A, C. There is a well-defined nodule in the right lower lobe, abutting the dome of the right hemi-diaphragm that is of mixed solid and fat density.

B, D. The nodule is hypermetabolic with SUVmax of 3.4, seen over the liver due to misregistration, a common artifact at the dome of the liver due to respiratory movement.

A pulmonary hamartoma is a relatively common benign lesion, usually discovered incidentally as a coin lesion on a chest x-ray. The lesion consists of connective tissue, commonly cartilage and fat. Whilst known as hamartomas, several features suggest that these lesions are neoplasms, including increased incidence with age and chromosomal aberrations.

Approximately 20% hamartomas may have high FDG uptake, dependent on size, as occurred in this case. The combination of anatomic and physiologic imaging in PET-CT results in improved accuracy for diagnosing a solitary pulmonary nodule as malignant or benign, compared to CT or PET alone. Where the sensitivity/ specificity for CT and PET alone are 93%/ 31% and 69%/ 85% respectively, the sensitivity/ specificity of PET-CT is 97%/ 85%, which reflects the combination of the high sensitivity of CT and high specificity of PET in this context.

Misregistration artifacts generated by motion can occur at many sites. In PET-CT, the major artifacts occur near the lung base, lung periphery and liver dome. Different respiratory phases during PET and CT acquisition can lead to an anatomic mismatch between the two data sets. A careful analysis of individual PET and CT image data sets with direct visual comparison may avert errors.