# Morphometric Analysis of Lateral Sulcus Asymmetry: Demographic Correlates and Neurosurgical Implications

## TL;DR

This study confirms that the lateral sulcus in the brain is longer on the left side and shows how this asymmetry varies with sex, handedness, and age.

## Contribution

The study provides fixation-adjusted morphometric data on lateral sulcus asymmetry and identifies demographic predictors.

## Key findings

- The lateral sulcus shows significant leftward asymmetry with a mean asymmetry index of 5.9%.
- Males and right-handed individuals exhibit greater asymmetry compared to females and left-handed individuals.
- Age negatively correlates with lateral sulcus asymmetry.

## Abstract

Background: The lateral sulcus (LS) serves as a vital neuroanatomical landmark involved in hemispheric lateralization, language processing, and neurosurgical navigation. However, discrepancies between cadaveric and imaging-based studies, along with limited demographic integration, have restricted the development of standardized anatomical references. This study aimed to generate fixation-adjusted morphometric data and examine the influence of sex, handedness, and age on LS asymmetry.

Methods: A retrospective observational study was conducted on 50 formalin-fixed adult human brains (27 males, 23 females; age range: 21-78 years). Bilateral measurements of the LS and its rami were obtained using digital vernier calipers by three blinded observers. All lengths were corrected for ~20% shrinkage due to formalin fixation based on published correction protocols. Handedness and demographic data were collected from institutional records and next-of-kin interviews. Statistical analysis included paired and independent t-tests, multivariate analysis of variance (MANOVA), Pearson's correlation, and multivariate regression. Effect sizes (Cohen’s d) and 95% confidence intervals were reported. Power analysis was performed using G*Power 3.1 (version 3.1, Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany).

Results: Significant leftward asymmetry of the LS was observed (mean left: 8.94 ± 0.35 cm; right: 8.43 ± 0.56 cm; p < 0.001; Cohen’s d = 1.12, 95% CI: 0.38-0.64), with a mean asymmetry index of 5.9% ± 3.2%. Males and right-handed individuals demonstrated greater asymmetry compared to females and left-handed individuals (p < 0.05). A negative correlation with age was noted (r = -0.32, p = 0.008). Multivariate regression revealed sex, handedness, and age as significant independent predictors (R² = 0.24, p < 0.001).

Conclusions: This cadaveric study affirms the presence of consistent leftward LS asymmetry and highlights its modulation by sex, handedness, and age. By incorporating fixation correction and robust statistical methods, the findings reconcile anatomical and radiological data, offering valuable morphometric benchmarks for neurosurgical planning and future neuroimaging studies. These results should be interpreted as normative anatomical references rather than diagnostic criteria due to the inherent limitations of retrospective postmortem research.