Thyroid Cysts

Thyroid cysts are common, and most are benign (not cancerous). A cyst is a fluid filled lump lined by epithelium cells. Thyroid cysts may have a solid component, and the solid component may be malignant. However pure thyroid cysts are seldom malignant.

Thyroid cysts may be classified as:

• Cystic > 90% cystic 
• Predominantly cystic: 50-90% cystic
• Mixed: solid and cystic. Less than 50% cystic

Most thyroid cysts are formed from degenerating thyroid adenomas (a benign tumour). Thyroid cysts may be solitary or multiple.

Thyroid cysts may cause no symptoms at all. As they enlarge, they cause compressive type symptoms including a pressure feeling in the neck, globus symptoms, feeling of a lump in the throat. They may cause trouble swallowing, voice change or shortness of breath from compression of the trachea. Most patients with thyroid cysts are euthyroid (making the correct amount of thyroid hormone). Patients may also simply complain of an unsightly lump in the lower neck.

Once the lump has reached a certain size it is usually obvious clinically and can be seen to move on swallowing. The cyst may feel either soft or firm.

An ultrasound scan is the investigation of choice. Thyroid nodules are classified according to the tirads (Thyroid Imaging Reporting and Data Systems) system.

Cystic nodules are usually tirads 1 or 2 and as such do not require ultrasound guided FNA (fine needle aspiration) cytology. Comet tail artefacts may be seen on ultrasound scan and indicate a benign thyroid cyst.

As with all thyroid pathologies, thyroid function tests (a simple blood test) are also recommended.

Patients with no symptoms and thyroid cysts classified as Tirads 1 or 2 require no treatment.

Patients with symptoms and a large thyroid cyst are best treated with ultrasound guided aspiration (needle drainage) of the thyroid cyst. The cyst contents are sent for cytology but usually the report comes back as non-diagnostic due to the low number of thyroid follicular cells present in the aspirate. About 80% of thyroid cysts recur after aspiration. However, 20% of patients are cured.

If the thyroid cyst recurs, then ultrasound guided ethanol ablation of the thyroid cyst is recommended. This is a simple procedure with a high chance of cure (90%). (See ethanol ablation section.)

If the cyst still recurs, then further ethanol ablation should be considered. For patients with a solid component to the thyroid cyst, ultrasound guided FNA (fine needle aspiration) cytology is recommended. If the FNA is benign then radiofrequency ablation can be considered. Alternatively thyroid lobectomy (hemithyroidectomy) can be performed.

Summary of Treatment for Thyroid Cysts

1. No symptoms: no treatment required
2. Tirads 3, 4, 5: ultrasound guided FNA depending on size
3. Tirads 1, 2: Simple aspiration under ultrasound guidance
4. Ethanol ablation under ultrasound guidance
5. Radiofrequency ablation under ultrasound guidance
6. Thyroid lobectomy

What would I do if I had a simple Thyroid Cyst?

I would get it aspirated and if it recurred, then I would find a specialist who performs ultrasound guided ethanol ablation of the thyroid cyst.