Comparison of pituitary stalk angle, inter-neural angle and optic tract angle in relation to optic chiasm location on 3-dimensional magnetic resonance imaging.

Optic chiasm location is critical in sellar surgeries and may be obscured by tumor invasion. This study evaluates inter-neural angle, pituitary stalk angle, optic tract angle in prefixed, normal and post fixed optic chiasms using 3-dimensional constructive interface in steady state (CISS) sequences of magnetic resonance imaging (MRI) in essentially normal studies. MRI Brain studies of 154 patients were retrospectively evaluated. Location and height of optic chiasm was noted. Interneural angle between intracranial segments of bilateral optic nerves, pituitary stalk angle between pituitary stalk and optic chiasm, optic tract angle between optic tracts were measured and compared in prefixed, normal and post fixed chiasms using ANOVA test. Optic chiasm was prefixed in 33 (21.4%) cases, normal in 111 (72.1%) cases and postfixed in 10 (6.5%) cases with mean height of optic chiasm of 3.33 mm. There was no statistically significant difference in height and type of optic chiasm between age groups and genders. Statistically significant difference between location of optic chiasm was seen with interneural angle (p = 0.013), was highly significant with pituitary stalk angle (p < 0.001) and was not seen in optic tract angle (p = 0.455). Optic chiasm location was divided into nine groups with frequency being highest in intermediate height, normal fixed chiasms (n = 62, 40.26%) and least in post fixed high, post fixed low groups (n = 1, 0.006%). A wider interneural angle, wider pituitary stalk angle with a more anteriorly placed stalk indicates a prefixed chiasm. 3-dimensional MRI is an effective tool in assessing the optic chiasm location, when its invaded by sellar and suprasellar tumours.