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AJR 2005; 184:S16-S18
© American Roentgen Ray Society

Case Report

Detection of an Intrathymic Parathyroid Adenoma Using Single-Photon Emission CT 99mTc Sestamibi Scintigraphy and CT

Paige B. Clark1, Nancy D. Perrier2,3 and Kathryn A. Morton1,4

1 Department of Radiology/Nuclear Medicine, Wake Forest University School of Medicine, Medical Center Blvd., Winston-Salem, NC 27157.
2 Department of Surgery, Wake Forest University School of Medicine, Winston-Salem, NC.
3 Present address: Department of Surgical Oncology, University of Texas M. D. Anderson Cancer Center, Houston, TX.
4 Present address: Department of Radiology, University of Utah Health Sciences Center, Salt Lake City, UT.

Received March 3, 2004; accepted after revision May 11, 2004.

 
Address correspondence to P. B. Clark.


Introduction
Top
 Introduction
Case Report
 Discussion
 References
 
Parathyroid adenoma is the most common cause of primary hyperparathyroidism. Preoperative localization before parathyroidectomy allows a minimally invasive surgical approach, thus avoiding cervical exploration. In most people, four parathyroid glands, two superior and two inferior, lie posterior to the thyroid lobe. When one of the glands undergoes adenomatous transformation, preoperative localization can be relatively simple with planar technetium-99m sestamibi scintigraphy. However, supernumerary and ectopic parathyroid glands can also become adenomatous, causing a diagnostic dilemma when they are difficult to localize preoperatively.

We describe the case of a 19-year-old man with symptomatic nephrolithiasis resulting from persistent hyperparathyroidism since the age of 16. Previous minimally invasive parathyroidectomy and cervical exploration were not curative. The patient had 99mTc methoxyisobutylisonitrile (MIBI) singlephoton emission CT (SPECT) of the neck and chest to localize a presumed ectopic parathyroid adenoma.


Case Report
Top
 Introduction
 Case Report
Discussion
 References
 
A 19-year-old man with symptomatic nephrolithiasis from persistent hyperparathyroidism had SPECT approximately 40 min after 20 mCi (740 MBq) 99mTc MIBI was injected IV. Serum parathyroid hormone was 147 (normal, 12-72) and serum calcium was 11.2 mg/dL (normal, 8.5-11.0 mg/dL). As previous cervical exploration identified the right superior, left superior, and right inferior parathyroid glands (all normal), the search focused on a possible ectopic inferior parathyroid adenoma.

Anterior planar scintigraphy images were unrevealing (Fig. 1A). Technetium-99m MIBI SPECT from the temporomandibular joint to the inferior heart was obtained. A focus of activity was present in the anterior mediastinum (Figs. 1B and 1C). After scintigraphy, contrast CT of the neck and chest was performed (Fig. 1D). CT confirmed a hyperattenuating nodule within residual thymic tissue, corresponding to the focus on 99mTc MIBI SPECT.



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  		Fig. 1A. —19-year-old man with recurrent hyperparathyroidism. Previous minimally invasive parathyroidectomy and cervical exploration were not curative. Ectopic parathyroid adenoma was suspected. Anterior planar images show no focus of activity suggesting parathyroid adenoma.

 


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  		Fig. 1B. —19-year-old man with recurrent hyperparathyroidism. Previous minimally invasive parathyroidectomy and cervical exploration were not curative. Ectopic parathyroid adenoma was suspected. Axial 99mTc MIBI SPECT image shows focus of increased activity (arrow) in anterior mediastinum caudal to level of aortic arch.

 


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  		Fig. 1C. —19-year-old man with recurrent hyperparathyroidism. Previous minimally invasive parathyroidectomy and cervical exploration were not curative. Ectopic parathyroid adenoma was suspected. Coronal 99mTc MIBI SPECT image shows focus of increased activity (arrow) in anterior mediastinum caudal to level of aortic arch.

 


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  		Fig. 1D. —19-year-old man with recurrent hyperparathyroidism. Previous minimally invasive parathyroidectomy and cervical exploration were not curative. Ectopic parathyroid adenoma was suspected. Axial contrast CT of neck and chest confirmed hyperattenuating nodule (arrow) within residual thymic tissue, corresponding to 99mTc MIBI SPECT focus.

 

Thorascopic thymectomy was performed. Gross pathologic and histologic examinations revealed a 0.8 x 0.6 cm, 308-mg parathyroid adenoma surrounded by normal thymus (Fig. 2). The patient's postoperative calcium was 8.5 mg/dL, at the lower limits of normal.



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  		Fig. 2. —Thorascopic thymectomy was performed in the same 19-year-old man. Histologic examination revealed 0.8 x 0.6 cm, 308-mg parathyroid adenoma (arrowhead) surrounded by normal thymus (arrow).

 


Discussion
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 Introduction
 Case Report
 Discussion
References
 
In 85% of patients with primary hyperparathyroidism, a solitary parathyroid adenoma is the culprit [1]. Up to 20% of solitary parathyroid adenomas can be located in ectopic sites [2]. Superior parathyroid glands arise from the fourth branchial complex along with the thyroid gland. Thus, minimal descent and close relationship to the thyroid make ectopic superior glands relatively uncommon (about 2%) [3]. Ectopic inferior parathyroid glands are more common. Since the thymus and the inferior parathyroid glands both arise from the third branchial complex and descend together, ectopic inferior glands can be found in the anterior mediastinum. It is also possible, although rare, to find an inferior parathyroid adenoma high in the neck resulting from early developmental arrest [4].

The value of 3D images and increased contrast provided by 99mTc MIBI SPECT in the evaluation of ectopic parathyroid adenomas is evident in this case, as the anterior planar scintigraphic images were unrevealing. A recent study by Lorberboym et al. [5] reports 79% sensitivity for planar scintigraphy versus 96% sensitivity for SPECT localization of parathyroid adenomas. In their study, SPECT was especially useful for identifying ectopic adenomas and distinguishing thyroid nodules from parathyroid adenomas.

For initial localization of parathyroid adenomas, scintigraphy has been shown as more sensitive than CT or MRI [6]. In the case of ectopic parathyroid adenomas, 99mTc MIBI SPECT followed by CT or MRI correlation is often performed for surgical planning. Many endocrine surgeons advocate two concordant imaging studies, such as 99mTc MIBI scintigrapy and CT, before reoperation on patients with recurrent primary hyperparathyroidism.

This case illustrates the importance of careful review of 99mTc MIBI SPECT parathyroid scintigraphy and correlative anatomic imaging in recurrent primary hyperparathyroidism. Before this study, several radiologic studies were performed on the patient, including 99mTc MIBI scintigraphy, CT, and MRI, without agreement that the abnormalities were, in fact, an ectopic parathyroid adenoma. Ultimately, thorascopic thymectomy and histology proved this an ectopic inferior parathyroid adenoma.


References
Top
 Introduction
 Case Report
 Discussion
 References
 

  1. Gupta VK, Yeh KA, Burke GJ, Wei JP. 99mtechnetium sestamibi localized solitary parathyroid adenoma as an indication for limited unilateral surgical exploration. Am J Surg1998; 176:409 -412[Medline]
  2. Casara D, Rubello D, Piotto A, Pelizzo MR. 99mTc-MIBI radio-guided minimally invasive parathyroid surgery planned on the basis of a preoperative combined 99mTc-pertechnetate/99mTc MIBI and ultra-sound imaging protocol. Eur J Nucl Med2000; 27:1300 -1304[Medline]
  3. Loevner L. Imaging of the parathyroid glands. Semin Ultrasound CT MR 1996;17:563 -574[Medline]
  4. Clark PB, Case D, Watson NE, Morton KA, Perrier ND. Experienced scintigraphers contribute to success of minimally invasive parathyroidectomy by skilled endocrine surgeons. Am Surg2003; 69:478 -484[Medline]
  5. Lorberboym M, Minski I, Macadziob S, Nikolov G, Schachter P. Incremental diagnostic value of preoperative Tc-99m-MIBI SPECT in patients with a parathyroid adenoma. J Nucl Med2003; 44:904 -908[Abstract/Free Full Text]
  6. Ishibashi M, Nishida H, Hiromatsu Y, Kojima K, Uchida M, Hayabuchi N. Localization of ectopic parathyroid glands using technetium-99m sestamibi imaging: comparison with magnetic resonance and computed tomographic imaging. Eur J Nucl Med1997; 24:197 -201[Medline]

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[Abstract] [Full Text] [PDF]

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