Asian Cardiovasc Thorac Ann 2006;14:e86-e87
© 2006 Asia Publishing EXchange Ltd
Thoracoscopic Findings of a Small Posterior Mediastinal Parathyroid Adenoma
Masanobu Taguchi, MD,
Shunsuke Endo, PhD,
Tsuyoshi Hasegawa, PhD,
Yukio Sato, PhD,
Yasunori Sohara, PhD
Division of General Thoracic Surgery, Department of Surgery, Jichi Medical School, Tochigi, Japan
For reprint information contact: Shunsuke Endo, MD Tel: 81 285 587 368 Fax: 81 285 446 271 Email: tcvshun{at}jichi.ac.jp, Division of General Thoracic Surgery, Department of Surgery, Jichi Medical School, Minamikawachi-machi, Kawachi-gun, Tochigi 329-0498, Japan.
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ABSTRACT
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We report herein the rare case of a posterior mediastinal parathyroid adenoma 8 mm in diameter, that was identified by both 99m-technetium-methoxyisobutylisonitrile scintigraphy (Tc-MIBI) and high-resolution chest computed tomography (HRCT). Thoracoscopy clearly showed a mediastinal parathyroid adenoma which was successfully removed.
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INTRODUCTION
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Ectopic parathyroid adenoma in the mediastinum is occasionally detected in patients with hyperparathyroidism, but most ectopic mediastinal adenomas are located in the upper anterior mediastinum near the thymus.1 Video-assisted thoracoscopic surgery (VATS) has been advocated as an alternative to conventional procedures. The success of VATS depends on accurate localization during surgery. We report herein thoracoscopic findings of a rare upper posterior mediastinal parathyroid adenoma, measuring only 8 mm in diameter and removed by VATS.
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CASE REPORT
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A 67-year-old man was referred to our department 2 years after parathyroidectomy because his serum parathyroid hormone (PTH) concentration had remained elevated. Upon admission, serum concentrations of ionized calcium and intact PTH were 12.7 mg·dL–1 and 250 pg·dL–1, respectively. Tc-MIBI scintigraphy revealed an area of increased uptake in the upper right mediastinum (Figure 1A
). High-resolution chest computed tomography scan depicted a round tumor about 1 cm in diameter, located between the right lateral wall of the esophagus and the anomalous right subclavian artery. The anomalous artery branched off at the distal portion of the aortic arch and transversed the posterior mediastinum behind the trachea and esophagus, and thereafter arose in the posterior mediastinum (Figure 1B, C). Careful dissection of mediastinal tissue beside the anomalous right subclavian artery was performed, taking care not to damage the right vagal nerve (Figure 2). Subsequently, video-assisted right thoracoscopy revealed a brown tumor measuring 8 x 7 x 6 mm in size that had a distinct appearance from lymph nodes. The tumor was extirpated, and the specimen was diagnosed histologically as a parathyroid adenoma. The duration of surgery was 55 minutes. The postoperative course was uneventful. Serum concentrations of ionized calcium and PTH were normalized to 9.1 mg·dL–1 and 36 pg·dL–1 on postoperative day 1 and remained at normal values 6 months after surgery.
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Figure 1. 99m-technetium-methoxyisobutylisonitrile scintigram (A) shows an area of uptake in the upper right mediastinum; high-resolution chest computed tomography scans (B, C) show a small spherical tumor located between the right lateral wall of the esophagus and the right subclavian artery (white arrow), transversing the posterior mediastinum behind the trachea and esophagus after branching off at the distal portion of the aortic arch, and subsequently arising in the posterior upper mediastinum.
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Figure 2. Thoracoscopy revealed a brown tumor measuring 8 x 7 x 6 mm after the upper posterior mediastinal pleura was opened. The parathyroid adenoma (black arrowhead) had different thoracoscopic findings from mediastinal lymph nodes (white arrowhead). Black arrow; right anomalous subclavian artery, white arrow; right vagal nerve.
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DISCUSSION
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Primary hyperparathyroidism is caused by parathyroid adenoma in approximately 80% of patients, by glandular hyperplasia in more than 15%, and by parathyroid adenocarcinoma in a few rare cases.2 Ectopic parathyroid adenoma, located in the retropharyngeal, retroesophageal, or tracheoesophageal grooves of the thymus gland account for 12–33% of cases of parathyroid adenoma.3 The pathogenesis of these lesions is embryologic.4 The parathyroid bodies arise as endodermal cell proliferation at the lateral tips of the third and fourth pharyngeal pouches. The third pouch gives rise to the inferior parathyroid glands and to the thymus, which migrates down to the mediastinum. The fourth pouch gives rise to the superior parathyroid glands, is less closely associated with the migrating thymus, and is more closely associated with the laterally developing thyroid lobes. The inferior parathyroid reportedly migrates into the upper mediastinum along with the thymus in 10% of healthy persons.3 Furthermore, parathyroid glands can arise ectopically and be found anywhere from the angle of the jaw to the pericardium due to variation in glandular tissue migration during embryonic life.
99mTC-MIBI scintigraphy is an effective tool for identifying lesions that arise ectopically during embryonic life. Reliability of this method is reported at about 85%.5 Parathyroid glands measuring more than 1.5 cm in diameter can usually be detected on conventional chest CT scans, but smaller glands may be difficult to identify. Combined use of 99mTc-MIBI scintigraphy and HRCT may permit identification of ectopic mediastinal parathyroid tissue, even if it is less than 1 cm in diameter.
More accurate identification requires a difficult surgical procedure. Parathyroid adenoma located in the upper anterior mediastinum can be removed via a collar incision, and sternotomy or lateral thoracotomy is sometimes necessary.1 However, a lesion in the upper posterior mediastinum is difficult to approach. Neither sternotomy nor lateral thoracotomy can reliably provide a sufficient surgical view of the posterior upper mediastinal tumor. Video-assisted thoracoscopic surgery can be advocated as an excellent alternative to standard procedures for removal of upper posterior adenomas, measuring even less than 1 cm. The success of VATS depends on accurate localization during surgery.6 There has been successful result on VATS combined with intraoperative radionuclide-guided dissection for a small adenoma.7 In our patient, the anomalous right subclavian artery and thoracoscopic findings of the tumor were revealed after a careful dissection of a mediastinal tissue. Thoracoscopy navigated its localization, leading to successful removal by VATS. Thus, VATS can be an effective technique to localize small adenomas in the upper posterior mediastinum.
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REFERENCES
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- Rossi RL, Cady B. Surgical anatomy. In: Cady B, Rossi RL, editors. Surgery of the thyroid and parathyroid glands. Philadelphia, PA: Saunders, 1991; pp 13–30.
- Sanders LE, Cady B. Embryology and developmental abnormalities. In: Cady B, Rossi RL, editors. Surgery of the thyroid and parathyroid glands. Philadelphia, PA:Saunders, 1991; pp 5–12.
- Taira N, Doihara H, Hara F, Shien T, Takabatake D, Takahashi H, et al. Less invasive surgery for primary hyperparathyroidism based on preoperative 99mTc-hexakis-2-methoxyisobutylisonitrile imaging findings. Surg Today 2004;34:197–203.[Medline]
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- Ott MC, Malthaner RA, Reid R. Intraoperative radioguided thoracoscopic removal of ectopic parathyroid adenoma. Ann Thorac Surg 2001;72:1758–60.[Abstract/Free Full Text]
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ABSTRACT
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