The “suprasellar notch,” or the tuberculum sellae as seen from below: definition, features, and clinical implications from an endoscopic endonasal perspective

Laboratory investigation

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Object

The tuberculum sellae is a bony elevation ridge that lines up the anterior aspect of the sella, dividing it from the chiasmatic groove. The recent use of the endoscopic endonasal transtuberculum approach has provided surgeons with a method to reach the suprasellar area, offering a new surgical point of view somehow “opposite” of this area. The authors of this study aimed to define the tuberculum sellae as seen from the endoscopic endonasal view while also providing CT-based systematic measurements to objectively detail the anatomical features of such a structure, which was renamed the “suprasellar notch.”

Methods

The authors analyzed routine skull CT scans from 24 patients with no brain pathology or fractures and measured the interoptic distance at the level of the limbus sphenoidale, the chiasmatic groove sulcal length and width, and the angle of the suprasellar notch.

Indeed, the suprasellar notch was defined as the angle between 2 lines, the first passing through the tuberculum sellae midpoint and perpendicular to the cribriform plate, and a second line passing between 2 points, the midpoints of the limbus sphenoidale and the tuberculum sellae. Moreover, the authors performed on 15 cadaveric heads an endoscopic endonasal transplanum transtuberculum approach with the aid of a neuronavigator to achieve a step-by-step comparison with the radiological data. The whole CT scanning set was statistically analyzed to determine the statistical interdependency of the suprasellar notch angle with the other 3 measurements, that is, the sulcal length at the midline, the interoptic distance at the optic canal entrance, and the interoptic distance at the limbus.

Results

Based on the endoscopic endonasal view and CT imaging analysis, the authors identified a certain anatomical variability and thus introduced a new classification of the suprasellar notch: Type I, angle < 118°; Type II, angle of 118°–138°; and Type III, angle > 138°. They then analyzed the surgical implications of the endoscopic endonasal approach to the suprasellar area, which could be affected by each of these structural types.

Conclusions

The new classification identifies 3 different types of suprasellar notch and, accordingly, their surgical relevance. Above all, the authors found that the different types of suprasellar notch can affect the osteodural defect reconstruction technique, namely the positioning/wedging of the buttress in the extradural space. A precise endoscopic anatomical knowledge of the neurovascular and bony relationships—especially in cases of a less pneumatized sphenoid sinus—is crucial when approaching the anterior skull base via a transtuberculum transplanum route.

Abbreviations used in this paper: ICA = internal carotid artery; IDL = interoptic distance at the limbus sphenoidale; IDOC = interoptic distance at the optic canal entrance; MAD = median absolute deviation; Me = median; SLM = chiasmatic groove sulcal length at the midline; SNA = suprasellar notch angle; SSN = suprasellar notch.

Article Information

Address correspondence to: Domenico Solari, M.D., Department of Neurological Sciences, Division of Neurosurgery, Università degli Studi di Napoli Federico II, Via Pansini 5, 80131 Naples, Italy. email: d.solari.md@gmail.com.

Please include this information when citing this paper: published online December 23, 2011; DOI: 10.3171/2011.11.JNS111162.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    The suprasellar notch angle is defined as the indentation between the superior aspect of the sella turcica and the declining part of the planum sphenoidale. It can be described as the angle between 2 lines, the first passing through the center of the tuberculum sellae and perpendicular to the cribriform plate, and the second line passing between 2 points, that is, the midpoint of the limbus sphenoidale and the tuberculum sellae. Photograph (A) showing the main landmarks of the sphenoid bone in a midline sagittal plane. High-resolution sagittal CT scan (B) showing the measurement technique for the SNA. Endoscopic view (C) of the endonasal transplanum transtuberculum approach. Asterisk indicates sphenoid septation at the level of the sellar floor extending toward the left parasellar internal carotid artery. Double asterisks indicate sphenoid septation at the level of the planum sphenoidale extending over the left optic nerve protuberance. Note the main landmarks over the posterior wall of the sphenoid sinus. Photograph (D) showing the main landmarks of the sphenoid bone from a superolateral perspective. ACP = anterior clinoid process; C = clivus; DS = dorsum sellae; FL = foramen lacerum; FO = foramen ovale; FR = foramen rotundum; ICAc = clival segment of the ICA; ICAs = parasellar segment of the ICA; LOCR = lateral opticocarotid recess; LS = limbus sphenoidale; MCP = middle clinoid process; MOCR = middle opticocarotid recess; OC = optic canal; OP = optic protuberance; OS = optic strut; PCP = posterior clinoid process; PS = planum sphenoidale; SF = sellar floor; SOF = superior orbital fissure; SS = sphenoid sinus; TS = tuberculum sellae.

  • View in gallery

    Endoscopic endonasal transplanum transtuberculum approach. Endoscopic image (A) showing the neuronavigation probe pointing to the suprasellar notch. Main neuronavigation screen (B) of the same specimen showing the suprasellar notch in the axial, sagittal, and coronal CT reconstructions. OCR = opticocarotid recess.

  • View in gallery

    Photograph and CT scans showing the main anatomical structures measured around the SSN. A: Blue line indicates the IDL; red line, the IDOC; and the purple line, the SLM. B: Red line indicates the IDL. C: Red line indicates the IDOC. D: Red line indicates the SLM.

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    Boxplot representations showing the interdependency of each variable, that is, SLM, IDOC, and IDL, with the 3 types of SSN.

  • View in gallery

    Type I SSN. Virtual computer-based 3D model from different perspectives: endoscopic endonasal view (A), a special light endoscopic simulator was created to highlight the angle; transcranial view (B); and sagittal CT scan (C) of the same specimen.

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    Endoscopic endonasal transplanum transtuberculum approach. Anatomical pictures showing 3 different types of SSN: Type I SSN (A), Type II SSN (B), Type III SSN (C). Please note how in Type III SSN, mostly as compared with Type I, the planum and the SSN seem to lie on the same plane granting better access to the suprasellar area. Asterisk indicates the septum inside the sphenoid sinus. C = clival recess; CP = cribriform plate; Locr = lateral opticocarotid recess.

  • View in gallery

    Photograph showing the sphenoid bone in the midline sagittal plane with classification of the 3 different types of SNAs: Type I, angle < 118°; Type II, angle of 118°–138°; Type III, angle > 138°.

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    Type II SSN. Virtual computer-based 3D model from different perspectives: endoscopic endonasal view (A), a special light endoscopic simulator was created to highlight the angle; transcranial view (B); and sagittal CT scan (C) of the same specimen.

  • View in gallery

    Type III SSN. Virtual computer-based 3D model from different perspectives: endoscopic endonasal view (A), a special light endoscopic simulator was created to highlight the angle; transcranial view (B); and sagittal CT scan (C) of the same specimen.

  • View in gallery

    Endoscopic endonasal approach to the suprasellar area for the removal of a tuberculum sellae meningioma. Preoperative sagittal MR image (A) showing the lesion arising from the tuberculum sellae. Note the wide SNA (Type III), which favors lesion removal via an endoscopic endonasal route (B) with excellent exposure on both supra-(1) and subchiasmatic (2) corridors. Close-up view (C) of the suprachiasmatic area after lesion removal. Ch = optic chiasm; on = optic nerve.

  • View in gallery

    Endoscopic endonasal approach to the suprasellar area for the removal of a recurrent craniopharyngioma. Preoperative sagittal MR image (A) showing the lesion involving the infundibular and ventricular area. In this case a narrow SNA (Type I) favors lesion removal via an endoscopic endonasal subchiasmatic corridor (B). pg = pituitary gland.

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