18F-FDG PET-CT postoperative changes after maxillectomy: Findings and pitfalls in interpretation

Objective: We investigated the findings and pitfalls of FDG-PET/CT scanning after maxillectomy with reconstruction/rehabilitation procedures, in patients with head and neck malignancies treated during nine years at one tertiary medical centre. Methods: Fourteen patients (10 males), aged 22–84 years, underwent 17 reconstruction/rehabilitation maxillectomy surgeries and 35 PET/CT scans. Postoperative PET/CT findings were correlated with clinical and imaging follow-up. Results: Increased FDG uptake, mean SUVmax 2.4 ± 1.4 (range 0.3–4.3), was observed at the postoperative bed following 12 of 17 surgeries (71%; 10 obturators, two mesh reconstructions). Following the remaining 5/17 surgeries (three with a fat flap and two without any reconstructions), abnormal FDG uptake was not observed at the postoperative bed. CT features of postoperative sites included: non-homogeneous mixed iso/hyperdense structures (hollow or filled) with multiple surrounding and/or inside air bubbles (“sponge appearance”) and mucosal thickening along the postoperative bed wall (in all cases with obturator implants); rich fat density material in reconstructions with a fat flap and in closures without reconstruction, and radiopaque elongated structures in mesh reconstructions. No correlation was found of the mean SUVmax in initial scans, with the time from the surgery date (10 ± 6 months; r=0.04, P=0.90), or with the mean SUVmax in final scans (at 25± 17 months, P=0.17). Conclusions:: Increased FDG uptake, together with corresponding non-specific CT features, may persist for a prolonged period after surgery with obturators and mesh implantations, mimicking malignancy or infection. Awareness of variations in postoperative PET-CT appearance can help avoid false interpretations and redundant invasive procedures.