"Cracking thyroid is a term given to a very rare complication of thyroid fine needle aspiration (FNA) biopsy, where there is acute pain and transient but marked thyroid swelling characterised by hypoechoic avascular septations on ultrasound 1,2. Onset occurs within a few minutes to a few hours post-procedure, and thyroid volume can temporarily increase up to threefold, but this increase is self-limiting 1,2. In one series, the complication was suggested to occur in 0.1% of cases 2,3. Although simple analgesia, cooling packs, and steroids have been used to treat, there is no evidence that they change the duration of symptoms. Ultrasound appearances usually resolve within a few hours, but symptoms may persist longer 1-3."