Primary hyperparathyroidism (PHPT) is a condition characterized by an excess secretion of parathyroid hormone by adenomatous or hyperplastic glands [1][2]. The accurate preoperative localization of parathyroid adenomas is important to reduce the operative failure rate [2] [3]. Tc-99m sestamibi (MIBI) scintigraphy is a useful preoperative diagnostic tool for PHPT [4] [5]. The association of a functional parathyroid cyst with a parathyroid adenoma is an uncommon finding [6] [7][8][9]. It was reported that in some patients with PHPT and a functioning parathyroid cyst, Tc-99m MIBI scintigraphy failed to detect a parathyroid tumor [6][7]. There have also been some reports of radio-guided surgery for PHPT [10][11][12][13][14][15][16][17][18][19]. We recently demonstrated that in scan-positive patients identified by preoperative Tc-MIBI, Tc-MIBI scintigraphy with the use of a hand-held gamma camera, the eZ-SCOPE AN (Anzai Medical Co. Ltd., JAPAN), is useful for navigation surgery for PHPT and minimally invasive parathyroidectomies [18][19].

The eZ-SCOPE AN is designed to be used as a hand-held, regional diagnostic imaging device, which is a new compact-type semiconductor gamma camera based on the use of a cadmium zinc telluride (CdZnTe) [18][19][20][21]. We report here a rare case of a patients with a functioning parathyroid cyst in whom MIBI scintigraphy failed, but in whom a gamma camera could detect a parathyroid tumor

The eZ-SCOPE AN is designed to be used as a hand-held, regional diagnostic imaging device [17][18][19][20]. This compact-type semiconductor gamma camera made of CdZnTe has 256 semiconductors representing the same number of pixels. Each semiconductor is a 2-mm square and is located in 16 lines and rows on the surface of the detector. The outer dimensions of the camera are 74×72×210 mm, and it weighs 820 g. The most significant differences between it and previous cameras include the spatial resolution, sensitivity, high count rate characteristics, and energy resolution [18] [19][20][21].

The patient was a 70-year-old Japanese man with a history of hepatocellular carcinoma with chronic hepatitis C. Hypercalcemia and a high level of intact parathyroid hormone (PTH) had been detected 27 months prior to his admission to our hospital. Neck ultrasonography and computed tomography (CT) scan revealed a right parathyroid tumor, but a Tc-99m MIBI scintigraphy examination failed to detect a parathyroid tumor. He had been followed up because he was also suffering from the hepatocellular carcinoma with liver cirrhosis. His serum calcium level had been significantly elevated, and thus he was referred to our hospital for further examination and treatment of hypercalcemia and the high level of intact PTH. On admission, his serum calcium was 14.4 mg/dL, albumin was 3.7 g/dL, and the intact PTH level was 423 pg/mL. Computed tomography scan of his neck showed a hypodense mass in the right side of the neck with peripherally enhancing walls measuring approximately 3.0×2.0 cm (Figure 1).

Magnetic response imaging (MRI) scan showed a mass in the right neck, which showed low to intermediate signal intensity on T1-weighted images and high signal intensity on T2 images compared to the surrounding tissues (Figure 2). Neck ultrasonography (US) revealed a cystic mass measuring 3.0×1.5 cm in the right neck (Figure 3). Tc-99m MIBI scintigraphy was performed to diagnose primary hyperparathyroidism and examine other parathyroid glands, but it failed to detect a parathyroid tumor (Figure 4). As there was suspicion of hyperparathyroidism due to the functioning parathyroid cyst, we performed resection of the right cystic mass. Scintigraphy images of the neck were acquired with the eZ-SCOPE AN before the skin incision, and ex vivo imaging of the specimen was performed (Figure 5). This gamma camera was useful for the navigation surgery and minimally invasive parathyroidectomy.

The intact PTH level was measured 10 min after the removal of the cystic mass, and we confirmed a decrease in the intact PTH level. Histopathology showed a parathyroid adenoma with prominent cystic degeneration (Figure 6). Our follow-up of the patient has remained uneventful, with no sign of recurrent disease.

Tc-99m MIBI scintigraphy has been widely used with high accuracy for the detection and localization of parathyroid tumors [4] [5]. Here we encountered a rare case of a patient with PHPT with a functioning parathyroid cyst in whom Tc-99m MIBI scintigraphy failed to detect a parathyroid tumor. Cystic lesions of the parathyroid gland are very uncommon, and the association of a functional parathyroid cyst with a parathyroid adenoma is an uncommon finding[6] [7][8][9]; the most common cause is cystic degeneration of the adenomas, which is consistent with our case. Computed tomography scan, magnetic resonance imaging scan and ultrasonography could demonstrate our patient's cystic parathyroid adenoma, whereas the Tc-99m MIBI scintigraphy failed to detect the cystic adenoma.

Although the exact mechanisms of the visualization of abnormal and hyperfunctioning parathyroid tissue by MIBI scintigraphy are not clear, false-negative diagnostic results have been reported in cystic parathyroid adenoma [6] [7]. In our previous study, we found that for single adenomas and cases with positive Tc-MIBI scans, radio-guided surgery is an effective tool in the surgical management of primary hyperparathyroidism [18] [19]; however, in cases that are scan-negative due to cystic disease, radio-guided surgery is also thought to be useful.

We have reported a rare case of a patient with a cystic parathyroid adenoma presenting hyperparathyroidism in whom a gamma camera could detect the parathyroid tumor. Preoperative diagnoses can be challenging for cystic parathyroid adenomas. In some cystic hyperfunctioning scan-negative parathyroid tumor cases, the eZ-SCOPE AN may be useful for the localization and the navigation surgery of primary hyperparathyroidism due to a cystic parathyroid tumor.

We would like to thank Saitoh Y, Yano T, Matsui Y, Ishida A, Ishikubo A for their secretarial assistance.

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