Relationship between the pituitary stalk angle in prefixed, normal, and postfixed optic chiasmata: an anatomic study with microsurgical application

The relationship between the optic apparatus and the skull base is important during approaches near the sella turcica. One relationship that dictates which approach is taken is whether the optic chiasm is prefixed or postfixed or in a "normal" location, (centered over the diaphragma sella). The relationship between the position of the chiasm and the angulation of the pituitary stalk has not been investigated. Forty adult cadavers without intracranial pathology were dissected and parasagitally hemisected lateral to the sella turcica. The angulations between the pre- and postfixed and normal chiasm and the pituitary stalk were evaluated under magnification. Additionally, 50 MRIs performed among patients evaluating headache were analyzed for these relationships. For cadavers, the chiasm was prefixed in 7.5 % (n = 3), normal in 85 % (n = 34), and postfixed in 7.5 % (n = 3). On imaging, the chiasm was prefixed in 4 % (n = 2), normal in 88 % (n = 44), and postfixed in 8 % (n = 4). For all, the relation between the type of chiasm and the pituitary stalk was more often (p < 0.05) 90A degrees or greater for prefixed chiasmata and acute angles for normal or postfixed chiasmata. These data may assist skull base surgeons when approaching pathology near the optic chiasm and pituitary stalk.