Abstract Introduction Human pulmonary dirofilariasis is a rare zoonotic infection caused by Dirofilaria immitis, in which humans serve as accidental, dead-end hosts. Immature worms embolize to distal pulmonary arteries, where they degenerate and incite localized infarction with necrotizing granulomatous inflammation. These lesions often appear spiculated and FDG-avid on PET imaging, frequently mimicking primary lung cancer. Definitive diagnosis requires histopathologic confirmation. Case report A 74-year-old man, lifelong nonsmoker with a history of urothelial carcinoma of the bladder, underwent routine surveillance PET-CT for malignancy follow-up, which revealed a 14-mm spiculated posterior right upper lobe nodule with focal hilar uptake highly suspicious for primary pulmonary malignancy. The patient underwent robotic video-assisted thoracoscopic wedge resection. Gross examination demonstrated a firm, tan-white subpleural lesion. Histopathologic evaluation revealed a necrotizing granuloma containing degenerated parasitic structures consistent with Dirofilaria immitis. No evidence of malignancy was identified. The postoperative course was uneventful. Surgical resection was both diagnostic and therapeutic, and no antiparasitic therapy was required. Discussion Pulmonary dirofilariasis is often discovered incidentally during evaluation for presumed lung cancer. Because Dirofilaria immitis cannot mature in humans, the organism undergoes intravascular degeneration eliciting granulomatous inflammation that can exhibit FDG avidity on PET imaging due to inflammatory response rather than neoplastic activity. Diagnosis requires histopathologic confirmation, and surgical excision is both diagnostic and curative. Awareness of this entity is important, particularly in areas where canine heartworm disease is endemic, as considering it within the differential diagnosis of solitary PET-avid lung nodules may prevent unnecessary extensive oncologic evaluation or lung parenchymal resection. Conclusion Pulmonary dirofilariasis should be recognized as a rare but important malignancy mimic. Tissue diagnosis remains essential in distinguishing parasitic granulomas from true neoplastic processes. This abstract is funded by: None
Whuking et al. (2026) studied this question.