Risk for positive surgical margins at the apex of the prostate

New research has suggested that “apical prostate depth” (as a measure of the anatomic situation of the prostate) is an independent risk factor for positive surgical margins at the apex (bottom) of the prostate at the time of radical prostatectomy.

It has long been well known to urologists that a deep and narrow pelvis makes radical prostatectomy a more challenging operation — regardless of the type of surgery — because it becomes harder for the surgeon to accurately remove all of the prostate tissue at the bottom tip of the prostate, farthest from the bladder.

Matikainen et al. set out to measure the impact of a deep and narrow pelvis on positive surgical margins (PSMs) at the apex of the prostate after radical prostatectomy (RP), while controlling for other clinical and pathological variables and for two surgical approaches, i.e. open retropubic (RRP) vs laparoscopic (LRP).

They identified 512 consecutive patients who received preoperative prostate magnetic resonance imaging (MRI) and underwent RRP or LRP at their institutions between July 2003 and January 2005, with no previous radio- or hormonal therapy. They also identified an additional 74 patients with preoperative MRI who underwent RP between December 2001 and June 2007, and who also had an apical PSM. Thus their total cohort was 586 patients.

Based on the preoperative MRI films, the authors were able to measure bony and soft-tissue pelvic dimensions, including interspinous distance (ISD), bony (BFW) and soft tissue (SW) pelvic width, apical prostate depth (AD) and symphysis pubis angle. They defined the pelvic dimension index (PDI), bony width index (BWI), and soft-tissue width index (SWI) were defined as ISD/AD, BFW/AD and SW/AD, respectively.

The results of their analysis showed that:

  • There was no significant difference in ISD, BFW, SW, or symphysis angle between patients with and without apical PSMs.
  • The AD was significantly greater in men with an apical PSM and PDI, BWI and SWI were significantly lower in men with an apical PSM.
  • The PDI, AD, BWI, and SWI were each significant independent predictors of apical PSMs, independent of surgical approach and other clinicopathological variables.

 The authors are careful to point out two key limitations of their study: it was retrospective, and there were relatively few patients with apical PSMs.

Even with these limitations, however, it appears that pre-surgical MRI scans can be used to assess the risk of apical PSMs in men being surgically treated from prostate cancer. What might be helpful would be knowing whether there are other gross physical features that could be used to assess the value of carrying out the MRI. Is it possible, for example, for the surgeon to be able to eliminate the need for the MRI in patients whose bony pelvic width is greater than some fixed distance? The cost of carrying out MRIs in all patients undergoing an RP would seem to be excessive if this can be reasonably avoided.

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