Transfacial Approaches to the Craniovertebral Junction
Lesions of the craniovertebral junction (CVJ) and midline skull base can be accessed through facial routes by application of craniofacial surgical techniques.1–41 Paul Tessier′s well-established principles for correction of congenital anomalies are fundamental42: (1) the craniofacial skeleton can be stripped of its periosteum, units osteotomized and repositioned, and the fragments still survive; (2) the eyes can be moved without causing visual loss; and (3) combined intracranial and extracranial exposures can be performed without undue risk of infection. Tessier′s principles have proven valuable in allowing removal or retraction of facial skeletal units to access complex lesions of the CVJ and midline skull base.
Single-stage resection with shorter operating times and low morbidity rates are a tribute to these techniques. Direct anterior approaches to the CVJ and midline skull base have several advantages over anterolateral and lateral approaches: (1) the midline plane is relatively avascular; (2) vital neurovascular structures, the temporomandibular joint, and the muscles of mastication are avoided; (3) and wide exposure is possible by degloving, thereby diminishing the need for facial incisions.
Classification of Transfacial Approaches
The anatomical site of lesions of the CVJ and midline skull base guides the level of the transfacial approach. The kyphotic shape of the skull base is perpendicular to the vertical plane of the face and thus requires that lesions that extend anteriorly be accessed from a more superior approach (i.e., through the frontal nasal region), whereas posteriorly located lesions with more superior extension, especially those extending posterior to the sella turcica, be accessed through a more inferior or transmaxillary surgical approach. The most advantageous angle of approach to the lesion is the most important determining factor in selecting the level of transfacial exposure.
We have found it useful to classify transfacial approaches into six levels ( Fig. 24.1 and Table 24.1 ).1,43 The transfrontal (level I) approach yields access to lesions of the anterior cranial fossa. Exposure is achieved by removal of the supraorbital bar ( Fig. 24.2A–C ).
The transfrontal nasal (level II) approach is indicated for lesions of the cribriform plate, nasopharynx, frontal and sphenoid sinuses, and tumors of the clivus that exhibit anterior growth. Vertical access to the midline portion of the anterior foramen magnum is possible. Additional exposure is achieved over the level I approach by retaining the nasal and medial orbital wall complex on the supraorbital bar ( Fig. 24.2D–F ).
Larger lesions of the same region can be accessed with the transfrontal-nasal-orbital (level III) approach. Greater lateral exposure is obtained by the ability to laterally retract the globes. This lateral retraction is made possible by including the lateral orbital walls and orbital roofs on the fragment ( Fig. 24.2G–I ).
The fragments removed in these three intracranial approaches are variations of the supraorbital bar ( Fig. 24.3 ). The subfrontal access achieved by the removal of the supraorbital bar is extended vertically to include the entire midline skull base to the CVJ by retaining the nasal complex and medial orbital walls on the supraorbital bar. Greater horizontal exposure is achieved by adding the lateral orbital walls and orbital roofs to the fragment.
Wider posterior exposure with the level II and III approaches can be achieved with a circumferential cribriform plate osteotomy ( Fig. 24.4 ).44 This osteotomy allows retraction of the cribriform plate. Preservation of the cribriform plate is possible when the region is not involved with tumor. Its preservation also has the advantages of preserving olfaction, diminishing the incidence of cerebrospinal fluid (CSF) leak, and simplifying skull base reconstruction.
The transnasomaxillary (level IV) approach provides wide extracranial exposure of the entire midline skull base and CVJ, allowing resection of large nasopharyngeal, paranasal sinus, or clival lesions that extend in any direction. The upper cervical vertebrae are readily accessible through this route for tumors that extend into these regions. Exposure is achieved through a modified Weber-Ferguson incision and a LeFort II osteotomy. The fragment is split at the nasal process on one side and at the palatal midline ( Fig. 24.5A–D ).
Clival and CVJ lesions with superior and inferior extension and moderately sized nasopharyngeal lesions can be accessed via the transmaxillary (level V) approach. The exposure is accomplished through a LeFort I osteotomy with or without a palatal split. This exposure provides a good angle of view for clival lesions that extend superiorly behind the sella turcica and for CVJ lesions that extend to the upper cervical vertebrae ( Fig. 24.5E–G ).
The transpalatal (level VI) approach provides access to the lower clival and CVJ region for resection of small lesions. The hard palate is removed and the soft palate is split to provide this exposure ( Fig. 24.5H–J ).
The extracranial approaches are variations of maxillary osteotomies. Increasing exposure is possible as more of the maxilla is removed ( Fig. 24.6 ). Although the transnasomaxillary approach provides exposure of the entire midline skull base, the transmaxillary approach provides access to the lower half and the transpalatal approach to the lower third of the skull base. The overlapping exposure shared by these six approaches provides great flexibility. Each can be used in isolation, or the intracranial and extracranial approaches can be combined to allow simultaneous intracranial and extracranial tumor resection.
Technique
Intracranial Approaches
Preoperative Workup
After a thorough understanding of the patient′s clinical presentation and deficits related to the tumor, additional workup should include cephalometric X-rays, computed tomography (CT) with true coronal cuts of the orbits, magnetic resonance imaging (MRI), and life-size photographs.
Informed Consent
Counseling is essential to relate the potential risks and complications as well as the expectations and limitations of the procedure. In addition to the risks associated with a craniotomy, these risks include possible alteration of orbital adnexal function, such as alteration of blink dynamics, tear production or drainage, extraocular muscle imbalance, visual loss, and altered globe position within the orbit. The patient can lose olfaction or experience diminished facial sensation, either temporarily or permanently. Furthermore, brow weakness or paralysis is possible, as well as a change in the orbital nasal configuration. The latter is only significant when major soft tissue and skeletal resection is needed to achieve complete removal of the tumor. When temporalis and frontal galeal muscle flaps are utilized, soft tissue contour defects can be noted in the forehead and temporal fossa regions.
Patient Positioning
The patient is positioned on the operating table in the supine position, and general anesthesia is induced utilizing an orotracheal tube. The tube is secured to the lower dentition with a 26-gauge wire to assure a secure airway, as well as to eliminate the need for any tape that could obstruct the surgeon′s view of the face. After monitoring lines and intravenous lines are placed, the patient is given prophylactic antibiotics and a lumbar drain is placed, if indicated. If the dura is opened intraoperatively, the lumbar drain reduces the postoperative incidence of CSF leaks and infections. The patient′s head is positioned in a Mayfield headholder. A localizing device, such as the Stealth-Station S7 (Medtronic Navigation, Louisville, Colorado), is useful intraoperatively. The wand is clamped directly on the Mayfield frame and sterilely draped. The pins of the Mayfield skull fixation device are positioned posterior to the ears to allow a posteriorly positioned bicoronal skin incision. After electroencephalographic (EEG) leads are placed and fiduciary reference points for the localizing wand are confirmed, the patient′s face and scalp are prepared and draped. Temporary tarsorrhaphy sutures of 5–0 cardiovascular silk are placed in the eyelids to protect the corneas.
Incision
The bicoronal incision is positioned in the middle or posterior aspect of the calvarium to preserve adequate length of pericranial and frontal galeal flaps for use in the skull base reconstruction after the tumor resection.
Dissection
The anterior scalp flap is reflected by microneedle dissection,45 as it is more hemostatic and preserves the important pericranial and temporalis tissues for possible use as flaps. The scalp flap is reflected to the superior orbital rims on either side, then inferiorly into the temporalis region beneath the intermediate temporalis fascia to avoid the innervation of the frontalis muscle. The pericranial flap can be based either anteriorly, preserving its axial blood supply, or laterally on the temporalis muscle. The pericranium is scored against the calvarium at the midline or asymmetrically if it is anticipated that a laterally based pericranial flap of greater length will be needed from one side. The entire pericranium can be mobilized from one temporalis muscle, if needed. Even if the pericranial flap is not needed for skull base reconstruction, its attachment to the temporalis muscles is useful in reattaching the temporalis muscles in their anatomical position in the temporal fossa ( Fig. 24.7 ).
For level II and III exposures, the pericranium and temporalis muscles are reflected, the periorbita is stripped 360 degrees, and the periosteum in the region of the nasal process of the maxilla is stripped. Great care is taken to preserve the nasolacrimal ducts. The medial canthal ligaments are detached from the bone or, if desired, a small island of bone, attached to the medial canthal ligament, can be preserved to facilitate reattachment. The upper lateral nasal cartilages are detached from the undersurface of the caudal margin of the nasal bones. The nasal mucosa is dissected from the underside of the nasal bones.
Bifrontal Craniotomy
The bifrontal craniotomy is performed, and the dura is retracted from the anterior cranial fossa. If the cribriform plate is to be preserved, the posterior margin of the bifrontal craniotomy must be positioned at the level of the coronal suture, and the cranial osteotomy must extend laterally and inferiorly to the skull base in the temporal region. This configuration is necessary to allow the reciprocating saw to be positioned perpendicular to the planum sphenoidale.
Osteotomies
After the soft tissue dissection is completed, a sterilized pencil is used to mark the facial and cranial osteotomy lines. For the transfrontal-nasal-orbital (level III) approach, lines are marked along the lateral orbital walls from the inferior orbital fissures superiorly. The lines continue along the inferior margin of the temporal limbs of the supraorbital bars ( Fig. 24.4B ). The lines are usually positioned ~2 cm posteriorly from the superolateral orbital rim. Lines are also marked from the superior margins of the zygomatic arches to the inferior orbital fissures in the region of the inferolateral orbital floors. Medially, a line is drawn across the nasal process of the maxilla, brought anteriorly and medially to the nasolacrimal ducts, and then positioned posteriorly along the lower aspects of the medial orbital walls to within 1 cm of the optic canals. The line then extends superiorly along the medial orbital wall onto the orbital roof to maintain most of the orbital roof on the fragment. This orbital roof osteotomy extends laterally to intersect with the lines on the lateral orbital walls.
The frontal lobes are retracted gently, and an extradural exposure of the floors of the frontal and middle fossa is performed. Parasagittal osteotomies are planned lateral to each cribriform plate, posteriorly in the region of the planum sphenoidale, and anteriorly in the region of the crista galli. The same lines are placed symmetrically on the opposite side ( Fig. 24.4A ).
Before the osteotomies are made, small plates are bent for passive adaptation across the planned osteotomy sites in the region of the zygomatic arch and lateral orbital wall. Drill holes are placed, and the plates are labeled and set aside.
The osteotomies are then performed in the same order on both sides. Great care is taken to preserve the periorbita and dura, as well as the nasolacrimal duct and nasal mucosa. After the osteotomies are completed with a reciprocating saw, an osteotome is positioned anteriorly and inferiorly through the crista galli osteotomy site to separate the bony septum. The entire single fragment can now be mobilized and removed ( Fig. 24.2G ).
Related posts:
Posterior Neuroendoscopic Applications at the Craniovertebral Junction
Brief Overview of Surgical Approaches to the Craniovertebral Junction
Stereotactic Methods of Localization and Image-Guided Surgery
Approaches to the Jugular Foramen
Bypass Options for the Posterior Fossa
Suboccipital and Retrosigmoid Approaches
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