FDG-PET/CT Skull Base to Mid-Thigh FDG-PET/CT has traditionally been used in initial staging of rectal cancer to further evaluate equivocal findings on CT/MRI, to definitively exclude extrahepatic metastatic disease before surgical resection/liver directed therapy, and to identify occult disease in patients with rising carcinoembryonic antigen [73,74]. It is widely considered a specific but not sensitive examination for evaluating distant rather than local disease [75]. A meta-analysis of a combined 1,262 patients with LARC in 19 studies assessed the accuracy of both local tumor restaging as well as regional nodal restaging as determined by restaging MRI compared to surgical pathology of the Circumferential resection margin (involvement or close approximation of the tumor to the mesorectal fascia) assessment may be slightly less predictive at post-CRT MRI compared with pretreatment MRI, again likely due to overstaging by post-CRT imaging [89]. Tumor height on pre- and post-CRT MRI has shown excellent correlation with endoscopic findings, however, and sphincter involvement/distance, with IV contrast MRI, is more helpful in defining the relationship to the sphincter [90,91]. Additional studies confirming that N+ patients had significantly larger nodes than N0 patients both pre- and post- CRT used size cutoff for post-CRT ypN-stage prediction of <2.5 mm and >5mm at MRI [97-99]. Conversely, with luminal tumor apparent complete response, lymph nodes over 7 mm to 8 mm have been more strongly correlated with locoregional node positive (N+) [100,101]. MRI has demonstrated 75% sensitivity and 71% specificity in determining node positive disease [93]. More recently, change in nodal size or DWI signal on restaging MRI has shown more promise in assessment of nodal disease. Lack of a lymph node signal on DWI high b value 1,000 was associated with a sensitivity of 100% and a specificity of 14% [102]; the positive predictive value was 24%, and the negative predictive value was 100%.
Staging of Colorectal Cancer. FDG-PET/CT Skull Base to Mid-Thigh FDG-PET/CT has traditionally been used in initial staging of rectal cancer to further evaluate equivocal findings on CT/MRI, to definitively exclude extrahepatic metastatic disease before surgical resection/liver directed therapy, and to identify occult disease in patients with rising carcinoembryonic antigen [73,74]. It is widely considered a specific but not sensitive examination for evaluating distant rather than local disease [75]. A meta-analysis of a combined 1,262 patients with LARC in 19 studies assessed the accuracy of both local tumor restaging as well as regional nodal restaging as determined by restaging MRI compared to surgical pathology of the Circumferential resection margin (involvement or close approximation of the tumor to the mesorectal fascia) assessment may be slightly less predictive at post-CRT MRI compared with pretreatment MRI, again likely due to overstaging by post-CRT imaging [89]. Tumor height on pre- and post-CRT MRI has shown excellent correlation with endoscopic findings, however, and sphincter involvement/distance, with IV contrast MRI, is more helpful in defining the relationship to the sphincter [90,91]. Additional studies confirming that N+ patients had significantly larger nodes than N0 patients both pre- and post- CRT used size cutoff for post-CRT ypN-stage prediction of <2.5 mm and >5mm at MRI [97-99]. Conversely, with luminal tumor apparent complete response, lymph nodes over 7 mm to 8 mm have been more strongly correlated with locoregional node positive (N+) [100,101]. MRI has demonstrated 75% sensitivity and 71% specificity in determining node positive disease [93]. More recently, change in nodal size or DWI signal on restaging MRI has shown more promise in assessment of nodal disease. Lack of a lymph node signal on DWI high b value 1,000 was associated with a sensitivity of 100% and a specificity of 14% [102]; the positive predictive value was 24%, and the negative predictive value was 100%.