Magnetic resonance (MR) pelvimetry as a predictor of difficulty in laparoscopic operations for rectal cancer

Abstract

Laparoscopic surgery for rectal cancer is now well estab-lished. Recent studies have shown no difference in survivalor oncologic outcomes when laparoscopic surgery iscompared to open procedures [1, 2]. The laparoscopicapproach does, however, present the surgeon with inherentchallenges. Previous abdominal surgery, tumours closer tothe anal verge, high body mass index (BMI), and preop-erative radiotherapy have been shown to increase the dif-ficulty of laparoscopic procedures in the pelvis [3–6].It is often assumed that laparoscopic resections for rectalcancer are also complicated by a deep, narrow pelvis inwhich access and vision are both restricted by pelvicanatomy. Although a majority of patients undergo preop-erative pelvic magnetic resonance (MR) staging, radio-logical measurement of the bony pelvis––pelvimetry––hasnot been fully assessed as a predictor of difficult laparo-scopic operations.Male sex has been shown to correlate with surgeons’perceived difficulty of laparoscopic resections, althoughmore objective evidence of increased difficulty, in the formof longer operating times or more frequent involvement ofthe circumferential resection margin (CRM), is sparse [6].Indeed, while some authors have demonstrated significantdifferences in pelvic measurements between the sexes [7,8], others have shown considerable overlap [9], suggestingthat the measurements themselves may be a more usefulpredictor of difficulty than sex alone.MR pelvimetry has been evaluated for potential appli-cation in predicting the technical difficulty and outcomes ofopen rectal resection and prostatectomy [3, 4, 7, 10].Various dimensions of the bony pelvis thought to be ofimportance during surgery were studied; all studies used acombination of anteroposterior (AP) measurements in themid-sagittal plane and some form of transverse measure-ment to describe the breadth and depth of the pelvis. Someauthors measured angles and dimensions on the mid-sag-ittal slices to define the acuity of the sacral curve and theother boundaries of the pelvis [3, 7, 10]. One author wentfurther, developing a synthetic measurement designed tobetter describe the pelvic depth observed by the surgeonperforming open radical prostatectomy––the apical depthof the pelvis divided by the transverse interspinous distance[11]. None of these measurements were shown to signifi-cantly predict any objective or subjective measure ofoperative difficulty and pelvimetry seems to have beenabandoned as a predictor in open resections.It is reasonable to expect that pelvic anatomy may bemore important in laparoscopic resections. A prominentsacral promontory, an acutely curved sacrum, or a pelvisparticularly narrow in the transverse plane could conceiv-ably represent anatomical bottlenecks, impeding vision,access, and space in which instruments can be manipulated.Indeed, initial research has shown correlations betweenlonger operating times and a larger pelvic outlet [4] and asmaller lower pelvis diameter [5] and between CRMinvolvement and shorter transverse interspinous distances[12]. Further ascertainment of the influence of pelvic