A pulmonary nodule is a small lesion found incidentally in about one out of every 500 chest x-rays, according to the University of Rochester Medical Center. Most pulmonary nodules are benign, but they can represent early cancer. It is important to distinguish between benign and cancerous nodules as early as possible. There are several causes of pulmonary nodules, most of which are infectious.
Infectious Causes
A benign pulmonary nodule, reports MedlinePlus, is usually a granuloma, which is a collection of inflammatory cells that occurs as a result of previous infection with tuberculosis or atypical bacteria. Granulomas are also commonly a response to old fungal infections including histoplasmosis, coccidioidmycosis, cryptococcosis and aspergillosis. According to the National Lung Health Education Program, fungal granulomas are typically caused by Coccidioides in the southwestern United States and by Histoplasma in northern Mississippi. A history of travel to tropical regions would suggest parasitic granulomas from Dirofilaria, Toxocara or Wuchereria. Most infectious granulomas do not require treatment unless the patient is immunocompromised from AIDS or other chronic diseases. Often the cause of a pulmonary nodule is never diagnosed. Once the nodule is determined to be benign, no further workup is usually undertaken.
Miscellaneous Causes
The National Lung Health Education Program reports that a pulmonary nodule may represent a benign tumor; called a hamartoma, which is a lesion composed of a mixture of cells, tissue and calcium. A hamartoma is thought to be an organ that did not develop correctly. Once identified, it requires no treatment. Other unusual causes of pulmonary nodules include rheumatoid arthritis with inflammation of the air sacs, cysts, vascular malformations, lymph node overgrowth and, rarely, blood clots.
Cancerous Nodules
According to the University of Rochester Medical Center, about 40 percent of pulmonary nodules are malignant. The incidence of these nodules is highest in patients older than 50 years of age with a history chronic obstructive pulmonary disease and smoking, and a growing lesion on serial chest X-rays or CT scans. Diagnosis is made with CT or PET scans, needle biopsy and other tests. The cancerous nodule is usually removed surgically, often followed by chemotherapy or radiation. Up to 80 percents of patients will survive to at least five years if diagnosis and treatment is begun when the pulmonary nodule is less than one centimeter, reports the National Lung Health Education Program, so early detection and diagnosis is important.
