Large Anterior Mediastinum Mass Activity on 99mTc-Tetrofosmin Myocardial Perfusion Imaging

Introduction: ^99mTc-Tetrofosmin is part of the diphosphine chemical class (chemical name: 6,9-bis [2-ethoxyethyl]-3,12-dioxane-6,9 diphosphatetradecane). ^99mTc-sestamibi shares the same mechanism up as ^99mTc -tetrofosmin because both agents are lipophilic cations that become fixed in the mitochondria of the myocardial cell. ^99mTc -Tetrofosmin is a perfusion agent and allows visualization of changes in the perfusion of the heart muscle. (Harvey at el, 2014, p 378).This makes it a good agent for assessing ischemia and other heart diseases. In addition, it has been found that ^99mTc-Tetrofosmin can indicate other extracardiac conditions such as; parathyroid adenomas, lymphomas, and thymomas. ^99mTc-Tetrofosmin has an 83.3% sensitivity in detecting ectopic parathyroid glands. (Demetriadou at el., 2004). It has been reported in a different study that ^99mTc-Tetrofosmin sensitivity for detecting the primary mass is 96% and 50% for lymph node involvement. (Sioka at el.,2016)

Methods: A 71 -y- old female was seen in the emergency department, complaining of chest pain and shortness of breath (SOB). She also experienced occasional symptoms of dyspnea. Her cardiac risk factors included a history of hypertension and diabetes. With this medical history, the patient was at high risk of developing coronary artery disease (CAD).

The patient was taken to perform a chest Computed Tomography (CT) scan without contrast (Fig. 1). The CT showed that the patient had a homogeneous mass seen in the left anterior mediastinum. Differential diagnoses from the scan were either a thymic neoplasm cyst with proteinaceous material or lymphoma. The patient was referred to cardiac nuclear medicine for a better evaluation of the lesion.

The patient arrived at the cardiac nuclear medicine department and followed exam preparations which included nothing by mouth (NPO) for 4-6 hours, no caffeine for 24 hours, and withholding all cardiac medication. Upon physical examination in the nuclear medicine department, the blood pressure was 154/71 mm Hg, the heart rate was 73 beats per minute and the respiratory rate was 15 breaths per minute. The patient’s height was 160.02 cm and weight was 187.08Ib, and 38’ D cup size. The patient was given 0.4mg regadenoson over 10-15 seconds and then immediately injected with 11.2mCi of ^99mTc- Tetrofosmin. After 45 minutes, the patient was laid supine with her hands above her head. In addition, dynamic images were acquired anteriorly with left lateral views.

Results: The result revealed a superior mediastinal mass located superiorly to the myocardium. A perfusion abnormality, with an ejection fraction of 27% was seen and poor image quality due to extracardiac activity (Fig. 2). For further investigation of the patient, a PET/CT scan was requested by the physician. The PET/CT showed that the previously characterized lobulated left-sided prevascular/anterior mediastinal mass was morphologically unchanged. It exhibited patchy, mild hypermetabolic activity with a max SUV of 4.0 which was greater than the mediastinal blood pool. Due to low mass activity on the PET/CT images (Fig 3), the diagnosis of lymphoma is highly unlikely. The patient was referred for Magnetic Resonance Imaging (MRI), for a suspected thymic tumor. The MRI showed that the enhancing mediastinal mass and prominent mediastinal lymph node, was unchanged in size from the previous CT, and it was likely a thymic neoplasm rather than lymphoma (Fig. 4).

Conclusions: Based on these findings, the physicians decided to send the patient for a sternotomy and resection of the mass. In addition, the patient underwent esophageal dilation prior to surgery in order to minimize the risk of significant postoperative aspiration. In conclusion, ^99mTc-Tetrofosmin radiopharmaceutical helps to diagnose thymomas through a non-invasive procedure in the nuclear medicine department

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