Cyst
A fluid-filled sac — and on a scan report, usually a reassuring finding.
What it means
A closed sac containing fluid rather than solid tissue.
"Simple cyst" is one of the more reassuring phrases in radiology. Simple means thin-walled, filled with clear fluid, with no solid parts — and simple cysts in the kidney, liver, breast and ovary are almost always harmless.
Kidney and liver cysts are so common with age they are near-universal findings, and most need nothing at all.
"Complex cyst" is the phrase that carries weight — solid components, thick walls or internal divisions — and those get investigated further.
In practice
On ultrasound, CT and MRI reports, usually as an incidental finding.
Also in dermatology, where a sebaceous or epidermoid cyst under the skin is a common and benign thing.
Why it matters
If it says "simple cyst", take the reassurance — it is genuine.
If it says "complex", ask what the plan is, since that usually means further imaging or a specialist opinion.
An ovarian cyst causing sudden severe one-sided pain is different and urgent, because a cyst can twist or rupture. That needs same-day assessment.
Clinically reviewed by Dr Mohammad Zubair Khan, GMC 7563469
Last reviewed
August 30, 2026