Rationale

• Expanded endonasal approach (EEA) is a minimally invasive, endoscopic technique increasingly utilized to allow access to the ventral skull base from crista galli to the odontoid (Fig. 1) and laterally as far as the middle/infratemporal fossae, without disturbing the face or skull.
• This technique has the advantage of avoiding the retraction or transgression of important neurovascular structures that traditional posterior or lateral approaches cross.

Fig.: Fig. 1. Sagittal CT reconstruction in a patient with a large calcified meningioma demonstrates the extent of rostral and caudal reach of EEA. The Kassam line (K-line), is drawn from the nasal bridge through the back of the hard palate and defines the most caudal reach of EEA.

Sella and Parasellar Lesions

• Sella and parasellar lesions are among the most commonly accessed lesions using EEA.
• Traditional pterional and subfrontal approaches to the sella are limited by the optic chiasm from above.

Surgical Technique

• Two surgeons (neurosurgeon and otolaryngologist) employ a binarial approach (Fig. 2).

Fig.: Fig. 2. Photograph showing binarial approach.

• All EEAs begin with an intial exposure, which creates a single large rectangular space within the sphenoid sinus. This cavity is accomplished by performing wide bilateral sphenoidotomies, resecting a small portion of the posterior nasal septum, and resecting the right middle turbinate.
• For sella/parasellar lesions, the sphenoidotomy is extended to include the lateral sphenoid recess beyond the level of the carotid canal and rostrally to the posterior ethmoid air cells, and the floor of the sphenoid is resected back to the level of the clivus.
• Key to EEA is careful preoperative planning and intraoperative guidance with special attention to sinus anatomy and its relationship to the skull base.
• Ultimate goal is complete resection, but often this is not possible. In these cases, tumor debulking and cytoreduction are performed in order to decrease mass effect and patient symptoms.

Anatomy

• Following surgical exposure, the next step is identification of key anatomical landmarks (Figs. 3 and 4), which help guide the surgeons to stuctures that lie deep to the osseous skull base.

Fig.: Fig. 3. Endoscopic view following surgical exposure for sella/parasellar approach with key anatomical landmarks. ON = optic nerve; LOCR = lateral opticocarotid recess; MOCR = medial opticocarotid recess; ICA = internal carotid artery.

Fig.: Fig. 4. Illustration of key neurovascular structures as viewed endoscopically during surgery. mOCR=medial opticocarotid recess; ICA=internal carotid artery. Also note the vidian nerve (VN) within the vidian canal, a key anatomic landmark for resection of lesions beyond the sella/parasellar region.

• Medial opticocarotid recess (mOCR): Osseous indentation between the carotid canal, traveling vertically adjacent to the sella, and the optic canal, traveling in an AP-oblique orientation (Figs. 5A-C)
• • Drilling posteriorly through this recess, one encounters the middle clinoid process, representing the lateral border of the anterior sella
  • Careful and complete removal of bone to the level of the mOCR exposes the paraclinoid ICA as well as the optic nerves within the optic canal.
  • As a result, less medial retraction of tumors is necessary and the risk of neurovascular injury is reduced

Fig.: Fig. 5A. Axial CT image shows the carotid canal containing the paraclinoid internal carotid artery (curved arrows) caudal and slightly lateral to the mOCR. SS=sphenoid sinus.

Fig.: Fig. 5B. More cranially, axial CT image illustrates the middle clinoid processes (arrowheads) immediately deep to the medial opticocarotid recesses (arrows). This relationship is key for a safe surgical approach to the sella/parasellar region.

Fig.: Fig 5C. Further cranially, axial CT image shows the optic canals (curved arrows) superior to the mOCR. Anterior clinoid processes (arrowheads) are also seen.

• The anatomic relationship of pathology to ossesous structures of the sella and posterior sinuses (Figs. 6 and 7) is essential to preoperative planning.

Fig.: Fig. 6. 3D volume-rendered image of the osseous skull base as viewed from above. Note the relationship of the middle clinoid process, which lies deep to the mOCR.

Fig.: Fig. 7. Sagittal CT reconstruction image illustrates the anatomic relationship of the planum sphenoidale (arrowhead), tuberculum sellae (curved arrow) and dorsum sellae (straight arrow). SS=sphenoid sinus, C=clivus

• Soft tissue structures are generally better assessed with MRI, as illustrated in this patient with a pitutary microadenoma (Fig. 8).

Fig.: Fig. 8. Coronal and sagittal post-contrast T1-weighted MR images illustrate neurovascular anatomy of the skull base in a patient with a left inferior pituitary microadenoma (asterisk). The pituitary gland (white arrow) and infundibulum (thin arrow) are minimally displaced, and the anterior cerebral arteries (arrowhead) and optic chiasm (curved arrow) are nondisplaced.