Solitary thyroid nodule - Thyroid axis

Solitary thyroid nodule

Definition

A solitary mass within the thyroid gland that may be solid or cystic.

Incidence

5% of population have a palpable solitary thyroid nodule. Up to 50% of population have a solitary nodule at postmortem.

Aetiology/pathophysiology

Solitary thyroid nodules are most commonly benign (over 90%). Causes include the following:

·        Benign follicular adenoma: Single lesions with well-developed fibrous capsules. Adenomas are not under the control of TSH and continue to secrete thyroid hormones, which may result in hyperthyroidism. There are low levels of circulating TSH and hence suppression of the remainder of the thyroid gland.

·        Colloid nodule that may be a dominant nodule in a multinodular goitre.

·        Malignant tumours of the thyroid follicle cells.

·        Thyroid cyst (15–25%): These may be simple cysts or bleeding into a colloid nodule or adenoma. About 15% are necrotic papillary tumours.

Clinical features

Patients may present with a palpable lump or may be diagnosed on incidental imaging. Features suggestive of malignancy:

·        Rapid painless growth.

·        Family history of thyroid tumours or MEN 2 syndrome.

·        History of neck irradiation exposure.

·        Hoarseness and vocal cord paralysis suggesting recurrent laryngeal nerve palsy.

·        Malignancy is more common in children and patients over 60 years.

Investigations

·        Thyroid function tests are used to determine thyroid status. Isotope scans may also be used to demonstrate either a cold nodule, a hyperactive gland (toxic multinodular goitre) or a ‘cold’ gland containing a ‘hot’ nodule (toxic adenoma). Cold nodules suggest malignancy.

·        Ultrasound scan may be used to determine the anatomy of the lesion and distinguish solid from cystic nodules.

·        Fine needle aspiration for cytology is used to differentiate benign cells, suspicious cells or malignant cells.

Management

Benign lesions only require treatment if they cause hyperthyroidism or for cosmetic reasons. Treatment options include surgical excision and radioactive iodine.

If suspicious cells are identified on cytology a thyroid lobectomy should be performed.