A Rare Case of Thyroid Ectopia Mimicking Parathyroid Adenoma in a 19-Year-Old Filipino Female

Introduction: Parathyroid adenoma (PA) is the leading cause of primary hyperparathyroidism, but rarely, present without any clinical manifestations. Reported cases of asymptomatic PA are few, with limited knowledge about their behavior and management.  Case: The 19-year-old patient presented with a left anterior neck mass. Baseline bloodwork including serum calcium levels, thyroid and parathyroid function tests were normal. Further examination, consisting of ultrasound, CT scan, and parathyroid scintigraphy, demonstrated a solid mass posteroinferior of the left thyroid lobe suggesting exophytic left thyroid mass, parathyroid adenoma, or malignancy. Lobectomy of ectopic thyroid lobe was done. On pathologic examination, nodular hyperplasia was noted with immunoreactivity to TTF-1 and not to Chromogranin A and Synaptophysin consistent with a follicular nodular disease with hyperplastic features, arising from a sequestered thyroid nodule.  Conclusion: PA without hyperparathyroidism are rare and diagnosis is a challenge. While imaging modalities aid in the diagnosis, pathologic examinations are essential in confirming the definite diagnosis.