Cysts can form in various parts of the body and at any age. The causes are diverse.
Some cysts develop due to a blockage in a cavity that produces or contains fluid. For instance, if the duct of a sebaceous gland in the skin is blocked, a sebaceous cyst (a type of blackhead) can form.
In other cases, cysts arise due to chronic diseases (such as lung cysts in cystic fibrosis), genetic disorders (like polycystic kidney disease or cystic liver), tumors, or developmental disorders in the embryo.
Infections with parasites (such as the dog or fox tapeworm: echinococcosis) can also cause organ cysts. Additionally, cysts can form under the influence of hormones, such as in the breast, ovaries, or testicles.
Common types of cysts include:
- Kidney cysts
- Liver cysts
- Ovarian cysts
- Hydrocele (fluid in the scrotum)
- Baker’s cyst (behind the knee)
- Thyroid cysts
- Cysts in glands of the eyelid
- Sebaceous cyst (atheroma)
- Breast cysts
- Bone cysts
- Root cysts of teeth
A “true cyst” is lined with cells, while a pseudocyst is surrounded by connective tissue.
Symptoms and Examinations of Cysts
Symptoms
The symptoms caused by cysts depend on their type, location, and size. Some cysts are noticeable due to a visible or palpable swelling, such as a breast cyst. A Baker’s cyst behind the knee, when large enough, can also be felt, possibly causing a vague pressure sensation, pain, and even numbness in the lower leg.
Other cysts go unnoticed for a long time because they are located in internal organs (such as the kidney or liver). Whether a cyst causes discomfort or not does not indicate whether it is benign or malignant (most cysts are benign).
Examinations
Cysts in internal organs that do not cause symptoms are often discovered incidentally—during an ultrasound, for example, performed for other reasons or as part of a routine examination.
Additional tests may sometimes be necessary to determine the cyst’s size and cause, including:
- Computed tomography (CT)
- Magnetic resonance imaging (MRI)
- X-rays
- Blood tests
- Cyst aspiration (a doctor uses a fine hollow needle to withdraw fluid from the cyst to examine it in a lab)
Kidney Cysts
Kidney cysts can appear singly or in clusters on one or both kidneys. They typically do not cause symptoms and are often discovered by chance. Large cysts, however, can cause pain in the back or abdomen.
Kidney cysts may become inflamed, rupture, or bleed. Rarely, they turn malignant. Occasionally, they are associated with a tumor of the blood vessels (hemangioblastoma) of the cerebellum or retina. This inherited disease is known as von Hippel-Lindau syndrome.
Kidney cysts are rare in people under 30. With increasing age, they become more common—over 20% of people over 60 have one or more kidney cysts. A cyst in the kidney that causes no issues generally does not require treatment. Large cysts causing pain or complications can be punctured by a doctor to drain the fluid, which can then be examined under a microscope. In some cases, the cyst may need to be sclerosed or removed surgically.
Polycystic Kidney Disease (PKD)
Simple kidney cysts should not be confused with polycystic kidney disease (ADPKD). This genetic disorder affects about one in every 1,000 people. Due to genetic mutations (in the PKD1 or PKD2 genes), patients develop more and more kidney cysts over time, eventually impairing kidney function. By ages 50 to 60, most patients experience kidney failure.
The disease can also affect other organs, leading to cysts in the pancreas, liver, lungs, spleen, ovaries, uterus, testicles, or thyroid. Some patients also develop bulges in the walls of the main artery (aortic aneurysm) or intestinal walls (diverticulosis).
ADPKD can lead to various complications and is currently incurable. Treatment is only necessary when symptoms like urinary retention or urinary tract infections occur.