Alveolar cell carcinoma presenting as malignant pericardial effusion: diagnosis by electron microscopy.

The cytologic, immunocytochemical, and ultrastructural findings in a 68-year-old man who presented with a malignant pericardial effusion are reported. Radiologic studies failed to identify a primary neoplasm over the next 6 months. Ultrastructural examination of a repeat pericardiocentesis fluid specimen revealed cells with intranuclear tubular inclusions and cytoplasmic lamellar bodies typical of alveolar cell carcinoma. Review of the chest radiographs showed nonresolving patchy infiltrates in the upper lobe of the left lung clinically thought to represent pneumonia; in retrospect, however, these were consistent with the pneumonic form of alveolar cell carcinoma.