What Are Potential Causes of Dark Spot on Lung CT?

Updated February 21, 2017

Computerised tomography, or CT, scanning can often reveal cancerous tumours or other lung problems as dark spots on the image. The Mayo Clinic adds, however, that some dark spots on a CAT scan indicate no current health problems.

Harmless Findings

Dark spots in a lung CAT scan may simply display natural physical structures. According to the Mayo Clinic, many of the discolourations seen on CAT 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 CAT 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 CAT scan depends on the size of the area and its implications. A small spot indicating a node, for instance, may require follow-up scans to monitor its progress before identifying it as cancer. Patients must also realise that CAT scans involve a small degree of radiation exposure.

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