Computerized tomography, or CT, scanning can often reveal cancerous tumors or other lung problems as dark spots on the image. The Mayo Clinic adds, however, that some dark spots on a CT scan indicate no current health problems.
Dark spots in a lung CT scan may simply display natural physical structures. According to the Mayo Clinic, many of the discolorations seen on CT scans come from old scars contributed by smoking or previous infections.
According to the RG Radiology Group, nodules from lung cancer may cause small black spots to show up on a lung CT scan. The Mayo Clinic adds that large dark spots or "holes" may represent bullae, distended air sacs resulting from destroyed lung tissue common in cases of emphysema or lung infections.
Response to a dark spot on a lung CT scan depends on the size of the area and its implications. A small spot indicating a node, for instance, may require followup scans to monitor its progress before identifying it as cancer. Patients must also realize that CT scans involve a small degree of radiation exposure.