699P - High incidence of metastases detected on 18F-FDG PET-CT in patients with gall bladder cancer incidentally discovered after laparoscopic cholecystectomy

Abstract

Gall bladder cancer (GBC) is a relatively rare disease with clinical and imaging features similar to benign gall bladder diseases (BGBD) like gall stone disease or cholecystitis. A few of the BGBD patients who undergo laparoscopic cholecystectomy (LC) are later found to have GBC. In these patients, it is important to evaluate the extent of disease for further management. This study was conducted to evaluate the incidence of metastases in patients referred for 18F-fluorodeoxyglucose positron emission tomography-computed tomography (FDG PET-CT) following incidental discovery of GBC after LC for BGBD. We retrospectively evaluated the data of patients referred to our department between January 2011 and December 2015 for FDG PET-CT with GBC diagnosed on histopathology (HP) after LC for BGBD. Abnormal FDG uptake on PET images corresponding to morphological abnormalities on contrast enhanced CT images was considered positive for disease. HP examination and clinical or imaging follow-up were used as the reference standard for confirmation of diagnosis. FDG PET-CT imaging was performed 1-8 (median 3.5) months after LC in 44 patients (8M, 36F) aged 30-75 (median 50.2) years. PET-CT was positive in 32/44 (72.7%) and negative in 12/44 patients (27.3%). Loco-regional disease was detected in 30/44 patients (68.2%) involving the gall bladder fossa, liver or regional lymph nodes. Metastatic seeding to the omentum, mesentery or laparoscopic port sites was found in 15 (34.1%) and distant metastasis in 5 patients (11.3%). Based on the reference standard, 28 patients had true positive scans. Findings in 4 scan-positive patients could not be confirmed; these were presumed false positive and remain on follow-up. All 12 scan-negative patients were true negative. PET-CT showed sensitivity, specificity, PPV, NPV and accuracy of 100%, 75.0%, 87.5%, 100%, and 90.9% respectively in detecting residual / recurrent disease. There is high propensity for seeding metastasis when GBC is discovered after LC for BGBD. FDG PET-CT has high diagnostic performance in detecting residual / recurrent disease as well as metastases in these patients.