# Statistical Evidence for Bimodal Age Distribution in Pediatric Orchiopexy: Support for Congenital and Acquired Cryptorchidism Subtypes

## TL;DR

This study finds evidence that the age distribution of orchiopexy surgeries in children is bimodal, suggesting two possible subtypes of cryptorchidism.

## Contribution

The study provides statistical evidence for a bimodal age distribution in pediatric orchiopexy, supporting the hypothesis of congenital and acquired cryptorchidism subtypes.

## Key findings

- The dip test rejected unimodality with strong statistical significance.
- Gaussian mixture modeling identified two distinct age components for orchiopexy procedures.
- A bimodal age distribution was confirmed with an intersection point at 3.8 years.

## Abstract

Objective: This study aims to characterize the age distribution of orchiopexy procedures and assess whether bimodal patterns exist that may correlate with hypothesized congenital and acquired cryptorchidism subtypes.

Materials and methods: We analyzed age-at-orchiopexy data from 659 consecutive patients (ages zero to 18 years) at a single tertiary pediatric center. Bimodality was assessed using (1) Hartigan's dip test for unimodality, (2) kernel density estimation with bootstrap mode stability analysis, and (3) Gaussian mixture modeling with information criterion-based model selection.

Results: The dip test decisively rejected unimodality (dip = 0.134, p < 0.001). Gaussian mixture modeling strongly favored a two-component model over unimodal (ΔBIC = 407.7). The optimal model identified an early component (mean = 1.31 years, SD = 0.80, weight = 54.2%) and a late component (mean = 6.28 years, SD = 3.35, weight = 45.8%), with an intersection at 3.8 years. Bootstrap analysis confirmed a stable bimodal structure.

Conclusions: Age-at-orchiopexy demonstrates statistically robust bimodality, with early (1.31 years) and late (6.28 years) components. This bimodal pattern is consistent with, and may correlate with, clinically hypothesized congenital and acquired cryptorchidism subtypes, but it does not by itself prove distinct biological entities. The intersection at 3.8 years may offer a quantitative reference point for age-specific management strategies and surveillance protocols and should be interpreted as hypothesis-generating rather than prescriptive.