Study on microanatomy of the lamina terminalis approach

Objective To study the relative microanatomical structures of the lamina terminalis approach. Methods The lamina terminalis, optic recess and adjacent structures were observed in 15 cadaveric heads under the operating microscope. Results The lamina terminalis stretches were downward from the anterior commissure to the mid-portion of the superior surface of the optic chiasma. The thickness of the lamina terminalis was about 0.25 mm. The mean length and maximal width of the lamina terminalis were (14. 1± 2. 7) mm and 5. 0 mm respectively. The optic recess was superior to the posterior half of the optic chiasma in the median line. The mean length of the recess was (5.8 ± 1.3) mm. The height of the anterior or posterior border was 0 - 0.4 mm and 0.6 -2.4 mm respectively. The mean width of the third ventricle near the recess was (2.2±1.1) mm. The anterior communicating artery superior right to the lamina terminalis was found only in less than one fourth of the cases observed. Conclusion The lamina terminalis approach is a surgical ladder-shaped interspace obtained when the lamina terminalis has been opened. The posterior border of the interspace is the anterior communicating artery and the bilateral A1 segments that have been pushed posteriorly. The anterior border is the posterior superior margin of the optic chiasma. The lateral border is the hypothalamic tissue and the optic tract. The median crest and the bulge of the central area are both important signs for the identification of the lamina terminalis. It is safe to incise the lamina terminalis on the midline at the point 11 mm posterior to the anterior margin of the optic chiasma.