대한흉부영상의학회 Korean Society of Thoracic Radiology

Discussion

Diagnosis With Brief Discussion

Diagnosis

Minimally Invasive Thymoma with infarction

Radiologic Findings

CT scans show an anterior mediastinal mass with central necrotic low attenuation.

Pathologic specimen consisted of an encapsulated soft tissue mass, measuring 9 x 5 cm in size.
On section, it showed a relatively well-defined yellowish and ovoid infarcted area in the central portion, associated with small multiple nodular lesions in the peripheral area.

Brief Review

The term "invasive thymoma" is a description of any tumor that has spread beyond the capsule. Approximately 30 % of thymomas are invasive, which infiltrate adjacent structures or result in pleural or pericardial implants. Until mediastinal invasion has occurred, distinguishing benign from invasive thymoma even with CT is not possible.
Histologic appearances do not allow a reliable differentiation between benign and malignant thymoma; malignancy can only be established by documenting the presence of tumor growth into or through the tumor capsule. Thus, thymomas are most appropriately referred as invasive or noninvasive.
This neoplasm grows (a) to invade local mediastinal structures, including the superior vena cava, great vessels, and even the airways; (b) to invade the adjacent lungs or chest wall; or (c) to spread by contiguity along pleural reflections, usually on one side of the chest cavity only, potentially seeding even the diaphragmatic surfaces with consequent direct extension into the abdomen.
Transpleural spread may occur as a sheet of neoplastic tissue extending outward from the primary thymic tumor, or it may manifest as a discrete "drop metastasis" at a distance from the primary lesion. Pleural implants, when present, are often unilateral, and unlike other tumors resulting in pleural metastases, are usually unassociated with pleural effusion. Thus, CT cans show focal, well-defined pleural masses, not obscured by pleural fluid.
Invasive thymomas growing along pleural surfaces can reach the posterior mediastinum and extend downward along the aorta to involve the crus of the diaphragm and the retroperitoneum. Blood-borne metastasis is rare.
There are three stages for invasive thymomas; stage 1, in which the capsule is either intact, or the tumor has not spread beyond the capsule; stage 2, in which the tumor has spread into the mediastinal fat; stage 3, in which there is invasion of adjacent organs or pleural spread at a distance from the primary tumor.
Surgery is undertaken in all three stages, with radiation therapy given for stage 2, and radiation therapy combined with chemotherapy given for stage 3.

References

1. Naidich DP, Webb RW, Muller NL, Krinsky GA, Zerhouni EA, Siegelman SS. Computed tomography and magnetic resonance of the thorax. 3rd ed. Philadelphia-New York: Lippincott-Raven, 1999:63-71

2. Marino M, Muller-Hermelink HK. Thymomas and thymic caarcinoma: relation of thymoma epithelial cells to the cortical and medullary differentiation of the thymus. Virchows Arch 1985;407:119-149

3. Zerhouni EA, Scott WWJr, Baker RR, Wharam MD, Sielgelmann SS. Invasive thymomas: diagnosis and evaluation by computed tomography. J Comput Assist Tomogr 1982;6:92-100

4. Armstrong P, Wilson AG, Dee P, Hansell DM. Imaging of disease of the chest. 2nd ed. St. Louis: Mosby, 1995:732-736

5. Morgenthaler TI, Brown LR, Colby TV, Harper CM, Coles DT. Thymoma. Mayo Clin Proc 1993;68:1110-1123

Keywords

Mediastinum, Malignant tumor,