Discussion
More than 50% of patients with RCC are diagnosed incidentally by
abdominal ultrasound or non-enhanced CT for other medical reasons
(10,11). Radiological T stage of a renal cancer is a major factor in
predicting prognosis and survival in these patients. Some studies have
reported that multi-phasic CT or MRI for the diagnosis of RCC have
accuracy of up to 90% (12-14). In this study, using a large sample
size, we also showed that there was a substantial concordance between
radiological and pathological staging in Turkey. In addition, the
results showed that CT (75.8%) is being used three times more commonly
than MRI (24.2%) for the diagnosis and staging of RCC. The reason why
urologists prefer CT rather than MRI for renal imaging may be due to the
fact that CT is less time consuming and cheaper than MRI, and the
urologists are more familiar with CT images rather than MRI images.
Although the accuracy of CT and MRI in the diagnosis and staging of RCC
is generally high, the sensitivity and specificity values are found to
be lower in T3 cases compared to other stages (15). Renard et al.,
retrospectively, investigated the diagnostic accuracy of CT in
predicting pT3a RCC in 96 cases (15). Renal sinus fat infiltration,
peri-nephric fat infiltration and renal venous wall involvement were
assessed by two radiologists specialized in urological imaging and
compared with the histopathologic staging. The authors found that
assessment of renal tumor extension into perinephric fat remained a
difficult task, leading to reduced accuracy in T3a staging. Similarly,
the results of our study showed that the diagnostic accuracy of CT or
MRI in stage III RCC was lower than other stages. The importance of
these findings is that in all RCC types prognosis worsens with stage
(2), and this is also true for stage III cases compared to those with
stage I and II tumors. Chevinsky et al. reported pathological stage T3a
as a poor prognostic factor in RCC regardless of tumor size and also
demonstrated that there was an increased rate of risk of recurrence with
perinephric fat invasion compared to those with pT1/T2 tumors (16).
Therefore, radiologic under-staging in pT3a cases, will underestimate
the risk of cancer recurrence and survival rates, and the patient will
be misinformed regarding prognosis of his/her tumor during patient
counselling before surgery.
Although, both renal vein invasion and perirenal fat invasion are
classified as T3a disease, it was reported in recent studies that
patients with pT3aN0M0 RCC with renal vein invasion have a significantly
poorer prognosis than those with fat invasion (17). In TNM sub-group
analysis of Stage III, we found that the sensitivities of perirenal fat
and renal vein invasions were 15.4% and 11.3%, respectively. Although
these values are very low compared to values reported in other studies
(15), other studies also showed that peri-nephric fat and renal vein
invasion in RCC are difficult to evaluate radiologically (5). By using
the Surveillance Epidemiology and End Results registries Srivastava et
al. reported that from the patients undergoing partial nephrectomy, the
estimated proportion up-staged to pT3a was 9.5%, and 19.5% for cT1b,
and cT2, respectively (5). In our study, incidence of up-staging from
localized stages to stage III was 17.5%, which is consistent with the
results reported in literature. Therefore, preoperative imaging in
patients with stage III RCC has to be improved. Advanced MRI techniques
such as diffusion weighted and perfusion-weighted imaging are being
explored for renal mass assessment and staging (18).
Presence of PSM on final pathology creates uncertainty in terms of
further management options. Some have performed an immediate or delayed
nephrectomy whereas others followed patients without complete
nephrectomy (19,20). The incidence of PSM ranges from 0–10.7% in
literature and the rate of PSM may be influenced by tumour stage, fat
invasion and tumor grade (19,20). Bansal et al, by looking at the
partial nephrectomy patients included in the Canadian Kidney Cancer
information system database, reported that higher stage (≥T3) and grade
were associated with a higher risk of PSM (19). In our study, PSM rate
was 8.4% in patients up-staged from localized tumor to pathologically
stage III and 12.4% in radiologically stage III cases with concordant
pathology (p=0.08). As there is no statistically significant difference
between these two rates, during surgery one should also be as cautious
as possible in radiologically localized disease in order not to have a
PSM.
The present study is limited by its retrospective nature. In addition,
central pathological and radiological review could not be performed.
Patients were included from different centres and therefore the quality
of radiologic and pathologic evaluation is probably variable. However,
the aim of our study was to evaluate the accuracy of radiological
staging of RCC in daily routine urology practice, rather than assessment
of radiological techniques or surgical procedures. So, we did not
perform any comparison between radiological techniques, surgical
procedures or centers.
There was a substantial concordance between radiological (CT and/or MRI)
and pathological T staging in RCC. However, this is not true for stage
T3 cases. The reason is that, it is difficult to evaluate peri-nephric
fat and renal vein invasion radiologically. Therefore, the sensitivity
of preoperative radiological imaging in patients with pT3a tumors is
insufficient and lower than the other stages. Consequently, preoperative
imaging in patients with T3 RCC has to be improved, in order to better
inform the patients regarding prognosis of their disease.