(Radiographics. 1999;19:823-825.)
© RSNA, 1999
General Case of the Day1
Samy F. Saleeb, MD and
Steven K. Teplick, MD
1 From the Department of Radiology, University of South Alabama College of Medicine, 2451 Fillingim St, Mobile, AL 36617. From the 1998 RSNA scientific assembly. Received November 19, 1998; revision requested December 29 and received February 2, 1999; accepted February 3. Address reprint requests to S.F.S.
Index Terms: Mediastinum, CT, 67.12112, 67.3159 • Mediastinum, neoplasms, 67.3159 • Parathyroid, neoplasms, 67.3159 • Parathyroid, radionuclide studies, 67.12166 • Radionuclide imaging, in diagnosis of neoplasms, 274.12175, 67.12166, 67.3159
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HISTORY
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A 44-year-old woman presented with recurrent renal stones. The patient had a long history of kidney stones with a delayed diagnosis of primary hyperparathyroidism, for which she underwent exploratory neck surgery. Three parathyroid glands were removed at that time. Persistent hypercalcemia was seen postoperatively. Abdominal and chest radiography, upper abdominal computed tomography (CT), and anterior chest scintigraphy with technetium-99m sestamibi (MIBI) (Cardiolite; DuPont-Merck, North Bellerica, Mass) were performed.
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FINDINGS
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Abdominal radiography revealed bilateral staghorn calculi and subchondral bone resorption at the ileal aspect of the sacroiliac joints (Fig 1). Chest radiography demonstrated several healed rib fractures and subchondral bone resorption of the distal clavicle at the acromioclavicular joint (Fig 2). Abdominal CT showed a localized area of hypoattenuation with central calcification in the tail of the pancreas as well as staghorn calculi (Fig 3). Anterior chest scintigraphy with MIBI showed focal uptake in the superior mediastinum (Fig 4).
DIAGNOSIS: Ectopic retrosternal parathyroid adenoma.
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DISCUSSION
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MIBI is a commonly used radiopharmaceutical in myocardial imaging. Numerous studies have shown MIBI to have good sensitivity (85%–100%) and specificity (
95%) in detecting and localizing parathyroid adenomas. Hyperfunctioning parathyroid tissue is detected as a focus of persistent activity on early and delayed images of the neck or as an ectopic focus in the neck or mediastinum. The routine use of MIBI for presurgical planning in patients with hyperparathyroidism remains controversial due to the high success rate of experienced surgeons and the somewhat limited sensitivity of MIBI in the detection of parathyroid hyperplasia. Preoperative imaging with MIBI may improve the success rate for the surgeon with limited experience with the parathyroid and for high-risk patients (1). MIBI may also prove cost-effective by allowing unilateral surgical exploration and detection of ectopic parathyroid adenomas (2,3). Gamma probes have been used during surgery for localization. An added benefit of preoperative localization is preservation of the normal parathyroid tissue to avoid inadvertent removal of normally functioning parathyroid glands as occurred in this case. MIBI uptake in brown tumors has been reported (4). The pitfalls of MIBI imaging include false-positive results due to uptake by thyroid adenomas, multinodular goiter, and metastatic medullary carcinoma. Uptake of MIBI in the mediastinum may be seen with metastatic lung cancer, mediastinal seminoma, and lymphoma. The role of MIBI imaging in tumor localization, screening, and monitoring after cessation of therapy continues to expand. Several studies have evaluated the role of MIBI imaging in tumors of the brain, bone, and thyroid gland (5). It has been postulated that the retention of this radiotracer in myocardial cells and possibly in other tissues with high metabolic rates (eg, tumors) is the result of electrostatic interaction with the mitochondria. Breast scintigraphy with MIBI has been approved by the U.S. Food and Drug Administration and was used to evaluate a subgroup of patients who underwent nondiagnostic or limited preliminary work-up with mammography and ultrasonography (6).
Primary hyperparathyroidism may be caused by a single adenoma (80%–85% of cases), multigland hyperplasia (14%–19%), and parathyroid carcinoma (1%). On rare occasions, it is caused by familial isolated hyperparathyroidism and multiple endocrine neoplasia syndromes (type 1 and type 2 MEN). Other imaging modalities used for localization of parathyroid adenomas include ultrasound, CT, and, more recently, magnetic resonance imaging, which demonstrates adenomas as hyperintense relative to the thyroid gland on fast spin-echo fat-suppressed T2-weighted images (7). Radiographic manifestations of hyperparathyroidism include subperiosteal (phalanges), subchondral (distal clavicle), and cortical (decreased bone mineral content) bone resorption but are rarely encountered since the advent of direct laboratory testing for parathyroid hormone. Brown tumors may develop in the jaw, pelvis, and long bones. The joints may demonstrate chondrocalcinosis and erosive arthropathy. Renal manifestations include nephrolithiasis and nephrocalcinosis. In a study by Mixter et al (8), pancreatic calcifications were reported in 45% of patients.
The differential diagnosis of nephrolithiasis with hypercalcemia includes renal tubular acidosis, immobilization, milk-alkali syndrome, and vitamin D intoxication.
Abdominal CT showed bilateral staghorn calculi and a hypoattenuating pancreatic mass with central calcification. Histologic analysis of the mass demonstrated inflammatory cells. Anterior neck and chest scintigraphy with MIBI revealed an area of focal uptake in the midline in the anterior mediastinum. In retrospect, a retrosternal nodule was present on the chest CT scan but was inconspicuous due to the lack of vascular contrast material enhancement. As a result of the scintigraphic findings, the patient underwent repeat exploratory neck surgery, which revealed a 4-cm parathyroid adenoma retrosternally. The adenoma was successfully removed, and the patient is doing well.
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References
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Carter WB, Sarfati MR, Fox DD. Preoperative detection of sporadic parathyroid adenomas using technetium-99m-sestamibi. Am Surg 1997; 63:317-321.[Medline]
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Denham DW, Norman J. Cost-effectiveness of pre-operative sestamibi scan for primary hyperparathyroidism is dependent solely upon the surgeon's choice of operative procedure. J Am Coll Surg 1998; 186:293-305.[Medline]
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Sofferman RA, Nathan MH. The ectopic parathyroid adenoma: a cost justification for routine preoperative localization with technetium Tc 99m sestamibi scan. Arch Otolaryngol Head Neck Surg 1998; 124:649-654.
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Muthiah A, Jr, Kalani JG, Katz DS. Uptake of Tc-99m sestamibi by brown tumors in a patient with primary hyperparathyroidism. Clin Nucl Med 1998; 23:83-85.[Medline]
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Taki J, Sumiya H, Tsuchiya H, Tomita K, Nonomura A, Tonami N. Evaluating benign and malignant bone and soft-tissue lesions with technetium-99m-MIBI scintigraphy. Comment J Nucl Med 1997; 38:501-506.
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Khalkali I, Mena I, Jouanne E, et al. Prone scintimammography in patients with suspicion of carcinoma of the breast. J Am Coll Surg 1994; 178:491-497.[Medline]
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Lee V, Spritzer CE, Coleman RE, Wilkerson RH, Coogan A, Leight G. The complementary roles of fast spin-echo MR imaging and double-phase 99m Tc sestamibi scintigraphy for localization of hyperfunctioning parathyroid glands. AJR 1996; 167:1555-1562.[Abstract/Free Full Text]
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Mixter CG, Jr, Keynes WM, Chin M, Cope O. Further experience with pancreatitis as diagnostic clue to hyperparathyroidism. N Engl J Med 1962; 266:265-272.
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HISTORY
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