Solitary thyroid nodule and thyroid malignancy

Prevalence and baseline risk. Thyroid nodules occur with increasing frequency in older people and about 95% are benign. Palpable nodules are found in 3–7% of the population, but prevalence rises to about 50% on ultrasound or at autopsy. Crucially, the risk of malignancy is the same for a solitary nodule as for a multinodular goitre — so a multinodular gland does not reassure.

Red flags requiring urgent referral. A nodule that is growing rapidly over a few weeks, or is associated with stridor, hoarseness or cervical lymphadenopathy. Otherwise, routine evaluation is appropriate.

Start with TSH, and let it direct the pathway. If TSH is low or suppressed, perform a radioisotope scan: a "hot" (autonomous) nodule is treated as hyperthyroidism and does not require FNAB, whereas a "cold" nodule requires FNAB. If TSH is normal, proceed directly to ultrasound and FNAB. If TSH is raised with positive antithyroid antibodies and low free T4, treat with levothyroxine.

FNAB is the cornerstone. Fine-needle aspiration biopsy is the most accurate method of evaluating a thyroid nodule and determines who is referred for surgery; its accuracy is improved by high-resolution ultrasound guidance. FNAB is recommended for nodules ≥10 mm with any of: irregular margins, chaotic intranodular vascular spots, a shape more tall than wide, or microcalcifications. For nodules <10 mm, FNAB only if clinical information or ultrasound features are suspicious.

Limitations and risk stratification. A significant limitation of FNAB is an inadequate or indeterminate result in 10–25% of cases, after which surgery is usually recommended for diagnosis — though the majority prove benign. No ultrasound finding is diagnostic on its own. EU-TIRADS malignancy risk: category 2 benign ≈ 0%, 3 low risk 2–4%, 4 intermediate 6–17%, 5 high risk 26–87%.

Malignancy in old age, and what not to do. Thyroid cancer in old age is generally well differentiated, but its course is frequently less predictable than in younger patients; lymphoma of the thyroid and undifferentiated (anaplastic) cancers occur with increasing frequency in the elderly. Malignant or suspicious nodules are treated surgically; radioiodine is first choice for thyroid autonomy and hyperthyroidism; surgery is advised for large non-toxic goitres with compressive symptoms. Routine TSH-suppressive levothyroxine for benign nodules is NOT recommended — the potential harm outweighs benefit, and in multinodular goitre it may produce exogenous hyperthyroidism with cardiac and bone adverse effects. Thyroid nodule → measure TSH ↓ TSH low → radioisotope scan TSH normal / high → ultrasound Hot = treat hyperthyroidism (no FNAB) Suspicious features or ≥10 mm → US-Cold = FNAB guided FNAB ↓ Malignant / suspicious → surgery Benign → ultrasound surveillance (no TSH suppression)

Natural-history data have shifted practice towards active surveillance rather than intervention in the older adult. In a prospective multicentre study of 992 patients with cytologically and sonographically benign nodules, only 11.1% grew over five years, thyroid cancer was diagnosed in just 0.3%, and age ≥60 was associated with a LOWER risk of nodule growth than in younger participants. Current practice is therefore ultrasound at 12 months, then at progressively longer intervals of 2–5 years, with repeat FNA only for substantial growth (>50% change in volume or ≥20% increase in at least two dimensions), new suspicious ultrasound features, or new symptoms. In parallel, active surveillance of low-risk papillary microcarcinoma is now an accepted alternative to immediate surgery in older adults, where the competing risk of death and the operative risk often outweigh the risk from the tumour.