* AP: Anteroposterior, Lat: Lateral

Tumor diameter, tumor length, depth of penetration, distance from the anal verge, deep and narrow pelvic dimension have been associated with affecting outcomes in pelvic surgery. We aimed to identify the best preoperative radiological predictor of a difficult pelvic dissection with prognostic significance

Purpose

User interface of software

inlet

outlet

Mid pelvis

Aimal Khan1, Ahsan Raza1, Sanda Tan1, Robert Zlotecki2, Luis Chihray2, Atif Iqbal1

Department of Surgery1, Department of Radiation Oncology2

University of Florida College of Medicine

Predicting a bad day in the OR: Objective prediction of a difficult pelvic dissection from preoperative imaging

Patients who underwent low LAR (low anterior resection) or APR (abdomino-perineal resection) for a lesion within 10 cm of the anal verge between 2009 and 2014 were divided into ‘Routine’ or ‘Difficult’ cases.

Difficult cases were defined as those needing unplanned conversion to APR, intraoperative need for a 2nd surgeon, surgeon’s use of a 22 modifier due to subjective sense of a difficult pelvic dissection or reoperation due to a complication related to procedural difficulty.

‘Velocity’ software was used to generate 3D reconstructions and measurements in all preoperative CT scans.

Methods

This is the most comprehensive assessment of preoperative pelvic measurements to date with inclusion of novel pelvic surgery specific measurements (length to the pelvic floor, soft tissue pelvic volumes and anorectal angle).

Preoperative imaging can be used to predict a difficult pelvic case and morbidity. Deep and narrow pelvic dimensions rather than rectal mass diameter play a role. Prospective application of these measurements is needed in the future.

Conclusions

A total of 40 patients (20 males) were included (mean age=57, mean BMI=27). There were 20 patients in each group (Routine vs. Difficult cases) with a mean follow up of 15 months.

Difficult cases were significantly associated with 12 pelvic measurements including a longer and narrower pelvis, lower pelvic volume, deeper pelvic floor, more curved sacrum and more acute anorectal angle as shown in Table 1. Rectal mass diameter was not associated with a difficult case. No ureteral injury, recurrence or mortality was noted and complications were similar between groups.

Of the 12 measurements, 3 with the strongest association to difficult cases were determined with appropriate cutoffs (Table 2). Length from promontory to pelvic floor >130 mm, soft tissue pelvic volume <250 cm3 and lateral pelvic outlet diameter <95 mm were reliably able to predict a difficult pelvic dissection (R2=0.95) which took significantly longer in the OR, had higher blood loss, longer hospital stay and higher overall costs.

ResultsTable 1: Comparison of pelvic measurements for routine and difficult cases

Measurements included: a) Linear measurements: Pelvic inlet AP and lateral diameter, pelvic outlet AP and lateral diameter, pelvic length to coccyx and to the pelvic floor, anterior and posterior pelvic depth, distance of pelvic floor from pubis, tumor or rectal diameter.b) Volumetric measurements: Bony and soft tissue pelvic volumesc) Anorectal angle and d) Degree of sacrococcygeal curve

Outcome variables included blood loss, Surgical time, hospital stay, mortality, recurrence and complications such as ureteral injury, pelvic bleeding, leak, SSI, nerve injury.

Predictors of difficult pelvic dissection* R2 p value

Length from promontory to pelvic floor >130 mm

0.95 <0.0001Soft tissue pelvic volume <250 cm3

Lateral pelvic outlet diameter <95 mm

Table 2: Reliable predictors of a difficult pelvic case* Associated with longer OR time, higher EBL, longer hospital stay & higher cost