Ann Thorac Surg 2001;71:699-701
© 2001 The Society of Thoracic Surgeons
Case report
Middle mediastinal parathyroid: diagnosis and surgical approach
Robin P. Boushey, MDa,
Thomas R.J. Todd, MDb
a Division of General Surgergy, The Toronto General Hospital, University of Toronto, Toronto, Ontario, Canada
b Division of Thoracic Surgery, The Toronto General Hospital, University of Toronto, Toronto, Ontario, Canada
Accepted for publication April 22, 2000.
Address correspondence to Dr Boushey, Toronto General Hospital University Health Network, 101 College St, CCRW 3-838, Toronto, Ontario M5G 2C4 Canada
e-mail: robin.boushey{at}utoronto.ca
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Abstract
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We report two cases of middle mediastinal parathyroid ectopia associated with chronic renal disease. In both patients the diagnosis was delayed and prolonged due to the unusual location of the ectopic parathyroid tissue. The surgical approach was in error in 1 patient and corrected during the second procedure. We describe the surgical technique for exposing and excising parathyroid tissue from this area.
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Introduction
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Retrospective studies have suggested that 1% to 3% of all patients undergoing parathyroid operations have a functional mediastinal parathyroid tumor [1, 2, 5]. The majority of these tumors are located in the superior aspect of the anterior or posterior mediastinum, making them accessible through a cervical incision, with 1.4% to 20% of patients requiring sternotomy [2–4]. Interestingly, very few cases of ectopic middle mediastinal parathyroid tissue have been reported and little information is available regarding the surgical approach to this problem [5]. We report two cases of tertiary hyperparathyroidism involving a supernumerary parathyroid in the middle mediastinum and outline the diagnostic and therapeutic dilemmas encountered with an emphasis on the surgical approach.
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Case reports
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Patient 1
A 36-year-old man was started on hemodialysis in 1993 for renal failure caused by a congenital urinary tract obstruction. Tertiary hyperparathyroidism ensued and medical attempts to manage the elevated serum calcium levels failed. In September 1995 the patient underwent a surgical excision of 3
parathyroid glands, however, serum calcium and parathyroid hormone (PTH) levels remained elevated. A computed tomographic scan of the thorax demonstrated a calcified lesion over the left main bronchus and right pulmonary artery. Selective venous sampling did not provide any additional information. In May 1996 the remaining portion of parathyroid gland was excised and a segment of gland cryopreserved and the remaining portion reimplanted into the patient’s forearm. Postoperative serum calcium levels remained in the high normal range suggesting that the middle mediastinal lesion seen on computed tomographic scan was likely parathyroid tissue. In October 1996 a sternotomy was performed and the area in question exposed transpericardially and the lesion excised along with the entire thymus. Histologic analysis of the lesion confirmed hypercellular parathyroid tissue. Serum calcium and parathyroid hormone levels have remained within the normal range to date.
Patient 2
A 35-year-old man with congenital medullary cystic kidney disease underwent a cadaveric renal transplant in 1972. After chronic rejection of the allograft the patient was restarted on dialysis in 1987. Multiple fractures ensued and a diagnosis of secondary hyperparathyroidism was established. A total parathyroidectomy with transplant into the left forearm and cryopreservation of the remaining hyperplastic parathyroid tissue was performed in 1988. Calcium levels returned to normal shortly after the operation. However, by March 1990 the patient once again demonstrated hypercalcemia on the basis of elevated PTH levels. Parathyroid tissue previously implanted in the patients forearm was excised but did not result in any biochemical or clinical improvement. Subsequent exploration of the neck and anterior mediastinum through a sternotomy failed to reveal additional parathyroid tissue. However, a computed tomographic scan of the thorax demonstrated a fairly well demarcated 2.2 cm mass just above the proximal right pulmonary artery lying on the anterior aspect of the proximal left main stem bronchus. Selective venous catheterization for PTH failed to lateralize the lesion and a left thoracotomy performed at another institution was unsuccessful in identifying the lesion. In June 1992 a sternotomy was performed at our hospital and the area in question was exposed transpericardially and the lesion excised. Histologic analysis verified an ectopic parathyroid gland and both serum calcium and PTH levels have remained within the normal range to date.
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Comment
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Parathyroid tissue in the middle mediastinum is a rare occurrence that presents several challenges to the surgeon both in terms of diagnosis and surgical approach [5, 6]. Although surgical excision is often performed through a standard left posterolateral thoracotomy, the frequent absence of ectopic calcification combined with the soft texture and small size (3 cm or less) of these tumors make identification and removal quite difficult with this surgical approach. This was certainly the problem with patient 2. A sternotomy offers two advantages: (1) It permits adequate exploration of the anterior mediastinum with a concomitant thymectomy to ensure that there is no residual parathyroid tissue. (2) Most importantly the approach to the middle mediastinum is superior to that obtained at thoracotomy. Figure 1 is an artist’s rendition of the exposure of the airway by this approach. After thymectomy the pericardium is opened and the incision is carried superiorly to permit mobilization. The aortic arch and superior vena cava are retracted laterally by division of the posterior pericardium. This latter incision continues overlying the right pulmonary artery as it courses through the subcarinal space. The origin of the left main stem bronchus is then identified (Fig 2). Dissection proceeds laterally on the anterior surface of the bronchus in order to avoid the left recurrent laryngeal nerve. The avoidance of the nerve is much more straightforward through the anterior approach than it is through a posterolateral thoracotomy. The parathyroid gland is visualized and excised with the aorta retracted. As noted the gland usually has the consistency of lymphatic tissue and digital palpation may be difficult unless it is peripherally calcified as in patient 1. A portion of the gland is quickly frozen for future implantation in the forearm.
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Fig 1. Artist’s rendition of the surgical approach illustrating complete exposure of the subcarinal space and right pulmonary artery after lateral retraction of the superior vena cava and aortic arch. In both patients a parathyroid gland was identified just above the right pulmonary artery lying on the anterior aspect of the proximal left main stem bronchus.
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Fig 2. Intraoperative photograph demonstrating the surgical exposure obtained at the time of tracheal resection. A similar exposure was used to resect ectopic parathyroid tissue after identification of important landmark structures including the following: A = right pulmonary artery; B = trachea; C = left main bronchus; D = superior vena cava.
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These two cases illustrate the following points: (1) In the presence of an elevated parathyroid hormone level after standard subtotal parathyroidectomy, a computed tomographic scan demonstrating a lesion in the middle mediastinum is most likely an ectopic parathyroid gland. (2) Sternotomy is the procedure of choice for the reasons previously mentioned.
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References
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Scholz D.A., Purnell D.C., Wolner L.B., Clagett O.T. Mediastinal hyperfunctioning parathyroid tumors: review of 14 cases. Ann Surg 1973;178:173-178.[Medline]
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Russell C.F., Edis A.J., Scholz D.A., Sheedy P.F., VanHeerden J.A. Mediastinal parathyroid tumors: experience with 38 tumors requiring mediastinotomy for removal. Ann Surg 1981;193:805-809.[Medline]
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Clark O.H. Mediastinal parathyroid tumors. Arch Surg 1988;123:1096-1100.[Abstract/Free Full Text]
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Nathaniels E.K., Nathaniels A.M., Wang C. Mediastinal parathyroid tumors: a clinical and pathological study of 84 cases. Ann Surg 1970;171:165-170.[Medline]
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Curley I.R., Wheeler M.H., Thompson N.W., Grant C.S. The challenge of the middle mediastinal parathyroid. World J Surg 1988;12:818-824.[Medline]
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Doppman J.L., Skarulis M.C., Chen C.C., et al. Parathyroid adenomas in the aortopulmonary window. Radiology 1996;201:456-462.[Abstract/Free Full Text]
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Abstract
Introduction
