Dog heartworm causing necrotizing granuloma of the lung

Pulmonary dirofilariasis was diagnosed in a 70-year-old woman by tissue examination after she underwent a right thoracotomy. The preliminary clinical diagnosis was pulmonary coin lesion of probable neoplastic nature. Pulmonary dirofilariasis, caused by the dog heartworm, is occurring with increased frequency in the United States and must be considered in the differential diagnosis of pulmonary coin lesions. We describe the clinicopathological features of this case with special emphasis on the gross examination of the specimen.