Timo Soeterik

16 CHAPTER 1 MRI can help localize the side of present EPE so that only the ipsilateral neurovascular bundle has to be resected in order to achieve negative surgical margins following robot- assisted radical prostatectomy (RARP). 33 Although a recent meta-analysis of prior studies on this subject did not show nerve sparing to be associated with increased risk of positive surgical margins, it is generally assumed that preservation of the neurovascular bundle increases the risk of positive margins. 34 This assumption is best supported by reviewing the anatomy during the surgical procedure (Figure 1). As shown in Figure 1, preservation of the neurovascular bundle requires close dissection to the prostate. Therefore, when nerve sparing is preferred by the patient, accurate risk estimation of EPE should be performed to ensure the safety of the procedure. Since there are two neurovascular bundles crossing both posterolateral sides of the prostate, EPE risk assessment should be performed in a side-specific manner. Although mpMRI has the potential to overcome the limitations of DRE with regard to local tumour staging, the technique still has its limitations. This is reflected by a recent meta-analysis, showing that the pooled sensitivity of mpMRI for the detection of EPE is 57%. 35 The low sensitivity is mainly attributable to the very limited ability of mpMRI to detect microscopic EPE. An example derived from routine clinical care is presented in Figure 2A & 2B. In Figure 2A, the index tumour lesion is visualized via mpMRI, interpreted by the radiologist as “organ-confined”. However, on histopathological evaluation, microscopic EPE was present (Figure 2B). FIGURE 1. Nerve sparing robot-assisted radical prostatectomy A: Procedure of preserving the left neurovascular bundle (NVB) (arrow) during prostatectomy. B: After removal of the prostate; resulting in preserving neurovascular bundle tissue or greater thickness (spared NVB), compared to the residual neurovascular tissue after a wide excision (non-spared NVB).