Location of petrous apex (PA) by the posterior point of inferior turbinate (IT) in the sagittal plane.

<p><b>D</b>_<b>PA</b>: Distance between the posterior point of IT and PA; <b>R</b>_<b>A</b>: Angle between the line from the posterior point of IT to PA and the horizontal plane; <b>Line H:</b> the horizontal line; <b>IT:</b> inferior turbinate; <b>ICA:</b> internal carotid artery; <b>PA:</b> petrous apex.</p

Distance between the medial wall of the ICA and mid-sagittal line (mm).

<p><b>D1</b>: Distance between the medial wall of the ICA and mid-sagittal line in plane B</p><p><b>D2</b>: Distance between the medial wall of the ICA and mid-sagittal line in plane C</p><p><b>D3</b>: Distance between the medial wall of the foramen lacerum and mid-sagittal line in plane D</p><p><b>D4</b>: Distance between the medial wall of ICA and mid-sagittal line in plane E</p><p>Distance between the medial wall of the ICA and mid-sagittal line (mm).</p

Safe Corridor to Access Clivus for Endoscopic Trans-Sphenoidal Surgery: A Radiological and Anatomical Study

<div><p>Purpose</p><p>Penetration of the clivus is required for surgical access of the brain stem. The endoscopic transclivus approach is a difficult procedure with high risk of injury to important neurovascular structures. We undertook a novel anatomical and radiological investigation to understand the structure of the clivus and neurovascular structures relevant to the extended trans-nasal trans-sphenoid procedure and determine a safe corridor for the penetration of the clivus.</p><p>Method</p><p>We examined the clivus region in the computed tomographic angiography (CTA) images of 220 adults, magnetic resonance (MR) images of 50 adults, and dry skull specimens of 10 adults. Multiplanar reconstruction (MPR) of the CT images was performed, and the anatomical features of the clivus were studied in the coronal, sagittal, and axial planes. The data from the images were used to determine the anatomical parameters of the clivus and neurovascular structures, such as the internal carotid artery and inferior petrosal sinus.</p><p>Results</p><p>The examination of the CTA and MR images of the enrolled subjects revealed that the thickness of the clivus helped determine the depth of the penetration, while the distance from the sagittal midline to the important neurovascular structures determined the width of the penetration. Further, data from the CTA and MR images were consistent with those retrieved from the examination of the cadaveric specimens.</p><p>Conclusion</p><p>Our findings provided certain pointers that may be useful in guiding the surgery such that inadvertent injury to vital structures is avoided and also provided supportive information for the choice of the appropriate endoscopic equipment.</p></div

Measurement of the clivus in the sagittal plane of the CT image.

<p><b>1A:</b> Measurement of the length and angle clivus in sagittal plane in CT image (bone window); <b>Rc: </b>The angle between the clivus and the horizontal plane; <b>Lc:</b> the length of the clivus; <b>Line H:</b> The horizontal line. <b>1B:</b> Distance from the lowest point of the sellar floor (SF) to the clivus and vertebral artery in CT image (soft-tissue window): <b>D</b>_<b>A</b>: The horizontal distance from the lowest point of SF to the posterior boundary of the clivus; <b>Point B:</b> The middle lowest point of the SF.</p

Distance between ICA and the mid-sagittal line in the position superior and inferior of the petrous apex (PA).

<p><b>6A</b>: Position of the axial plane selected for the measurement: <b>Line P:</b> Position of the axial plane through PA; <b>Line P1</b>: Position of the axial plane 10 mm superior to Line P; <b>Line P2</b>: Position of the axial plane 10 mm inferior to Line P. <b>6B:</b> Axial plane 10 mm superior to PA. <b>Line M</b>: mid-sagittal line; <b>D</b>_<b>P1</b>: distance between ICA and the sagittal middle line; <b>ICA:</b> internal carotid artery; <b>6C:</b> Axial plane through PA. <b>Line M:</b> mid-sagittal line; <b>D</b>_<b>P</b>: distance between ICA and the sagittal middle line; <b>ICA</b>: internal carotid artery; <b>6D:</b> Axial plane 10 mm inferior to the petrous apex. <b>Line M</b>: mid-sagittal line; <b>D</b>_<b>P2</b>: distance between ICA and the mid-sagittal line; <b>ICA</b>: internal carotid artery.</p

The location of the soft palate in the view of endoscopic trans-nasal surgery to clivus region.

<p><b>D</b>_<b>H</b>: Distance between the nostril and the anterior part of the soft palate in sagittal middle plane.</p><p><b>R</b>_<b>H</b>: The angle between horizontal direction of soft palate and the direction of the soft palate in mid-sagittal line.</p><p><b>D</b>_<b>H1</b>: Distance between the nostril and the initial point of the soft palate in the position 10 mm right to the mid-sagittal plane.</p><p><b>R</b>_<b>H1</b>: The angle between horizontal direction of soft palate and the direction of the soft palate in the position 10 mm right to the mid-sagittal plane.</p><p><b>D</b>_<b>T</b>: Vertical distance between the inferior turbinate and soft palate in the coronal plane through the anterior part of the soft palate.</p><p><b>D</b>_<b>T1:</b> Vertical distance between the inferior turbinate and soft palate in the coronal plane through the posterior part of the inferior turbinate.</p><p>The location of the soft palate in the view of endoscopic trans-nasal surgery to clivus region.</p

Measurement of safe region for penetration of the clivus.

<p><b>7A:</b> Position of the axial plane selected for the measurement: <b>Line B:</b> Position of axial plane through middle lowest point of SF in Fig 7B; <b>Line C:</b> Position of the axial plane through apertura sinus sphenoidalis in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137962#pone.0137962.g006" target="_blank">Fig 6C</a>; <b>Line D:</b> Position of the axial plane through the upper aspect of foramen lacerum in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137962#pone.0137962.g006" target="_blank">Fig 6D</a>; <b>Line E:</b> Position of the axial plane passing through the superior margin of the nostril in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137962#pone.0137962.g006" target="_blank">Fig 6E</a>. <b>7B:</b> Axial plane through the lowest central point of the SF: <b>Line M:</b> mid-sagittal line; <b>Point B:</b> lowest, central point of the SF; <b>ICA:</b> internal carotid artery; <b>D1:</b> distance between the medial wall of the internal carotid artery and mid-sagittal line. <b>7C:</b> axial plane through apertura sinus sphenoidalis: <b>Line M:</b> mid-sagittal line; <b>ASS:</b> apertura sinus sphenoidalis; <b>ICA:</b> internal carotid artery; <b>SPS</b>: sulcus of the inferior petrosal sinus; <b>D2:</b> Distance between the medial wall of the ICA and mid-sagittal line. <b>D5:</b> Distance between sulcus of the inferior petrosal sinus and the mid-sagittal line. <b>7D:</b> axial plane through upper of the foramen lacerum: <b>Line M:</b> the mid-sagittal line; <b>SPS:</b> sulcus of the inferior petrosal sinus; <b>FL:</b> foramen lacerum; <b>D3:</b> Distance between the medial margin of the foramen lacerum and mid-sagittal line; <b>D6:</b> Distance between the sulcus of the inferior petrosal sinus and the mid-sagittal line. <b>7E:</b> axial plane through the superior margin of the nostril: <b>Line M:</b> mid-sagittal line; <b>SPS:</b> sulcus of the inferior petrosal sinus; <b>D4:</b> Distance between the medial wall of the ICA and mid-sagittal line; <b>D7:</b> Distance between the sulcus of inferior petrosal sinus and the mid-sagittal line. <b>7F:</b> Distance between foramen jugulare to mid-sagittal line at SF. <b>D</b>_<b>F</b>: Distance between the foramen jugulare to the mid-sagittal line at SF; <b>Line M:</b> the sagittal midline; <b>FJ:</b> foramen jugulare.</p

Location of trigeminal nerve in the MR image.

<p><b>9A</b>: Distance from the initial part of the trigeminal nerve to the mid-sagittal line; <b>Line M:</b> mid-sagittal line; <b>TN</b>: trigeminal nerve; <b>D8:</b> distance between the root of the trigeminal nerve and the mid-sagittal line. <b>9B: Line S:</b> Position of the axial plane in plane 8A; <b>PG:</b> the pituitary gland; <b>D9:</b> the distance between the axial plane through the root of trigeminal nerve and lowest, central point of the SF.</p

Location and measurement of soft palate in the view of endoscopic trans-nasal surgery.

<p><b>10A:</b> Sagittal middle plane: <b>D</b>_<b>H</b>: Distance between the nostril and the anterior part of the soft palate. <b>R</b>_<b>H</b>: The angle between horizontal direction of soft palate and the direction of the soft palate. <b>Line HP:</b> The line in accordance with the horizontal direction of the hard palate. <b>10B:</b> Sagittal plane 10 mm right of mid-sagittal plane. <b>D</b>_<b>H1</b>: Distance between the nostril and the anterior part of the soft palate. <b>R</b>_<b>H1</b>: The angle between horizontal direction of soft palate and the direction of the soft palate. Line HP: <b>10C:</b> Coronal plane through the anterior point of soft palate. <b>D</b>_<b>T</b>: Vertical distance between the inferior turbinate and soft palate in the coronal plane through the anterior part of the soft palate; <b>D</b>_<b>T1</b>: Vertical distance between the inferior turbinate and soft palate; <b>IT:</b> inferior turbinate; <b>SP:</b> soft palate. <b>10D:</b> Coronal plane through the posterior point of inferior turbinate. <b>D</b>_<b>T1</b>: Vertical distance between the inferior turbinate and soft palate.</p

The distance between the middle turbinate (MT) and anterior margin of foramen magnum.

<p><b>D</b>_<b>N</b>: The distance between the posterior point of MT and anterior margin of foramen magnum; <b>R</b>_<b>N</b>: The angle between the line from the posterior point of MT to anterior margin of foramen magnum and the horizontal plane; <b>Line H:</b> the horizontal line; <b>MT:</b> middle turbinate; <b>FM:</b> foramen magnum.</p