Optimal diagnostic criteria for lateral pelvic lymph node metastasis in rectal carcinoma

The purpose of this study was to determine the optimal diagnostic criteria for lateral pelvic lymph node metastasis in patients with rectal carcinoma.

From July 1997 to June 2005, fifty-one patients with locally advanced middle or lower rectal carcinoma underwent preoperative MRI examination, followed by total mesorectal excision with lateral pelvic node dissection. Factors of lateral pelvic lymph nodes evaluated were size, shape and internal structure. The size of lymph nodes was measured in both long and short axis diameters. The shape of lymph nodes was categorized into ovoid or irregular. The internal structure of lymph nodes was categorized into homogeneous or non-homogeneous. Optimal preoperative criteria on MRI were clarified by area under receiver operating characteristic curves (AUC). To clarify the optimal diagnostic criteria for diagnosing lateral pelvic lymph node metastasis, these basic four categories were analyzed. Subsequently, combined criteria comprising 11 categories were also evaluated to clarify optimal criteria.

Detection of lateral pelvic lymph node on MRI was significantly higher in the metastatic group. The basic four categories were evaluated to define each optimal criterion for metastasis. In category 1, the optimal criteria for long axis diameter of 10 mm or larger showed the largest AUC of 0.711. In category 2 (short axis diameter), the criterion of 5 mm or larger showed the largest AUC of 0.736. In category 3, an ovoid shape showed an AUC of 0.722. In category 4, heterogeneity of the internal structure gave the largest AUC of 0.708. Based on these results, fifteen categories (category 1-15) were defined. Among them, category 8 (an ovoid shape with a short axis diameter) showed the largest AUC of 0.75, representing 67% sensitivity, 83% specificity, and 78% overall accuracy.

An ovoid shape with a transverse axis diameter of 5 mm or larger on MRI was considered as the optimal criterion for diagnosing lateral lymph node metastasis in patients with rectal carcinoma.