Thymoma

Thallium (Tl) 201 and technetium (Tc) 99m tetrofosmin single-photon emission CT are routinely used in the evaluation of coronary artery disease. Mediastinal tumors demonstrate Tl 201 and Tc 99m tetrofosmin uptake. We report a 56-year-old man who developed chest pain after a previously successful angioplasty and stent of the left anterior descending coronary artery. He underwent a Tl 201, Tc 99m tetrofosmin exercise study. Abnormal mediastinal activity was visualized in both the Tl 201 and Tc 99m tetrofosmin images. Subsequently, the patient underwent resection of a stage II thymoma. Unanticipated focal extracardiac accumulation during myocardial scintiscanning should lead to further investigation to exclude mediastinal tumor.

(CHEST 2000; 118:550-551)

Key words: technetium 99m tetrofosmin; thallium 201; thymoma

Abbreviations: SPECT = single photon emission CT; Tc = technetium; Tl = thallium

CASE REPORT

A 56-year,old white male smoker had undergone left anterior descending coronary artery angioplasty and stent placement for symptomatic coronary artery disease. After the procedure the patient remained asymptomatic while receiving aspirin and a calcium-channel blocker. Routine follow-up exercise thallium (Tl) 201 single-photon emission CT (SPECT) imaging 2 months later was negative.

Two years after angioplasty and stent placement, the patient underwent dual isotope Tl 201 and technetium (Tc) 99m tetrofosmin SPECT exercise testing for recurrent chest pain. All images were obtained on an Optima SPECT scanner, a two-detector system with camera heads configured at 90 [degrees], and reconstructed on a GENIE workstation (General Electric Medical Systems; Milwaukee, WI). Four mCi of Tl 201 (Mallinckrodt Medical; St. Louis, MO) were injected IV for the resting phase. After a 20-min delay to allow for myocardial uptake, resting images were acquired. Acquisition parameters included the following: a 30% energy window centered on a photopeak of 72 keV and a 20% energy window centered on a 167 keV photopeak; a high-resolution collimator on each detector; a 64 x 64 x 16 computer matrix with 64 frames at 20 s/frame; and a 180 [degrees] circular acquisition arc in a step-and-shoot motion.

A treadmill stress test was performed using a standard Bruce protocol. Exercise was terminated at 7 min 36 s, at a maximum heart rate of 130 beats/min (79% predicted), due to dyspnea and fatigue, At peak exercise, 30 mCi of Tc 99m tetrofosmin (Myoview; Nycomed Amersham; Arlington Heights, IL) were administered. After a 30-min delay to allow clearance of hepatic uptake, stress images were obtained. Additional acquisition parameters consisted of ECG gating for R-wave trigger information and a 15% energy window centered on a photopeak of 140 keV. There was uniform perfusion of the left ventricle. Extracardiac mediastinal activity was visualized on both the resting and stress images (Fig 1).

[Figure 1 ILLUSTRATION OMITTED]

The patient was referred to the oncologist for further evaluation of the SPECT abnormalities. Physical examination, laboratory studies, and chest radiographs were normal. MRI demonstrated a 6-cm, inhomogenously enhancing mass, with areas of necrosis in the anterior superior mediastinum (Fig 2). [Alpha]-Fetoprotein (2.7 ng/mL) and human chorionic gonadotropin (2 mIU/mL) levels were normal.

[Figure 2 ILLUSTRATION OMITTED]

Median sternotomy and resection of the tumor were accomplished. There were no complications, and the patient was discharged on the fourth postoperative day. Pathologic examination demonstrated thymoma, mixed lymphoepithelial type, with extension through the capsule, stage II. The patient received 50 Gy postoperative mediastinal radiation. He was free of chest pain at the time of this report.

DISCUSSION

Mediastinal tumors, including thymoma, seminoma, and lung cancer, demonstrate Tl 201 and Tc 99m tetrofosmin uptake.[1] Of all thymomas found, 70% will be positive on Tl 201 scanning.[2] In the vast majority of cases, however, the patient receives an established clinical diagnosis of mediastinal mass. The patient is usually undergoing noninvasive cardiac testing prior to resection.[1,3] While the extracardiac uptake of isotope is interesting in such cases, the SPECT study does not normally lead to the diagnosis of a previously unsuspected mediastinal tumor.

The current case report is unusual. The patient developed recurrent chest pain in the setting of known coronary artery disease and underwent exercise Tl 201, Tc 99m tetrofosmin myocardial imaging. Chest radiograph was normal. While myocardial perfusion was normal, there was extracardiac uptake in the mediastinum. This single nuclear finding led to further investigation and, ultimately, to resection of a stage II thymoma.

Maticke et al[4] reported a 78-year-old woman with previous left anterior descending coronary artery stent and recurrent chest pain. Tl 201 stress study showed normal myocardial perfusion, but uptake in the mediastinum. CT scan of the chest revealed a 5-cm mediastinal mass. The patient underwent resection of a benign thymic mass. Adalet et al[5] described a 72-year-old man with exertional chest pain, Tl 201 reversible myocardial defects, and mediastinal uptake of Tl 201. The mediastinal mass was a benign thymoma. However, the uptake was not entirely unsuspected, because the chest radiograph clearly demonstrated the mediastinal mass. Tl 201 and Tc 99m tetrofosmin uptake by thymomas may also provide a sensitive means of detecting recurrence after surgery and radiation.[6]

In conclusion, we report the unusual discovery of an unsuspected stage II thymoma during a Tl 201 and Tc 99m tetrofosmin SPECT exercise stress test performed in a patient with coronary artery disease. Extracardiac uptake should lead to further studies to exclude mediastinal tumor.

REFERENCES

[1] Ishibashi M, Fujimoto K, Ohzono H, et al. Tc 99m tetrofosmin uptake in mediastinal tumours. Br J Radiol 1996; 69: 1134-1138

[2] Yuzuriha H, Morimoto M, Inokawa K, et al. Scintiscanning demonstration of thymoma: comparative study on scintiscans using Tl 201, Ga 67, Se 75. Jpn J Surg 1986; 16:250-256

[3] Campeau R, Ey E, Varma D. Thallium-201 uptake in a benign thymoma. Clin Nucl Med 1986; 11:524

[4] Maticke G, Sokol J, Jozwiak J, et al. Detection of thymomas by SPECT thallium imaging. J Nucl Cardiol 1998; 5:449-450

[5] Adalet I, Kocak M, Ece T, et al. Tc99m MIBI and Tl-201 uptake in a benign thymoma. Clin Nucl Med 1995; 20:733-734

[6] Ohta H, Taniguchi T, Watanabe H, et al. Tl-201 and Tc99m HMPAO SPECT in a patient with recurrent thymoma. Clin Nucl Med 1996; 21:902-903

(*) From the Departments of Thoracic Surgery (Dr. Paull), Nuclear Medicine (Drs. Graham and Forgetta), Cardiology (Dr. Turissini), and Oncology (Dr. Saidman), Wilkes Barre General Hospital, Wilkes Barre, PA.

Manuscript received November 23, 1999; revision accepted December 30, 1999.

Correspondence to: Douglas E. Paull, MD, FCCP, 200 S. River St., Plains, PA 18705; e-mail: dep78@aol.com

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