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Primary hyperparathyroidism and metastatic papillary thyroid cancer
A case with a false positive parathyroid sestamibi and neck ultrasound scans.
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A 68-year-old woman was referred to the endocrine clinic for hypercalcemia and elevated parathyroid hormone. She had no history of fractures, constipation, nephrolithiasis or head and neck radiation but she had osteoporosis on DPX bone density scan with a significant decrease in density over the past three years. Her neck exam revealed a small firm thyroid gland without palpable thyroid nodules, neck masses or adenopathy. Her laboratory tests showed an elevated ionized calcium of 6 (reference range: 3.8-5.3 mg/dL) and serum calcium of 11.2 (reference range: 8.4-10.2 mg/dL) with an albumin of 4.6 (reference range: 3.5-4.8 g/dL), intact parathyroid hormone level of 78 (reference range: 11-80 pg/mL), calculated fractional excretion of calcium 2.6%, TSH of 1.15 (reference range: 0.35-5.5 uIU/mL) and thyroid peroxidase antibody level of 146 (reference range <20 IU/mL).
 Stephanie L. Lee |
 Lisa S. Usdan |
Prior to her endocrine consultation, thyroid sonography revealed multiple sub-centimeter thyroid pseudo-nodules and a hypoechoic, heterogeneous echotexture consistent with chronic thyroiditis. A nuclear parathyroid localization scan with 99m pertechnetate sestimibi was performed in addition to a thyroid scan with 99m pertechnetate because of her known thyroid pathology.
Early images of the sestimibi scan were compared to the thyroid scan and revealed excess isotope accumulation inferior to the left lower pole of the thyroid gland (see figures 1A vs. 1B). Late images of the sestimibi scan demonstrated uniform washout of the isotope. Although early washout of isotope is not typical for parathyroid adenomas, an experienced nuclear medicine radiologist assessed the scan and found it to be consistent with a left parathyroid adenoma inferior to the left thyroid lobe.
Continued investigation
A thyroid ultrasound (see figure 2) in our endocrine clinic showed a hypervascular, hypoechoic nodule without microcalcifications located inferior and separate from the left thyroid lobe corresponding to the location of the parathyroid adenoma suggested by the nuclear medicine scan. The thyroid parenchyma was heterogeneous and hypoechoic consistent with the history of thyroiditis but no significant thyroid nodule was seen. This extra-thyroidal mass was felt to be consistent with a parathyroid adenoma because of the concordant sestimibi scintigraphy and ultrasound scans.
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Source: S. Lee |
The patient underwent a minimally invasive parathyroidectomy. Intraoperative parathyroid hormone levels remained elevated after excision of the 1.5 cm mass located inferior to the left lower pole of the thyroid. Frozen section of the mass revealed a lymph node containing thyroid cells consistent with a differentiated thyroid carcinoma metastasis. Her surgery was modified to a conventional parathyroidectomy with a total thyroidectomy. A right superior parathyroid adenoma was identified and removed with intraoperative parathyroid hormone levels by rapid assay falling in 15 minutes by 86.5%, from 104 pg/mL to 14 pg/mL. The final pathology described a left level VI lymph node containing papillary thyroid cancer, Hashimoto’s thyroiditis with a 0.3 cm focus of papillary thyroid carcinoma in the left lobe, and a 300 mg (normal 35-50 mg) right superior parathyroid adenoma.
Positive nuclear scans generally reflect increased radiopharmaceutical trapping in the thyroid and parathyroid glands with a washout of isotope from the thyroid tissue and persistence of the isotope in the abnormal parathyroid adenoma. False positives on 99mTc sestamibi scans have been described in nodular thyroid disease including adenomas, colloid nodules and carcinomas as well as parathyroid hyperplasia and benign lymph nodes. False negative scans, such as in this patient, can occur with superior parathyroid adenomas which are located posterior to the thickest portion of the thyroid gland. Patients with false positive 99mTc sestamibi scans are of particular interest as they have biochemical evidence of primary hyperparathryoidism and radiographic localization of a suspicious lesion; however the lesion is not the parathyroid adenoma. Preoperative confirmation of a parathyroid adenoma by iPTH analysis of a needle aspiration would avoid surgical removal of a false positive mass whether intra- or extra-thyroidal. Fine needle aspiration biopsy for cytology and iPTH analysis of the needle washed with 1 mL of normal saline is an extremely sensitive (91%) and specific (95%) technique.
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Source: S. Lee |
This is a unique situation of two concordant false positive parathyroid adenoma localization scans, 99mTc sestimibi and ultrasound, of a metastatic node of papillary thyroid carcinoma with a false-negative 99mTc sestimibi of a contralateral superior parathyroid adenoma. Misdiagnosis would have been avoided if the potential for both false positives was recognized and if a preoperative ultrasound-guided fine needle aspiration biopsy of the suspected mass with needle washings analyzed for both iPTH and thyroglobulin levels was performed.
Stephanie L. Lee, MD, PhD, is an Associate Chief in the Section of Endocrinology, Diabetes and Nutrition and an Associate Professor of Medicine at Boston Medical Center.
Lisa S. Usdan, MD, is an Instructor in the Section of Endocrinology, Diabetes and Nutrition and an Instructor of Medicine at Boston Medical Center.
For more information:
- Abraham D, Sharma P, Bentz J, et al. Utility of ultrasound-guided fine-needle aspiration of parathyroid adenomas for localization before minimally invasive parathyroidectomy. Endocr Pract. 2007;13;333-337.
- Norman JG, Jaffray CE, Chheda H. The false-positive parathyroid sestamibi a real or perceived problem and a case for radioguided parathyroidectomy. Ann Surg. 2000;231;31-37.
- Smith JR and Oates ME. Radionuclide imaging of the parathyroid glands: patterns, pearls, and pitfalls. Radiographics. 2004;24:1101-1115.
- Westerdahl J and Bergenfelz A. Sestamibi scan-directed parathyroid surgery: potentially high failure rate without measurement of intraoperative parathyroid hormone. World J Surg.2004; 28;1132-1138.