The diagnostic role of Dual phase F-18 FDG PET-CT and lymphoscintigraphy for the detection of sentinel lymph node in the patients with T1-4 N0-3 M0 oral cavity cancers

Aim: Our objective was to evaluate the diagnostic role of F-18 FDG PET-CT in the patients with oral cavity cancer. We also investigated the diagnostic accuracy of the lymphoscintigraphy for the detection of sentinel lymph node (SLN) in the patients with oral cavity cancer. In terms of the diagnostic role of F-18 FDG PET-CT, we investigated the F-18 FDG uptake difference in metastatic lymph nodes according to regional neck levels, the correlation between F-18 FDG uptake in the primary tumor and lymph node metastases, comparison with the conventional imaging methods, and cutoff values for detection of malignant lesions, and the additional diagnostic value of dual phase imaging.We also searched that the impact of F-18 FDG PET-CT and sentinel lymph node biopsy (SLNB) together in decision making of the patients with oral cavity cancer.Methods: 16 patients (4 female; 12 male, age range, 29-81 years) were included in this retrospective study. F-18 FDG PET-CT and lymphoscintigraphy (2 hours before the surgery) were performed for all the patients before surgery. PET-CT scans were performed one (early) and two hours (delayed) after injection 8-12mCi (296-444 MBq) of F-18 FDG. Diagnostic CT or MR was evaluated by an experienced radiologist on head and neck radiology. In the PET-CT, malignancy in the lymph nodes was evaluated according to 3 criteria: 1: Visual assessment 2: The ratio of SUVmax in tumor/ adjacent muscle tissue (T/M), 3: SUVmax adjusting to the size of lymph nodes. The evaluation of malignancy in the lymph nodes was done separately for early and delay scans. The histopathological evaluation of the surgey was recorded according to the neck levels. Furthermore, the ratio of SUVmax in tumor/liver uptake (T/L) in the lymph nodes was calculated. The sensitivity, specificity, negative (NPV) and positive predictive values (PPV) in F-18 FDG PET-CT for early and delay scans were calculated for each malignancy criteria expect T/L. T/L ratios were calculated just for early images. ROC curves were obtained for SUVmax, T/M and T/Kc. The threshold values were calculated in the terms of highest sensitivity and specificity points.Results: Histopathological evaluations revealed 5 patients had metastatic lymph nodes (N+) whereas 11 patients had benign lymph nodes (N-). 14 of 43 lymph nodes that were visualized in CT of F?18 FDG PET-CT were evaluated as malignant whereas 29 of 43 lymph nodes were evaluated as benign. There was no statistical difference between the N(+) ve N(-) patients in the terms of age, depth of primary tumor and the number of mitosis. However, there was significant difference in the terms of early and delay F?18 FDG uptake of primary tumors between the N(+) ve N(-) patients (P=0,011). The average of SUVmax, T/M and T/L ratios of visually malignant lymph nodes were 7,67±4,95, 7,10±3,18, 2,85±1,83 in early scan respectively. The average of SUVmax and T/M ratio were 8,0±5,68 and 9,08±4,31 in delay scan. The average of SUVmax, T/M and T/Kc ratios of visually benign lymph nodes were 1,69±0,43, 1,49±0,48 ve 0,59±0,22 respectively in early scan. The average of SUVmax and T/M ratios were 1,66±0,36 and 1,66±0,69 in delay scan. There was significant difference in the value of SUVmax (p=0.00) and in the T/M ratios (p=0.01) between early and delay scans for the lymph nodes. There was no statistical difference in the value of SUVmax and T/M ratios between early and delay scans for the benign lymph nodes. The highest sensitivity, specificity, NPV and PPV were obtained in the criteria of T/M ratios for both early and delay scan. With the treshold value of early SUVmax as 3,4 and early T/M ratio as 3,2; delay SUVmax as 4,0 and delay T/M ratios as 3,8 which is obtained from our population using ROC curve, 93% sensitivity, 96% specificity were calculated. With the treshold value of T/L ratios as 1,0 we found 93% sensitivity and specificity. 40 lymph nodes were displayed with lymphoscintigraphy, 31 lymph nodes were detected with gama probe. There were 32 metastatic lymph nodes in 5 N(+) patients. 5 lymph nodes were detected with lymphoscintigraphy and gama probe in 3 patients. Metastasis were proven with hematoxylin-eosin (H&E) in 2 of 5 metastatic lymph nodes and metastatis were proven with immunohistochemistry in 3 of 5 metastatic lymph nodes. SLNB was false negative in 2 patients. F-18 FDG showed skip lymp node metastases in these SLNB negative patients.Conclusion: This study indicates that F?18 FDG PET-CT is a reliable method for the correct evaluation of primary tumor and N staging in oral cavity cancers. It might catch skip metastasis in lymph nodes which can be missed with SLNB. We found that delay scans may cause to decrease the sensitivity and specificity in our study. In addition, since there was significant difference in the terms of early and delay F?18 FDG uptake of primary tumors between the N(+) ve N(-) patients, FDG uptake in primary tumor might be an independent factor showing the aggressivity of primary tumor and might predict N(+) disease. This study showed that T/M ratios in the lymph nodes can be used to evaluate malignancy with a high diagnostic accuracy. The further studies with the high number of patients are needed.