Quantitative anatomy of the fourth ventricle floor: a cadaveric morphometric study

Abstract

Background: The floor of the fourth ventricle contains critical surface landmarks overlying brainstem nuclei. Despite advances in microsurgical techniques, detailed morphometric data on these landmarks remain limited.

Aims: To perform a morphometric analysis of the fourth ventricle floor using cadaveric specimens, with emphasis on dimensions, symmetry, and proportional relationships relevant to surgical planning.

Methods: Forty formalin-fixed adult human brainstems were used. Sixteen anatomical parameters were assessed, including twelve linear distances and four qualitative observations. Key landmarks-including the facial colliculus, sulcus limitans, striae medullares, and the hypoglossal and vagal trigones-were measured under magnification. Anatomical ratios were calculated, and findings were compared to prior cadaveric studies.

Results: The mean floor length and width were 33.58 ± 2.49 mm and 20.0 ± 1.83 mm, respectively. The facial colliculus consistently divided the floor into symmetrical rostral and caudal segments (~ 43% each). The hypoglossal and vagal trigones, measured for the first time, occupied 25.44% and 12.69% of the caudal floor length. The safe midline corridor between sulci limitans comprised only 30.59% of the floor width. Statistically significant asymmetry was found in lateral recess lengths (p = 0.003) and striae medullares bundle counts (p = 0.044). Most measurements differed significantly from previously published data (p < 0.001).

Conclusion: This is the first cadaveric study to define the hypoglossal and vagal trigones quantitatively. The findings clarify the topographic relationships of safe and high-risk surgical corridors in the fourth ventricle floor and provide normative data to support safer microsurgical planning.

Keywords: Brainstem; Facial Colliculus; Fourth Ventricle; Hypoglossal Trigone; Rhomboid Fossa; Vagal Trigone.