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A CASE OF BASE RATE BIAS, OR ARE TEENAGERS REALLY AT A HIGHER RISK
OF DEVELOPING COMPLICATIONS AFTER CATHETERIZABLE URINARY CHANNEL
SURGERY?
Konrad SZYMANSKI, Benjamin WHITTAM, Rosalia MISSERI, Chandra FLAK, Katherine HUBERT, Martin KAEFER, Richard
RINK and Mark CAIN
Riley Hospital for Children, Pediatric Urology, Indianapolis, USA
PURPOSE
Teenagers are considered at high risk for complications after genitourinary reconstruction. This impression may be due
to base rate bias, where clinicians favor specific information (“numerator:” number of teenagers with complications),
while ignoring more general information (“denominator:” overall number of teenagers being followed). We previously
reported long-term results with appendicovesicostomy (APV) and Monti techniques. We aimed to assess whether age
was a risk factor for subfascial revision after catheterizable channel procedures.
MATERIAL AND METHODS
We retrospectively reviewed consecutive patients <21 years old undergoing APV and Monti surgery at our institution
(1990-2013), collecting demographic and surgical data. Time to major revision was assessed by age stratification (<8,
8-13, 13-18, ≥18 years old) and Cox proportional-hazards regression. Two secondary analyses used another age
stratification (<8, 8-12, 12-16, ≥16 years old) and age as a continuous variable.
RESULTS
Of 510 patients with catheterizable channels (median age at surgery: 7.9 years), 63 (12.4%) had a subfascial revision
(median follow-up: 6.8 years). Most revisions (61.9%) occurred in 8-18 year olds. Study participants were 8-18 years
old for 62.9% of 3263.9 person-years of the study. Over 4/5 of revisions occurred within 5 years of surgery, regardless
of age at surgery (p=0.57). On multivariate analysis, no age group had increased risk of revision (p≥0.70). Overall
stomal location, concomitant surgeries, gender and date of surgery were not associated with risk of subfascial revision
(p≥0.23). Montis were 2.1 times more likely than APV to undergo revision (p=0.03). Findings were similar on
secondary analyses.
CONCLUSIONS
While the risk of complications was twice as high in Monti channels than APV, no age group was at increased risk. The
impression that teenagers are a high-risk group appears to be due to base rate bias.