Intrathyroidal Parathyroid Adenomas in Primary Hyperparathyroidism: Clinical and Imaging Findings.

Objectives: Primary hyperparathyroidism (PHPT) is a common endocrine disease. Ectopic adenomas may cause a failed surgery which results in persistence or recurrence. Intrathyroidal parathyroid adenoma (ITPA) is a rare reason for PHPT and site of ectopia. Herein, we aimed to investigate the clinical and imaging features of patients with ITPAs and the effectiveness of radiological tools for localization at a tertiary reference center. Methods: The files of 708 consecutive patients who underwent parathyroidectomy for PHPT in our department between January 2007 and December 2021 were investigated retrospectively. PHPT patients with ITPA were included in the study. Patients with missing data were excluded from the study. Clinicopathological features of the patients and radiological evaluation findings were investigated. Results: Twenty-eight (28/708: 3.9%) patients were included in the study. The complete intrathyroidal gland and subcapsular parathyroid gland were observed in 8 (1.1%) and 20 (2.8%) patients, respectively. The ultrasound and parathyroid scintigraphy revealed the accurate localization of ITPA in 25 (89.3%) and 18 (64.3%) patients, respectively. Additional imaging modalities were applied for 10 patients in which conventional localization studies were discordant or inconclusive. ITPAs were most commonly found in the lower gland (n=20) localization. All patients had a successful parathyroidectomy and neither persistence nor recurrence was occurred in the study group. Conclusion: The ITPAs are rare in PHPT. The ultrasound has a high diagnostic rate in experienced hands. The second-line imaging methods may be favorable in the presence of negative or discordant scans. The pre-operative localization studies can detect the ITPAs in most patients, so blind thyroidectomy should be avoided.