Anatomy of the lamina terminalis and the cisterna chiasmatica: a cadaveric study at the university teaching hospital Lusaka Zambia

Abstract

The Lamina Terminalis represents an important neuroanatomical structure by which third Ventriculostomy could be performed into the subarachnoid space (Cisterna Chiasmatica). Recent studies have indicated a role for LT fenestration in approaching pathologies of the third ventricle. However, there is limited knowledge on the anatomical features, variations and the vasculature of the LT in a Zambian population. This study was aimed to explore the anatomy of the Lamina Terminalis, the Cisterna Chiasmatica and its neurovascular relationships as seen in a Zambian population and compare with the findings in the literature. This was a descriptive cross-sectional design in which 32post-mortem human cadaveric brains were systematically sampled. The LT region was examined in 27male cadavers and five female cadavers of age range 25 and 66 years (mean 34.05 ± 9.24years). Data was collected using a data collection form, entered and analyzed by descriptive statistics using Statistical Package for Social Sciences (SPSS) software version 22. Mean and standard deviations were used to describe variables. The base of the brain was detached from the floor of the cranial cavity and the LT exposed fully by retracting both optic nerves and the optic Chiasma posteroinferiorly. The triangular LT measurements were performed as the distance between the midportion of the upper aspect of the chiasma and the lower aspect of the anterior commissure (height), which averaged 8.62 ±1.00mm. The distance between the medial edges of the optic tracts (base) averaged 13.11 ±1.12mm and the area averaged 56.93 ± 11.56mm2. The LT membrane showed variations in appearance; 20were transparent with a large dark midline gap and 10 were less transparent with a slender midline gap and two were indistinct. The Cisterna Chiasmatica was observed as a dilated subarachnoid space adjacent to the Optic Chiasma. For neurovascular relationships, 24 cadavers showed arterioles arising from the posterosuperior aspect of the anterior cerebral artery to perforate the anterior perforating substance(s), supplying the chiasma, and optic tracts; whereas, eight cadavers showed arterioles arising posteroinferiorly and ramifying on the LT. The LT membrane is variably developed. There are variations in the membrane appearance, measurements and neurovascular relationships. These findings will supplement a knowledge gap in neuroanatomy and help prevent complications during Lamina Terminalis fenestration in approaching pathologies of the third ventricle. Key words: Lamina Terminalis, Cisterna Chiasmatica, Third Ventriculostomy