Parathyroid adenoma apoplexy mimicking a thyroid bleeding cyst: a seemingly innocent condition that can be life-threatening.

Summary: Primary hyperparathyroidism most commonly presents with hypercalcaemia. Rarely, parathyroid apoplexy or haemorrhage mimicking a thyroid bleeding cyst is the first presentation of a parathyroid adenoma. A woman presented with a sudden-onset painful 'goitre'. Ultrasound showed a cystic nodule located posterior to rather than in the right thyroid lobe, suggesting parathyroid adenoma bleeding. Biochemistry showed mild primary hyperparathyroidism. 99mTc-pertechnetate/sestamibi showed no uptake in the nodule, which was interpreted as a cold thyroid nodule. 18F-fluorocholine PET/CT showed uptake in the nodule, suggestive of a parathyroid adenoma. Persistent mild primary hyperparathyroidism complicated by nephrolithiasis and osteopenia favoured parathyroidectomy over a wait-and-see approach. The patient was referred for parathyroidectomy along with right thyroid lobectomy. Pathology showed an adenoma, with an eccentrically located cystic structure filled with red blood cells surrounded by a thickened fibrous capsule. In conclusion, cervical pain/haemorrhage with hypercalcaemia points to the diagnosis of parathyroid apoplexy, mimicking a thyroid bleeding cyst. Workup with ultrasound and, if available, 18F-choline PET/CT allows for timely surgery, minimizing the risk of recurrent and severe bleeding.

Learning Points: A bleeding cyst may be located posterior to rather than in the thyroid, suggesting a parathyroid haemorrhage. Neck pain and/or haemorrhage along with primary hyperparathyroidism point to parathyroid apoplexy. A two-step presentation has been described, with a first phase of local symptoms to be followed by visible and possibly life-threatening compressing bleeding. Therefore, an expedited workup is needed, allowing for timely surgery.