Japanese Journal of Clinical Oncology 34:155-158 (2004)
© 2004 Foundation for Promotion of Cancer Research
Parathyroid Adenoma without Hyperparathyroidism
1 Department of Surgery and 3 Department of Pathology, Omiya Medical Center, Jichi Medical School, Saitama and 2 Department of Surgery, Jichi Medical School, Kawachi-gun, Tochigi, Japan
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ABSTRACT |
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A 45-year-old female patient was admitted to our hospital presenting with a right anterior cervical tumor that was elastic, hard, painless and 3.5 x 3.5 cm in size. Laboratory data including serum calcium level, thyroid and parathyroid hormonal functions revealed no abnormalities. Further examination, consisting of computed tomography (CT), magnetic resonance imaging (MRI), ultrasonography (US) and radioisotope (RI)-imaging demonstrated that it was a solid tumor located behind the right thyroid lobe. The tumor, whose origin was unclear, was successfully removed with right thyroid lobectomy. Macroscopically, it appeared as reddish solid tumor consisting of small cystic lesions storing chocolate-colored mucous. Immunohistology confirmed that there was proliferation of chief cells with positive parathyroid hormone (PTH) staining. Thus the tumor was diagnosed as parathyroid adenoma despite a lack of clinical evidence for hyperparathyroidism. The reason for the lack of clinical features of hyperparathyroidism in this adenoma still remains unclear, however, there might be inactivation of hormone excretion, possibly due to insufficiency of blood supply. This was a very rare case of parathyroid adenoma exhibiting no clinical evidence of hyperparathyroidism.
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONCASE REPORTDISCUSSIONREFERENCES |
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In general, parathyroid tumors are classified into adenoma, hyperplasia, cystic changes and carcinoma. The differentiation between adenoma and hyperplasia is often difficult in usual histopathological examinations. Compared to hyperplasia, parathyroid adenomas often present a higher increase in the level of serum parathyroid hormone (PTH). Bone fractures, calculi of the urinary tract and higher serum calcium levels are more frequently the first symptoms of parathyroid adenomas than of hyperplasias. This case report presents a rare case of PTH producing parathyroid adenoma with normal levels of serum PTH and calcium.
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CASE REPORT |
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The patient was a 45-year-old female with the chief complaint of right cervical swelling. There was nothing particular in her family history and past history. In 1995, the patient recognized right cervical swelling that was left untreated because there were no other symptoms. In early 1997, the patient consulted a local doctor, where a deviation of the trachea to the left side was pointed out on chest X-ray. She was referred to our hospital for further examination. The patient was 164 cm in height and 78 kg in weight with a normal blood pressure of 124/70 mmHg and normal pulse rate of 70 per minute. There was no anemia, jaundice or cervical node swelling. A tumor measuring 3.5 x 3.5 cm was present in her right anterior cervical region. The tumor was smooth on the surface, well demarcated and mobile. There was no tenderness at the site of the tumor. No other abnormal finding was observed in the chest or the abdomen on physical examination. Laboratory data revealed a serum calcium level of 9.4, phosphate level of 3.5 mg/dl, high sensitivity-PTH level of 312 pg/ml, and PTH allegro (intact-PTH) level of 28 pg/ml. All of these laboratory data were within normal limits. There was no abnormality in the hormonal levels of the thyroid gland. Urinalysis and blood chemistry were also normal. Ultrasonography of the cervical region indicated a well-demarcated tumor with a partially uneven echo level that was depicted behind the right lobe of the thyroid gland. Ultrasonography indicated no swelling of the cervical lymph nodes (Fig. 1). Aspiration cytology of the tumor was performed, which revealed a proliferation of eosinophilic cells suggesting an adenoma of either the thyroid gland or parathyroid gland. Computed tomography (CT) scan of the cervical region showed a tumor with an uneven low density situated behind the right lobe of the thyroid gland (Fig. 2). CT with enhancement indicated uneven staining within the tumor, and the boundary between the tumor and the thyroid gland was unclear. Magnetic resonance imaging (MRI) of the neck also showed a tumor with an uneven intensity. MRI did not reveal any findings of invasion in the vascular structures around the tumor (Fig. 3). The origin of the tumor was unclear based upon the CT scan and MRI findings. 201Tl scintigraphy showed an accumulation of radioactivity within the tumor and washout of the radioactivity was delayed. 123I scintigraphy showed no accumulation in the tumor. Based upon the findings of these preoperative investigations, a thyroid or parathyroid tumor was suspected and surgery was performed. The tumor was present just behind the right lobe of the thyroid gland. The surface of the tumor was smooth and it was easily dissected from the surrounding structures except for a small area in the lower pole of the right thyroid gland, where there was an adhesion between the tumor and the thyroid gland. Two normal-sized parathyroid glands were identified on the left side; however, identification of normal parathyroid glands on the right side was not possible. The tumor was removed together with the right lobe of the thyroid gland. Histological examination showed a tumor measuring 67 x 27 x 38 mm in size, and no boundary between the right side of the thyroid gland and the tumor at the site of the adhesion was noted. The tumor was elastic-hard on palpation and, except for a small area of the adhesion, it was almost entirely encapsulated. The cut surfaces of the tumor revealed brownish-red solid tumor tissue with scattered small cystic changes containing fluid with a chocolate-like color (Fig. 4). The HS-PTH level and PTH allegro level of the fluids in the cyst were 16 500 and 123 pg/ml, respectively (normal ranges: HS-PTH 180~568 pg/ml, PTH allegro 13~53 pg/ml). On histology, the tumor showed a medullary proliferation in the chief cell of the parathyroid gland including eosinophilic cells (Fig. 5). There was diffuse positive immunohistochemical staining of PTH in the tumor cells (Fig. 6). Based upon the clinical and histopathological findings, the tumor was diagnosed as parathyroid adenoma without hyperparathyroidism originating in one of the parathyroid glands.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONCASE REPORTDISCUSSIONREFERENCES |
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Most parathyroid adenomas are functional and manifest hypercalcemia causing bone fractures and urinary tract calculi (1–3). The parathyroid tumor in the current case displayed a medullary growth of adenomatous tissue of the parathyroid chief cells.
There were small cystic changes and hemorrhages within the tumor, but necrosis was not observed. The tumor was considered to have arisen in one of the right parathyroid glands. The remaining parathyroid adenoma on the right side probably became atrophic because of the expanding nature of the tumor. There were two normal-sized parathyroid glands on the left side, which led to the diagnosis of parathyroid adenoma rather than hyperplasia. In the current case, levels of serum PTH, calcium and phosphate were normal despite the positive PTH immuno-staining of the tumor cells. We think that such a case is extremely rare because nearly all parathyroid adenomas reported have been functional with an increased level of serum PTH and manifestations of hyperparathyroidism. There were reported cases of ‘normocalcemic hyperparathyroidism’, in which renal calculi and hypercalciuria were present while the serum levels of total calcium and intact PTH were normal and the serum ionized calcium level was elevated (4). Parathyroid adenomas were present in some of the cases reported as normocalcemic hyperparathyroidism (5). The present case was different from those previously reported as normocalcemic hyperparathyroidism because there were no manifestations such as urinary tract calculi or hypercalciuria. We discovered two reports of parathyroid adenomas that were not associated with hyperparathyroidism (6,7). There was one report of cats in which asymptomatic parathyroid nodules were present (8). None of these reports, however, discussed any mechanism for how parathyroid adenomas become non-functional. Fujimoto classified parathyroid cysts into two categories: functional and non-functional (9). He speculated that parathyroid cysts become functional if secondary degeneration of parathyroid adenoma tissue results in leaving residual parathyroid adenoma tissue in the cyst wall. Lydiatt et al. reported that there had been 20 cases of functional parathyroid cysts reported as of 1995 (10). On the other hand, non-functional parathyroid cyst was defined as a lesion in which there is no parathyroid adenoma tissue in the cyst wall and no manifestations of hyperparathyroidism (11–14). There would be two possible reasons for having a non-functioning parathyroid adenoma with positive PTH staining in the current case: either a low level of PTH production or inhibition of the release of the hormone into the bloodstream. However, the exact mechanism for the non-functional nature of the parathyroid adenoma was not apparent in the current case. There were no glandular cells in the wall of the cystic part of the lesion, which might be a reason for not having the hormone secreted into the bloodstream. However, the mechanism of formation for the solid part of the lesion remained unclear. The measurement of intact PTH in the blood of both left and right middle thyroid arteries might allow the differentiation between functioning and non-functioning adenoma of the parathyroid gland.
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FOOTNOTES |
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+ For reprints and all correspondence: Osamu Sekine, Department of Surgery, Omiya Medical Center, Jichi Medical School, 1–847 Amanuma-cho, Omiya-ku, Saitama-shi, Saitama, Japan. E-mail: kankon{at}jichi.ac.jp
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REFERENCES |
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Received October 22, 2003; accepted January 9, 2004
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