Often this pattern of multi-focal intense symmetric uptake along the neck, supraclavicular, mediastinum, and paraspinal regions can be seen. The fusion images localize the uptake to areas of fat on the CT images. In particular, it is the brown adipocytes that take up FDG. Brown adipocytes become activated as one of the initial steps in thermogenesis in response to cold. Through sympathetic innervation, glycolysis is significantly increased. Higher levels of circulating catecholamines in anxious patients may also play a role in some patients.

Possible limitations:

• It may be difficult to detect true disease in these regions.
• Detection of metastatic lymph node disease in the cervical and supraclavicular regions is particularly difficult.

Preventive measures:

• Keep the injection rooms at warmer temperatures.
• If confident interpretation is not possible, premedication with a small dose of oral valium can help prevent it on a repeat study.