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False-positive parathyroid ultrasound caused by branchial pouch remnant
A 49-year-old woman presented with hypercalcemia. She had been experiencing weight loss, polyuria, nocturia, constipation and change in mood for 1 month. She had no personal or family history of hypercalcemia, kidney stones or bone fractures.
Laboratory evaluation revealed elevated serum calcium of 12.2 mg/dL (reference range, 8-10.5 mg/dL), normal albumin level of 4 g/dL, low phosphorous of 2.2 mg/dL, elevated intact parathyroid hormone (PTH) of 185 pg/mL (reference range, 11-90 pg/mL), and mildly low 25-hydroxyvitamin D level of 28 ng/dL (reference range, 30-100 ng/dL).
An ultrasound showed a normal thyroid gland. A hypoechoic mass measuring 0.9 cm x 0.6 cm x 0.5 cm (longitudinal x anteroposterior x transverse) was visualized outside the thyroid capsule adjacent to the upper pole of the right thyroid lobe (Figure). The patient was started on vitamin D supplementation and referred for the removal of the probable right upper parathyroid adenoma.
Surgical pathology
Intraoperatively, the surgeon identified the right upper neck mass in the expected position based on the preoperative ultrasound. The mass was removed, but it did not have the typical solid texture and appearance of a parathyroid adenoma.
The surgeon did not obtain a post-resection intraoperative PTH level, but continued to explore the remainder of the neck. The right lower parathyroid gland could not be located. The left upper parathyroid gland was normal in location, size and appearance. The left lower parathyroid gland was found to be enlarged and was removed. Intraoperative PTH showed a baseline of 132 pg/mL, and 10 minutes after removal of the left lower gland, that level fell by more than 50% to a normal level of 35 pg/mL. This was interpreted as a successful removal of a PTH adenoma, and the surgery was terminated.
Surgical pathology of the right upper neck mass revealed an unremarkable normal parathyroid gland and a respiratory epithelium-lined remnant. Surgical pathology of the left lower parathyroid gland revealed a small hypercellular parathyroid gland (0.5 cm x 0.5 cm x 0.5 cm; weight < 100 mg) consistent with a parathyroid adenoma. Even after knowing the location, the 0.5-cm inferior left parathyroid adenoma was not identified on the left transverse and longitudinal cine loops of the preoperative ultrasound. Postoperatively, the patient’s levels of calcium at 9.2 mg/dL and vitamin D at 43 ng/mL normalized.
Parathyroid ultrasound
Bilateral neck exploration under general anesthesia had been the standard for the definitive treatment of hyperparathyroidism. However, significant improvements in preoperative imaging and intraoperative rapid parathyroid assay have changed the standard of care to a minimally invasive surgical approach. In general, the literature has supported neck ultrasonography for the initial imaging modality because of the simplicity, lack of radiation and low cost. A recent report demonstrated that sonographic localization of solitary eutopic parathyroid adenoma has a 90% positive predictive value compared with 86% for sestamibi scintigraphy.
The success of localization is dependent on the experience and expertise of the sonographer and the absence of thyroid pathology. A large thyroid gland, whether due to adenomatous nodules or thyroiditis, reduces the penetration of the ultrasound beam, decreasing the ability to discriminate a small mass from the surrounding tissue. False-positive ultrasound evaluation for PTH adenoma is uncommon with the exception of perithyroidal benign reactive lymph nodes associated with thyroiditis. Other perithyroidal solid or cystic lesions that may result in a false-positive parathyroid localization ultrasound include malignant lymph nodes, branchial pouch remnant, cervical bronchogenic cyst, dermoid cyst, neuroma, esophageal diverticulum, cervical thymus and abscess.
Parathyroid adenoma identification
In this case, the small hypoechoic mass mistaken by ultrasound for a parathyroid adenoma was identified by the ciliated respiratory epithelium as a branchial pouch remnant. Even with careful examination of the ultrasound images, through-transmission of the ultrasound beam (hyperechogenicity posterior to a fluid-filled mass) was not noted that could have alerted us to a fluid-filled cyst. The proximity of the branchial pouch remnant and a normal parathyroid gland found on the pathology specimen suggest that the two structures may have traveled together as the upper and lower parathyroid glands developed from the third and fourth branchial pouch, respectively.
The experience of our parathyroid surgeon allowed him to recognize that the upper right neck mass was not typical of a parathyroid adenoma and to continue with a standard four-gland parathyroid exploration until the adenoma was found on the contralateral side in the left inferior position. Although sometimes difficult, the ultrasonographer should confirm that the tentatively identified perithyroidal mass is solid and not cystic to avoid misidentifying the branchial pouch cystic remnant or other cystic structures as a hypoechoic parathyroid adenoma.
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- For more information:
- Stephanie L. Lee, MD, PhD, ECNU, is an Endocrine Today Editorial Board member. She is associate professor of medicine and director of thyroid health in the Section of Endocrinology, Diabetes and Nutrition at Boston Medical Center. She can be reached at Boston Medical Center, 88 E. Newton St., Boston, MA 02118; email: stephanie.lee@bmc.org.
- Devina Willard, MD, is an endocrinology fellow in the Section of Endocrinology, Diabetes and Nutrition at Boston Medical Center.
Disclosure: Lee and Willard report no relevant financial disclosures.