Efficacy of Positron Emission Tomography in Diagnosis of Lateral Lymph Node Metastases in Patients with Rectal Cancer: A retrospective study

Background: The presence of lateral pelvic lymph node (LLN) metastasis is an essential prognostic factor in rectal cancer patients. Thus, preoperative diagnosis of LLN metastasis is clinically important to determine the therapeutic strategy. The aim of this study was to evaluate the efficacy of preoperative positron emission tomography/computed tomography (PET/CT) in the diagnosis of LLN metastasis. Methods: Eighty-six patients with rectal cancer who underwent LLN dissection at Osaka University were included in this study. The maximum standardized uptake value (SUV max ) of the primary tumor and LLN were preoperatively calculated using PET/CT. Simultaneously, the short axis of the lymph node was measured using multi-detector row computed tomography (MDCT). The presence of metastases was evaluated by postoperative pathological examination. Results: Of the 86 patients, LLN metastases developed in the left, right, and both LLN regions in 7, 8, and 2 patients, respectively. The diagnosis of the metastases was predicted with a sensitivity of 84%, specificity 94%, positive predictive value 62%, and negative predictive value 98% when the cutoff value of the LLN SUV max was set at 1.5. The cutoff value of the short axis set at 7 mm on MDCT was most useful in diagnosing LLN metastases, but SUV max was even more useful in terms of specificity. Conclusions: The cutoff value of 1.5 for lymph node SUV max in PET is a reasonable measure to predict the risk of preoperative LLN metastases in rectal cancer patients.