In the current study, assessment of renal masses by non-contrast CT, XP11 translocation carcinoma (n = 11) (Fig. 1) had the highest pre contrast attenuation values than other RCC sub types (n = 55) (41.7 ± 6.8 versus 34.3 ± 5.1HU with P < 0.001). the same result by Sungmin et al. [8] found that CT high pre contrast attenuation in tumors correlated with Xp 11, while Wang et al. [9] found Xp 11 mildly hyperdense on unenhanced CT than other lesion (Fig. 1).
Lipid-poor angiomyolipoma (AML) (n = 10) came second in high pre-contrast attenuation value (38.18 ± 4.36 HU). These results agree with Kim et al. [10] who found that 53% of AMLs (containing minimal fat) had high attenuation, in the same-study about 22% of RCCs (regardless their subtype) had also high attenuation on unenhanced scans. In other studies [11,12,13] lipid poor AMLs showed high pre contrast attenuation.
AMLs with minimal fat may have undetectable fat on CT. This makes them hard to differentiate from RCCs [10]. All cases of angiomyolipoma (10/10- 100%) in our study have had minimal fat (lipid poor angiomyolipoma) [14].
Papillary RCC (Fig. 2) shows third high pre-contrast attenuation value (n = 14) (35.47 ± 4.23 versus 28.8 ± 3.8 with P = 0.02), same results were found by El-Esawy et al. [15] and Fujimoto et al. [16] and Chen et al. [17] who found that CT high attenuation in tumors has been shown to correlate with PRCC.
Based on the current study data in assessment of the enhancement pattern and the degree of enhancement:
The renal tumors can be classified into two groups; The 1st group included the lesions that enhanced avidly in the corticomedullary phase (CMP) with wash out in the following phases (n = 54). This group included four tumor types which were CCRCC (Fig. 3)and CHRCC (Fig. 4) and RCC unclassified, oncocytoma. The 2nd group included the remaining solid renal lesions (n = 45) including PRCC and Lipid poor AML, Metanephric adenoma,Xp11 RCC these lesions showed lower degree of enhancement with prolonged enhancement pattern. Through measurement of the post contrast attenuation value in various post contrast phases, the 1st group showed significantly higher values than the second group at the CMP (P < 0.0001) and nephrographic phase (P < 0.0001using attenuation value) and excretory phase (EP) (P = 0.004 using attenuation value) ( Table 3).
Zehang et al. [18] found in their study over 193 patients with renal tumors that CCRCCs and oncocytomas enhanced strongly in CMP, whereas CHRCC and lipid-poor AML enhanced intermediatly and PRCC enhanced the least.
In the current study, multi-phasic contrast enhanced CT was able to differentiate between RCC subtypes and other masses through the pattern and degree of enhancement at different phases. The CCRCC (Fig. 3) showed the highest enhancement at CMP (n = 16) (151.9 ± 20.4) Oncocytoma (n = 13) (137.5 ± 19.15) followed by followed by CHRCC lesions (n = 15)(123.6 ± 16.6HU) then Xp11 RCC (n = 11) (91.1 ± 29.09HU)then unclassified RCC (n = 10) ( 89.06 ± 18.1) and PRCC (n = 14) (59.9 ± 4.8). followed by Metanephric adenoma (n = 10) which showed the lowest values (57.1 ± 17.4) (Table 5).
Attenuation value of CCRCC was much higher than PRCC in the CMP and NP and EP.
Chai Jung et al. [19] found that the CCRCC differ in enhancement from prcc significally in corticomedullary phase and differ in enhancement significally in nephrogenic phase from non-clear cell types.
In other studies, Kim et al. [14]found that the mean enhancement of CCRCC is 149 HU ± 46, however the mean enhancement of PRCC is 91 HU ± 12 and CHRCC enhanced to 90 ± 14 while Wang et al. [20] found that papillary subtype differ from the clear cell subtype in enhancement is due to differences in the vascularity due to micro-vessel density.
In our study 8 out of 10 (lipid poor type) showed prolonged enhancement pattern with arterial phase attenuation of 79.2 ± 13.6. Kim et al. [14] found the matching results as 58% of the AML in their study showed prolonged enhancement pattern.
We used three phases of contrast enhancement in our study (coticomedullary phase, nephrogenic, excretory phases), also pre-enhanced phase is used.
Two post contrast phases are used to differentiate between renal masses some studies used the CMP and NP [21]. OTHER utilized CMP and EP [22, 23], also some auther used the nephrogenic and excretory phases in differentiation [23].
If MAV in the CMP is 95 HUs or more,it could predict clear cell renal cell carcinoma or chromophobe renal cell carcinoma with high sensitivity and specificity and greater than 95% and 82%.
ΔH is 65 HUs or more Could predict clear cell renal cell carcinoma or chromophobe renal cell carcinoma with high sensitivity and specificity and greater than 95% and 75%.
Choi J H et al. [24]found higher mean HU values of nephrogenic phase were highly predictive of renal oncocytoma as there is significant difference in enhancement between renal oncocytoma and RCC in nephrogenic phase (P < 0.001) [24].
One auther found rapid washout in clear cell RCC which differentiate it from other renal masses [24]. Some authors did not observe this rapid washout in CCRCC because their protocol containing only pre-enhanced, nephrographic, and excretory phases, excluding the corticomedullary phase, which is essential in differentiating solid renal masses in our and other study [16, 25]. Our results suggest that high corticomedullary attenuation in a lesion suggest clear cell RCC than an oncocytoma, while biopsy [26], still necessary to differentiate them.
Smaller values of MAV or ΔH is more likely with diagnosis of PRCCs and XP11RCC and benign lesions.
Nephrogenic and excretory phases have a high cutoff point with high positive and negative predictive value in discriminating the 2 groups (CCRCCs and ChRCCs) from PRCCs and xp11RCC and benign lesions. This is due to they do not show significant washout in NP. This pattern of washout explain significance of incorporation corticomedullary and nephrogenic and excretory phases in our study.
Excretory phase differentiate significally PRCCs from benign lesions. Where PRCCs show a slow washout in most of cases, delayed enhancement in EP with higher attenuation values than the prior phases. The characteristic pattern of enhancement observed in papillary renal cell carcinoma, however benign masses showed considerable washout (P ≤ 0.05). Thus, using excretory phase is important in differentiation malignant renal masses from benign by measuring washout of the contrast.
Our results ensure that using three phases of post contrast is important in differentiation of different renal masses in addition to the precontrast phase.
Our result found that combination of pre enhanced phase and CMP can predict lipid poor angiomyolipomas …..hyperdense unenhanced attenuation greater than 45 HU renal mass that shows homogeneous peak attenuation in the corticomedullary phase is more likely to be lipid-poor angiomyolipoma.
The hyperdense lipid-poor angiomyolipoma has been explained in several researches [14, 27, 28], most recently by Yang et al. [1], who said that pre-enhanced high attenuation was the only parameter signify differentiation between lipid-poor angiomyolipoma and clear cell RCC.
In our study, CCRCC and ChRCCs was Characterized from PRCCs and benign renal masses on principle of attenuation value more than 95 in the CMP with sensitivity of 95%, specificity of 82%, PPV of 96%, and NPV of 100%.
Our quantitative results showed that Arterial ∆H (MAV with tissue enhancement in arterial phase—MAV in the unenhanced scan) greater than 65 has sensitivity of 95%, specificity of 75%, PPV of 94%, and NPV of 96% used quantitative parameters to differentiating CCRCC,ChRCCs from PRCCs, benign renal masses, Other masses with lower MAV or ∆H will be suggestive of PRCCs and benign lesions.
Absolute washout nephrogenic and relative washout nephrogenic cutoff points (16% and 5%)were revealed a sensitivity and specificity of 85% and 75%, and 81% and 83% in characterization CCRCC and CHRCC from PRCC and benign lesions.
Absolute washout excretory and relative washout excretory cutoff points (14% and 30%) were revealed a sensitivity and specificity of 85% and 100%, and 72% and 82% in characterization clear cell renal cell carcinoma and chromophobe renal cell carcinomas from papillary renal cell carcinoma and benign lesions.
Table 7 contains The PPV and NPV of each cutoff point.
My research is unique because of large number of cases and different type of lesion and complete quantitative analysis of each lesion.
Our study has many restrictions. Its prospective planning may introduce improper randomization. Our specialized hospital in which patients may have a higher incidence of malignancy in contrast to general population. We involved renal lesion which were proven pathologically with biopsy, which may be source of error. Second, we didn't include the tumor staging system in our study.