This study evaluated data from multiple studies (number of patients n = 5119) to assess the diagnostic performance of MDCT in N staging of GC in Eastern Asia.62 Meta-analytical statistical methods were used to integrate and subgroup the data and it was found that the preoperative diagnostic performance of MDCT was not very reliable and the pooled accuracy of N staging was only 67% (95% CI 0.62–0.72).63 And the sensitivity of MDCT in the clinical diagnosis of GC (especially EGC) N staging was not satisfactory.64
The data were grouped according to the reference diameter of LNM and the proportion of DTI.65 The subgroup analysis results indicated that when the reference diameter of LNM was < 8 mm or ≥ 8 mm, the sensitivity of MDCT for N + staging was significantly different, and the sensitivity of the former was significantly greater than that of the latter.66 Preoperative LNM can be determined from the size of the LN, morphology, strengthening methods to comprehensive analysis.67 The American Joint Committee for Cancer (AJCC) and the Japanese Gastric Cancer Association (JGCA) are currently widely recognized TNM staging criteria for GC.68 However, the above two staging systems did not provide a reference standard for the preoperative determination of positive LNs by MDCT.69 Therefore, the preoperative diagnosis of LNM in GC has always been the focus of research.70 Generally, the diameter of LN is ≥ 8 mm, and LNs are considered to be involved.71 For the grouping of DTI, MDCT in patients with mostly AGC was more sensitive for N + staging than that in patients with mostly EGC, suggesting that the proportion of DTI was an important variable affecting the sensitivity, while MDCT was poor in determining N staging with EGC.72 In AGC with LNM, large or clustered LNs are usually found around the primary lesion [34].73 However, EGC with few LNM usually has very small metastatic LNs and is less typical in MDCT imaging than in AGC [35].74 Microscopic metastases found in the LNs of patients with EGC are often classed as negative because the diameters do not meet the criteria for LNM, which makes accurate N staging more difficult in EGC than in AGC [12].75 This means that MDCT is challenging in the proper clinical evaluation of LN involvement in EGC.76 Early reports showed that the accuracy of preoperative N staging for GC ranged from 51–76%, and the sensitivity of N staging ranged from 48–91% [12].77 Fukuya et al. [36] took > 5 mm as the standard, with N staging sensitivity of 75% and specificity of 42%.78 D 'elia et al. [37] took the shorter diameter of perigastric LN > 6 mm and the shorter diameter of peripheral LN > 8 mm as the standard, and the sensitivity and specificity of N staging were 97.2% and 65.7%, respectively.79 Research reports from different periods have shown that due to the effect of DTI on LN status not considered and the lack of reliable preoperative reference diameter criteria for the determination of positive LNs, the results fluctuated widely.80 Therefore, whether in Eastern Asia or elsewhere, in the preoperative evaluation of GC with MDCT, we need to establish more refined and specific criteria for LNM to detect LN status under different conditions.81
The effect of LNs at different locations on the accuracy of MDCT was also widely discussed.82 Pan et al. [38] showed that the results of LNs evaluation by MDCT at different sites showed different sensitivities compared with those of pathology, in addition, among the various metastatic LNs, MDCT showed better sensitivity in the splenic hilum, splenic artery and the sites with less curvature.83 The results of Jia et al. [22] indicated that the examination of LNs on CT depended on the contrast of surrounding structures, and clear anatomical structure, close to the large blood vessels, more fat in the abdominal cavity and LNs in the stomach area were easier to detect.84 In their study, group location diagnosis was adopted.85 For MDCT, according to the fifth edition of the AJCC TNM staging, the sensitivity of LNs in groups 1, 3, 7–9, and 11 was high, and the sensitivity of LNs in groups 4 and 5 was poor.86 Therefore, the lack of one-to-one correspondence between the LNs evaluated by MDCT before operation and those detected by pathology after operation may make the accuracy of MDCT unreliable.87
As mentioned above, the existing accuracy of MDCT is not sufficient for the preoperative evaluation of EGC.88 In order to select appropriate surgical methods (ESD, gastrectomy + perigastric LN resection or enlarged resection) for patients to achieve precision medicine, hierarchical assessment may be effective according to the result of the subgroup analysis.89 In order to achieve the hierarchical assessment and standard development, imaging technicians should first assess the T staging of GC, and then stratify the patients according to the T staging: EGC (T1,T2) with < 8 mm(such as 6 mm) as the reference diameter of LNM, or AGC (T3,T4) with ≥ 8 mm(such as 8 mm or 10 mm) as the reference diameter of LNM. This hierarchical assessment can take into account both the effect of DTI on LNs and the effect of reference diameter of LNM on the sensitivity.90 Such a diagnostic process may greatly improve the accuracy of preoperative staging of EGC, avoid patients from being overtreated or timely adjust the surgical method to expand the scope of surgery.91 About the LNs in different locations, a criterion for clinical diagnosis of N stages is needed.92 MDCT in the preoperative assessment of LNs status should be accurate to mark specific location of the suspected LNs, surgeons should accurately remove and mark the corresponding LNs to achieve a one-to-one relationship with the pathology.93 This not only enables a real preoperative evaluation of N staging with MDCT, but also enables a more accurate understanding of the biological behavior of LNM in GC.94