The anatomy of structures of the sellar and parasellar regions varies widely. For example, the sella turcica is described in different ways by many authors with differing values of normality. Axelsson and col (Axelsson et al. 2004) believe that these differences are due to choices of reference points and different radiological techniques.
The sphenoid sinus varies in size, shape and degree of pneumatização (Guerrero 1999; Rhoton et al. 1979; Scuderi et al. 1993; Yonetsu et al. 2000). Hamberger and col (Hamberger et al. 1961) classified within of three types: conchal, presellar and sellar depending on the pneumatization extent. Using the same criteria of classification, Rhoton (Rhoton 2002) in a study of cadavers, found the presellar type in 24% and sellar in76%. In the current study, we used a classification of Hamberger (Hamberger et al. 1961) modified by Guerrero (Guerrero 1999) but excluding semisellar and Non-pneumatized sphenoid sinus. The postsellar type represented 15.3%, while 78.9% had type sellar, 5.8% presellar.
In the sample, the width of the sphenoid sinus under the sella, showed a variation of 6–48 mm and observed that from the 41–60 year old male had widths greater than women. That is, the width of the sphenoid sinus increased with increasing age. These findings are not compatible with Yonetsu and col (Yonetsu et al. 2000) study that showed the opposite.
Knowing the variations of the sphenoid sinus is crucial when trying to reach the sellar region or surrounded structures through sphenoid bone (Rhoton 2002). In this study, due to inability to locate the ostium of the sphenoid sinus on MRI, the distances measures of columella -sphenoid sinus and columella-pituitary were performed on an imaginary line that passes between the implantation point of the columella and the presellar point (Figure 3). In this way, was considered that this would be a standard of measurement. In this study, regardless of age, males presented greater distances from the nasal columella to anterior wall of sphenoid sinus and pituitary-columella than female; but age does not differ between the genders. These distances help to define the size of the specula and instruments to be used in surgery of sellar region.
The surgical approach to sellar region by trans-sphenoidal, is already an established procedure in Neurosurgery and its complications are well described by some authors (Rhoton 2002; Elias & Laws 2000; Hamid et al. 2008; Romero et al. 2012; Laws & Kern 1976). Anatomical variations of this region are the causes of complications in this procedure. The most vulnerable structures along the sinus are: the internal carotid artery near the anterior wall of the sella, and optic nerves, located superolaterally(Rhoton 2002). The study had no aim to determine whether any of these structures were exposed within the sinus.
In a study performed on cadavers Pianetti and col (Pianetti & Henriques 2000) reported that the distance from the optic chiasm to the tuberculum sella ranged from 1.5 to 8 mm (mean 4.02 ± 1.72 mm). Bergland and col (Bergland et al. 1968) described three positions to the optic chiasm: prefixed, normal-fixed and postfixed. Renn & Rhoton (Renn & Rhoton 1975) found the chiasm normal-fixed in 70% of cases, prefixed at 15% and postfixed in the remain.
The inter carotid distances in coronal plane, beside the sella, ranged from 6 to 31 mm. In cases with smaller distance, the pituitary gland showed a different conformation, similar to the findings of Rhoton (Rhoton 2002).
According to Handfas and col (Handfas et al. 2002) the pituitary gland also presents great variation in shape among different people, changing in size throughout life. Elster and col (Elster et al. 1991) reported major changes in the pituitary gland in females during puberty, pregnancy and the postpartum period, secondary to physiologic hypertrophy. In the present study, there was no significant difference in pituitary mean height between males and females.
The position of the chiasm is important in trans-sphenoidal and trans-frontal surgeries. Usually, chiasm stays prefixed or very close to the sellar tubercle blocking the passage, in both directions, between the sellar and suprasellar compartments. Alternatively, some surgeons remove the tubercle and even the sphenoidal plane (Rhoton 2002; Ciric et al. 2002; Cavallo et al. 2005). The position of the chiasm may leads to differences in the symptoms of patients with diseases in sellar and parasellar regions (Cavallo et al. 2005; Anderson et al. 1999).
Wagner and colaboradores (Wagner et al. 1997) studying magnetic resonance imaging in 123 patients, found that the width of the chiasm ranged from 8.0 to 21.0 mm (mean 14.0 ± 1.68 mm) with no differences between the genders. In this study, the width of the chiasm ranged from 8.0 to 19 mm, the height ranged from 1.0 to 4.0 mm, and was similar between genders and age group. Only one difference was detected, the difference between females of different age groups.
The height of the optic chiasm, in the present study, was homogeneous throughout the sample may reflects the limitation of this applicative to very small measures, since the eFilm Workstation software works with only one decimal place.
Among neuroimaging techniques, the MRI is the method able to provide the details of the structures of the sellar and perisselar regions. It has unique characteristics such as high sensitivity to detect subtle changes in concentration of tissue water, and high discrimination between them and multiplanar capability.