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

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.

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.

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.

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).

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.