Lamina terminalis: Radiological analysis with a proposed anatomical classification

The lamina terminalis (LT) is a thin membrane forming the anterior wall of the third ventricle, serving as a crucial anatomical landmark in neurosurgical procedures. Despite its clinical relevance, radiological characterization of the LT remains limited. The main Objective is to evaluate the radiological dimensions of the LT and propose a classification system based on its angulation.

This retrospective cross-sectional study used 160 brain magnetic resonance imaging (MRIs) of adults (≥18 years) with no ventricular pathology. The MRIs were performed at the Neurosurgery Teaching Hospital in Baghdad from January 2021 to December 2023. All MRIs were performed on a 1.5 Tesla MRI. Measurements included the following: the LT length, width, angle, LT-AComA distance, and the position of the optic chiasm. Two blinded observers performed all. All analyses were performed using the software package SPSS version 25.0. The level of significance used was P < 0.05.

A total of 160 MRI studies were included. The LT demonstrated a mean length of 10.7 mm (range, 4.2-15.3 mm) and a mean width of 3.75 mm (range, 1.5-7.2 mm). The average distance from the midpoint of the LT and the AComA was 6.43 mm. Based on the angulation of the LT relative to the line connecting the anterior and posterior commissures, a novel radiological classification of the lamina configuration was proposed: type 1 indicates an angle of <100°, Type 2 denotes an angle between 100° and 110°, and Type 3 describes a more obtuse angle of >110°. Of the three angle types, type 2 was the most common, representing 47.5% of cases, followed by type 3 (33.1%) and type 1 (19.4%). Most optic chiasms were suprasellar (80.6%), while postfixed and prefixed positions were found in 10.6% and 8.8%, respectively. Subgroup analysis of the LT angle types revealed a significant association with the position of the optic chiasm (P = 0.015). No statistically significant differences were found in LT dimensions across angle types.

The LT is a morphologically diverse and clinically relevant structure forming the anterior wall of the third ventricle. Its radiological parameters, including length, width, and angulation, exhibit individual variability. Variations in its angulation are significantly associated with the position of the optic chiasm. These anatomical insights hold important implications for neurosurgical planning and intervention.