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Malignant Mesenchymal Spindle Cell Tumor

Milos J Janicek, MD, PhD
Kitt Shaffer, MD, PhD

March 5, 1996

Presentation

An 83-year-old white man presented with an incidental finding of a 5 cm mass adjacent to the left cardiac border on his pre-cholecystectomy chest radiograph.

Imaging Findings

Plain chest radiograph, AP and lateral views
T1-weighted sagittal MRI
T2-weighted sagittal MRI
T1-weighted sagittal MRI after gadolinium
Frontal MRI

Anteroposterior (AP) and lateral chest radiographs demonstrate a 5 cm round mass inseparable from the lateral cardiac contours but well delineated against the lung parenchyma (arrow).

The obtuse angles between the mass and cardiac contour in the axial plane suggest a pleural origin, but myocardial or pericardial origin of the mass cannot be ruled out. Lung parenchymal abnormality extending to the pleural surface is another possibility. The cardiomediastinal silhouette is otherwise unremarkable, and the lungs are clear. A small accumulation of pleural fluid is visible on the left.

MR images were obtained to narrow the differential diagnosis. T1-weighted and T2-weighted sagittal images demonstrate the solid nature of the mass, which is slightly inhomogeneous and has an intermediate signal intensity on both sequences (arrows). The mass is well separated from myocardium but inseparable from pleura and parietal pericardium. There is no evidence of increased pericardial fluid. Delineation of the mass from the lung is relatively sharp. Pleural effusion on the left has higher signal intensity on T1 and lower intensity on T2, which may suggest the presence of degradation blood products. After gadolinium injection the T1-weighted sagittal image shows certain inhomogeneity of otherwise bright enhancement. The presence of pleural effusion, along with the suggestion of blood products, is a worrisome finding that denotes the possibly aggressive nature of this lesion.

Differential Diagnosis

The imaging characteristics of this solid mass appear to represent a tumor originating from the pleura, or less likely from the peripheral lung (based on: absence of hilar lymph nodes, lack of infiltration of the lung parenchyma and absence of pericardial effusion) with pleural/pericardial invasion. Cystic lesions, such as pericardial cyst, loculated pleural effusion, mesothelial cyst, and hematoma, as well as organized empyema, can be excluded. Solid tumors of pleural origin can be either benign, such as a fibrous tumor of the pleura, mesenchymal tumors such as fibroma, neurofibroma, neurinoma or schwannoma, and leiomyoma, or malignant, including rare conditions like pleural osteosarcoma or pleural squamous cell carcinoma. The presence of the same types of connective tissue structures in both the pleura and the lung parenchyma may give rise to the same spectrum of tumors. Primary lymphoma involving pericardial lymph node can also be considered.

MRI excludes subpleural lipoma due to the absence of a fat signal within the mass. A solitary lesion of this size, without other pleural masses, makes malignant mesothelioma unlikely, as well as pleural seeding of metastases (melanoma, breast, or lymphoma).

Diagnosis

Malignant mesenchymal spindle cell tumor most consistent with leiomyosarcoma with myoblastic differentiation of either pleural or lung origin. (Pericardial and lung resection margins clear.)

Discussion

Incidental finding of a pleural-based, solid, slightly heterogeneous enhancing mass, in association with pleural effusion, warrants a biopsy for fear of malignancy. Radiographic features of this mass do not allow further characterization, other than to exclude the possibility of various benign processes, such as lipoma, pericardial cyst, or loculated fluid collection. The smooth lateral margin of this lesion favors a pleural, as opposed to a lung parenchymal, origin.

References

1. Stark P. Pleura. In: Taveras JM, Ferrucci JT, editors. Radiology Diagnosis-Imaging-Intervention. Philadelphia: Lippincott, 1994:1-29.

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