Thyroid Cyst vs Nodule: What Is the Difference?

A thyroid cyst is one kind of thyroid nodule. ‘Nodule’ is the general word for any lump in the thyroid; a cyst is a nodule that is filled with fluid, or partly fluid and partly solid. Cleveland Clinic notes that cystic nodules pose a low risk of cancer, while the risk is higher in solid nodules.

Most thyroid nodules of any kind are benign. Cleveland Clinic and the American Thyroid Association both state that more than 90% of nodules found in adults are not cancer. This guide explains the wording you may see on an ultrasound report. It cannot tell you what your own nodule is or what should happen next.

Many cysts are found by chance, on a scan done for another reason, rather than as a lump someone can feel. Ultrasound is the main test used to tell a fluid-filled nodule from a solid one. The American Thyroid Association notes that ultrasound can easily show whether a nodule is solid or cystic, and that some ultrasound features are seen more often in thyroid cancer than in benign nodules. That is why the report describes several features, not just the size.

Most thyroid cysts cause no symptoms. A large nodule can press on the windpipe or food pipe. Contact a clinician promptly if you have new or worsening trouble swallowing, a feeling of choking, or hoarseness or voice changes that do not settle.

If you are struggling to breathe or have noisy breathing, call your local emergency number. Do not wait for a planned scan or biopsy appointment.

MedlinePlus advises contacting a provider if you see or feel a new lump in your neck. If you already have a known cyst and notice that it looks or feels noticeably bigger, tell the team managing it rather than waiting for the next routine scan.

Radiologists describe a nodule's make-up, called its composition, using standard words. The American College of Radiology's TI-RADS system scores composition as one of five ultrasound features.

• Purely cystic, or cystic or almost completely cystic: the nodule is fluid with little or no solid tissue. This scores 0 points for composition.
• Spongiform: the nodule is made mostly of many tiny fluid spaces, like a sponge. This also scores 0 points for composition.
• Mixed cystic and solid: there is a solid part as well as fluid. This scores 1 point, and the solid part's other features are then assessed.
• Solid or almost completely solid: little or no fluid. This scores 2 points.

Composition is only one feature. The radiologist also looks at echogenicity (how dark the tissue appears), shape, margins and small bright spots called echogenic foci. In a mixed nodule, these features in the solid part can add points, so two mixed nodules can end up with quite different overall scores.

A cyst that is fluid only usually scores very low overall. In the ACR reporting template, the two lowest categories, TR1 and TR2, carry a recommendation of no biopsy and no follow-up. For how scores and nodule size combine in the middle categories, see our guide to TI-RADS 3 thyroid nodules rather than trying to score a report yourself.

Fine needle aspiration (FNA) uses a thin needle, usually guided by ultrasound, to take cells from a nodule for a pathologist to examine. Whether it is advised depends on the full ultrasound pattern and the nodule's size, not on the word ‘cyst’ alone. Cleveland Clinic notes that larger cysts may be monitored or biopsied.

Cystic nodules can be harder to sample. The American Thyroid Association says a nondiagnostic result is common when the nodule is a cyst, and may lead to a second biopsy. An Endotext chapter on FNA advises draining the fluid fully and then sampling any remaining solid tissue, because fluid alone often contains too few cells to give an answer.

When cells are obtained, the report usually places the sample in one of several standard result groups. Cleveland Clinic's thyroid biopsy page lists these as benign, atypia of undetermined significance, follicular neoplasm, suspicious, malignant and nondiagnostic. Each group leads to a different next step, so ask your clinician which group your result falls into and what it means in your case. The American Thyroid Association adds that a nodule that grows over time may need another biopsy in the future.

Yes. Drawing off the fluid with a needle (aspiration) can shrink a cyst that causes pressure or a visible lump, and the fluid is usually sent for testing. RadiologyInfo describes the procedure as typically taking under 30 minutes as an outpatient, with possible soreness for a day or two and rare complications such as bleeding or infection. Tell the team if you take blood thinners.

For benign cysts that keep causing symptoms, specialists may discuss other options. Endotext describes percutaneous ethanol injection, in which a small amount of alcohol is injected after the fluid is drained, as a treatment used for predominantly cystic benign nodules. Ask whether these are offered locally and what the evidence is for your situation.

Bring the full ultrasound report, not only a summary line, along with any earlier scans and thyroid blood test results. MedlinePlus notes that TSH and other thyroid blood tests are usually part of the assessment.

• Is my nodule purely cystic, spongiform, or mixed with a solid part?
• What TI-RADS or other risk category did the radiologist give, and what does it mean for me?
• Is FNA recommended, and if so, will the solid part be sampled?
• If the result was nondiagnostic, what happens next?
• Would draining the cyst help my symptoms, and could it refill?
• Do I need a follow-up scan, and when?
• Which symptoms should make me contact you sooner?

On SameCase, patients and verified doctors share de-identified cases. Seeing how other people with cystic or mixed thyroid nodules described their reports, biopsy results and follow-up plans may help you notice what to ask about your own.

No two nodules are exactly alike, and another person's case cannot tell you whether your nodule needs a biopsy. Use similar cases only to prepare questions for the clinician who has seen your scan.