False-positive findings on 18-Fluoro-deoxy-glucose positron emission tomography due to granulomatous inflammation in a rectal cancer patient with an extensive tattoo

Abstract

Introduction: In patients with colorectal cancer a combined 18-Fluoro-deoxy-glucose positron emission tomography with computed tomography (CT) may be useful in advanced or recurrent disease to assess distant metastases. In the interpretation several pitfalls must be considered. Case Report: A 37-year-old woman presented with metachronous liver metastases three years after the first diagnosis of rectal cancer. A second-line chemotherapy and stereotactic radiofrequency ablation was performed. Six months after the intervention, the follow-up magnetic resonance imaging revealed new liver lesions with indefinite diffusion impairment and pathologic contrast enhancement in portal venous and hepatobiliary phase. Further investigation with combined 18-Fluoro-deoxy-glucose positron emission tomography with CT showed for malignancy suspicious glucose-uptake in the respective liver lesions and additional in unilateral enlarged inguinal lymph nodes. Because of the uncommon findings, histologic specimen was obtained. Histology revealed no malignancy, but granulomatous hepatitis and lymphadenitis consistent with sarcoid-like reaction. Furthermore, deposition of tattoo pigment was found in the enlarged lymph nodes, most likely deriving from a large tattoo located on the right lower extremity. Conclusion: We describe a case of a rectal cancer patient with misleading imaging findings on combined 18-Fluoro-deoxy-glucose positron emission tomography with CT. Awareness of rare conditions such as granulomatous inflammation and false-positive findings is key in the presence of uncommon findings, like in this case, suggested spread outside the metastatic pathway.