Subcutaneous & Intramuscular Medical Injections

A majority of patients presenting for PET/CT imaging will be receiving subcutaneous and/or intramuscular injections – either related to their cancer therapy or other medical conditions (e.g. diabetes, flu shots). 

If the injection is recent, it will often appear as extremely ill-defined density/stranding within the subcutaneous fat or muscle, which can demonstrate variable metabolic activity (usually mild to moderately avid).

These findings are most commonly seen in the gluteal regions, anterior abdominal wall and deltoid musculature.

Do not confuse these FDG-avid injection sites with metastatic lesions.

Flu Shots:

Flu shots injected in the deltoid muscle can occasionally be associated with ipsilateral FDG-avid axillary nodal uptake.  

When unexpected axillary nodal uptake is seen, it is worth checking the ipsilateral deltoid muscle for associated FDG uptake. If present, consider a recent flu shot as a diagnosis (a quick phone call to the clinician or patient usually elicits the appropriate history).