basic principles remain the same whether we’re talking about an abdominal aortic aneurysm, a brain aneurysm, a hose aneurysm, or even a balloon.

In medicine, an aneurysm occurs when there is a weakness in the walls of a blood vessel. As the weakness worsens, the walls of the blood vessel  around the weakness begin to balloon out. As the walls balloon out, they get weaker. The cycle continues until eventually the wall breaks.
Think of a balloon. When you first start blowing up the balloon, it is usually a lot more difficult to get the first breath of air inside. After that, it gets easier and easier to blow more air into the balloon until you reach the limits of the tensile strength in the balloon walls and … POP.

Aneurysms almost always occur under pressure, so they almost exclusively occur in arteries. Venous aneurysms can occur, but are rare. This makes sense. Go back to the balloon analogy. If you don’t blow to put pressure inside the balloon, it won’t get bigger. Now think of the hose analogy. My kids didn’t notice the swelling in the hose initially because they didn’t have the spray nozzle on the hose and the water ran freely out of the end – therefore no pressure built up inside the hose. Once the spray nozzle was in place, the water had nowhere to drain, causing pressure to build up inside the hose and making the aneurysm bulge.
Think about the human body. Higher blood pressure puts more pressure on aneurysm walls. Therefore, it’s a good idea to keep your blood pressure down with aneurysms.

Blood Vessel Walls

Blood vessels have many layers. Because arteries are under higher pressure than veins, arteries have more layers of reinforcement. See the picture above which was originally posted on Wikipedia. Note how there are more layers in the artery and how the smooth muscle layers are thicker than in the veins? Just like layers of clothing in the winter help to keep in warmth, layers in blood vessel walls help to maintain the blood vessel’s strength.

There are two basic types of aneurysms. Fusiform aneurysms are similar to what happens when you partially inflate a “twisty balloon”. Fusiform aneurysms involve the entire diameter of the blood vessel.
Berry or saccular aneurysms involve a bulge in the side of a blood vessel or can also occur where a blood vessel divides (often in the brain). Our hose had a berry aneurysm.

Now here’s the cool part of the hose analogy (click on the pictures to enlarge).

Note the yellow nylon coating covering the hose. Now note where the aneurysm occurred. See how the aneurysm is bulging between the torn area on the nylon reinforcement? The same thing happens in blood vessels. If one or more layers of a blood vessel weaken or break down, an aneurysm is more likely to occur at that weak spot. As the bulge gets larger, it gets weaker and weaker.

After I saw the hose, I went back inside and got my camera so I could take pictures of it. I took a few initial pictures and went around to the side of the house to turn off the water so that I could show what an aneurysm looks like when it isn’t under pressure. Before I got there, I heard the kids yelling. I went back to the driveway and … the aneurysm had ruptured. Water was squirting out from the end of the hose.
A post mortem picture of the hose shows how thin the walls of the aneurysm had become.

Keep in mind that there are many differences between the hose model and the human body. The purpose of this post was to help non-medical people understand the basics about aneurysms. You can still learn a lot from an old garden hose, though.

Need more information about aneurysms? The links in the article should help. You can always ask your doctor for more information. I’ll try to update this post if I find other helpful links.


  1. Nicely done, WC…
    Love those kinds of lessons!!

  2. What,? No attempt at old fashion extra vascular repair with duct tape? ER docs must be making a lot of money taking out staples.

  3. I’m surprized you didn’t fix it the Vascular surgeon’s way–stick a catheter in way far away, run it to the defect, and then stent it. Charge a bunch of bucks.

  4. Good lesson for the kids and all of us. I appreciate your creativity.

    My grandfather died of an aneurysm in his sleep, although don’t know what kind. Peaceful way to go.

    Ha – the duct tape might have worked. :)

    I thought you were going to say that they got water everywhere …in windows, the car and on them. :)

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