Why thyroid nodules happen

What is actually in my neck

In April a scan described a nodule in my thyroid. By the autumn the same nodule measured two and a half centimetres, and I am not reading that number off a report any more. I can feel it. Swallowing is not what it was.

Before that scan I asked for a full panel of my thyroid hormones. I have been taking medication for my thyroid, on and off, for ten years. The doctor decided, before the scan existed, that I did not need the panel.

So I went and had the scan anyway, because my neck was telling me something that nobody at a desk had heard.

“I have had more ultrasounds in the last four years than in the rest of my life put together. That is not anxiety. That is what it looks like when you decide to watch your own body instead of waiting to be called.”

Why ultrasound, and why I had to say that out loud

I need to separate two things that get called the same word, because I nearly lost years to the confusion.

Radiation as treatment saved my life. At one point there was a tumour ten centimetres across on the left side of my neck, sitting next to my thyroid and pushing my windpipe over to the right. I could not swallow properly. It had grown there while I did not know, because nobody had looked. Radiation killed those tumours. I will not have a word said against it.

Radiation as imaging is a different conversation. Repeated scans with contrast and injected radioactive glucose are not the treatment. They are the looking. And in 2024 I decided that the treatment part of my life was finished, and that the looking part was going to be done differently.

So my last full body scan of that kind was in June 2025. Since then I have been monitoring with ultrasound, blood work and two tumour markers. There will be a point when I have another full scan. I am not pretending otherwise and I am not avoiding it.

The way I counted it, almost all of me was well, and I had spent sixteen years letting other people decide what went into my body on a calendar that was not mine. So I stopped rushing. Once in a while, with a reason, beats every four or five weeks because that is how the appointment book runs.

Said plainly. I am not telling you to turn down a scan. I am not telling you to do what I did. I am telling you that I made a decision about my own body with my eyes open, that I monitor instead of ignoring, and that an ultrasound of a neck is a real examination and not a consolation prize. What a decision like that needs is a plan with triggers, and that is a post of its own.

The word on the paper

Nodule. That is the word. It sits in a sentence with four others you do not know, usually next to a number in millimetres, and there is nobody in the room to read it with you, because the report arrives after the appointment and not during it.

Medicine, in my experience of the last sixteen years, has become a counter. You ask for the thing. Somebody hands you a bag. You pay, you take it home, and you open it on your own kitchen table. What is in the bag is your problem.

This post is what I would have wanted on the table next to that bag.

What a nodule is

A thyroid nodule is a lump of thyroid tissue that is a different density from the tissue around it, which is why an ultrasound can see it at all. That is the whole definition. It is not a word for cancer, it is not a word for a tumour, and it is not a word for anything being wrong. It is a word for a lump that showed up on a picture.

Some are solid. Some are fluid filled, which gets called cystic. Some are a mixture. Composition is the first thing a radiologist writes down, because it is the first thing that changes the answer.

How common they actually are

This is the number I wish somebody had said to me first.

Ultrasound finds thyroid nodules in up to 68 per cent of healthy people. Not sick people. Healthy ones, being scanned for something else entirely. They also turn up on about 16 per cent of CT and MRI scans of the neck, as an incidental finding, which means the scan was looking for something else and tripped over this.

They are about four times more common in women, and they get more common with age.

So if you are a woman over forty holding a report with that word on it, the first correct response is not alarm.

Why they happen

Here is the honest part, and it is the part left out of every article like this one. For most individual nodules, nobody can tell you why yours is there. What exists instead is a list of things that make them more likely across a population.

• Being a woman. Four times more common, and nobody has fully explained why.
• Age. The older the population, the more nodules it has.
• Iodine deficiency. Nodules are more common where diets are low in iodine. That is why iodised salt exists.
• Ionising radiation. A real risk factor for thyroid cancer, and it counts most when the exposure happened young.
• Body mass index. Nodule prevalence rises with it.
• Family history. Thyroid cancer in the family, or one of the inherited syndromes, changes the picture.

The number to hold on to

Notice what is not on that list. Stress is not on it. Something you ate is not on it. Something you did wrong is not on it.

Ninety to ninety five per cent of thyroid nodules are benign. That is not reassurance I am offering to be kind. It is the figure in the guidelines, and it is the reason a whole system of watching rather than cutting exists.

What actually decides whether yours needs anything

Not its existence. Not whether you can feel it. Not how frightened you are, which is the one that caught me for years.

Two things decide it: what it looks like and how big it is. They work together, and that is the part nobody explains.

A radiologist scores five features and adds up the points. Solid scores more than cystic. Very dark tissue scores more than bright. Taller than wide scores more than wider than tall. Ragged edges score more than smooth. Tiny bright specks score most of all. The total gives a level from one to five.

Only then does size come into it. The more suspicious the picture, the smaller the thing has to be before anybody puts a needle in it.

• TR1. Cancer in about 0.3 per cent. No biopsy at any size.
• TR2. About 1.5 per cent. No biopsy at any size.
• TR3. About 5 per cent. Biopsy from 2.5 cm.
• TR4. About 9 per cent. Biopsy from 1.5 cm.
• TR5. About 35 per cent. Biopsy from 1 cm.

Mine is on a line in that list

Under five millimetres nobody biopsies anything, even at the top level. Below those thresholds the answer is not nothing, it is a repeat scan on a schedule, which is a different thing from being sent away.

Look at the third line. Two and a half centimetres is not a number I chose for effect. It is the exact figure where the lowest of the levels that get biopsied at all starts getting biopsied.

My ultrasound did not describe the features that make a radiologist write the words that start an urgent process. That is not the same thing as a result. It means the picture is not alarming, and I am going to find out properly rather than decide at home that I am fine, because deciding at home that I am fine is exactly the habit that cost me years.

And there are two other things in my neck that muddy it, which I am saying out loud because yours will have its own version.

• Fibrotic tissue on the left, from my last radiation. Tissue that has been through treatment does not behave like tissue that has not, and it is already there before anybody measures anything.
• Medication that gives me anxiety if I do not take it, and anxiety makes me swallow badly. So the symptom I can feel has at least two possible authors, and I am not qualified to tell them apart by sitting still and worrying.

What counts as growing

That is the honest shape of it. Not a diagnosis. A question with a number attached.

This next part is the thing that saves you from a year of measuring yourself in the mirror.

Growth, in the sense that changes anything, means more than fifty per cent increase in volume, or twenty per cent in at least two dimensions. A nodule that was eleven millimetres and is now twelve has not grown in any meaningful sense. It has been measured twice, by two people, with two hands.

If a first biopsy came back benign, the usual next look is at twelve to twenty four months, and if nothing has changed the gap can stretch to three to five years.

The part that is genuinely uncomfortable

Everything above assumes that finding nodules is good. It is not obviously good, and the people who study this say so out loud.

The United States Preventive Services Task Force recommends against screening for thyroid cancer in people with no symptoms, by feeling the neck or by ultrasound. Their reasoning is that screening finds a great many cancers that were never going to hurt anybody, and treating those cancers does hurt people.

The evidence they point at is South Korea, where widespread screening multiplied thyroid cancer diagnoses by about fifteen, and the number of people dying of thyroid cancer did not move.

Fifteen times the cancer. The same number of deaths. Every one of those extra diagnoses was a real person who was told they had cancer.

“Finding something is not the same as finding something that was going to harm you. Nobody explains that difference to the person holding the report.”

Watching a cancer on purpose

It goes further, and this is the fact that changed how I think about my own neck.

For small papillary thyroid cancers, one centimetre or less, with no sign of spread, there is an accepted option that is not surgery. It is called active surveillance, and it means scanning it and leaving it alone. It began in Japan in 1993 and the American Thyroid Association accepted it in 2015.

In the two largest series, followed for about five to seven years, this is what happened.

• Around 7 to 8 per cent grew by three millimetres or more within ten years.
• Around 1 to 4 per cent spread to a lymph node in the neck.
• 17 per cent got smaller.
• Nobody developed distant spread, and nobody died of thyroid cancer.
• Of those who chose surgery later anyway, none had a recurrence.

What I stopped doing with a piece of paper

Meanwhile the operation is not free. Temporary trouble with calcium levels afterwards ran at about seventeen per cent. I am not telling you to refuse an operation. I am telling you that watching is a real decision, made by real specialists, with real evidence behind it, and that if somebody offers it to you they are not fobbing you off.

This blog has a series about the things I stopped. This is that series, applied to one sheet of A4.

• I stopped putting it in the drawer. The drawer where the frightening paper goes is the most expensive piece of furniture in any house.
• I stopped waiting to be told. If a result exists it exists now, and I ask for it, in writing, every time.
• I stopped accepting a decision made before the evidence. A hormone panel refused before a scan is not a clinical judgement. It is a decision about me taken without me.
• I stopped treating one opinion as the answer. One opinion is one opinion.
• I stopped going quiet when my body was saying something. I can feel this one when I swallow. That is data, and it belongs on the table with the picture.
• I stopped staying with people who do not listen. I left the doctor who had been in charge of my health for more than ten years. Since then I have sat in front of five more who talked over me, decided for me and told me what they had already decided to tell me.

I do not have a tidy ending for you

I am still looking for the next one. I have no general practitioner at the moment, I have a report that needs reading properly, and I have to decide whether to go through the insurance I have paid for out of my work for my whole adult life, or pay privately again. In the last five months I have spent over ten thousand euro on private doctors and did not come away with so much as a rehabilitation plan for the condition I already have.

So I do not have a tidy ending for you on that one. I have the question, and I am going to keep asking it.

Where these numbers come from. Thyroid Nodules: Advances in Evaluation and Management, American Family Physician, September 2020, for the prevalence, the benign proportion, the biopsy criteria, the follow up intervals, the task force position and the South Korea figure. ACR TI-RADS, American College of Radiology, 2017, with the 2018 analysis of 3,422 nodules for the risk at each level. American Thyroid Association 2015 guidelines, for active surveillance. The Kuma Hospital Kobe series of 1,235 patients and the Cancer Institute Hospital of JFCR Tokyo series of 409 patients, for the surveillance figures.