Abstract

Primary hyperparathyroidism(PH) is most commonly caused by parathyroid adenoma and 1-3% of these parathyroid adenomas can be found ectopically. Approximately 20% of all ectopic parathyroid glands are present in the mediastinum, and 2% of these are not accessible through a cervical incision. These cases require sternotomy or thoracotomy. We report the rare case of a 23-year-old patient with PH due to an ectopic mediastinal parathyroid adenoma located in the anterior mediastinum between the ascending aort and sternum. Surgical resection of adenoma was performed through a partial sternotomy. Serum Ca and Parathormone(PTH) levels returned within normal range postoperatively.

Introduction

Primary Hyperparathyroidism results from inappropriate overproduction of parathyroid hormone from one or more parathyroid glands, and causes hypercalcemia(1). The major reason of primary hyperparathyroidism is parathyroid adenomas. In some patients, adenomas can be found ectopically. Mediastinum is one of the ectopic locations of parathyroid adenomas(2). We report the case of a young patient with PH due to an ectopic mediastinal parathyroid adenoma located in the anterior mediastinum, that was excised through a partial sternotomy.

Case Presentation

A 23-year-old man presented to the our clinic with a one-month history of fatigue associated with headache and lethargy. There was no significant past medical illness. On examination, the patient was conscious and alert. His serum calcium and phosphorus levels were 15 mg/dL and 1.06 mg/dL, respectively Intact parathormone level was 861 pg/mL (normal range 15 to 60 pg/dL). The patient was treated with saline hydration and serum calcium level decreased to 10.1mg/dL.

A neck ultrasound showed a normal thyroid gland and no evidence of the parathyroid adenoma was found in the neck.Tc-99m sestamibi scintigraphy showed a focal intense uptake and retention of tracer in the anterior mediastinum, which was suggestive of an ectopic parathyroid adenoma (Figure 1). Finally a magnetic resonance image(MRI) of the neck and thorax revealed a 15x11x20 mm mass in thymus at the anterior mediastinum between the ascending aort and sternum.

The patient underwent partial median sternotomy and the thymus gland along with the perithymic fat tissue and a suspicious nodular tissue was removed together with cardiothrocic surgeons. The resected mass in thymus was an oval nodule measuring 2.5 cm × 2.0 cm × 1.5 cm and covered by a thin capsule(Figure 2).Frozen section from the mass confirmed that the sample represented parathyroid tissue. Intraoperative PTH (iPTH) assays was performed, and a reduction of iPTH from 861pg/ml to 140pg/ml within ten minutes of excision was seen and the reduction of iPTH confirmed successful surgery.

The histopathological examination revealed a reddish brown capsulated nodular lesion embedded in thymus glandular tissue and the permanent section confirmed the diagnosis of parathyroid adenoma. PTH serum level and calcemia decreased promptly to normal ranges 30 pg/ml and 8.7 mg/dl respectively and he was supported only with oral calcium. The post-operative course was uneventful and the patient was discharged in 5th post-operative day.

Discussion

Primary hyperparathyroidism occurs in approximately 1% of the adult population and is commonly due to solitary parathyroid adenomas (85%). Other causes of primary hyperparathyroidism are related to multiple gland hyperplasia affecting all parathyroid glands (10%), double adenomas (4%) and parathyroid carcinoma (1%) (3). The treatment of PH is surgery and consists in the excision of the oversecreting parathyroid glands(4).

The embryological origin of parathyroid glands is the endoderma of the third and fourth pharyngeal pouches(5). The parathyroid glands arise in an ectopic area in 1-3% of the cases and may be found anywhere from the angle of the jaw to the pericardium as a consequence of a variability in the glandular tissue migration during the embryologic life (6). 11%–25% of all ectopic parathyroid glands are present in the mediastinum, and 2% of these are not accessible through a cervical incision(2). These cases require sternotomy or thoracotomy, which has a morbidity rate that approaches 20%(7). Open surgical excision remains the standard treatment for mediastinal parathyroid adenoma. Thoracoscopic removal, robotic procedures and angiographic ablation could be considered for treatment of ectopic parathyroid adenomas.(8-10). That approaches are less invasive than sternotomy and thoracotomy, and they are promising methods for resection of ectopic parathyroid glands in the mediastinum.

Preoperative localization studies can reduce complication rates and shorten operating time by directing the surgeon to the site or the sites of ectopic parathyroid glands(11). Localization of ectopic parathyroid glands are important, Mariette et al reported that failed parathyroid operation was due to an ectopic parathyroid gland in 75% of cases(12).

Currently used non-invasive diagnostic techniques include Tc-99m MIBI (technetium-99m-2-methoxy-isobutylisonitrile) scanning with or without SPECT (Single-photon emission computed tomography), US(Ultrasound), CT(Computed Tomography) imaging and MRI(Magnetic resonance imaging )(13). The most reliable and practical procedure is Tc-99m MIBI scanning.(14,15).During the last decade, localization studies before the initial operation have been used widely and minimally invasive parathyroidectomy procedures are commonly applied. Many centers agree on the value of performing Tc-99m MIBI scintigraphy alone or combined with high-resolution cervical US in the preoperative workup of patients with HPT before initial surgery(13).

Conclusion

Ectopic parathyroid adenomas account for about 1%–3% of primary hyperparathyroidism and approximately 20% of ectopic parathyroid adenomas locates in mediastinum. Surgical resection results in cure of the disease but accurate preoperative localization of an ectopic parathyroid adenoma is important for a successful surgical therapy. Multi-disciplinary team involving the endocrinologist, surgeons experienced in parathyroid surgery, cardiothrocic surgery and radiologists is necessary for management of ectopic mediastinal parathyroid adenomas.

References

1. Feder JM,Sirrs S,Anderson D,Sharif J,Khan A.Primary Hyperthyroidism:An overview. Int J Endocrinol 2011:8.
2. Dincer SI, Demir A, Kara HV and Gu¨ nlu¨ oglu MZ. Thoracoscopic removal of a maternal mediastinal ectopic parathyroid adenoma causing neonatal hypocalcemia: a case report. Ann Thorac Cardiovasc Surg 2008; 14:325–328.
3. AACE/AAES Task Force on Primary Hyperparathyroidism. AACE and AAES position statement on the diagnosis and management of primary hyperparathyroidism. Endocr Pract 2005; 11:49-54.
4. Cupisti K, Dotzenrath C, Simon D, Roher HD, Goretzki PE. Therapy of suspected intrathoracic parathyroid adenomas. Experiences using open transthoracic approach and video-assisted thoracoscopic surgery. Langenbecks Arch Surg 2002; 386 (7): 488-93.
5. Okuda I, Nakajima Y, Mıura D, Maruna H, Kohno T, Hırata K. Diagnostic localization of ectopic parathyroid lesions: developmental consideration. Jpn J Radiol 2010; 28: 707-713.
6. Curly I, et al. The challenge of the middle mediastinal parathyroid. World J Surg 1988; 12: 818.
7. Prinz RA, Lonchyna V, Carnaille B, Wurtz A and Proye C. Thoracoscopic excision of enlarged mediastinal parathyroid glands. Surgery 1994; 116: 999–1005.
8. Smythe WR, et al: Thoracoscopic removal of mediastinal parathyroid adenoma. Ann Thorac Surg 1995; 59: 236.
9. Bodner J, Wykypiel H, Greiner A, Kirchmayr W, Freund MC, Margreiter R, et al. Early experience with robot-assisted surgery for mediastinal masses. Ann Thorac Surg 2004;78:259–65.
10. Doherty GM, Doppman JL, Miller DL, Gee MS, Marx SJ, Spiegel AM, et al.Results of a multidisciplinary strategy for management of mediastinal parathyroid adenoma as a cause of persistent primary hyperparathyroidism. Ann Surg 1992;215: 101-6.
11. Shen W, Duren M, Morita E, et al.Reoperation for persistent or recurrent primary hyperparathyroidism. Arch Surg 1996:131: 861-867.
12. Mariette C, Pellissier L, Combemale F, Quievreux JL, Carnaile B, Proye C.Reoperation for persistent or recurrent primary hyperparathyroidism. Langenbecks Arch Surg 1998; 383: 174-9.
13. Mariani G, Gulec SA, Rubello D, et al, 2003 Preoperative localization and radioguided parathyroid surgery. J Nucl Med 44: 1443-1458.
14. Peeler BB, Martin WH, Sandler MP, Goldstein RE, 1997 Sestamibi parathyroid scanning and preoperative localization studies for patients with recurrent/persistent hyperparathyroidism or significant comorbid conditions: development of an optimal localization strategy. Am Surg
15. 63: 37-46.
16. Wells SA Jr, Debenedetti MK, Doherty GM, 2002 Recurrent or persistent hyperparathyroidism. J Bone Miner Res 17: 158-162.