Relevant clinical information was a past history of prostate cancer treated by surgery 5 years before, and of colorectal cancer treated by surgery + chemotherapy 2 years before.

Melanoma of the right arm was diagnosed 1 year before the PET-CT procedure. 

Enlarged axillary lymph nodes were detected and the patient was sent to PET-CT for staging purposes.

Nodal relapse was clearly visible on the PET and CT images, as illustrated by Figure 1.

Moreover, a hot spot in the left pelvis was detected.

On the fusion image, the uptake is located in a left lateral pelvic mass visible on the CT, heterogeneous, with some higher density areas.

The hypothesis made at the time of the reading of PET-CT was confirmed by a very simple diagnostic test : a plain X-ray of the lower abdomen ! 

The picture shows the typical pattern of the hyperdense material in a gauze

Indeed... The high FDG uptake was due to granulomatous reaction around a retained gauze, left there by either the urologist or abdominal surgeon !