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Ectopic carotid sheath parathyroid adenoma found in 56-year-old male
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A 56-year-old male was referred to the endocrine clinic for the evaluation of hypercalcemia. His first renal stone was diagnosed 10 years ago and was associated with hypercalcemia. The stone was treated with lithotripsy, and he was told to have surgery for the hypercalcemia, but he declined since it was his first episode of nephrolithiasis.
Earlier this year, he passed another 7 mm x 7 mm x 5 mm brown stone that was analyzed as 70% calcium oxalate monohydrate, 15% calcium oxalate dehydrate and 15% calcium phosphate. A CT scan demonstrated two obstructing renal stones. He did not have a family history of renal stones, thyroid disease or pituitary disease. He denied polyuria, constipation, problems with memory or higher executive function, height loss or fractures. His prior labs showed calcium levels in the low 10s 3 years ago, but more recently his laboratory tests showed a calcium level of 11.1 mg/dL, parathyroid hormone (PTH) level of 103 pg/mL (average level, 10-60 pg/mL), and 25-hydroxyvitamin D level of 19.8 ng/mL. His bone mineral density was normal with a lumbar spine density (L2-L4) of 1.172 g/cm2 (T-score=0.04) and femoral neck density of 0.994 g/cm2 (T-score=–0.92).
Imaging analysis
An office ultrasound was attempted, but because of cervical spine arthritis, the patient could not cooperate with neck hyperextension for a complete exam. The thyroid was normal and there was no mass seen posterior or inferior to the thyroid gland. Nuclear medicine technetium-99 sestamibi parathyroid and thyroid scintiscans were performed. On planar imaging, the isotope had a homogeneous uptake in the thyroid and an asymmetric increased uptake over the left submandibular gland (Figure 1A). On delayed images, there was an expected washout of activity from the thyroid gland seen on the early uptake but persistent uptake just superior and lateral to the left of the thyroid, which was separate from the thyroid and the left submandibular gland (Figure 1B). The finding was suspicious for an atypical ectopic parathyroid adenoma.
Stephanie L. Lee
A CT scan of the neck was obtained and showed a homogeneously enhancing soft tissue mass located 2 mm from the superior/posterolateral margin of the left thyroid lobe and immediately posterior to the left common carotid artery at the level of the thyroid cartilage (Figure 2). This mass measured 13 mm x 8 mm x 13 mm (SAGXAPXTR). At the time of surgery, a 1-cm mass was found posterior to the common carotid artery within the carotid sheath that was separate from the thyroid. A nerve was seen entering the superior and inferior poles of the adenoma. Stimulation of the nerve inferior to the adenoma resulted in stimulation of the left side vocal cord consistent with the recurrent laryngeal nerve. It was attempted to enucleate the adenoma from the nerve sheath and blood samples were obtained from the left internal jugular vein about 12 and 15 minutes following the removal of the adenoma. The intraoperative PTH levels dropped from 245 at baseline to less than 5 on the two final blood draws. Pathology revealed a 0.79 hypercellular parathyroid adenoma. Postoperatively, his PTH normalized to 28 pg/mL with normal calcium of 9.5 mg/dL. Additionally, the patient was found to have a hoarse voice and paralysis of the left vocal cord consistent with damage to the recurrent laryngeal nerve.
Indications for surgery
Nephrolithiasis and hyperparathyroidism are an indication for parathyroid surgery. The initial evaluation by ultrasound was limited because the patient was unable to cooperate due to neck pain. Approximately 84% of parathyroid adenomas in normal positions just posterior or inferior to the thyroid can be detected by ultrasound. The remainder of patients should have preoperative localization with technetium-99 sestamibi parathyroid imaging with attention toward expected ectopic locations.
Sagittal CT scan of the head and neck. After contrast administration and enhancement of the carotid artery, an ectopic parathyroid adenoma within the carotid sheath (red arrow) with enhancement was located posterior to the carotid artery superior and separate from the thyroid gland. A. Transverse image at the level of the thyroid cartilage. JV: jugular vein. CA: carotid artery. B. Sagittal image with the parathyroid adenoma (red arrow) posterior to the carotid artery.
Ectopic parathyroid glands occur between 6% and 22% of patients with hyperparathyroidism. In one study of 202 patients with ectopic glands, 89% were a single adenoma and 11% were double adenomas. The ectopic parathyroid glands were predominantly located in the thymus (38%); retroesophageal region (31%); intrathyroidal (18%); and <1% in the carotid sheath. Preoperative MIBI scans had a sensitivity of 89% and ultrasound had a sensitivity of 59% for detecting ectopic glands. Combined, the imaging modalities had a positive predictive value of 90%. Function and anatomy are combined when the sestamibi planar images are combined with single-photon emission computed tomography/computed tomography (SPECT/CT) and has the advantage of exact localization of ectopic parathyroid adenomas. In one study of 16 patients, SPECT/CT identified 39% more lesions compared with SPECT imaging alone.
Technetium-99 sestamibi parathyroid scan showing an ectopic parathyroid adenoma. Anteroposterior images obtained 15 minutes and 2 hours after isotope administration. A. Early images show homogeneous uptake in a normal appearing thyroid gland (yellow arrow) and increased uptake of a mass near the left submandibular gland (blue arrow). B. Late images show normal isotope washout of the thyroid gland with persistent trapping in the ectopic parathyroid adenoma located lateral to the thyroid gland near the submandibular gland (blue arrow). C. Non-specific isotope trapping occurs in the nasopharynx and salivary glands (outlined in white).
In other comparisons of planar, SPECT and SPECT/CT imaging modalities, SPECT/CT permitted the highest confidence in localization of ectopic adenomas. When available, superior anatomical localization is determined by the combined sestamibi SPECT/CT imaging. It is encouraged that contrast be given with a diagnostic quality CT for the best preoperative localization.