Topographic variations of the optic chiasm and the pituitary stalk: a morphometric study based on midsagittal T2-weighted MR images

Purpose This study was conducted to characterize topographic variations of the optic chiasm (OC) and the pituitary stalk (PS) in situ based on MR images. Methods Normal T2-weighted midsagittal MR images were obtained in 157 children and 323 adults. The height of OC (PC) and the inclination angle of PS (PS–AP angle) were measured in each case. All chiasms were classified into prefixed, normal and postfixed types, and low, medium and high types, respectively. All stalks were performed classification (prefixed, centered and postfixed PS) and grading (Grade 1–3 according to the relationship between PS and the dorsum sellae), respectively. Results PC averaged 4.33 ± 1.59 mm. Adults had a greater PC ( P = 0.023) than children. There were 80 (16.7 %) prefixed, 354 (73.8 %) normal and 46 (9.6 %) postfixed chiasms, and 112 (23.3 %), 295 (61.5 %) and 73 (15.2 %) cases with low, medium and high OC, respectively. High OC was more frequent in adults than in children ( P = 0.001). The mean PS–AP angle of the whole group was 59.47 ± 8.62º. Children had a greater PS–AP angle than adults ( P = 0.012). Adults had a greater percentage of postfixed ( P = 0.000) and grade 3 ( P = 0.000) PS than children, whereas centered ( P = 0.002) and grade 1 ( P = 0.001) PS were more prevalent in children than in adults. Conclusions The classifications of OC and PS based on MR images reflect the topographic variations of their real position in vivo. It would be helpful to identify and characterize the anomalies involving OC and PS and understand the anatomical and physiological influence in pathological situations.