18F-FDG PET-CT Postoperative Changes after Maxillectomy: Findings and Pitfalls in Interpretation.

Johnatan Nissan 3 Tima Davidson 1,2 Maria Krichmar 4 Eyal Lotan 2 Shai Shrot 5 Ella Nissan 2 Iris Gluck 6 Philp Lawson 5 Simona Ben-Haim 1 Shay Duvdevani 7
1Department of Nuclear Medicine, Chaim Sheba Medical Center, Israel
2Sackler School of Medicine, Tel Aviv University, Israel
3Ruth and Bruce Rappaport Faculty of Medicine, Technion, Israel Institute of Technology, Israel
4Department of Orofacial, Chaim Sheba Medical Center, Israel
5Department of imaging, Chaim Sheba Medical Center, Israel
6Department of oncology, Chaim Sheba Medical Center, Israel
7Department of otolaryngology, Chaim Sheba Medical Center, Israel

PURPOSE: PET-CT is the mainstay of disease surveillance in head and neck cancer following local resection. However, increased FDG-uptake in the surgical bed may be non-specific and present diagnostic challenges.

MATERIAL & METHODS: This is a review of FDG- PET-CT studies of head and neck cancer patients with a history of maxillary surgery treated during 2008-2017. Findings on postoperative PET-CT were correlated with clinical and imaging follow-up.

RESULTS: PET-CT studies of 17 reconstructive maxillary surgeries of 14 patients (10 males, mean age 57 ± 16 years, range 22-77) were reviewed. Increased FDG uptake in the postoperative bed was demonstrated in 12 (71%; 10 obturator, 2 mesh reconstructions), mean SUV max 2.4 ± 1.4 (range 0.3-4.3). In the remaining 5/17 studies (3 with a fat flap and 2 without any reconstructions), there was no abnormal FDG uptake at the postoperative bed. CT features in postoperative sites included a combination of: non-homogeneous mixed hyperdense material with multiple air bubbles; 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; radiopaque hyperdense elongated structures in mesh reconstructions. In 8/9 patients with more than one postoperative PET-CT, there were no significant differences between the studies. One patient had a new FDG-avid lesion in the nasopharynx adjacent to the surgical bed, which was confirmed by pathology as recurrence of the disease. No correlation was found of the mean SUV max in initial scans with the time from the surgery date (10 months; ± 6; r=0.04, P=0.90), or with the mean SUV max in final scans (25 months; ± 17; 2.4 ± 1.4 vs. 1.6 ± 1.7; P=0.17). In 4 patients, biopsies obtained from the FDG-avid changes showed fragments of fibrotic or granulation tissue, with no evidence of malignancy. All patients in this study who had obturator or mesh reconstructive surgery after maxillectomy demonstrated FDG avid postoperative changes, which persisted more than four years after surgery.

CONCLUSION: Radiologists should be aware of variations in postoperative PET-CT appearance, including increased FDG uptake, even years after surgery, to avoid overcalling these lesions as malignance.

Johnatan Nissan
Johnatan Nissan