IMAGING

High-resolution multidetector CT in the preoperative evaluation of patients with renal cell carcinoma
Catalano C, Fraioli F, Laghi A, Napoli A, Pediconi F, Danti M, Nardis P, Passariello R
From the Department of Radiology, University of Rome “La Sapienza,” V. le Regina Elena 324, 00161 Rome, Italy
AJR Am J Roent. 2003; 180: 1271-7

• Purpose: The purpose of our study was to evaluate the accuracy of multidetector CT (MDCT) using a high-resolution protocol in the preoperative assessment of patients with renal cell carcinoma who are possible candidates for nephron-sparing surgery.
• Materials and Methods: Forty patients with suspected renal cell carcinoma underwent MDCT. Contrast-enhanced acquisitions were obtained during arterial, nephrographic, and urographic phases using a thin-slice protocol. One-millimeter-thick source images were evaluated by two observers on a dedicated workstation for the identification and characterization of the tumor, presence of a pseudocapsule or invasion of perirenal fat, involvement of adrenal glands or surrounding tissues, presence of satellite lesions within Gerota’s fascia, infiltration of renal vein and inferior vena cava, involvement of lymph nodes, and presence of distant metastases. Imaging findings were compared with surgical specimens using criteria from the Robson and TNM classification systems.
• Results: The presence and size of all lesions were correctly shown in all patients. In evaluating Robson stage I of renal cell carcinoma, we were able to diagnose 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%. One hundred percent accuracy was achieved in staging high-grade lesions.
• Conclusion: High-resolution MDCT is accurate in the preoperative evaluation of patients with renal cell carcinoma.
  
• Editorial Comment
  Robson’s Stage I (T1-T2) tumors are defined on spiral CT as a tumor confined within the kidney with an intact renal capsule. This is usually characterized when the perinephric fat and renal fascia adjacent to the lesion are preserved. Until now, the most specific sign of extension of the tumor to these structures has been the presence of a discrete mass measuring at least 1 cm in diameter projecting into the perinephric space. Although this finding is 98% specific for Robson’s stage II (T3a) tumors, its sensitivity is too low (only 46%) as this finding is absent in the majority of patients with perinephric extension (1). As the perinephric fat and Gerota’s fascia are resected during a radical nephrectomy, the radiological distinction between T1 and T3a has not been very important. More recently, however, renal conservative surgery has been performed with more frequency including the laparoscopic approach; thus, an accurate preoperative radiological staging is essential.
  The point of this report is that the use of 1-mm-thick-multidetector CT images (MDCT) allowed the differentiation between Robson stage I (T1-T2) and T3a renal cell carcinoma, with 96% sensitivity, 93% specificity, 95% accuracy, 100% of positive predictive value and with 93% of negative predictive value. These results are very enthusiastic but studies with a larger series of patients are desirable. As we know CT-false positives diagnoses has been described in up to 50% of patients with Robson’s Stage I disease. This can be explained because perinephric stranding and fascial thickening can occur due to perinephric edema (very nicely illustrated in one case of this report), fat necrosis and fibrosis from remote inflammation (2). Obviously, these data are related to studies performed with single slice spiral CT that has lower spatial resolution than the new generation of MDCT. Multidetector CT provides substantial improvement in volume coverage over single-slice spiral CT. More rapid image acquisition allows better definition of renal capsule and greater separation of arterial and venous phases, thus facilitating multiphasic acquisition. This improvement was very well shown by the superb high resolution multiplanar reconstruction of the kidneys and renal vessels showed in this interesting manuscript.

References
1. Johnson CD, Dunnick NR, Cohan RC, Illescas FF: Renal adenocarcinoma: CT staging of 100 tumors. AJR Am J Roent. 1987: 148: 59-63.
2. Parks CM, Kellett MJ: Review: staging renal cell carcinoma. Clin Radiol. 1994; 49: 223-30.

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