Accurate preoperative staging of RCC is important,
permitting optimal patient management [1,2].
The T component of the TMN staging classification system is a major factor in predicting prognosis and survival in these patients.
Local staging and differentiation between T1/T2 and T3a stages is significant in determining best surgical approach (conservative versus radical nephrectomy and laparoscopic versus open incision) [1,2].
Detection of perinephric fat invasion in RCC represents one of the commonest staging errors at CT examination [1,2,15,16].
Johnson et al in a retrospective study of 100 RCCs using a conventional CT scanner reported 46% sensitivity and 98% specificity in detecting perinephric fat invasion.
The presence of a soft-tissue perinephric nodule suggested tumor extension into the PN fat in this study [16].
Kopka et al in a prospective study of 76 RCCs evaluated with a dual-phase helical CT reported 91% overall staging accuracy,
with three understaged carcinomas,
in which tumor spread to the PN fat tissue was not identified [15].
Catalano et al reported 96% sensitivity,
93% specificity and 95% accuracy in diagnosing PN fat invasion in a prospective study of 42 RCCs,
using a multidetector CT scanner.
CT criteria used to diagnose neoplastic invasion of the perirenal fat tissue were hyperdense streaks and nodules surrounding RCC in this report [2].
The present study was a retrospective review of 48 histologically proven RCCs,
including 18 (37.5%) cases with perinephric and/or renal sinus fat invasion.
The diagnostic performance of multiphase multidetector CT with multiplanar reformations in detecting infiltration of the PN and/or RS fat invasion was evaluated.
Multiple logistic regression analysis was performed to assess which CT features were more predictive for the diagnosis of invasion.
The results of logistic regression analysis indicated that the presence of contrast-enhancing nodules in the perinephric space and tumoral margins were the two most significant predictors in diagnosing PN fat invasion.
Using perinephric nodules and tumoral margins as CT criteria to detect RCC extension into the perinephric fat,
we had 85.4% overall accuracy,
with a sensitivity of 66.6% and 50%,
respectively and a specificity of 94.4% and 97.2% respectively.
Contrast-enhancing nodules in the PN fat has been reported as the most specific finding of stage T3a disease,
although sensitive in 45-50% of cases [1,2].
This was also proved in this report.
Perinephric stranding and presence of perinephric collateral vessels are not considered as reliable or specific signs in diagnosing neoplastic infiltration of the perirenal fat tissue,
and this was seen in this study.
Both CT signs had low accuracies (50% and 60.4%,
respectively) in detecting tumor extension into the PN fat.
Perinephric stranding was defined as thickening of the bridging septa of the perinephric space.
These septa (Kunin septa) divide the perinephric space into multiple compartments and are divided into several groups [29,30].
Group I septa arise from the renal capsule and extend to the renal fascia.
Group II septa are attached to the renal capsule,
paralleling more or less the renal surface.
Group III representing the commonest type,
connect the anterior and posterior leaves of the renal fascia [29].
A variety of pathologic conditions,
including neoplastic and nonneoplastic processes may involve the perirenal space,
causing thickening of the bridging septa [29,30].
Perinephric stranding is reported in about half of patients with RCC confined within the kidney,
and this was also seen in our study [1,2].
Other causes resulting in thickening of the bridging septa in the vicinity of RCC include edema,
vascular engorgement,
previous inflammation,
perinephric hematoma or perinephric fat necrosis [1,2].
Neoplastic infiltration of the perirenal fat tissue resulted in hyperdensity of the perinephric fat close to RCC in this study.
Measurements of the CT density values of PN fat in cases of histologically proven neoplastic invasion had higher values when compared with both the PN fat in the vicinity of RCCs confined within the kidney and the PN fat of the normal contralateral kidney.
However,
logistic regression analysis indicated that the CT density measurement of the perinephric fat is not a significant predictor for the diagnosis of tumor extension into the perirenal fat tissue.
The renal sinus is a central compartment formed by the extension of the perinephric space into the medial surface of renal parenchyma [32].
The fibrous capsule surrounding the cortex terminates near the renal hilum and does not separate the columns of Bertin from the renal sinus,
resulting in absence of any barrier preventing the extension of cancerous cells into the rich network of lymphatics and venules within the renal sinus [32].
Renal sinus fat invasion from RCC was reported to be associated with aggressive neoplasms at risk for dissemination [10-14].
Bertini et al reported that RS fat invasion in clear cell RCC significantly affects cancer specific survival in patients without lymph node or distant metastases [13].
Bonsib et al reported that RS fat invasion was associated with clear cell variant on histopathology,
higher nuclear grade and larger tumor size [11].
Thompson et al reported that patients with SF invasion were 63% more likely to die of clear cell RCC compared to those with PN invasion [14].
These were also proved in the present study.
Eleven (61.5%) out of 18 RCCs with histologically proven infiltration of the PN and/or RS fat were of clear cell histology,
10 (55.5%) tumors were of high histologic grade and 16 (89%) neoplasms were larger than 4 cm in diameter.
Using a 16-row CT scanner we demonstrated 90.9% sensitivity,
94.6% specificity and 93.7% overall accuracy in the diagnosis of RS fat infiltration.
The results of multivariate logistic regression analysis indicated that pelvicaliceal system invasion was the single most significant predictor of RS fat invasion.
Results also indicated that neither tumor extension into the renal sinus,
nor proximity to the pelvicaliceal system could contribute to the diagnosis of RS fat invasion.
Some neoplasms may distort the renal sinus and protrude,
without invading the renal sinus complex,
and this was seen in this report.
The proximity of a tumor to a neighboring structure,
as the pelvicaliceal system,
does not always correspond to neoplastic infiltration on histopathology,
and this was proved in the present study.
The above results confirm the improved diagnostic performance of multidetector CT in the preoperative evaluation of renal cell carcinoma.
MDCT with the improvement of spatial resolution and the ability to obtain multiphase imaging and multiplanar reformations in any desired plane,
with excellent anatomic details resulted in satisfactory results when assessing the presence or absence of neoplastic infiltration of the perirenal fat tissue and/or renal sinus fat compartment in patients with RCC.
In concluding,
multidetector CT provides satisfactory results in detecting perinephric and/or renal sinus fat invasion in patients with RCC.
The presence of contrast-enhancing nodules in the perinephric fat and tumoral margins was the most significant predictors in diagnosing tumor extension into the perinephric fat tissue.
Invasion of the pelvicaliceal system was the single most significant predictor in diagnosing neoplastic invasion of the renal sinus fat compartment.