Pre-Sacral Soft Tissue After Rectal Surgery

After resection of all or part of the rectum, ill-defined and often intensely FDG-avid pre-sacral soft tissue will often be present.  Initially, this density will reflect post-operative inflammatory changes, which may later be replaced by non-avid scarring and fibrosis. As these patients will also often receive radiation therapy, these hypermetabolic inflammatory changes can persist for many months.

Distinguishing these ill-defined hypermetabolic inflammatory changes from malignancy during the first few weeks after surgery can be a challenge.  For this reason, it is generally recommended to delay post-operative PET/CT imaging for at least 8 weeks after surgery.

Frequently, a follow up PET/CT exam will be required to exclude residual/active malignancy:

“Post-operative changes of the rectum are now present. Prominent, ill-defined pre-sacral soft-tissue density is noted, moderate to intensely FDG-avid (SUV 2.4). While active malignancy cannot be excluded, this may simply reflect post-operative inflammatory changes.  Follow-up is recommended to exclude underlying disease.”

Increased Suspicion for Malignancy:

• Soft tissue is intensely avid > 3 months after surgery/radiation.
• Hypermetabolic activity is limited to only a focal or nodular portion of the pre-sacral soft tissue density.
• Any increase in size and/or metabolic activity of the soft tissue on a follow-up exam.
• Evidence of co-existing active malignancy exists (e.g. adjacent hypermetabolic nodes).