Goitre, Thyroid
Nodules and Cancer
Goitre
The term goitre refers to
enlargement of the thyroid gland. Up to 15% of the UK population have a goitre
on ultrasound (although most are not palpable), and 5% have a discrete thyroid
nodule. Thyroid malignancy is rare, but should be considered in any patient
presenting with a thyroid lump.
Diffuse goitre
The most common cause of diffuse
goitre worldwide is iodine deficiency (endemic goitre), occurring in
land-locked areas including Africa, the Himalayas and the Andes. In the UK,
diffuse thyroid swelling is idiopathic (simple goitre) or autoimmune (Figure
14.1a). A tender diffuse goitre with systemic symptoms suggests a viral
thyroiditis. Riedel’s thyroiditis is a rare condition characterised by thyroid
fibrosis.
Multinodular goitre
This occurs in up to 40% of the
population, the frequency increasing with age. Patients with nodular thyroid
disease are euthyroid, frankly hyperthyroid (toxic nodular goitre) or have
subclinical hyperthyroidism (autonomous thyroid function) (Figure 14.1b). If
TSH is suppressed and fT4 is normal, fT3 should be checked to exclude
T3-toxicosis. Patients may rarely present with compressive symptoms of stridor
and dysphagia, which can require thyroidectomy. If there is inferior extension
into the thorax (retrosternal goitre), surgery is more difficult and may
require a thoracotomy.
Solitary thyroid nodule
Malignancy should be excluded in
this situation although the vast majority of nodules will turn out to be
benign. Rapid enlargement, lymphadenopathy, extremes of age, family history of
thyroid cancer, hoarse voice and previous neck irradiation are worrying
features (Figure 14.1c). Sudden painful enlargement suggests haemorrhage within
a thyroid cyst. The presence of a hard, fixed, craggy mass with lymphadenopathy
is concerning. Benign lesions are smooth and mobile with no lymphadenopathy.
Solitary thyroid nodules can cause hyperthyroidism so clinical and biochemical
assessment of thyroid status is important.
Investigation
Fine needle aspiration (FNA) is the
first line investigation of a thyroid nodule, either by palpation or under
ultrasound guidance. Cytology may reveal a clearly benign or malignant lesion.
If the FNA result is inadequate or indeterminate, it should be repeated. The
Thy classification system ensures consistent reporting of cytology and will
establish which nodules require surgery.
Serum fT4, fT3, TSH and thyroid
antibodies should be checked. Thyroid ultrasound must be performed by a
dedicated thyroid radiologist, as radiological characteristics can help predict
the likelihood of malignancy.
Management
Toxic nodular goitres are managed
with anti-thyroid medication, RAI or surgery. Indications for surgery in
non-toxic nodular thyroid disease includes compressive symptoms, cosmetic
issues or suspicion of malignancy.
Thyroid cancer
Differentiated thyroid cancer
Thyroid cancer is rare, comprising
0.5–1% of all malignancies. Differentiated thyroid cancer is the most common
type, and is papillary or follicular. The prognosis of differentiated thyroid
cancer is good if detected early and managed appropriately. Papillary thyroid
cancer is usually obvious after FNA cytology. Follicular carcinoma can be
difficult to distinguish from benign follicular adenoma on FNA, and requires a
hemi-thyroidectomy for histological confirmation.
Anaplastic cancer, Hürthle cells
and lymphoma
Anaplastic carcinoma is rare,
making up 5% of thyroid cancer. It occurs in elderly patients and is a highly
aggressive and invasive tumour carrying a poor prognosis. Cytology may reveal
Hürthle cells, which are derived from follicular epithelium; surgical removal
may be necessary to distinguish benign from malignant lesions. Rarely, FNA
reveals thyroid lymphoma, which requires haematology referral and chemotherapy.
Medullary thyroid cancer
Medullary thyroid cancer (MTC) is a
rare neuroendocrine tumour arising from the calcitonin-secreting C-cells of the
thyroid. C-cell hyperplasia is a precursor to MTC. MTC can be associated with a
mutation in the RET oncogene as part of multiple endocrine neoplasia
type 2 (MEN-2). Familial isolated MTC, which is also associated with RET mutations,
can also occur in the absence of MEN-2. Detection of a RET mutation has
major implications for family
screening; prophylactic thyroidectomy is indicated in children carrying the
mutation. Serum calcitonin is a tumour marker in MTC, and high levels can lead
to symptoms including flushing, sweating and diarrhoea.
Management of differentiated
thyroid cancer
The first line treatment of
papillary or follicular thyroid cancer is surgery. A hemi-thyroidectomy is
initially performed. If the lesion is >4 cm or there are any adverse
histological features, the remaining thyroid lobe is removed (complete
thyroidectomy). Such patients are deemed high risk and are given ablative RAI
therapy, using higher doses than those used for benign hyperthyroidism.
Ablation of all thyroid tissue leads to undetectable thyroglobulin levels,
which is used as a tumour marker. Iodine uptake scans can be used to localise
any residual or recurrent thyroid tissue. During follow-up, thyroxine is given
in higher doses than for primary hypothyroidism, to suppress TSH, beca s can be
a driver for residual or recurrent
tumour growth.
