ABSTRACT: Low back pain with radiation to lower limbs is due to nerve root impingement or involvement in most cases. F-FDG PET/CT has shown sacral nerve root involvement in several peripheral nerve pathologies, including neurolymphomatosis, peripheral nerve sheath tumor, and plexopathies. We present 2 cases of a low back pain with ulcerative colitis and metastatic neuroendocrine tumor who underwent F-FDG PET/CT and Ga-DOTANOC PET/CT, respectively. PET/CT can be used as an adjunct tool to evaluate sacral nerve root involvement to look for malignant or inflammatory nerve involvement.