The neurosurgical anatomy of the sphenoid sinus and sellar floor in endoscopic transsphenoidal surgery

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Object

A considerable degree of variability exists in the anatomy of the sphenoid sinus, sella turcica, and surrounding skull base structures. The authors aimed to characterize neuroimaging and intraoperative variations in the sagittal and coronal surgical anatomy of healthy controls and patients with sellar lesions.

Methods

Magnetic resonance imaging studies obtained in 100 healthy adults and 78 patients with sellar lesions were reviewed. The following measurements were made on midline sagittal images: sellar face, sellar prominence, sellar angle, tuberculum sellae angle, sellar-clival angle, length of planum sphenoidale, and length of clivus. The septal configuration of the sphenoid sinus was classified as either simple or complex, according to the number of septa, their symmetry, and their morphological features. The following measurements were made on coronal images: maximum width of the sphenoid sinus and sellar face, and the distance between the parasellar and midclivus internal carotid arteries. Neuroimaging results were correlated with intraoperative findings during endoscopic transsphenoidal surgery.

Results

Three sellar floor morphologies were defined in normal adults: prominent (sellar angle of < 90°) in 25%, curved (sellar angle 90–150°) in 63%, flat (sellar angle > 150°) in 11%, and no floor (conchal sphenoid) in 1%. In healthy adults, the following mean measurements were obtained: sellar face, 13.4 mm; sellar prominence, 3.0 mm; sellar angle, 112°; angle of tuberculum sellae, 112°; and sellar-clival angle, 117°. Compared with healthy adults, patients with sellar lesions were more likely to have prominent sellar types (43% vs 25%, p = 0.01), a more acute sellar angle (102° vs 112°, p = 0.03), a more prominent sellar floor (3.8 vs 3.0 mm, p < 0.005), and more acute tuberculum (105° vs 112°, p < 0.01) and sellar-clival (105° vs 117°, p < 0.003) angles. A flat sellar floor was more difficult to identify intraoperatively and more likely to require the use of a chisel or drill to expose (75% vs 25%, p = 0.01). A simple sphenoid sinus configuration (no septa, 1 vertical septum, or 2 symmetric vertical septa) was noted in 71% of studies, and the other 29% showed a complex configuration (2 or more asymmetrical septa, 3 or more septa of any kind, or the presence of a horizontal septum). Intraoperative correlation was more challenging in cases with complex sinus anatomy; the most reliable intraoperative midline markers were the vomer, superior sphenoid rostrum, and bilateral parasellar and clival carotid protuberances.

Conclusions

Preoperative assessment of neuroimaging studies is critical for characterizing the morphological characteristics of the sphenoid sinus, sellar floor, tuberculum sellae, and clivus. The flat sellar type identified in 11% of people) or a complex sphenoid sinus configuration (in 29% of people) may make intraoperative correlation substantially more challenging. An understanding of the regional anatomy and its variability can improve the safety and accuracy of transsphenoidal and extended endoscopic skull base approaches.

Abbreviations used in this paper: ICA = internal carotid artery; OCR = opticocarotid recess.

Article Information

Address correspondence to: Gabriel Zada, M.D., USC Department of Neurosurgery, 1200 North State Street, Suite 5046, Los Angeles, California 90089. email: gzada@usc.edu.

Please include this information when citing this paper: published online January 14, 2011; DOI: 10.3171/2010.11.JNS10768.

© AANS, except where prohibited by US copyright law.

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Figures

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    Measurements obtained on midsagittal MR images of the sella turcica. A: The sellar face length was defined by a line from the tuberculum sellae to the sellar-clival angle (red line). The prominence of the sella was defined as the maximal length from the sellar face line to the most prominent point on the sellar floor (blue line). B: Method of obtaining the sellar angle. C: Depicts angle measurements of the tuberculum sellae angle and sellar-clival angle.

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    Sagittal MR images demonstrating the wide variability of sellar floor morphology in healthy adults. A: Representative example of the “prominent” sellar type (sellar angle < 90°) identified in 25% of individuals. B: Example of the intermediate “curved” sellar type (sellar angle 90°–150°) identified in 63% of individuals. C: Example of the less conspicuous “flat” sellar type (sellar angle > 150°) identified in 11% of individuals and often associated with a presellar sphenoid sinus.

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    Sagittal (A and B) and coronal (C and D) CT (A and C) and MR (B and D) images showing an example of a “conchal,” or nonpneumatized, sphenoid sinus. This variation was identified in 1% of normal subjects and in no patients with sellar tumors.

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    Examples of MR images obtained in obtained in patients with sellar masses and a prominent sellar type (43% of tumor patients), likely due in part to sellar expansion.

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    Examples of MR images obtained in patients with sellar masses and a flat sellar type (10% of tumor patients). In general, the floor of the sella associated with this morphological type is more difficult to identify intraoperatively and has a tendency to be thicker. A–C: Images demonstrating a flat sella in association with a presellar sinus. D: Image demonstrating a flat sellar face with no presellar sphenoid sinus. Without careful consideration, the sellar-clival angle could be mistaken for the tuberculum sellae in such a situation.

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    Coronal, postcontrast MR images obtained in patients with sella-based lesions and a simple sphenoid sinus morphological type. Various subtypes represented in this category include no vertical septations (A), 1 midline vertical septum (B), 1 slightly eccentric septum (C), and 2 vertical septa creating a symmetric tripartite sinus (D).

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    Coronal, postcontrast MR images obtained in patients with sella-based lesions and a complex sphenoid sinus morphology. These patients had more than 2 vertical septations or a combination of horizontal and vertical septa.

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    Examples of variation in the distance between the parasellar ICAs associated with tumor size. The inter-ICA distances in these images are 9 mm (A), 16 mm (B), and 25 mm (C).

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    Sagittal MR imaging and intraoperative endoscopic images of the sellar floor and morphology. A: Example of a prominent sella that is easily identifiable intraoperatively. B: Example of an intermediate sellar type. C: Example of a flat sella that is very difficult to differentiate from the clivus. Intraoperative neuronavigation was extremely useful in this case.

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    Examples of intraoperative findings–imaging correlation of vertical septa in patients with simple sphenoid sinus morphology. The presence of 1 midline vertical septum (A and B, white arrow) can be used to identify the anatomical midline. The presence of 2 symmetric vertical septa (C and D, white arrows) can typically be used to identify the lateral boundaries of the sellar exposure and extrapolate the midline location.

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    Intraoperative endoscopic photographs demonstrating the benefit of relatively constant midline markers, such as the base of the vomer (A and B, white arrows) or superior rostrum of the sphenoid (C, white arrow). These anatomical structures tend to be reliable midline markers despite the presence of eccentric sphenoid sinus septa (B).

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    Intraoperative endoscopic photographs demonstrating the benefit of bilateral anatomical markers, including the OCRs (A, black arrows), carotid protuberances (B, black arrows), and clival-carotid prominences (C, white arrows). Note the prominent sellar curvature in B that substantially facilitates intraoperative identification.

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    Sagittal MR images obtained in 4 patients with pituitary adenomas and clival erosion without obvious erosion of the sellar floor.

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    Intraoperative endoscopic photographs during the sellar phase of a transsphenoidal operation following removal of the bony sellar floor. In approximately one-half of patients, a midline dural filum (white arrows) is noted that correlates with the midline.

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    Coronal, postcontrast MR images obtained in 2 patients with prominent ICA projection into the sphenoid sinus (present in 4%–10% of patients), warranting additional caution during the sphenoid phase of a transsphenoidal operation.

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