Thyroid lesions found on CT or ultrasound scan for non-thyroid reasons are the most common endocrine incidentalomas. It has been suggested that 4-7% of the UK population have palpable nodules, with the American Thyroid Association stating that in an iodine-replete part of the world, such as the UK, 5% of women and 1% of men will have them, as will 19-68% of randomly selected individuals, with the highest frequency seen in older women. At post-mortem, incidental thyroid nodules can be seen in 45%-65% of people, with multinodular features being three to four times more common at postmortem. Solitary nodules, however, are three times more common on clinical examination.
Another common situation is people who are noted to have a thyroid mass when seen for other reasons. In that situation, a blood test should be done to assess thyroid function as well as an ultrasound scan of the thyroid.
The main concern is to exclude thyroid cancer, which in 2008 occurred in 5.1 per 100,000 women and 1.9 per 100,000 men per year in the UK, resulting in 2,654 new cases, and 346 deaths in the UK in 2010.
The 2014 British Thyroid Association guidelines recommended changes to ultrasound reporting of thyroid nodules, as outlined in box 1 (below). So some patients who would previously have been investigated further can be reassured, as no repeat ultrasound investigation is needed. In our department this means the 60% of nodules classified as U2 do not require fine-needle aspiration biopsy. For a U1 thyroid, the recommendation is to check thyroid function and thyroid peroxidase antibodies if TSH is elevated, but no further investigation is required.
Box 1: Ultrasound grading criteria for thyroid nodules
- U1: normal (no nodules)
- U2: benign
- U3: indeterminate
- U4: suspicious
- U5: malignant
Incidental asymptomatic U2 nodules with normal thyroid function can be monitored in primary care, particularly if they have incidental non-palpable nodules smaller than 1cm on ultrasound scanning, classified as U2. The same goes for patients with thyroid nodules who have no worrying features (adults with no history of neck irradiation, no family history of thyroid cancer, no palpable cervical lymphadenopathy, and no stridor or hoarseness). Repeat ultrasound scanning is not needed unless symptoms change, but thyroid function should be monitored every six to 12 months.
All patients with a U3, U4 or U5 nodule will need referral for further investigation.
A non-urgent referral to an endocrinologist should be considered in anyone with single or multiple nodules with abnormal thyroid function tests. Pain in a thyroid nodule should also be referred, as there may have been bleeding into a pre-existing nodule, although thyroid cancer in that situation is unlikely. Fine-needle aspiration biopsy of these is sometimes indicated.
More urgent referral, potentially via a two-week rule pathway, is indicated if a thyroid nodule is found in a child, or there is any unexplained hoarseness with an associated goitre (even if incidentally noted) associated cervical lymphadenopathy with a thyroid mass, or a rapidly enlarging painless thyroid mass, over weeks. The latter is of particular concern, as it can indicate an anaplastic thyroid tumour, with a worse prognosis. Previous radiation exposure, associated cervical lymphadenopathy or stridor are also features suggesting an urgent referral is needed.
In all these situations, assessment of thyroid function is useful to aid referral, and most will require fine-needle aspiration biopsy and potentially further interventions depending on the results.
In our unit, repeat ultrasound scanning will downgrade a U3 nodule to a U2 in about a quarter of cases. Of those having a fine-needle aspiration, more than half have normal benign cytology, with only 10% requiring a thyroid lobectomy to provide a diagnosis. Less than 2% will receive a diagnosis of thyroid cancer.
Dr Edson Nogueira is a specialist registrar in endocrinology and diabetes and Dr Kevin Shotliff is a consultant in endocrinology and diabetes, both at Chelsea and Westminster Hospital NHS Foundation Trust