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Original Investigation |

The Endoscopic Endonasal Approach to the Hypoglossal Canal The Role of the Eustachian Tube as a Landmark for Dissection

Satyan B. Sreenath, MD1; Pablo F. Recinos, MD2,3,4; Stanley W. McClurg, MD1; Brian D. Thorp, MD1; Kibwei A. McKinney, MD1; Cristine Klatt-Cromwell, MD1; Adam M. Zanation, MD1,2
[+] Author Affiliations
1Department of Otolaryngology–Head and Neck Surgery, University of North Carolina at Chapel Hill, Chapel Hill
2Department of Neurosurgery, University of North Carolina at Chapel Hill, Chapel Hill
3Rosa Ella Burkhardt Brain Tumor and Neuro-Oncology Center, Cleveland Clinic, Cleveland, Ohio
4Head and Neck Institute, Cleveland Clinic, Cleveland, Ohio
JAMA Otolaryngol Head Neck Surg. 2015;141(10):927-933. doi:10.1001/jamaoto.2015.1749.
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Importance  Improvements in endoscopic technology and reconstructive techniques have made the endoscopic endonasal approach (EEA) a viable option to approach ventromedial lesions in the region of the hypoglossal canal. Prior to contemplating this surgical corridor, a thorough understanding of anatomic relationships and landmarks is essential to safely approach this region of the posterior skull base through an EEA.

Objective  To describe the surgical technique and anatomic landmarks in the EEA to the hypoglossal canal through referencing nasopharyngeal and posterior skull base anatomy.

Design, Setting, and Participants  Study of latex-injected cadaveric heads at the North Carolina Eye Bank Multidisciplinary Surgical Skills Laboratory at the University of North Carolina.

Interventions  An EEA to the hypoglossal canal was carried out bilaterally in 5 embalmed, latex-injected cadaver heads.

Main Outcomes and Measures  Cadaveric measurements of anatomic landmarks and relationships in the approach were obtained using a 10-cm surgical ruler and were reported as mean distances. Additionally, high-quality endoscopic images demonstrating the operative technique and anatomic relationships were obtained.

Results  The distance between the lacerum segment of the internal carotid arteries, the superolateral boundary, was 23.6 mm (SD, 11.8 mm). The distance between the anterolateral edge of the occipital condyles, the inferolateral boundary, was 19 mm (SD, 0.80 mm). The supracondylar groove was identified in the same anteroposterior plane as the nasopharyngeal orifice of the eustachian tube, and the anterior-most edge of the occipital condyle was 14 mm (SD, 0.82 mm) from the posterosuperior edge of the salpingopharyngeal fold. Additionally, the transtubercular corridor was on the same plane as the superior edge of the torus tubarius in the anteroposterior axis. The distance to the hypoglossal canal from midline was 10 mm, which was found after completing drilling in the transcondylar and transtubercular corridors. Last, the hypoglossal nerve rootlets were identified entering the canal 6 mm inferiorly and 8 mm laterally from the vertebrobasilar junction.

Conclusions and Relevance  The eustachian tube and other elements of nasopharyngeal anatomy are fixed landmarks that provide important points of reference when approaching the hypoglossal canal through an EEA. A thorough understanding of these anatomic relationships is vital in safely navigating this direct, surgical corridor to the posterior fossa.

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Figure 1.
Nasopharyngeal Dissection to the Craniovertebral Junction

Photographs A and B show the dissection of nasopharyngeal and prevertebral fascia and musculature in approaching the inferior clival region and craniovertebral junction. SF indicates salpingopharyngeal fold; RF, Rosenmüller’s fossa; ET, eustachian tube; TT, torus tubarius; PB, pharyngobasilar fascia.

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Figure 2.
Sinonasal, Clival, and Craniovertebral Junction Exposure

With complete resection of the sphenoid sinus floor, full visualization of the middle and inferior clivus can be obtained. After total nasopharyngeal dissection, the craniovertebral junction can be appreciated. ET indicates eustachian tube; SF, salpingopharyngeal fold; TT, torus tubarius; OC, occipital condyle; C1, first cervical spine bone; ICA, internal carotid artery; B, basilar artery; VBJ, vertebrobasilar junction; Vert, vertebral artery; SCG, supracondylar groove; VC and blue rectangles, Vidian canal; and FM and green circle, foramen magnum.

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Figure 3.
Surgical Window and Anatomic Landmarks

A, Endoscopic image demonstrating the trapezoidal surgical window and critical anatomic landmarks in approaching the hypoglossal canal from an endoscopic endonasal approach. B, Demonstration of relationships between nasopharyngeal structures and posterior skull base structures with the use of a 45° nasal endoscope. ICA indicates internal carotid artery; B, basilar artery; AICA, anterior inferior cerebellar artery; VA, vertebral artery; JT, jugular tubercle; OC, occipital condyle; FM, foramen magnum; C1, first cervical spine bone; SF, salpingopharyngeal fold; BP, basopharyngeal fascia; RCA, rectus capitus anterior muscle; blue rectangle, Rosenmüller’s fossa; SCG and green circle, supracondylar groove; and FM and yellow circle, foramen magnum.

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Figure 4.
Exposure of the Hypoglossal Nerve and Canal

A, Intradural exposure of the hypoglossal nerve rootlets (cranial nerve XII) entering the hypoglossal canal through the view of a 45° nasal endoscope. B, Demonstration of the transcondylar and transtubercular approaches to the hypoglossal canal (cranial nerve XII). VBJ indicates vertebrobasilar junction; VA, vertebral artery; PICA, posterior inferior cerebellar artery; CN XII, cranial nerve XII (hypoglossal nerve); TT, transtubercular approach; TC, transcondylar approach.

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