Ann Thorac Surg 2006;82:719-721
© 2006 The Society of Thoracic Surgeons
Case report
Use of Fusion Imaging to Localize an Ectopic Thoracic Parathyroid Adenoma
Benjamin Harris, MDa,*,
Dale Bailey, PhDb,
Paul Roach, MDb,
David Marshman, MDc,
Aidan McElduff, MDd,
Greg King, MD, PhDa,e
a Department of Thoracic Medicine, Royal North Shore Hospital, University of Sydney, Sydney, Australia
b Department of Nuclear Medicine, Royal North Shore Hospital, University of Sydney, Sydney, Australia
c Department of Cardiothoracic Surgery, Royal North Shore Hospital, University of Sydney, Sydney, Australia
d Department of Endocrinology, Royal North Shore Hospital, University of Sydney, Sydney, Australia
e Woolcock Institute of Medical Research, Sydney, Australia
Accepted for publication December 7, 2005.
* Address correspondence to Dr Harris, Department of Thoracic Medicine, Level 8A, Royal North Shore Hospital, Pacific Highway, St. Leonards, Sydney, 2065 Australia (Email: bharris{at}med.usyd.edu.au).
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Abstract
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We report the use of fused computed tomography and single photon emission computed tomography parathyroid (99m technetium)-sestamibi images to localize an ectopic parathyroid adenoma.
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Introduction
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Parathyroid adenomas resulting in hyperparathyroidism can be ectopic in their location. If this occurs, a single photon emission computed tomography 99m technetium-sestamibi scan is often performed. We present a case and discussion in which image fusion of the single photon emission tomography 99m technetium-sestamibi together with computed tomography of the chest provided crucial information of the location of the ectopic gland. This information was subsequently used to plan a successful resection of a functioning thoracic ectopic parathyroid adenoma.
A 20-year-old woman (gravida 2, para 1) at 35 +3 gestation was admitted to a district hospital with a history of vomiting and headache. On admission she was found to be pre-eclamptic with a blood pressure of 140/100, and she had clinical evidence of mild hyperreflexia. The serum calcium was elevated at 3.72 mmol/L (normal: 2.10 to 2.55) with a mildly low serum phosphate of 0.76 mmol/L (normal: 0.78 to 1.43). The patient was subsequently transferred to a tertiary hospital, where further investigations revealed primary hyperparathyroidism (*parathyroid hormone *563 ng/L [normal: < 50]). A male infant was delivered by lower segment cesarean section on day 5. The patient's calcium remained elevated at 3.54 mmol/L.
On day 10 the patient underwent neck exploration and three parathyroid glands were found and excised, with one being reimplanted. At the time of exploration, the right superior gland was not identified despite extensive exploration. Postoperatively the patient's calcium and parathyroid hormone remained elevated at 2.93 mmol/L and 464ng/L, respectively.
A single photon emission tomography 99m technetium-Sestamibi study was performed the following day. This demonstrated a focal area of uptake in the mid-thorax, slightly to the right of the midline at approximately the hilar level. No uptake was seen in the neck. Computed tomography of the chest (200 mAs; 120 kVp; slice thickness, 5mm) was performed on a four-head spiral scanner (General Electric Lightspeed [General Electric, CT, Milwaukee]) after injection of 100 mL of intravenous contrast. This demonstrated a rounded 1.6 cm enhancing lesion in the anterior mediastinum in the region of the thymus, inferior to the level of the left brachiocephalic vein and anterior to the ascending aorta.
These scans were compared visually, and it was apparent that the lesion as demonstrated on computed tomography did not correlate anatomically with the lesion seen on the 99m technetium-Sestamibi study. In order to resolve this and better localize the abnormality, the images were combined using commercial fusion software.
Digital imaging and communication in medicine (DICOM) data from the computed tomographic scan was imported into a dedicated nuclear medicine workstation (HERMES [Nuclear Diagnostics AB, Stockholm Sweden]). Three-dimensional alignment of the single photon emission tomography and computed tomography (image co-registration) was performed using an automated iterative, mutual information technique [1]. The co-registration of the fused data set was inspected, and it was judged to be accurate on the basis of good alignment for the liver and the myocardium. The fusion images demonstrated that the focal uptake seen on the 99m technetium-Sestamibi was located in the pericardial fat pad, just anterior to the superior vena cava and superior to the right atrium. This area was distinct from the suspicious lesion originally located on computed tomography (see Fig 1).
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Fig 1. (A) Anterior mediastinal lesion (white arrow) demonstrated on initial computed tomographic (CT) image with no 99m technetium-sestamibi activity. This is anatomically distinct from the metabolically active lesion in the pericardial fat demonstrated in the (B) transverse, (D) coronal, and (E) sagittal planes. The lesion demonstrates intense activity on the fused single photon emission tomography parathyroid 99m technetium-sestamibi images and was proven at operation to be an ectopic parathyroid adenoma. (C) The initial CT image with contrast fails to visualize a lesion in this area.
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As a result of this fusion study, the surgical approach was changed. The patient underwent a right thoracoscopy with a mini-thoracotomy to allow digital palpation and instrumentation on day 13. This revealed a 1.5 cm nodule located within the pericardial fat pad in the exact location demonstrated on the fused images. The nodule was subsequently resected and demonstrated to be a parathyroid adenoma. Immediately postoperatively the parathyroid hormone had fallen, and later the same day the parathyroid hormone level was undetectable (< 1.0 ng/L). The calcium also fell and was normal 3 days later (corrected calcium, 2.38 mmol/L; parathyroid hormone, 3.4 ng/L).
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Comment
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The use of preoperative parathyroid imaging for patients with primary hyperparathyroidism has increased during recent years. Recently it has been proposed that it is appropriate to perform preoperative imaging in all patients with primary hyperparathyroidism due to a reduction in operating times and morbidity [2]. However this continues to be a controversial area, and a significant number of patients still undergo unilateral or bilateral neck exploration.
Parathyroid scintigraphy is now considered to be the gold standard imaging technique for preoperative parathyroid localization [3]. Although single photon emission tomography acquisition of these images has been reported to increase the ability to localize the parathyroid over planar imaging, it lacks anatomical detail. This anatomical detail can be critical for surgeons to plan an appropriate approach. There have been descriptions of preoperative localization of ectopic parathyroid adenomas using sestamibi and computed tomographic image fusion [4–6]. However in contrast to this case, all of these had adenomas visible on the original computed tomographic scan.
The fusion study allowed precise anatomical localization of the ectopic parathyroid, which considerably altered the surgical approach. Originally a mediastinoscopy and midline sternotomy were planned. However after reviewing the fused images, a right-sided thoracoscopy and mini-thoracotomy were subsequently performed, which avoided additional surgical procedures.
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Acknowledgments
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Work performed was supported by the Royal North Shore Hospital Staff Specialist Scholarship 2005.
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References
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Abstract
Introduction
