It is possibly confused with blood, water or even tumor. Therefor, some clinical history is necessary to help differentiate pneumonia from other possible pathology. Radiographic appearance predicated on infiltrate location, i.e. broncho-pneumonia vs. lobar pneumonia. The infection causing the pneumonia may lead to cavitation or destruction of the lung tissue forming abscesses. The three most common organisms that cause pulmonary abcesses are staph aureus, strep pyogenes, and clebsciella.
Gram negatives are also very common causes of abscesses.
Metastatic disease is hematogenously disseminated from another primary source such as colon or ovary which, more than likely, present as multiple nodules. Remember that since plain film specificity is not very high, carcinoma can resemble other pathology such as pneumonia. If the nodule is highly calcified, it is a benign process and is not life-threatening. They are typically a granuloma. The first step is to review the patients old chest films.