Transoral Neurosurgery

Posted by Dr. Thamburaj Dr. Thamburaj
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The transoral route is chosen ideally for extradural lesions confined to the clivus, the C-V junction, and the upper cervical vertebrae, basilar invagination. We can plan the extent of exposure step by step orienting it centrally first and extending it to the periphery as required depending on individual requirement.

Trans-pharyngeal odontoidectomy:
The most common procedure is trans-pharyngeal odontoidectomy. It is ideal for accessing the midclivus down to the level of the C2 vertebral body and laterally for 2 cm to either side of the midline.

Essential steps of the procedure:
 The patient is positioned supine with the head extended and skull traction in place. Alternatively, the head may be immobilized in the Mayfield frame.
 Endotracheal intubation with a flexometallic tube positioned at the side of the mouth is adequate; some surgeons prefer routine tracheostomy.
 The mouth is kept open with a gag that rests against the upper dental arch and depresses the tongue (tonsillectomy retractor).
 A rubber catheter may be used sometimes to retract the uvula and soft palate. Oral irrigation with an antiseptic solution is carried out.
 The posterior pharyngeal wall is infiltrated with 1/100,000 adrenaline solution.
 The soft palate may be retracted with stay stitches and the posterior pharyngeal wall is exposed; the soft palate may be split to gain better exposure.
 The posterior wall of the pharynx is incised with cutting diathermy from the roof down to C2-C3 disc or as required. Palpation of the anterior tubercle of the anterior arch of the atlas helps to keep the incision to midline.
 The prevertebral muscles are carefully dissected from the lower clivus, the arch of the atlas, and the C2 body on the subperiosteal plane.
 The arch of the atlas and the dens of the axis are drilled away. Lateral exposure at this level should not exceed 1.5 cm to avoid injury to the vertebral arteries. A median corpectomy of the body of C2 (about 1 inch in diameter) down to the C2-C3 disc level is recommended as a routine.
 Removal of the dens will expose the transverse limb of the cruciate ligament and residual alar and apical ligaments. This may be removed along with the lower most caudal tip of the clivus for better decompression.
 The pharyngeal wall may be closed in a single layer with absorbable suture material. The palate is closed in a single layer as well, if it had been split.



Transmaxillary approach:
Indicated or extradural tumors extending into the sphenoid and the upper and middle clivus with minimal lateral extension with inferior limit at the atlas level; but C2 vertebral body can also be accessed if maxilotomy is performed.

Essential steps of the procedure:
 The head maintained in traction
 An elective tracheostomy is necessary.
 A standard Le Fort I horizontal mucoperiosteal incision is made above the mucogingival reflection from the first molar tooth on either side, and the soft tissues are reflected subperiosteally to expose the anterior and lateral walls of the maxilla.
 The incision for the maxillary drop-down procedure starts at the lateral-most aspect of the anterior nasal cavity and extends to the buttress laterally beneath the infraorbital nerve exit as well as above the roots of the canine teeth. It is important to place the miniplates before the maxilla is sectioned, as precise location of the maxilla after osteotomy is essential if postoperative malocclusion of the teeth is to be avoided.
 Downfracture is completed with exposure of the nasal mucosa and the septum.
 The downfractured maxilla may be split in the midline, if necessary, and the halves rotated outward after the mucosa has been separated.



Transmandibular approach:
It is indicated for further exposure down to the C4 and for anterior lesions that have a paramedian extension.

Essential steps of the procedure:
 The head maintained in traction.
 An elective tracheostomy is necessary.
 A midline incision from the lower lip to the hyoid bone is made.
 A steplike osteotomy of the midline mandible. Removal of the central incisor tooth is not essential.
 Retention sutures are then placed on either side of the tip of the tongue to retract it superiorly.
 An electrocautery cutting apparatus is used to incise the tongue along the median raphe to the midline epiglottic fold posteriorly. The incision is extended anteriorly through the floor of the mouth between the orifices of the submaxillary glands and inferiorly to the hyoid bone.
 The mandibular lingual halves are spread laterally and held in place by self-retaining hinged scalp retractors.
 The exposure now can be carried down to the fifth cervical vertebra.
 Pharyngeal exposure is made in the midline; a pharyngeal flap is used for the entire exposure.
 The operation may then be accomplished as described for the transoral procedure.
 The posterior pharyngeal closure is made in layers.
 Next, the dorsum of the tongue is sutured from posterior to anterior. The intrinsic lingual musculature is brought together with 2-0 polyglycolic interrupted sutures, and the ventral surface of the tongue and the floor of the mouth are closed, in this order.
 The mandibular osteotomy is repositioned and held in place with miniplates.
 


Post operative Stabilization:
Despite the severe degree of abnormalities seen, the rate of instability after the ventral deformities are resected by the transoral approach is not always associated with initial instability; therefore, posterior occipitocervical fusion may not be necessary.
Congenital anomalies are more stable than rheumatoid or traumatic dislocations; 25% of my pts did not require stabilization, despite adequate decompression, as suggested by their clinical improvement.
I do not excise ligamentous structures, if stabilization is not planned.

Nevertheless, it is generally accepted that a stabilization procedure is necessary following anterior decompression either in the same sitting or as a 2nd stage procedure. Radiological assessment of instability is extremely difficult after ventral decompression as the bony landmarks (anterior arch of atlas and dens) have been excised. Posterior fixation techniques is the mainstay.

In my experience, absolute indications for stabilization are
 History of precipitating trauma,
 Symptoms suggestive of instability, such as suboccipital pain (occipital neuralgia), and worsening deficits on neck flexion,
 Radiological suggestion of instability,
 Patients under 40 years of age,


Ideal stabilization system is yet to come.
After 20 yrs of CVJ surgery, I prefer Occipito-cervical old fashioned wires and rods for stabilization(including the above two extensive decompressions). They provide adequate stability and preserve satisfactory neck movements, unlike the currently popular transpedicular and transarticular screws which provide the maximum stability but the resultant, near total, obliteration of motion is not accepted by many patients. They may require cervical collar for longer period than the pts with pedicle/ lateral masas screws
That’s why, perhaps, the companies are coming up with dynamic screws!  


To support my views I give following refs


Menezes AH, VanGilder JC: Transoral-transpharyngeal approach to the anterior craniocervical junction. Ten-year experience with 72 patients. J Neurosurg 69:895–903, 1988

Dickman CA, Locantro J, Fessier RG : The influence of transoral odonotoid resection on stability of the craniovertebral junction. J Neurosurg 1992; 77 : 525-530.

Dickman CA, Crawford NR, Brantley AGU, Sonntag VKH. Biomechanical effects of transoral odontoidectomy. Neurosurgery, 1995; 6:1146-1153.

Dickman CA, Crawford NR, Brantley AG, Sonntag VK. Biomechanical effects of transoral odontoidectomy. Neurosurgery. 1995 Jun;36(6):1146-52; discussion 1152-3.

Dickman CA, Crawford NR, Paramore CG: Biomechanical characteristics of C1-2 cable fixations. J Neurosurg 85:316–322, 1996.

Naderi S, Crawford NR, Song GS, et al: Biomechanical comparison of C1-C2 posterior fixations: Cable, graft, and screw combinations. Spine 23:1946–1955, 1998

Song GC, Cho KS, Yoo DS, Huh PW, Lee SB. Surgical treatment of craniovertebral junction instability : clinical outcomes and effectiveness in personal experience. J Korean Neurosurg Soc. 2010 Jul;48(1):37-45. Epub 2010 Jul 31.

Mummaneni PV, Haid RW. Atlantoaxial fixation: overview of all techniques. Neurol India. 2005 Dec;53(4):408-15. Review.