Pulmonary Dirofilariasis: A clinicopathologic study of 41 lesions in 39 patients

Forty-one cases of pulmonary dirofilariasis in 39 patients are presented. The patients, all Americans, were between 8 and 80 years old (median, 58 years), including 23 men and 16 women. Twenty-two patients were asymptomatic (56%), and the pulmonary nodule was discovered on chest radiographs during a routine physical examination. Seventeen patients (44%) presented with respiratory symptoms or systemic complaints. Peripheral eosinophilia was noted in only 10% of the patients. Radiographically, most lesions were located in the right lung (76%), with a predilection for the lower lobe. In five patients multifocal nodules were seen. All patients underwent thoracotomy with excisional lung biopsy or lobectomy. Pathologically, all cases featured a histiocyte-rimmed necrotic nodule containing fragments of a partially degenerated Dirofilaria immitis. In addition, adjacent lung parenchyma showed morphological features suggestive of other pulmonary processes such as extrinsic allergic alveolitis and/or pulmonary vasculitis syndromes. Three of the five patients with multiple nodules had solitary dirofilarial nodules and adjacent non-small cell carcinomas. The cases presented herein highlight the variable morphological features seen in human pulmonary dirofilariasis and emphasize the need to consider this diagnosis in all cases of necrotizing granulomas of the lung.