Objective:

To evaluate the diagnostic performance of preoperative 18F-FDG PET/CT for synchronous neoplasm detection in patients with acute left-sided obstructive colorectal cancer.

Approach:

• Method: Retrospective analysis of patients diagnosed with acute left-sided obstructive colorectal cancer who underwent preoperative 18F-FDG PET/CT.
• Method: Primary endpoints included the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of PET/CT in detecting synchronous colorectal neoplasms (sCRC) and colorectal synchronous neoplasms (CSN).
• Method: Reference standard for comparison included histopathological examination and clinical follow-up.

Key Findings:

• Invasive sCRC was confirmed in 9 patients (6.0%) and CSN in 17 patients (11.4%).
• For invasive sCRC, PET/CT sensitivity was 77.8%, specificity 95.0%, PPV 50.0%, and NPV 98.5%.
• For CSN, sensitivity was 52.9%, specificity 96.2%, PPV 64.3%, and NPV 94.1%.
• Among 135 PET-negative patients, only 2 (1.5%) had invasive sCRC.
• Secondary curative resection was required in 5 patients (3.4%) and therapeutic endoscopy in 8 (5.4%).

Interpretation:

Preoperative 18F-FDG PET/CT demonstrated a low rate of missed invasive synchronous cancer when negative (1.5%) and identified a subgroup requiring additional intraoperative assessment when positive.

Limitations:

• Findings are exploratory and require prospective validation.
• PET/CT is not a substitute for clearing colonoscopy and does not mandate extended resection.

Conclusion:

Preoperative 18F-FDG PET/CT can assist in identifying synchronous neoplasms in acute left-sided obstructive colorectal cancer but should not replace standard diagnostic procedures. ---