Cyst — What It Means on Your Imaging Report

Quick Answer

A cyst is a fluid-filled sac that appears on imaging — the vast majority of cysts are benign and do not require treatment.

What Is a Cyst?

A cyst is a closed, sac-like pocket of tissue that is filled with fluid, semi-solid material, or air. On imaging, cysts have a distinctive appearance: they are usually round or oval with smooth, well-defined borders, and their interior appears dark on ultrasound (because fluid transmits sound waves differently than solid tissue) or very dark on CT scans.

Cysts are one of the most common findings in medical imaging. They can occur in almost any organ, including the kidneys, liver, ovaries, breasts, thyroid, and brain. Most cysts form naturally and are simply part of how the body functions. For example, ovarian cysts frequently develop during the normal menstrual cycle and resolve on their own.

The key distinction radiologists make is between a simple cyst and a complex cyst. A simple cyst is entirely fluid-filled with thin, smooth walls — these are almost always benign. A complex cyst may contain solid components, thick walls, or internal divisions (called septations), and may require further evaluation.

When You Might See This on Your Report

Cysts show up frequently across many imaging types:

• Ultrasound — the best tool for evaluating cysts. Ovarian cysts, thyroid cysts, and breast cysts are commonly found on ultrasound.
• CT scan — kidney cysts are one of the most common incidental findings on abdominal CT. Liver cysts are also very common.
• MRI — cysts in the brain (such as arachnoid cysts), spine, or pelvis
• Mammogram — breast cysts may appear as well-defined round densities

Your report may describe the cyst as "simple," "complex," or "septated." It will usually include the cyst's size and location.

Should I Be Worried?

In the vast majority of cases, no. Simple cysts are almost universally benign. They are so common that radiologists often describe them as a normal finding, particularly in the kidneys and liver. Kidney cysts, for example, are found in roughly 50% of adults over age 50 on CT imaging and are virtually never a cause for concern.

Here is a general guide:

• Simple cysts — benign. Usually need no treatment or follow-up.
• Mildly complex cysts — almost always benign. May require a follow-up scan to confirm stability.
• Complex cysts with solid components — less common but may need further evaluation, such as additional imaging or, rarely, a biopsy.

The Bosniak classification system is used specifically for kidney cysts to categorize them from class I (simple, benign) to class IV (likely malignant). If you see a Bosniak score on your report, ask your doctor to explain what category your cyst falls into.

What Should I Do Next?

1. Check whether the cyst is described as "simple" or "complex" in your report. Simple cysts are benign and typically need no follow-up.
2. Read the Impression section for the radiologist's recommendation. Many cyst findings end with "no further workup needed."
3. Follow up with your doctor if the report recommends monitoring or further evaluation, especially for complex cysts.
4. Do not worry about simple cysts. They are extremely common, usually cause no symptoms, and almost never require treatment.
5. Track any cysts over time if your doctor recommends it. A follow-up scan showing a stable or shrinking cyst is very reassuring.