Diagnosis and treatment of mediastinal ectopic thyroid tissue with normally located thyroid gland and primary hyperparathyroidism: a case report

Mediastinal ectopic thyroid tissue (ETT) is rare entity, accounting for 1% of all mediastinal tumours. A 53-year-old lady, presented with cough and atypical chest pain. A computed tomography (CT) scan of chest showed a 95 mm × 75 mm × 115 mm tumour mass; CT guided biopsy of mediastinal mass showed ETT. Thyroid scintigraphy with Technetium-99m ( 99m Tc) pertechnetate showed homogenous and intense uptake in the thyroid gland (TG) lodge and in the mediastinum. Primary hyperparathyroidism (PHPT) was diagnosed during laboratory evaluation. Technetium-99m sestamibi ( 99m Tc-MIBI) parathyroid scintigraphy with single photon emission CT (SPECT)/CT showed uptake of radionuclide in two locations, one in the eutopic position [right inferior parathyroid gland (PTG)] and second ectopic (mediastinal). After surgery, histopathological examination confirmed mediastinal ETT and two PTG adenomas. During follow-up, laboratory analyzes were maintained within the reference range and the patient remained stable and free of symptoms and clinical signs, which supports a good prognosis. The existence of an ectopic mediastinal thyroid and an ectopic parathyroid tissue may be partly explained by a similar embryological origin. Diagnosis of ectopic thyroid and parathyroid tissues is demanding; requires a multidisciplinary team and approach using highly accurate radiological and nuclear imaging. The simultaneous existence of mediastinal ETT, nodular eutopic TG and PHPT for which two adenomas are responsible (cervical eutopic and mediastinal ectopic) is a complex diagnostic and therapeutic challenge, which we have described so far as unique. Comprehensive and multidisciplinary surgery planning is a cornerstone of treatment, when recommendations in guidelines are lacking.