Thyroid lumps are a common presentation, seen in up to 5% of the population, however only a small proportion of them are cancerous.
There are different types of cancer that can affect the thyroid gland, all of which can present with different features. The main types of thyroid cancer are papillary, follicular, medullary, anaplastic, and lymphoma.
Thyroid Cancer Subtypes
This is the commonest type of thyroid cancer (75%), most commonly seen between 40-50 years and in women.
There can be multiple lesions within the gland and they are rarely encapsulated. Histologically, cells are a mixture of papillary and colloid-filled follicles, with papillary projections and pale empty nuclei. They commonly spread via the lymphatics.
Usually seen at 40-60 years and in women, the second most common thyroid malignancy (15%).
They present as focal encapsulated lesions (multifocal disease is rare), with microscopic capsular invasion*. Where metastasis occurs, it is usually via haematogenous spread to bones and lungs.
*Hurthle cell tumours are a variant of follicular neoplasms in which oxyphil cells predominate
These make up around 3% of thyroid cancers and arise in the parafollicular cells (C-cells, derived from the neural crest cells). Consequently, they produce raised calcitonin levels and are associated (20% of cases) with MEN 2 syndrome (both 2a and 2b).
Medullary carcinoma can spread by both lymphatic and medullary routes; unfortunately nodal disease is associated with a very poor prognosis.
Anaplastic Thyroid Cancer
These rare tumours, accounting for 5% of thyroid cancers, usually present in the elderly and are very aggressive.
They tend to grow rapidly with early local invasion and often have spread by the time of presentation. Prognosis is poor and treatment is often supportive.
Thyroid lymphomas are very rare, making up only 1-2% of all thyroid cancers. They usually present in people over 60 years old.
They may grow quite rapidly, with marked compressive symptoms and B-Cell symptoms.
- Female gender
- Also includes relevant cancer syndromes (e.g. medullary subtype associated with Multiple Endocrine Neoplasia (MEN) Syndrome type IIa and IIb)
- Radiation exposure in childhood
- Full body radiotherapy for bone marrow transplant
- Predisposes to lymphoma subtype
Thyroid cancers may present as a palpable lump, multiple lumps, or be found incidentally on imaging of the neck.
The red flag signs to be aware of with any neck lump that may suggest a malignancy are:
- Rapid growth
- Cough, hoarse voice, or stridor
- Multiple enlarged cervical lymph nodes
- Tethering of the lump to surrounding structures
It is important to remember that most lumps or swellings of the thyroid are not malignant, however some of them may still require surgical intervention for diagnosis or management.
- Benign thyroid adenoma or thyroid cyst
Toxic multi-nodular goitre
- Toxic refers to excessive productive of thyroid hormone which results in the clinical features of hyperthyroidism
- Non-toxic multi-nodular goitre
Thyroglossal duct cyst* (not in the thyroid itself)
- Will move superiorly as the patient sticks out their tongue
*Thyroglossal cysts, prior to any suggested removal, should be fully investigated as the as the cyst may be the only functioning thyroid tissue that the patient has therefore would not warrant removal
Most patients with a neck lumps should have initial Thyroid Function Tests* (TFTs) performed. Any evidence of a toxic nodule (low TSH or raised T3 or T4, or radio-nucleotide imaging showing a “hot” nodule), then no further investigation for malignancy will be required as overactive nodules are very rarely malignant.
*Serum calcitonin may be useful for the diagnosis and monitoring of treatment response in medullary carcinoma.
Most cases of suspected thyroid malignancy require ultrasound thyroid scan (Fig. 4), used to assess the nodule and look for cervical lymphadenopathy. Suspicious features on ultrasound include:
- Irregular margin
A score will be allocated (U1-U5). U1-U2 lesions have low risk of malignancy and will not require fine needle aspiration cytology (FNAC), U3-U5 lesions should undergo FNAC.
Fine Needle Aspiration Cytology (FNAC) involves passing a needle into the thyroid nodule and aspirating cells out of it. These cells will be reviewed and the relevant score allocated (Thy1-Thy5); the TNM staging system is used for thyroid cancers once diagnosis is confirmed:
- Thy1 is inconclusive and requires a further sample
- Thy2 is non-malignant
- Thy3 is follicular lesion and requires diagnostic hemithyroidectomy for histology to determine between follicular adenoma (benign) or carcinoma
- Thy4 is suspicious and requires diagnostic hemithyroidectomy
- Thy5 is malignant and requires work up for appropriate treatment
Thyroid cancer should be managed by a multi-disciplinary team, including endocrinologists, histopathologists, radiologists, oncologists, and ENT surgeons, alongside of specialist nurses and speech and language therapists.
The management varies depending on the type of cancer as well as the stage. Management options include surgical, chemotherapy, radiotherapy, and radio-iodine therapy.
- Hemi-thyroidectomy – This involves removing half of the thyroid that contains the lesion, however is only suitable for certain tumours (e.g. small low grade non-metastatic malignancy)
- Total thyroidectomy – Most malignant disease will require a total thyroidectomy, which involves removing the whole thyroid (including the isthmus); patients will always need to take thyroid hormone replacement following this surgery
Locally advanced disease may also require neck dissection, to remove groups of lymph nodes from the surrounding region, both to aid diagnosis and attempt to reduce disease spread.
Complications of Thyroid Surgery
Bleeding immediately after the operation can result in a haematoma forming beneath the skin. Large haematomas can cause airway obstruction, which is an emergency. In this situation the surgical wound must be re-opened (on the ward!) to allow drainage of the haematoma and the patient will need to go back to theatre to stop the bleeding.
Hypocalcaemia may occur if there is damage to or removal of the parathyroid glands. After a total thyroidectomy, patients must be monitored for clinical features of hypocalcaemia, such as paraesthesia or tetany. PTH and serum calcium levels must be checked the next day (however levels can become significantly low within hours post-operatively)
The recurrent laryngeal nerves run close to the thyroid gland, hence care during surgery must to taken to prevent damage causing vocal cord paralysis. Unilateral palsy will result in a hoarse voice however a bilateral paralysis can result in a life-threatening stridor and tracheostomy may be warranted.
Radioiodine therapy involves administration of a radioactive iodine solution, which is taken up preferentially by residual thyroid tissue, acting a focal radiation targeting the malignancy (used for papillary or follicular carcinomas). Only effective after total thyroidectomy.
External beam radiotherapy can be used as primary or adjunct therapy (curative or palliative). Chemotherapy can also be used for similar means, classically lymphomas usually responding well to chemotherapy, and symptoms can improve within a few doses.
The prognosis of thyroid cancer depends on the histological subtype, the grade, and the stage of the malignancy.
- For papillary cancer, prognosis is quite good with 10 year survival of 90% (this drops considerably if the tumour has spread beyond the gland)
- Follicular cancer has a high 10 year survival at around 85% (haematogenous spread is a marker of poorer prognosis)
- Medullary cancer also has a good prognosis, with 10 year survival dropping only below 90% when nodal or metastatic spread is seen.
- For anaplastic cancer, there is a very poor prognosis with a 1 year survival of 10-20%
- Thyroid lumps are a common presentation however only a small proportion of them are cancerous
- The main types of thyroid cancer are papillary, follicular, medullary, anaplastic, and lymphoma
- Red flag signs for any thyroid lump include pain, rapid growth, a cough, hoarse voice, or stridor, lymphadenopathy, or tethering of the lump
- Diagnosis is made via Ultrasound Scan followed by Fine Needle Aspiration Cytology
- Management options available range from surgical to medical to palliative