Surg Radiol Anat DOI 10.1007/s00276-014-1265-y

Original Article

Topographic variations of the optic chiasm and the pituitary stalk: a morphometric study based on midsagittal T2‑weighted MR images Hao Long · Song‑tao Qi · Ye Song · Jun Pan · Xi‑an Zhang · Kai‑jun Yang 

Received: 15 March 2013 / Accepted: 28 January 2014 © Springer-Verlag France 2014

Abstract  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

H. Long · S. Qi (*) · Y. Song · J. Pan · X. Zhang · K. Yang  Department of Neurosurgery, Nanfang Hospital, Southern Medical University, No. 1838 North of Guangzhou Avenue, Baiyun District, Guangzhou, Guangdong Province, China e-mail: [email protected]

the anatomical and physiological influence in pathological situations. Keywords  Magnetic resonance imaging · Optic chiasm · Pituitary stalk · Sellar region

Introduction The sellar region, a common place to develop tumors of central nervous system, lies in the centre of the skull base and is characteristic of complicated and distinctive anatomy [10, 14, 22]. A considerable degree of variability exists in the anatomic locations of the optic chiasm (OC) and the pituitary stalk (PS), which are both vital sellar structures and often compromised in pathological conditions [10]. Thorough knowledge of these variations is important to neurosurgeons dealing with lesions in this region. As early as 1924, the variation of OC has been first described by Schaeffer [17], who named the “prefixed” and “postfixed” chiasms so as to distinguish them from normal chiasms. Afterwards, Bergland et al. and Renn et al. [2, 14] further confirmed the variation of OC and evaluated the proportion of various chiasm types based on cadaver specimens, respectively. The classic OC variation theory has been widely accepted for decades, but there are still some problems that remained unclear. Could the results based on autopsy be completely extrapolated to the living bodies? Is there any difference between children and adults? In addition, the classic OC classification only focused on the anteroposterior relative position between OC and the sella turcica, but how about the variations of superoinferior relative position between them? PS is the connection between the median eminence of the hypothalamus and the pituitary gland [16]. On

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midsagittal images, PS usually represents as a funnel-like structure leaning backward. Interestingly, Righini et al. [15] measured the angle formed by PS and the sellar plane (PS– SP angle) on prenatal MR images recently. They found that the PS–SP angle decreased significantly with gestational age, being less than 90° in all fetuses after gestational week 25. However, the data of the inclination angle of PS in the postnatal population are still lacking in literature. To our knowledge, the relationship between PS and the dorsum sellae has been first noticed by Taoka et al. [20] in probing late childhood onset of short stature. In their paper, the spatial relationship between them was divided into 4 grades, ranging from no contact to contact with bending or even bulging of PS. Recently, Gulsen et al. [7] also have noted that there are variations in the anatomic location of PS on the diaphragma sellae. It could be central or adjacent to the dorsum sellae or adjacent to the tuberculum sellae. But how much do various grades or types of PS occupy in the general population? Is there any difference between children and adults? In the current study, we aimed to characterize topographic variations of OC and PS in situ based on midsagittal T2-weighted MR images and to address the above-mentioned issues. The comparison with previous results was performed and related clinical issues were also discussed.

Materials and methods Inclusion criteria Following approval by the institutional review board, noncontrast sagittal T2-weighted MR imaging studies were reviewed at our institution over a period of 12 months. All examinations were performed on a 3.0-T superconducting magnet (Sigma Excite HD, GE Medical System, Germany). T2-weighted sagittal images were obtained using a spin echo sequence (TR/TE = 4,000–5,000/80–120 ms, FOV = 240 × 240 mm, matrix = 256 × 256, slice thickness = 3 mm, interslice gap = 0.5 mm) with an 8-channel phased-array head coils. Patients with sellar lesions, hydrocephalus, intracranial mass lesions, or other abnormalities such as empty sellae likely to affect the normal anatomic locations of OC and PS were excluded. To unify the standard of measurement, the criterion used to identify the midsagittal image was that the aqueduct of mesencephalon, the floor of the third ventricle, PS and OC could all be exhibited on the same scan.

Surg Radiol Anat

Fig. 1  Measurements obtained on midsagittal MR images of the sella turcica. The height of OC (PC) was defined as the shortest distance between the inferior margin of OC and the upper surface of the pituitary (blue line). The inclination angle of PS (PS–AP angle) was set as the angle formed by the central axis of PS and the anterior skull base plane (red lines) (color figure online)

formed by the central axis of PS and the anterior skull base plane (PS–AP angle). The height of OC was defined and measured as the shortest distance between the inferior margin of OC and the upper surface of the pituitary gland (PC) (Fig. 1). In terms of the anteroposterior relative position to the sellae turcica, all chiasms were classified into prefixed (OC overlies the tuberculum sellae), normal (OC overlies the diaphragma sellae), and postfixed types (OC overlies the dorsum sellae). In terms of the superoinferior relative position to the sellae turcica, all chiasms were classified into low (PC 

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

This study was conducted to characterize topographic variations of the optic chiasm (OC) and the pituitary stalk (PS) in situ based on MR images...
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