Case Author(s): Stephanie P.F. Yen, M.D. and Henry D. Royal, M.D. , 11/14/97 . Rating: #D2, #Q4

Diagnosis: Thymoma

Brief history:

62-year-old male with a history of coronary artery disease who presents with dyspnea on exertion and EKG changes.


Selected images from the raw projection data acquired during the exercise portion of the myocardial perfusion study.

View main image(mi) in a separate image viewer

View second image(ct). Axial image of chest from contrast-enhanced computed tomography

View third image(xr). Posteroanterior chest

Full history/Diagnosis is available below

Diagnosis: Thymoma

Full history:

62-year-old male with history of prior myocardial infarction who presents with dyspnea on exertion and EKG changes. Myocardial perfusion imaging was requested to evaluate for myocardial viability.


3.3 mCi Tl-201 chloride, i.v.; and 20.6 mCi Tc-99m sestamibi, i.v.


Selected images from the raw projection data acquired during the exercise portion of the myocardial perfusion imaging examination demonstrate a focus of increased activity in the retrosternal region. On the resting thallium projection data (not shown), a similar focus of increased activity is identified in the retrosternal region.

The patient subsequently underwent a computed tomography study of the chest on 12-01-97, which revealed a 2.8 X 4.2 X 4.0 cm homogeneously enhancing anterior mediastinal mass at the level of the carina as well as a small right pleural effusion. The mass was not contiguous with the thyroid. No significant mediastinal lymphadenopathy was seen. The computed tomographic appearance of this mass suggests the primary differential considerations of lymphoma and thymoma.

Posteroanterior chest radiograph performed on 1/12/98 shows a subtle contour abnormality in the region of the aortopulmonary window, corresponding to the patient's known anterior mediastinal mass. The mass is not well visualized on the lateral view (not shown).


The projection images from a myocardial perfusion imaging study are used to assess the technical quality of the examination, providing information on patient motion, as well as to confirm the presence of attenuation of myocardial activity by breast tissue or diaphragm suspected on the standard tomographic images. In addition, as this case illustrates, the projection data also allow for a survey of the entire thorax and axillae for abnormal extracardiac radiopharmaceutical accumulation. Both thallium-201 and Tc-99m methoxyisobutyl isonitrile (MIBI) have been shown to accumulate in pulmonary malignancies, breast tumors, lymphomas, and bone and soft tissue sarcomas. Abnormal axillary accumulation of Tc-99m sestamibi may reflect the presence of nodal metastases or the presence of significant extravasation of radiopharmaceutical at the time of injection. The diagnosis of such clinically significant findings may be missed if only standard tomographic images are reviewed.

Cases have been reported in the literature demonstrating the accumulation of Tc-99m sestamibi and thallium-201 in thymomas. Thymomas originate from the thymic epithelium and are most common in the anterior mediastinum. Thymomas may be encapsulated and noninvasive, or they may demonstrate invasion into the surrounding tissues or metastasize locally, with the pleura and pericardium being the most frequent sites. No histological difference has been demonstrated between those tumors that are noninvasive, invasive, or metastatic. The distinction between a "benign" or "malignant" thymoma is based on the absence or presence of invasiveness, respectively.

Patients with thymomas are usually 40 to 60 years of age and may present with nonspecific symptoms related to the presence of an anterior mediastinal mass, such as cough, dyspnea, chest discomfort, and dysphagia. Many syndromes and diseases have been shown to have an association with thymomas. Of these, myasthenia gravis, red cell aplasia, and hypogammaglobinemia are the most common. It is reported that surgical resection is the most effective treatment.

References: 1. Rosenberg JC. Neoplasms of the Mediastinum. In: Devita VT, Hellman S, and Rosenberg SA. Cancer Principles & Practice of Oncology, 4th ed. J.B. Lippincott Co., Philadelphia, PA, 1992: 764-769. 2. Adalet I, Kocak M, Ece T et al. Tc-99m MIBI and Tl-201 uptake in a benign thymoma. Clinical Nuclear Medicine. 20:733-734, 1995. 3. Campeau RJ, Ey EH, and Varma DGK. Thallium-201 uptake in a benign thymoma. Clinical Nuclear Medicine. 11:524, 1986.


A fine needle aspirate biopsy of the anterior mediastinal mass was performed under computed tomography guidance on 12/18/97. Pathology revealed features consistent with thymoma. Pathology remarked that FNA cytology cannot determine if the thymoma is invasive or malignant, nor can it determine the future behavior of the lesion. The patient subsequently underwent a thymectomy on 1/13/98. Pathology demonstrated thymoma, predominantly epithelial spinde cell type, with evidence of microinvasion of the capsule. None of the three regional lymph nodes sampled showed evidence of tumor (stage T2N0M0).

Major teaching point(s):

This case emphasizes the importance of viewing the projection images of myocardial perfusion imaging studies. Not only do the projection images provide information about patient motion during the exam and confirm the presence of attenuation of myocardial activity by breast tissue or diaphragm, but they also may reveal extracardiac abnormalities of the thorax which may be missed on the standard SPECT myocardial perfusion images.

Differential Diagnosis List

The classic differential diagnosis of an anterior mediastinal mass includes thymoma, lymphoma, germ cell tumors, and thyroid pathology.

ACR Codes and Keywords:

References and General Discussion of Myocardial Imaging (Anatomic field:Lung, Mediastinum, and Pleura, Category:Neoplasm, Neoplastic-like condition)

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Case number: mi012

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