A. Ectopic parathyroid lipoadenoma
The patient underwent transcervical excision of the mass, located in the retropharyngeal space posterolateral to the right inferior constrictor muscle at the level of the hypopharynx. There was intraoperative normalization of parathyroid hormone levels, and final pathological results confirmed parathyroid lipoadenoma. Thus, to our knowledge, the present case is the first reported ectopic parathyroid lipoadenoma within the retropharyngeal space. In addition, this case demonstrates how parathyroid lipoadenomas are less reliably detected by Tc-99m SPECT/CT than their typical parathyroid adenoma counterparts, which highlights the value of contrasted CT.
Parathyroid lipoadenoma is a rare variant of parathyroid adenoma with a similar presentation owing to hyperfunctioning parathyroid tissue. The presence of increased fatty stroma differentiates parathyroid lipoadenoma from parathyroid adenoma and also renders it more difficult to identify on preoperative imaging. Although it is uncertain where the fatty stroma originates from, it has been postulated that the same factors that drive growth of parathyroid chief cells are also responsible for fatty growth. Obesity and advanced age may increase this percentage of fatty tissue. Only 70 cases of parathyroid lipoadenoma have been described to date,1- 5 accounting for less than 1% of all cases of hyperparathyroidism, and most ectopic locations have been in the mediastinum.6 Of note, although a liposarcoma may have similar imaging findings to a lipoadenoma, corresponding primary hyperparathyroidism would be unlikely. The imaging characteristics are clearly not consistent with thyroid tissue. An isolated retropharyngeal abscess would be less likely without infectious symptoms as well.