Pre-sternal thyroid swellings: a case of rare aberrant site recurrence and review of literature

BACKGROUND: Thyroid swellings enlarge caudally into the mediastinum behind the sternum. Pre-sternal swelling of thyroid origin is very rare. We present our case of pre-sternal thyroid swelling which was albeit a surprisingly rare site of papillary thyroid carcinoma recurrence and review of pre-sternal thyroid swellings reported till date. CASE SUMMARY: A 60 year old female presented with a painless, progressive swelling on the anterior part of the chest for the past 2 years. A 15 cm × 8 cm vertically aligned, non tender, well defined swelling was present on the pre-sternal region, with consistency ranging from soft to firm. The swelling was fixed to the underlying tissues and a fixed level IV lymph node was palpable on the right side. Ultrasonography revealed a large mass of 15 × 7 cm with multiple cystic areas. Fine needle aspiration cytology was inconclusive twice. Patient had undergone a total thyroidectomy for papillary carcinoma 10 years back. Computed tomography findings revealed a large 15 × 6.6 × 7 cm lobulated, pre-sternal, soft tissue lesion with solid & cystic components. The mass was infiltrating the right sided strap muscles and sternocleidomastoid. FNAC was inconclusive and thyroid scan could not pick up any activity in the mass. Henceforth a PET scan was done that showed increased FDG uptake by the lesion and the level IV lymph node. The patient underwent wide excision of the mass with right functional neck dissection, along with removal with both sternal head of sternocleido-mastoid, the strap muscles and the surrounding fascia. Histopathology confirmed papillary thyroid carcinoma. Patient received post-operative radioactive iodine ablation and is healthy with no recurrence up to 30 months of follow up. DISCUSSION: The mechanisms for pre-sternal thyroid swelling are not understood due to paucity of cases. The mechanisms proposed are invasion of strap muscles and cervical linea alba and tumor cells spread anterior to sternum, truly ectopic thyroid tissue, de novo carcinogenesis in the embryonal remnants like the thyro-thymic residues, sequestered thyroid tissue which grows later or migration of thyroid cells, incomplete clearance at the time of primary surgery or intraoperative seeding. CONCLUSION: Pre-sternal region masses of thyroid origin are very rare. A proper work up, suspicion for thyroid mass and array of tests will be required to come to a provisional diagnosis. Since the masses reported in literature were primarily malignant, any such mass may be treated on lines of malignancy with radical surgery.