CASE REPORT Sestamibi Retention in a Breast Fibroadenoma in a Case of Hypercalcemia With Parathyroid Adenoma I ˙ nan Anaforog ˇlu, MD,* Ekrem Algu ¨n, MD,* Recep Sahin, MD,† and I ˙ smail Hakkı Ocak, MD‡ Abstract: Primary hyperparathyroidism is the most common cause of hypercalcemia in nonhospitalized patients. Recently, technetium-99m sesta- mibi (methoxyisobutylisonitrile, Tc-99m MIBI) imaging has been estab- lished as the best method for detecting a parathyroid adenoma. However, sestamibi accumulates in a number of nonparathyroid tissues. We report a patient with suspected primary hyperparathyroidism, who underwent sesta- mibi parathyroid imaging. In addition to sestamibi retention in a parathyroid adenoma, retention was observed in a breast fibroadenoma, which mimicked an ectopic parathyroid adenoma. Key Words: parathyroid adenoma, sestamibi, breast fibroadenoma, hyperparathyroidism (The Endocrinologist 2010;20: 17–18) P rimary hyperparathyroidism is the most common cause of hy- percalcemia in nonhospitalized patients. The most common cause of primary hyperparathyroidism is a solitary parathyroid adenoma, followed by parathyroid hyperplasia and carcinoma. 1 Preoperative localization studies shorten operative time and de- crease the extent of dissection by allowing the surgeon to find the abnormality early in the operation and guide the surgeon in resecting ectopic glands. 2,3 Recently, technetium-99m sestamibi (methoxy- isobutylisonitrile, Tc-99m MIBI) imaging has been established as the best method for detecting parathyroid adenomas. 1 Sestamibi is a monovalent lipophilic cation that accumulates in certain benign and malignant cells. 4,5 Many radionuclide imaging techniques are used in the detection of breast cancer. Sestamibi is the most commonly radiopharmaceutical used to detect breast cancer. Although sestamibi is avidly concentrated in breast cancer cells, increased uptake of the radiotracer can occur in benign breast lesions 6–8 ; breast fibroadenoma is a good example. 6,7 We report a patient with suspected primary hyperparathyroidism who un- derwent sestamibi parathyroid imaging. Sestamibi retention was ob- served in a parathyroid adenoma and in a fibrocystic breast gland that mimicked an ectopic parathyroid adenoma. CASE REPORT A 37-year-old woman with severe hypercalcemia was re- ferred to our department for further evaluation of possible primary hyperparathyroidism. She was found to have hypercalcemia, hy- pophosphatemia, and a high level of serum intact parathyroid hor- mone while being investigated for nausea, dizziness, and tingling of hands. Neck ultrasonography revealed a 12.0  8.5 mm, hypoechoic lesion in the lower portion of the right lobe of the thyroid glands. The thyroid parenchyma was otherwise homogeneous. Menstrual cycles were regular, she was taking no medication, and she had no family history of hypercalcemia or renal stones. The patient was 152 cm tall, and she weighed 67 kg. Vital signs were normal. Repeated laboratory studies confirmed hyperparathyroidism (Table 1). A sestamibi parathyroid scintigraphy was performed. Images of the neck and thorax were taken after 10 minutes and 2 hours. Both early and late planar studies revealed a parathyroid adenoma near the midline of the right lobe of thyroid. In addition, uptake in the right upper mediastinum was detected (Figs. 1, 2). A thoracic magnetic resonance imaging study was performed, and results were normal. The patient had a history of fibrocystic disease of the breast which was confirmed by a breast biopsy in the past. A breast ultrasonography demonstrated a homogeneous, hypoechoic, well shaped, 15.4  10.5 mm lesion with a posterior acoustic shadow. This lesion was not compatible with a fibroadenoma. Mammography findings were com- patible with a fibroadenoma. The patient was referred for parathyroid- ectomy. One of the parathyroid glands was enlarged, and it was removed. The parathyroid gland showed the typical histologic features of an adenoma. Results of the patient’s serum calcium and parathyroid hormone levels decreased to normal postoperatively. DISCUSSION Sestamibi scanning has a high specificity for parathyroid tissue. 9 However, sestamibi can accumulate in a number of non- parathyroid tissues. 4,5 In the neck, retention of sestamibi occurs in differentiated thyroid malignancies, remnant thymus, and enlarged submandibular salivary glands. 5,10,11 The other common nonartifac- tual accumulation sites are nodular thyroid disease, sarcoidosis, tuberculosis, brown adipose tissue, and neoplasm’s, such as lym- phoma, breast, lung, head, neck carcinomas, as well as their lymph node and osseous metastases. 11–14 Malignant tumors maintain a higher mitochondrial and plasma membrane potential than most nonmalignant tissue by virtue of in- creased metabolic requirements, and therefore can concentrate MIBI. 15 For example, MIBI can be used to detect bone marrow involvement with multiple myeloma. 16 –18 MIBI traces neoplastic plasma cell pro- liferation with a sensitivity and specificity of about 80%. 16,18,19 MIBI can be used to distinguish malignant bone metastases from benign bone lesions. 20 The clinical use of MIBI is approved for breast cancer imaging. 6–8 The prevalence of detectable benign lesions in different series varies between 16% and 59%. 21 MIBI is not suitable for early From the Departments of *Endocrinology and Metabolism, †Nuclear Medicine, and ‡General Surgery, Trabzon Numune Research and Training Hospital, Trabzon, Turkey. Reprints: I ˙ nan Anaforog ˇlu, MD, Trabzon Numune Eg ˇitim ve Aras ¸tırma Hastanesi, Endokrinoloji Klinig ˘i, 61000, Trabzon, Turkey. E-mail: ianaforoglu@ hotmail.com. Copyright © 2010 by Lippincott Williams & Wilkins ISSN: 1051-2144/10/2001-0017 DOI: 10.1097/TEN.0b013e3181cb480f TABLE 1. Results of the Patient’s Laboratory Investigations Tests Values Normal Range Serum calcium (mg/dL) 13.9 8.2–11 Serum phosphate (mg/dL) 2.6 2.5–4.5 Serum alkaline phosphatase (IU/L) 104 40–129 24-h urinary calcium (mg/d) 448 100–320 25-OH vitamin D (pg/mL) 34.5 19.9–67 Serum parathyroid hormone (pg/mL) 339 15–65 Albumin (g/dL) 4.7 3.4–4.8 The Endocrinologist • Volume 20, Number 1, February 2010 www.theendocrinologist.org | 17