Thyroid nodules

Overview

•A thyroid nodule is a discrete lesion within the thyroid gland - majority are benign; malignancy risk ~5-15%

•Defining clinical sign: neck mass that moves upward on swallowing (tethered to larynx/trachea via pretracheal fascia)

•Medullary thyroid cancer arises from parafollicular C cells (not follicular cells) - produces calcitonin as tumour marker

Investigations

🥇 First-line

•Serum TFTs (TSH, free T4) - establishes functional status; suppressed TSH suggests autonomous/toxic nodule

•First-line imaging: Thyroid ultrasound - characterises nodule (size, echogenicity, margins, calcification); guides management via U-classification (U1 normal to U5 malignant)

🏆 Gold standard

•Fine-needle aspiration cytology (FNAC) - USS-guided for suspicious nodules; reported as THY1 (non-diagnostic) to THY5 (malignant)

🥈 Second-line

•Thyroid scintigraphy - used when TSH is suppressed to distinguish hot (autonomous, almost never malignant) vs cold nodules; not first-line with normal TFTs

•CT/MRI neck - surgical planning for confirmed malignancy, retrosternal extension, lymph node staging; not first-line

⚠️

Normal TFTs + thyroid nodule = ultrasound next. Scintigraphy is not first-line when TFTs are normal - it is reserved for a suppressed TSH to identify autonomous (hot) nodules.

Thyroid cancer types

Differential diagnosis - neck lumps

•Thyroid nodule - moves on swallowing only

•Thyroglossal cyst - midline, below hyoid bone; moves on swallowing AND on tongue protrusion; congenital remnant of thyroglossal duct

•Cervical lymphadenopathy - does not move on swallowing

🎯

Thyroglossal cyst: midline neck lump below the hyoid that rises on tongue protrusion - this is the pathognomonic distinguishing feature from a thyroid nodule.

Malignancy red flags

Features raising malignancy risk

Age <20 or >70 years

Male sex

History of neck irradiation

Family history of thyroid cancer or MEN

Rapid painless growth

Hard, fixed, irregular nodule

Cervical lymphadenopathy

Hoarseness or stridor