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  Indian J Med Microbiol
 

Figure 2: Stepwise extended endonasal endoscopic approach to foramen magnum and craniovertebral junction. (a) Sphenoid stage of dissection has been completed. Right side infratemporal fossa has been dissected showing path of eustachian tube and branches of mandibular nerve in depth. On the left side, posterior wall of maxillary sinus in front of infratemporal fossa is still visible. (b) View of mucosa of rhino pharynx with eustachian tubes as lateral limits of this exposure. (c) Nasopharyngeal mucosa has been removed exposing basipharyngeal fascia overlying longus capitis muscle and median raphe attached to pharyngeal tubercle in midline. (d) Longus capitis muscle can be seen after the removal of fascia. It is attached lateral to pharyngeal tubercle along superior clival line. (e) Longus capitis muscle has multiple bellies and it is attached in layers to clivus as can be seen after partial removal from the right side. (f) On both sides, longus capitis is removed exposing median raphe part of anterior longitudinal ligament attached to pharyngeal tubercle and laterally forming thick, broad membrane called anterior atlanto-occipital membrane. (g) Both longus capitis and anterior atlanto-occipital membrane have been removed exposing anterior longitudinal ligament in midline and atlanto-occipital joint. Rectus capitis anterior muscle can be seen laterally attaching along clivus from inferior clival line to foramen magnum. (h) Anterior longitudinal ligament and rectus capitis anterior muscle are also removed here exposing foramen magnum and arch of C1 with both atlanto-occipital joints. Gap between C1 arch and foramen magnum is filled with dense connective tissue, which also encloses apical and alar ligaments attached to the dens of C2. Pharyngeal tubercle can be seen here. (i) Another specimen showing foramen magnum after the removal of anterior longitudinal ligament and anterior atlanto-occipital membrane. Supracondylar groove can be identified laterally with rectus capitis anterior (j) clivus after the removal of muscles with superior and inferior clival lines. Inferior clival line corresponds to supracondylar groove laterally. Anterior arch of C1 partially removed, thus exposing odontoid process. (k) Alar ligaments, which are thick, fibrous bands that attach to the posterolateral roughened surface of the odontoid and ascend obliquely lateral to attach the alar tubercles located on the medial side of occipital condyles. Odontoidectomy begins with drilling of central core as seen here. (l) Once dens is removed, transverse ligament can be seen as extending between transverse tubercles on the medial side of C1 lateral masses. Vertical part of cruciform ligament can be seen extending from transverse ligament to foramen magnum. (m) In few specimens, another transverse band of ligament may be present just above the transverse ligament attached to the medial side of occipital condyles and it is called transverse occipital ligament. Transverse ligament is broad in middle and tapered laterally. (n) Intradural exposure of vertebrobasilar complex with cranial nerves. Internal carotid artery can be seen on both sides from carotid canal up to intradural segment. Cervicomedullary junction can be seen which is demarcated by ventral rootlets of C1 nerve. AOM, atlanto-occipital membrane; ET, eustachian tube; FL, foramen lacerum; ICA, internal carotid artery; Inf cli line, inferior clival line; OC1, occipitocervical joint; postwall maxilla, posterior wall of maxilla; RCpA, rectus capitis anterior; SuCG, supracondylar groove; Sup cli line, superior clival line; Trans lig, transverse ligament; Trans occi lig, transverse occipital ligament

Figure 2: Stepwise extended endonasal endoscopic approach to foramen magnum and craniovertebral junction. (a) Sphenoid stage of dissection has been completed. Right side infratemporal fossa has been dissected showing path of eustachian tube and branches of mandibular nerve in depth. On the left side, posterior wall of maxillary sinus in front of infratemporal fossa is still visible. (b) View of mucosa of rhino pharynx with eustachian tubes as lateral limits of this exposure. (c) Nasopharyngeal mucosa has been removed exposing basipharyngeal fascia overlying longus capitis muscle and median raphe attached to pharyngeal tubercle in midline. (d) Longus capitis muscle can be seen after the removal of fascia. It is attached lateral to pharyngeal tubercle along superior clival line. (e) Longus capitis muscle has multiple bellies and it is attached in layers to clivus as can be seen after partial removal from the right side. (f) On both sides, longus capitis is removed exposing median raphe part of anterior longitudinal ligament attached to pharyngeal tubercle and laterally forming thick, broad membrane called anterior atlanto-occipital membrane. (g) Both longus capitis and anterior atlanto-occipital membrane have been removed exposing anterior longitudinal ligament in midline and atlanto-occipital joint. Rectus capitis anterior muscle can be seen laterally attaching along clivus from inferior clival line to foramen magnum. (h) Anterior longitudinal ligament and rectus capitis anterior muscle are also removed here exposing foramen magnum and arch of C1 with both atlanto-occipital joints. Gap between C1 arch and foramen magnum is filled with dense connective tissue, which also encloses apical and alar ligaments attached to the dens of C2. Pharyngeal tubercle can be seen here. (i) Another specimen showing foramen magnum after the removal of anterior longitudinal ligament and anterior atlanto-occipital membrane. Supracondylar groove can be identified laterally with rectus capitis anterior (j) clivus after the removal of muscles with superior and inferior clival lines. Inferior clival line corresponds to supracondylar groove laterally. Anterior arch of C1 partially removed, thus exposing odontoid process. (k) Alar ligaments, which are thick, fibrous bands that attach to the posterolateral roughened surface of the odontoid and ascend obliquely lateral to attach the alar tubercles located on the medial side of occipital condyles. Odontoidectomy begins with drilling of central core as seen here. (l) Once dens is removed, transverse ligament can be seen as extending between transverse tubercles on the medial side of C1 lateral masses. Vertical part of cruciform ligament can be seen extending from transverse ligament to foramen magnum. (m) In few specimens, another transverse band of ligament may be present just above the transverse ligament attached to the medial side of occipital condyles and it is called transverse occipital ligament. Transverse ligament is broad in middle and tapered laterally. (n) Intradural exposure of vertebrobasilar complex with cranial nerves. Internal carotid artery can be seen on both sides from carotid canal up to intradural segment. Cervicomedullary junction can be seen which is demarcated by ventral rootlets of C1 nerve. AOM, atlanto-occipital membrane; ET, eustachian tube; FL, foramen lacerum; ICA, internal carotid artery; Inf cli line, inferior clival line; OC1, occipitocervical joint; postwall maxilla, posterior wall of maxilla; RCpA, rectus capitis anterior; SuCG, supracondylar groove; Sup cli line, superior clival line; Trans lig, transverse ligament; Trans occi lig, transverse occipital ligament