Roentgenogram of the Month

A Solitary Pulmonary Nodule With Zoonotic Implications

Human pulmonary dirofilariasis (HPD) is a rare zoonotic disease caused by Dirofilaria immitis, the nematode responsible for canine cardiopulmonary dirofilariasis (dog heartworm). The incidence of HPD is on the rise throughout the world due to increased awareness and factors affecting the vector (mosquito). Humans are accidental hosts for D. immitis. Most patients are asymptomatic and present with an incidental pulmonary nodule that mimics primary or metastatic pulmonary malignancy. Some patients suffer from pulmonary and systemic symptoms in the acute phase of pneumonitis caused by pulmonary arterial occlusion by the preadult worms resulting in pulmonary infarction and intense inflammation. These patients may have ill-defined pulmonary infiltrate on chest radiology. Pulmonary nodules represent the end result of initial pneumonitis. There are no specific clinical, laboratory, or radiologic findings that differentiate HPD from other causes of a pulmonary nodule. Although serologic tests exist, they are usually not commercially available. The majority of patients are diagnosed by histopathologic identification of the decomposing worm following surgical resection of the lesion.

Human pulmonary dirofilariasis (HPD) is a rare zoonotic infection caused by Dirofilaria immitis. Dogs are the definite hosts and humans are infected occasionally via a vector, generally a mosquito. Most thoracic neurilemmoma arise in the mediastinum and fewer tumors originate peripherally from the intercostal nerves. Most patients with HPD or thoracic neurilemmoma are asymptomatic and these diseases are often discovered incidentally. We present a 53-year-old female who was found to have a pulmonary nodule and a chest wall nodule during a routine health examination. She underwent a video-assisted thoracoscopic surgery (VATS) with partial lung resection and local excision of the chest wall. The pathological examination revealed a coiled, degenerating Dirofilariasis immitis worm surrounded by granulomatous inflammation with caseous necrosis and a neurilemmoma composed of S-100 protein immunoreactive but smooth muscle actin negative spindle cells. Because these diseases are self-limiting and make further treatment unnecessary, video-assisted thoracoscopic surgery (VATS) is considered preferable and less invasive for definitive diagnosis and management.

Inflammatory myofibroblastic tumor (IMT) of the lung is a rare condition. Radiological properties and clinical presentation of this disease can mimic malignant process. We present a case of IMT of the lung in a 58 year old female patient with a single lung nodule. Tumor was unencapsulated, firm, and well circumscribed. Microscopically tumor had multinodular structure with single or multiple small blood vessels in the center of each nodule surrounded in circular pattern by connective tissue containing spindle cells embedded into the thick layers of extracellular matrix. Extracellular matrix was identified as type I and type III collagen fibrils embedded into type IV collagen and laminin. The tumor was surrounded by T-, B-lymphocytes and polyclonal plasma cells. Histological organization of this lesion's stromal component was unique, but cell composition was similar to inflammatory pseudotumor of the lung. In addition, tumor tissue sections exhibited strong positivity for IgG, weak positivity for IgA, 1Cq, but were negative for IgM, and C3. Mutational analysis of the EGFR, KRAS genes and ALK locus rearrangement were performed and did not reveal any mutations. This is the first report of an IMT associated with Sjögren's disease, systemic lupus erythematosus and Non-Hodgkin lymphoma developing in the lungs. Patient was clinically followed up for 18 months and no recurrence of the tumor observed.

Heartworm disease due to Dirofilaria immitis continues to cause severe disease and even death in dogs and other animals in many parts of the world, even though safe, highly effective and convenient preventatives have been available for the past two decades. Moreover, the parasite and vector mosquitoes continue to spread into areas where they have not been reported previously. Heartworm societies have been established in the USA and Japan and the First European Dirofilaria Days (FEDD) Conference was held in Zagreb, Croatia, in February of 2007. These organizations promote awareness, encourage research and provide updated guidelines for the diagnosis, treatment and prevention of heartworm disease. The chapter begins with a review of the biology and life cycle of the parasite. It continues with the prevalence and distribution of the disease in domestic and wild animals, with emphasis on more recent data on the spreading of the disease and the use of molecular biology techniques in vector studies. The section on pathogenesis and immunology also includes a discussion of the current knowledge of the potential role of the Wolbachia endosymbiont in inflammatory and immune responses to D. immitis infection, diagnostic use of specific immune responses to the bacteria, immunomodulatory activity and antibiotic treatment of infected animals. Canine, feline and ferret heartworm disease are updated with regard to the clinical presentation, diagnosis, prevention, therapy and management of the disease, with special emphasis on the recently described Heartworm Associated Respiratory Disease (HARD) Syndrome in cats. The section devoted to heartworm infection in humans also includes notes on other epizootic filariae, particularly D. repens in humans in Europe. The chapter concludes with a discussion on emerging strategies in heartworm treatment and control, highlighting the potential role of tetracycline antibiotics in adulticidal therapy.