The renal neoplasms can be divided into different subtypes according to their cell origin (table 1).
Renal cell carcinoma is the most common renal tumor and is divided in clear cell carcinoma (70-80%),
papillary (10-15%),
chromophobe (5%),
collecting duct carcinoma and renal medullary carcinoma (2-5%) [4].
Table 2 summarizes the main imaging characteristics of the renal cell carcinomas and other lesions that should be excluded when a mass is found,
including benign lesions that shouldn´t be treated.
Although there are multiple imaging characteristics about renal masses the radiologist should know,
none of them is specific and the definite diagnosis can only be made by biopsy [5].
When a renal mass is discovered and other,
non-neoplastic,
causes are excluded,
tumor characterization is the next step.
More important than trying to categorize the tumor subtype is to characterize the mass.
The scoring systems allow an objective,
standardized and reproducible anatomic classification of renal tumors,
helping in prediction the probability of complications of nephron-sparing surgeries.
Studies confirmed that the three scoring systems demonstrate reliability among observers and represent methods of quantitatively describing renal tumors [8].
R.E.N.A.L.
nephrometry:
The R.E.N.A.L.
system was the first renal tumor complexity scoring system.
It correlates with the tumor aggressiveness,
complexity and rate of surgical complications [9].
The acronym relates to (R)adius (the maximal diameter (cm) of the tumor in any single plane),
(E)ndophytic/exophytic properties (evaluates if the tumor abuts or not the renal capsule and in what percentage),
(N)earness (distance of the medial limits of the tumor from the nearest portion of the renal sinus or collecting system),
(A)nterior/posterior (evaluated by drawing a line in the axial plane paralleling the renal hilum and bisecting the renal parenchyma) and (L)ocation (masses are divided into polar or interpolar by drawing two lines in the axial or coronal planes that cross the medial lip of parenchyma interrupted by renal sinus fat) [10].
The parameters of this index are exposed in Table 3,
with the correspondent scoring and followed by pictorical explanation (Fig.
1 to 7).
P.A.D.U.A.
(Preoperative Aspects and Dimensions Used for an Anatomical classification of renal tumors):
This system was proposed to classify the renal tumors suitable for conservative treatment based on their anatomical aspects and dimensions and to predict the risk of complications in the peri-operative period.
The size of the tumor,
location,
face and exophytic/endophytic criteria are similar to those of R.E.N.A.L.
system.
The main differences are the involvement of the renal sinus and collecting system and the location of the mass relatively to the lateral or medial renal rims [11].
The parameters of this index are exposed in Table 4,
with the correspondent scoring,
followed by pictorical explanation.
(Fig.
8 to 13).
C–Index scoring:
The centrality index (C-Index) is a completely different system compared to the R.E.N.A.L.
and P.A.D.U.A.
because it involves a relatively complex mathematical concept.
The objective of this system is to quantify the proximity of the tumor to the renal central sinus,
since this parameter is of extreme importance for the surgical planning [12].
In order to calculate C-index a few steps have to be followed:
- localize the first and last image sections in which the kidney appears: image numbers of these sections are averaged to calculate the middle image;
- in the middle image,
calculate a central reference point,
which is the point in the center of an imaginary ellipse drawn around the periphery of the kidney;
- identify the hilar reference point: with the cursor stabilized on the central axial reference point scroll until finding the hilum;
- identify the image section with the largest tumor diameter;
- calculate distance y (cm): number of sections between the middle image and the image with the largest tumor diameter divided by image slice thickness;
- calculate distance x (cm): distance between the hilar axial reference point and the center of tumor;
- measure the tumoral diameter (draw a line paralleling the “x” line);
- calculate the tumoral radius (r) by halving its diameter;
- calculate “c” distance based on Pythagorean Theorem: √(x2+y2)
- calculate C-index: c/r.
A centrality index of 0 indicates that the tumor is concentric with the center of the kidney; a c-index of 1 means the periphery touches the kidney center and as the centrality index increases the tumor periphery becomes more distant from the kidney center. Figures 14 to 18 shows the application of centrality index in a renal mass.
A.B.L.A.T.E.
algorithm:
The A.B.L.A.T.E.
algorithm,
unlike the previous scoring systems,
was developed in order to create a systematic method of planning ablation therapies.
Ablation therapies such as cryoablation and radiofrequency ablation (RFA) are being used more often as they have proved to be effective in selected patients,
namely those with T1a (≤ 4 cm) tumors and high surgical risk [13]. Instead of calculating the risk of treatment complications,
it calls the attention to the critical characteristics of the renal masses that can difficult the ablation therapy and suggest treatment approaches to overcome them.
The parameters included in this system and their treatment suggestions are summarized in Table 5.