What is a cyst and how is it treated in a patient with a diagnosed cyst?

What is a Cyst?

A cyst is an abnormal, closed sac or pocket in your body that contains fluid, gas, or semi-solid material, usually surrounded by a thin membrane or lining. 1

Understanding Cysts in Simple Terms

Think of a cyst as a small balloon filled with liquid that forms inside your body where it shouldn't be. These can develop in many different parts of your body—your breasts, liver, kidneys, bones, or other organs. 1

Key Features of Cysts:

• They are usually benign (not cancerous), meaning most cysts are harmless and won't spread to other parts of your body 2
• They have a wall or lining that separates them from surrounding tissue 1
• They contain fluid or other material inside, which can be clear, bloody, or thick depending on the type 2
• They can vary greatly in size, from very small (a few millimeters) to quite large (several centimeters or more) 3, 4

Types of Cysts (Using Breast Cysts as an Example)

Doctors classify cysts based on what they look like on imaging tests like ultrasound: 2

Simple Cysts (Benign - Not Dangerous)

• Completely filled with clear fluid 2
• Have thin, smooth walls 2
• Round or oval shape 2
• These are considered benign and safe 2
• Usually just need routine monitoring 2

Complicated Cysts (Usually Benign - Low Risk)

• Contain some debris or cloudy fluid inside 2
• Still have thin walls with no solid lumps 2
• Very low cancer risk (less than 2%) 2
• May need monitoring every 6-12 months for 1-2 years 2

Complex Cysts (Need Further Testing)

• Have thick walls or solid parts inside 2
• Contain both fluid and solid tissue 2
• Higher cancer risk (14-23%) 2
• Always require a biopsy (tissue sample) to check for cancer 2, 5

How Cysts Are Treated

Treatment depends entirely on what type of cyst you have and where it's located:

For Simple Cysts:

• If causing no symptoms: Just routine screening, no treatment needed 2
• If causing pain or discomfort: Your doctor can drain the fluid with a needle (aspiration) 2
• If bloody fluid comes out during drainage, it needs to be tested under a microscope 2

For Complicated Cysts:

• Two options: Either drain the fluid or monitor with ultrasound every 6-12 months for 1-2 years 2, 6
• Draining may be preferred if you might miss follow-up appointments 2, 6
• If the cyst grows larger, it needs a biopsy 2, 6

For Complex Cysts:

• Always require a biopsy to rule out cancer 2, 5
• A core needle biopsy (taking a small tissue sample) is the preferred method 5
• Treatment after biopsy depends on whether cancer is found 5

Important Warning Signs

Seek immediate medical attention if you experience: 2

• Sudden, severe pain (may indicate bleeding into the cyst) 2
• Fever lasting more than 3 days (may indicate infection) 2
• Rapid enlargement of a known cyst 2

Common Pitfalls to Avoid

• Don't assume all cysts are the same—the type matters greatly for determining cancer risk and treatment 2, 5
• Don't skip follow-up appointments if your doctor recommends monitoring, as cysts can change over time 2, 6
• Don't confuse "complicated" with "complex"—these sound similar but have very different cancer risks and require different management 5, 6

The Bottom Line

Most cysts are harmless fluid-filled sacs that either need no treatment or simple drainage. However, cysts with solid parts inside (complex cysts) require a biopsy to ensure they're not cancerous. Your doctor will use imaging tests like ultrasound to determine what type of cyst you have and recommend the appropriate next steps. 2, 5