A 63-year-old man with coronary artery disease and hypertension presented with chest pain and dyspnea. The pain, which occurred during rest and exercise, was relieved by nitroglycerin. The patient's Thrombolysis in Myocardial Infarction (TIMI) score placed him at a 19% risk of all-cause death within 14 days because of unstable angina. He underwent a tetrofosmin treadmill stress test. Single-photon-emission computed tomographic (SPECT) images showed increased uptake of technetium (Tc) 99m lateral to the myocardium, suggesting either gastrointestinal uptake or malignancy (Fig. 1). The SPECT images were compared with a computed tomographic scan from the patient's archived records. It showed an intrathoracic left kidney in the region of increased uptake on SPECT imaging (Fig. 2). Calcification in the left anterior descending and right coronary arteries was also seen (Figs. 2A, 2B, and 2C). The patient declined diagnostic cardiac angiography.
Fig. 1 Horizontal A ) long-axis and B ) short-axis single-photon-emission computed tomographic images, on stress and rest, show technetium 99m uptake.
Fig. 2 A ) Coronal computed tomographic (CT) scan reveals an elevated, closed hemidiaphragm. The kidney, which is inferior to the diaphragm, is at the level of ribs 7–10. B ) Axial CT image shows the proximity of the left kidney to the heart. C ) Sagittal CT view shows the proximity of the left kidney to the myocardium. D ) Lateral image from the technetium 99m single-photon-emission CT scan is comparable to the sagittal image ( C ) and confirms the position of the left kidney next to the myocardium.
Comment
Technetium 99m SPECT imaging is widely used to detect reversible myocardial ischemia and to assist in disease management.1 The frequency of noncardiac findings on SPECT imaging ranges from 0 to 2.8%.2–4 The most common anomalies are malignancy and gastrointestinal uptake of the contrast agent (especially by the liver, gallbladder, and biliary system, given the clearance of Tc 99m by the hepatobiliary pathway).3,4 Other sites of uptake include the bone marrow, kidneys, esophagus, and vertebrae. Rescanning a patient after the ingestion of soda water can improve SPECT imaging when excessive gastrointestinal activity is present.3,4 This intervention was not helpful in our patient, which led us to suspect an alternative imaging problem.
An ectopic thoracic kidney is a rare anomaly5,6 that can complicate cardiac Tc 99m SPECT imaging. The incidence of ectopic thoracic kidney in patients undergoing thoracic surgery is 1 in 20,000.5 Most such kidneys are found during preoperative patient evaluation. They can present a diagnostic conundrum and may require sonography, excretory urography, or computed tomography for clarification.5,6
References
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