Benign thyroid tumours

Most thyroid lumps are benign but 4-6.5% are malignant and it is important to distinguish this sinister minority.¹ Benign thyroid lumps may include thyroid adenoma, thyroiditis, thyroid cysts and hyperplastic nodules.

Pathogenesis

Most thyroid nodules are adenomatous. Most are multiple and that is usually shown on ultrasound, scintigraphy and at surgery. The nodules are usually non-functioning (cold at scintigraphy), although a few may be hyper-functioning toxic adenomas (hot on scintigrams). They may also be a hyper-functioning adenoma in a multinodular goitre.

When solid, the nodules are poorly encapsulated, not well defined and merge into the surrounding tissue. Cystic adenomatous nodules are haemorrhagic, with irregular internal walls and particulate fluid content. Intratumoral calcification is occasionally seen.

Follicular adenomas are the most common and arise from follicular epithelium. They are usually single, well-encapsulated lesions. On ultrasound, adenomas may be hyperechoic or hypoechoic solid nodules with a regular hypoechoic area surrounding ring called the halo sign. Rarely, a parathyroid adenoma has an ectopic intrathyroid location. Whether solitary adenomas transform into follicular carcinoma is uncertain. Follicular adenomas are further classified according to their cellular architecture and relative amounts of cellularity and colloid into fetal (microfollicular), colloid (macrofollicular), embryonal (atypical) and Hürthle (oxyphil) cell types.

Epidemiology

About 60% of the general adult population have a single thyroid nodule, or multiple ones.² They are more common in women. Most nodules are benign. In most series, 8-65% of patients with clinically normal thyroid glands had one or more grossly visible nodules, whereas the incidence of malignancy was 2-4%.

Thyroid tumour symptoms

• Most patients with thyroid nodules are asymptomatic and most nodules are found on clinical examination or self-palpation.

• A single dominant or solitary nodule is more likely to represent carcinoma (malignancy incidence 2.7-30%) than a single nodule within a multinodular gland (malignancy incidence 1.4 to 10%).³

• Thyroid lumps are often asymptomatic and are noticed by family members or seen in the mirror.

• They may sometimes cause pain and (rarely) present with features of compression of the trachea.

• Ask about previous radiation.

Signs

• Ask the patient to drink some water and note the thyroid move as they swallow.

• Note enlargement or asymmetry.

• Stand behind a seated patient and use the second and third fingers of both hands to examine the gland as they swallow again.

• Note lumps, asymmetry, size and tenderness.

• Check for regional lymphadenopathy.

Differential diagnosis

• Non-toxic goitre - non-functioning nodules.

• Toxic nodular goitre - functioning nodules.

• Graves' disease - diffuse overactive thyroid gland.

• Hashimoto's disease - autoimmune destruction of the gland.

• Solitary thyroid nodule - 15-25% are cysts and can be aspirated.

• Thyroid cancer.

• Medullary cell carcinoma.

• Thyroid lymphoma - usually non-Hodgkin's.

• De Quervain's thyroiditis - neck pain, fever and lethargy soon after an upper respiratory infection or a viral illness.

• Acute suppurative thyroiditis - results from bacterial or fungal infection causing abscess.

Investigations²

• TFTs will show most patients to be euthyroid - refer those which are abnormal for endocrine opinion.

• Ultrasound is useful to detect and characterise most thyroid nodules. It can show cystic lesions 2 mm wide and solid lesions 3 mm wide. Ultrasound examination is far more sensitive than clinical examination and only 4-7% of nodules detected by ultrasound are clinically palpable. Risk stratification systems are used to identify those nodules most at risk of malignancy, so they can have a fine-needle aspiration biopsy.⁴

• Fine-needle aspiration (FNA) gives tissue for cytology. It is performed under ultrasound guidance (for maximum accuracy).⁵ It is safe, inexpensive and provides direct information. The false negative rate varies with the experience of the person performing the procedure. However, the false negative rate for cancer can vary from 1-6% (owing to wrong diagnosis or sampling errors) even when the operator is experienced and the sample is sufficient for diagnosis. These errors occur more commonly in nodules smaller than 1 cm or larger than 4 cm.

• Radionuclide isotope scanning looks at iodine uptake by the thyroid and has a limited role in the diagnosis of thyroid cancer. The National Institute for Health and Care Excellence (NICE) and the British Thyroid Association (BTA) do not support its routine use - it is 'usually non-diagnostic of cancer'.^{6 7} The American Thyroid Association recommends its use only in specific situations.⁸

• CT scans and MRI scans are valuable to detect local and mediastinal spread and regional lymph nodes.

Referral⁶

Patients with thyroid nodules who may be managed in primary care

• Patients with a history of a nodule or goitre which has not changed for several years and who have no other worrying features (ie adult patient, no history of neck irradiation, no family history of thyroid cancer, no palpable cervical lymphadenopathy, no stridor or voice change).

• Patients with a non-palpable asymptomatic nodule <1 cm in diameter discovered incidentally on neck ultrasound/CT/MRI scanning without other worrying features.

Patients who should be referred non-urgently

• Patients with nodules who have abnormal TFTs. These patients should be referred to an endocrinologist because thyroid cancer is very rare in this group.

• Patients with a history of sudden onset of pain in a thyroid lump (likely to have bled into a benign thyroid cyst).

Symptoms needing urgent referral (two-week rule)

• Unexplained hoarseness or voice changes associated with a goitre.

• Thyroid nodule in a child.

• Palpable cervical lymphadenopathy (usually deep cervical or supraclavicular region).

• A rapidly enlarging, painless thyroid mass over a period of weeks (a rare presentation of thyroid cancer and usually associated with anaplastic thyroid cancer or thyroid lymphoma).

Symptoms needing immediate (same day) referral

• Stridor associated with a thyroid mass.

Benign thyroid tumour treatment and management

Solitary thyroid nodules which are malignant or suspicious on FNA require removal (see the separate Thyroid Cancer article). Molecular analysis of the aspirate may determine which require surgery and which can be safely monitored.⁹

Most benign thyroid nodules do not require any specific intervention, unless there are local compressive symptoms from significant enlargement, such as dysphagia, choking, shortness of breath, hoarseness, or pain, in which case thyroidectomy should be performed. Other indications for surgery in benign nodules include the presence of a single toxic nodule, or a toxic multinodular goitre. Aspiration is the treatment of choice for thyroid cysts but the recurrence rate is high.¹⁰

Associated hyperthyroidism needs to be treated in the usual way.

Complications

Both surgery and alcohol injection can cause recurrent laryngeal nerve palsy, which should occur in fewer than 5% of procedures.⁶ The primary disease can cause nerve damage in both benign and malignant conditions.

Prognosis

After exclusion of malignancy, prognosis for thyroid disease is excellent.