Extracardiac abnormality on myocardial perfusion imaging - thyroid adenoma
Presentation
Chest pain.
Patient Data
Myocardial perfusion scan
Myocardial perfusion imaging using 10 mCi Tc99m Sestamibi IV at rest and 30 mCi Tc99m Sestamibi IV at stress. Tomographic images of the raw data demonstrates normal cardiac activity with intense physiologic activity in the gall bladder and bowel and mild homogeneous uptake in the liver and spleen. There is also an unexpected focus of moderately intense radiotracer uptake in the lower neck.
Splash view of the heart in short axis, vertical long axis (VLA) and horizontal long axis (HLA) in stress supine, stress upright, and rest upright. There is normal perfusion without fixed or reversible defects.
Ultrasound of the thyroid demonstrates a 4.1 cm solid nodule in the right thryoid lobe corresponding to the abnormal radiotracer uptake on prior MPS. Based upon appearance, the lesion was classified as TI-RADS 4, moderately suspicious.
Noncontrast CT of the neck shows a large hypodense nodule in the right thyroid lobe. There are no rim or macro calcifications. No adenopathy.
FNAB demonstrated a benign adenoma.
Given advanced age and co-morbidities, the patient chose to be managed with imaging surveillance.
Case Discussion
Raw data images from myocardial perfusion imaging are generally viewed as rotating cinematic images. These images allow the reader to evaluate the radiotracer distribution, and assess for attenuation and motion artifacts as well as interfering gastrointestinal activity.
Normal physiologic distribution of the MPI SPECT imaging agents includes activity within the heart, liver, gallbladder, small bowel, occasionally the stomach (due to enterogastric reflux) and kidneys. Mild uptake may also be seen in the lungs and skeletal muscle.
Any uptake outside of these normal structures requires further assessment as the radiotracers are nonspecific tumor imaging agents. Numerous reports in the literature described the identification of lung cancer, breast cancer, lymphoma, thyroid neoplasms and thymoma as unexpected extracardiac radiotracer uptake on MPS exams.
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