Thymic Carcinoma

Andrew T Walker, MD, PhD
Madeleine D Kraus, MD
Paul Stark, MD

March 16, 1994

Presentation

Imaging Findings

Posteroanterior (PA) and lateral views of the chest demonstrate a mass in the superior aspect of the anterior mediastinum (PA with arrow) (lateral with arrow). No calcification or bone destruction is demonstrated. There is an azygous fissure.

Contrast enhanced chest CT characterizes the plain film abnormality as a predominantly homogeneous, minimally enhancing, 6 x 9 cm anterior mediastinal mass (arrow) extending from the level of the manubrium to the base of the heart. A small area of irregular fluid attenuation at the inferior aspect of the mass suggests necrosis. No alcification or fatty component is visible. The mass surrounds the superior vena cava (SVC) (arrow), which is markedly narrowed and irregular in contour. Dense contrast in the azygos vein (arrow) after right arm injection suggests collateralization via the chest wall and hemiazygos veins due to SVC obstruction. A small pericardial effusion is present. No hilar, mediastinal, or axillary lymph node enlargement is visible.

Differential Diagnosis

Diagnosis

Discussion

Thymoma is the most likely consideration given the patient's age and the relative homogeneous nature of the mass. Its irregularity and aggressive appearance are not typical of simple thymoma and suggest some component of invasion. SVC syndrome is a rare complication of invasive thymoma. Radiographic determination of invasion is difficult but important as these tumors tend to recur and locally metastasize even though histologically they are benign. The aggressive nature of this tumor may warrant mentioning thymic carcinoma as a consideration. The histologic diagnosis of thymic carcinoma is reserved for neoplasms showing cytologic features of malignancy and is extremely rare with only 20 cases seen at the Mayo Clinic in a 75-year period.

Pathology

Thymic carcinoma is a malignant epithelial tumor of the thymus. In contrast to the clinically benign thymoma (which may or may not exhibit anaplastic features), thymic carcinoma exhibits cytologic and architectural features that accurately predict its aggressive behavior: it has large hyperchomatic and occasionally bizarre nuclei and invades adjacent structures. Morphologic variants exist, though all have varying proportions of malignant epithelial cells and a benign lymphoid population. The differential diagnosis may include metastatic lung carcinoma and non-Hodgkin's lymphoma.

ARROWS:Short arrow - tumor invading pericardial fat. Long arrow - pericardial surface.

References

2. Suster. Thymic Carcinoma: a clinicopathologic study of 60 cases. Cancer;67(4):1025-1032.

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