Presentation
Emergency presentation with chest pain. History of hypertension, hyperlipidemia and peripheral vascular disease.
Patient Data
Normal size heart, clear lungs, no effusion or pneumothorax, and no acute bony abnormalitie.
Myocardial perfusion
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 mediastinum.
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.
Time-activity-curve (TAC) of the left ventricle shows normal wall motion and ejection fraction (EF).
CT of the chest shows a non-invasive 3 cm solid mass in the anterior-superior mediastinum as well as moderate-to-severe coronary artery calcifications.
No lymphadenopathy. Normal pleura. No metastases.
Subsequent biopsy was performed which confirmed a diagnosis of thymoma.
Pathology: Sections show predominantly bland oval to spindled cells with minimal cytoplasm and indistinct cell borders with scattered admixed lymphocytes. Cytologic atypia or mitotic figures are not identified. Tumor cells are positive for LU-5, p63, PAX8 and negative for CD117 (nonspecific nuclear staining only). CD3 shows scattered T-cells and CD1a shows only rare positive T-cells. CD20 is essentially negative. Ki-67 shows less than 10% mitotic index. These findings favor Type A (or Type AB) thymoma, although definitive subtyping is deferred to resection specimen.
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.
In retrospect, on the chest x-ray lateral view there is abnormal density obscuring the retrosternal clear space.
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