Pulmonary and Critical Care Pearls: Reviews

Solitary Pulmonary Nodule in a 62-Year-Old Man

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.

Background. Pulmonary dirofilariasis is a rare entity caused by Dirofilaria immitis, the dog heartworm that is transmitted to humans by mosquitos. This filarial nematode enters the subcutaneous tissue, travels to the right ventricle where it dies, and then embolizes the pulmonary vasculature, causing a small pulmonary infarction, which subsequently appears as a solitary nodule. Although these nodules are usually identified incidentally by chest radiography in asymptomatic patients, the lesion is generally presumed to be neoplastic. Diagnosis is made by surgical excision.

Methods. We reviewed the pathology reports at Memorial Medical Center, Savannah, GA since 1990.

Results. There have been approximately 150 cases reported in the literature worldwide. We found 4 patients with pulmonary dirofilariasis diagnosed at our hospital since 1992. A review of the pathogenesis of the disease and clinical manifestations, diagnosis, and treatment of this entity are presented.

Conclusions. Pulmonary dirofilariasis is a benign condition, transmitted by mosquitos to humans that results in peripheral pulmonary nodules. Awareness of this entity is important in the differential diagnosis of pulmonary coin lesions.

To present the clinical, radiologic, and pathologic aspects of 24 cases of human pulmonary dirofilariasis (HPD) from Sao Paulo, Brazil.

Retrospective study of 24 patients with a confirmed diagnosis of HPD over a 14-year period (from February 1982 to June 1996).

Thoracic Surgery and Pulmonary Division, University of Sao Paulo and Hospital Albert Einstein, Sao Paulo, Brazil.

Seventeen patients were male (70.1%) and seven were female (29.9%). Their mean age was 51.4 years. Fifty-four percent of the patients were asymptomatic and 75% had a well-circumscribed noncalcified peripheral subpleural pulmonary nodule on the chest radiograph and thoracic CT scan, located preferentially in the lower lobes. The diagnosis was made after thoracotomy and wedge resections in 16 patients, by videothoracoscopy in six, after a pleural biopsy in one, and after necropsy in one. The pathologic examination of all the nodules revealed a central zone of necrosis, surrounded by a narrow granulomatous zone and peripherally by fibrous tissue. Pulmonary vessels exhibit varying degrees of endarteritis. In all cases, a dead worm, usually necrotic and fragmented, was found.

A subpleural, noncalcified pulmonary nodule in the appropriate clinical and epidemiologic setting should alert the clinician, radiologist, or pathologist to the possibility of Dirofilaria. HPD should be considered in the differential diagnosis of pulmonary nodules.