Endoscopic Endonasal Odontoidectomy

Ellina Hattar, Eleonora F. Spinazzi, Jean Anderson Eloy, Cristian Gragnaniello, and James K. Liu

41.1 Introduction

The transoral route has served as the gold-standard approach for treating pathologies of the craniocervical junction. Since its emergence, this microscopic transoral approach has been the preferred route for performing anterior odontoidectomy to decompress the craniovertebral junction.

Pathologies that have been treated with this route have included basilar invagination, platybasia with retroflexed odontoid process, rheumatoid pannus, chordomas, and chondrosarcomas.

Extended versions of the transoral approach used to increase visualization as well as the operative field have included the extended “open-door” maxillotomy, transpalatal, transmaxillary, and transmandibular approaches. In recent years, the endoscopic endonasal approach has emerged as a minimally invasive surgical alternative.

The technique is especially well suited for pathologies located above the palatine line. By avoiding the oral cavity and obviating the need for oral retraction, the endonasal route avoids complications associated with tongue swelling, prolonged intubation, tracheal swelling, velopharyngeal insufficiency, dysphonia, and dysphagia. The procedure is also associated with a shorter hospital stay and post-operative recovery. In this chapter, we describe the operative technique and surgical nuances for performing endoscopic endonasal odontoidectomy.

41.2 Indications

• Irreducible basilar invagination causing brainstem compression and myelopathy.

• Symptomatic and compressive rheumatoid pannus refractory to posterior stabilization.

• Os odontoideum.

• Retroflexed odontoid process associated with Type I Chiari malformation resulting in compressive myelopathy.

41.3 Patient Positioning (Figs. 41.1, 41.2)

• Position: The patient is positioned supine in neutral position with the head fixed with a Mayfield head holder.

• Body: The body is positioned horizontal.

• Head: The head is placed in neutral position, no flexion or extension, no head rotation are needed.

• Anti-decubitus device: All pressure points are adequately padded; an anti-decubital pad is placed on the sacrum.

• The nasal tip is the highest point in the surgical field.

• Gentle axial traction can be applied to the head before final fixation of the Mayfield head holder to allow for some decompression of the cervico-medullary junction.

• Use CT-based frameless stereotactic image guidance for intraoperative localization.

• Use somatosensory and motor evoked potential neurophysiologic monitoring.

41.4 Exposure and Incision

• Goldman elevator is used to lateralize the middle and inferior turbinates.

Fig. 41.1 Patient positioning. The patient is positioned supine with the head in a Mayfield head holder.

• Pedicled Nasoseptal Flap (PNSF) (See Chapters 38 and 39)

◦ Right flap is harvested with care to preserve the vascular pedicle supplied by the posterior septal branch of the sphenopalatine artery.

◦ Flap is elevated from the muco-perichondrium and muco-periosteum.

◦ Flap is tucked into the ipsilateral middle meatus until the reconstruction phase with the vascular pedicle superior to the level of the choana.

◦ PNSF harvesting is repeated on the contralateral side.

• Posterior septectomy (Fig. 41.3)

◦ The posterior and inferior aspect of the bony and cartilaginous septum are removed to allow triangulation of instruments using binostril access.

◦ The mucosal integrity of the posterior nasal septum is preserved.

41.4.1 Critical Structures

• Eustachian tubes.

• Bilateral upper cervical carotid arteries.

• Bilateral vertebral arteries.

• Sympathetic chain.

41.5 Soft Tissue Dissection

• Mucosal incision and pharyngeal muscles (Fig. 41.4)

◦ A longitudinal midline incision is made over the posterior or pharyngeal mucosal wall overlying the tubercle of the atlas (C1).

◦ The incision is extended vertically to expose the inferior clivus (superiorly), down to the second cervical vertebral (C2) body (inferiorly).

◦ The incision is extended through the mucosa along the midline raphe, between the pharyngeal muscles, and through the anterior longitudinal ligament down to the bone of C1.

◦ The longus colli and longus capitis muscles are mobilized laterally with an extended length and protected tip Bovie monopolar cautery in a subperiosteal fashion to better expose the anterior tubercle of C1.