Intrathyroidal Branchial Cleft Cysts Presenting as Bilateral Thyroid Nodules

Introduction: Intrathyroidal brachial cleft cysts are a rare entity and are usually associated with Hashimoto’s thyroiditis. Etiology is not very clear at this point, but they are thought to arise from the ultimobranchial body remnant during embryogenesis of the gland versus originating secondary to chronic inflammation as a form of squamous metaplasia. They are a common finding in the lateral neck but not with the thyroid. We present a case of a suspicious appearing bilateral thyroid nodules which were found to branchial cleft cysts on biopsy. Clinical Case: A 56-year-old woman presented to us for evaluation of thyroid nodules. Her past medical history was pertinent for endometrial cancer status post surgery and radiation, obesity, sleep apnea, hyperlipidemia and hypothyroidism. She was diagnosed with hypothyroidism around 30 years ago and had been on Levothyroxine since then. She was recently noted to have a low TSH level on routine labs done by her primary care provider and therefore her Levothyroxine dose was adjusted. She also underwent a thyroid ultrasound due to exam findings of a palpable thyroid nodule. The ultrasound revealed a suspicious 2.2 cm hypoechoic solid nodule with irregular margins and micro-calcifications in the left mid thyroid lobe. Additionally, she was also noted to have a 0.8 cm hypoechoic nodule with irregular margins in the right mid thyroid lobe. No concerning cervical lymphadenopathy was identified. She was hence referred to us for further evaluation. She denied having compressive symptoms and did not have history of head/neck radiation or family history of thyroid cancer. Both nodules were biopsied but were interpreted as non-diagnostic with insufficient follicular cells and colloid. She underwent repeat biopsy of both nodules which again was interpreted as non-diagnostic. After discussion with patient, given her suspicious ultrasound findings and inconclusive biopsy results she was referred to endocrine surgery for surgical evaluation. Shortly after she underwent total thyroidectomy with pathology consistent with bilateral benign branchial cleft like cysts associated with adjacent thyroid follicles undergoing squamous metaplasia admixed with chronic inflammation. Conclusion: Pathogenesis of these intrathyroidal branchial cleft cysts is still unclear and not many similar cases have been reported in the literature so far. These commonly present as a painless mass but sometimes can also be an incidental finding. There are not a lot of specific details in the literature regarding imaging or pathology characteristics of these lesions therefore resulting in surgical intervention to reach a definitive diagnosis.