Thyroid cysts: presentation, malignancy risk and management
THE CONTEXT
Clinically isolated thyroid swellings may be wholly or partly cystic. Ultrasound assessment of a solid component guides further investigation.
Presentation and natural history
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Fine-needle aspiration cytology (FNAC) or ultrasonography shows fluid in over 30% of clinically isolated thyroid swellings.
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Tense cysts may feel hard and mimic carcinoma.
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Bleeding into a cyst often causes sudden painful swelling, which may resolve to a variable extent over weeks without treatment.
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Aspiration yields altered blood, but fluid frequently reaccumulates.
Underlying pathology and malignancy
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About 55% of cystic swellings result from colloid degeneration or have uncertain aetiology because epithelial cells are absent from the lining.
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Most remaining cystic swellings result from involution within follicular adenomas.
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Some 10–15% of cystic follicular swellings are histologically malignant; the passage gives figures of 30% in men and 10% in women.
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Papillary thyroid carcinoma is often associated with cyst formation.
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Most patients with discrete swellings are women aged 20–40 years. Their malignancy risk is significant but low, so indications for surgery may be unclear.
Ultrasound assessment and treatment
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Ultrasonography is the most useful tool for assessing thyroid cysts. A cyst without a discernible solid element is almost certainly benign and does not require further investigation.
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When a solid element is present, consider targeting it with ultrasound-guided FNAC.
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Simple aspiration has a high rate of reaccumulation.
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For recurrent symptomatic cysts, consider ethanol or thermal ablation. Thermal methods include radiofrequency, microwave, laser and high-frequency ultrasound; ablation achieves cyst resolution in up to 90% of cases.
Indications for operation in thyroid swellings
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The listed indications include neoplasia with FNAC categorised as Thy3–5 and clinical suspicion assessed using age, male sex, hard texture, fixity, recurrent laryngeal nerve palsy and lymphadenopathy.
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Other listed indications include a recurrent cyst, toxic adenoma, pressure symptoms, cosmetic concerns and the patient’s wishes.