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MRI for preoperative staging of renal cell carcinoma using the 1997 TNM classification: comparison with surgical and pathologic staging
Ergen FB, Hussain HK, Caoili EM, Korobkin M, Carlos RC, Weadock WJ, Johnson TD, Shah R, Hayasaka S, Francis IR
Department of Radiology/MRI UH-B2B311, University of Michigan Health System, Ann Arbor, MI, USA
AJR Am J Roentgenol. 2004; 182: 217-25

  • Objective: The purpose of our study was to determine the accuracy of MRI for preoperative staging of renal cell carcinoma using the 1997 TNM classification.
  • Materials and Methods: We conducted a retrospective review of MRI performed in 40 consecutive patients with 42 renal cell carcinomas before radical (n = 35) or partial (n = 4) nephrectomy or exploratory laparotomy (n = 3). The interval between imaging and surgery ranged from 1 to 59 days (mean, 17.9 days). Imaging was performed with T1- and T2-weighted, dynamic gadolinium-enhanced, and time-of-flight sequences. MRI and surgical-pathologic staging was performed using the 1997 TNM staging system. MRI staging was compared with surgical-pathologic staging as the gold standard. Agreement between the two staging methods was assessed using the kappa statistic.
  • Results: Agreement between MRI and surgical-pathologic staging was good for T staging (kappa = 0.72 and 0.78 for reviewers 1 and 2 respectively), poor for N staging (kappa = 0.13, both reviewers), good for M staging (kappa = 0.66, both reviewers), and excellent for the assessment of venous involvement (kappa = 0.93, both reviewers). MRI overestimated the T stage in five patients and the N stage in five and underestimated the T stage in three, the N stage in four, the M stage in one, and the extent of venous thrombosis in two patients.
  • Conclusion: MRI is a reliable method for preoperative staging of renal cell carcinoma using the 1997 TNM classification, in particular for assessing venous involvement.

  • Editorial Comment
    The TNM staging system for renal cell carcinoma was revised by the American Joint Committee on Cancer (AJCC) and the International Union Against Cancer (UICC) in 1997. The 1997 TNM staging system for renal cell carcinoma reclassifies tumors using criteria for size and for extent of renal vein / vena cava involvement that are different from the criteria used in the 1987 staging system. With this new TNM staging classification the size limit for T1 tumor was changed from 2.5 to 7 cm.This paper adresses very clearly the problems of the imaging criteria for adequate preoperative evaluation of tumor size, presence of perirrenal extension and regional adenomegaly. It’s well known that on the basis of imaging features distinction between stage T1/T2 and stage T3a tumor cannot be reliably made. This occurs because the assessment of invasion of the renal capsule and Gerota’s fascia in tumor larger than 3 cm of diameter is based on the utilization of poor predictive radiological findings (perinephric stranding, perinephric collateral vessels and presence of discrete soft-tissue masses larger than 1 cm). Large exophitic masses may be stage T1 or T2 and tumors with a small extrarenal component may be stage T3a. Although accurate characterization of tumor size(T) is more difficult when we are dealing with larger renal tumors, the authors had a highly accurate T staging even evaluating large tumors(mean size 14.2 cm). An important contribution of this restrospective study was the finding that tumor size was not a good predictor for the presence of perinephric fat invasion.The authors found a major overlap between the sizes of tumors without and with perinephric fat invasion: mean size of T1 tumors, 3.4 cm (range, 0.8–7 cm); of T2 tumors, 14.2 cm (range, 8–19.3 cm); and of T3a tumors, 9.2 cm (range, 7.9–12 cm). The tumors of all four patients in their study who underwent partial nephrectomy were correctly staged as T1 (size range, 0.8–3 cm).
    One of the main limitations of this study, as the authors pointed out, is that most of their patients had advanced tumors. This is a relevant issue since nowadays as many as 30 - 40% of renal tumors are small, discovered incidentally and frequently appropriately treated with conservative surgery. In a recent study using multi-dectetor CT the authors were able to differentiate between stages T1/T2 and T3a (by diagnosing fat infiltration on 1-mm scans) with 96% sensitivity, 93% specificity, and 95% accuracy; the positive and negative predictive values were, respectively, 100% and 93%(1). Regarding the detection of lymph node metastase, the limitation of CT and MR imaging remains the same. This occurs because it is still based on lymph node size criteria only. With 10 mm as the limiting size for normal nodes, 4% of lymph nodes have a false-negative finding and the false-positive findings ranges from 3% to 43%. This is explained by the fact that nodal enlargement may be determined by reactive hyperplasia. In the group of patients with smaller lesions one might expect small number of patients with metastatic adenopathy. For the detection of stages T3 b and T3c, MR and MDCT imaging are excelent modalities. These methods are highy accurate in determining the presence and superior extent of thombus.
    The major advantages of MRI, however, are the differentiation between tumor thrombus and blood thrombus since blood thrombus does not adhere to the wall of the vein and can be easily extracted.
    Finally, it would be interesting to perform additional comparison of these results with the new and lower cutoff value of 4.5 cm proposed by some authors(2). It has been suggested that lowering the cutoff point resulted in better discriminatory power of the TNM classification (2).

References
1. Catalano C, Fraioli F, Laghi A, Napoli A, Pediconi F, Danti M, et al.: High-resolution multidetector CT in the preoperative evaluation of patients with renal cell carcinoma. AJR Am J Roentgenol. 2003;180: 1271-7.
2. Zisman A, Pantuck AJ, Chao D, Dorey F, Said JW, Gitlitz BJ, et al.: Reevaluation of the 1997 TNM classification for renal cell carcinoma: T1 and T2 cutoff point at 4.5 rather than 7 cm. better correlates with clinical outcome. J Urol. 2001; 166: 54-58.

Dr. Adilson Prando
Department of Radiology
Vera Cruz Hospital
Campinas, São Paulo, Brazil