Preoperative antibiotic prophylaxis is routinely administered 20 min before the operation starts. The nose is routinely prepared by iodine 5 % and naphazoline.

A 0° and 30° angled endoscopes with an HDD camera (Storz, Germany) and dedicated endoscopic tools are used (Storz and Aesculap, Germany). The procedure could be usually dealt either by two-hand (coupled to an holder harm) or by four-hand technique; we strongly believe that the former choice is strictly related to the surgeon’s skill and preference; for example, in the neurosurgical department of Foch Hospital in Paris, this procedure is ruled out using a two-hand technique by the senior author Dr. Stephan Gaillard; on the contrary, the same procedure in Strasbourg is realized using the four-hand technique by a combined neurosurgical and ENT team.

An endoscope, suction, and irrigation are typically introduced through the right nostril, while the dissecting instruments, the drill, and the navigation probes are entered through the left nostril. An inferior septectomy is performed, removing no more than 2 cm of vomer bone at its junction with the hard palate. We do not routinely perform a sphenoidotomy, and it is decided on a case by case basis depending on each patient’s anatomical constitution if it is necessary to get enough room to maneuver in. Normally we use the clivus–nasal septum junction, as the most superior dissection limit. At this stage, few important anatomical landmarks should be identified as follows:

Next step consists in creating an inverted U-shaped muco-pharyngeal flap using a diode laser or a monopolar electrocautery going from the level of the sphenoid floor to the level of the soft palate which is caudally reflected into the oropharynx during the bony removal and replaced back in its original site at the end of the procedure. Additional soft tissue is removed using a microdebrider to completely expose the body and arch of C1 and C2.

At this stage, a 3–4 mm diamond drill bit coupled to Kerrison rongeurs is used to remove the anterior arch of C1 that allow to expose the dens, which is then drilled at its base to excise the tip and body of the dens from the remaining vertebral ring. Then removal could often be challenging due to dural and/or bony adhesion depending on specific pathology. The odontoid process could be adherent to the adjacent brain stem and/or spine dura with all associated connective tissue, and a CSF leak might occur. In some cases, instead of an “en-block” resection, an odontoid piecemeal removal may be required. Brain stem decompression is considered satisfactory when a wide dural pulsatile field is achieved (see also Figs. 27.3, 27.4, 27.5, and 27.6).

The reconstruction is completed by the placement of a multilayered Gelfoam/Surgicel and fibrin glue overlied by the pedicled regional paraspinal muscle and muco-pharyngeal flap which is also sealed by fibrin glue. If a CSF leak occurs, the multilayered closure is coupled to fascia lata and fat (for a better comprehension of the technique principal step, see also Video 27.1).