Preoperative diagnosis of such lesions is complicated by several limitations. First, the differential diagnosis is broad including an extensive number of inflammatory and infectious processes. Second, positron emission tomography (PET), which identifies regions of increased metabolic activity, may be falsely negative due to the slow growth of early adenocarcinoma lesions. Transbronchial needle biopsy is also unreliable to confirm or exclude disease in non-solid type lesions.