♦ Preoperative
Operative Planning
- Obtain careful history and physical exam for findings associated with neurofibromatosis type 1 (NF-1)
- NF-1 patients with optic nerve/pathway glioma have a better prognosis than those without NF-1
- Some experts advocate expectant management for minimally symptomatic optic nerve tumors in patients with documented NF-1
- NF-1 patients with optic nerve/pathway glioma have a better prognosis than those without NF-1
- Review imaging (magnetic resonance imaging [MRI], computed tomography)
- Determine whether the lesion affects a single optic nerve, both optic nerves, the chiasm alone, or the chiasm and one or both nerves
- Visual field examination
- Ophthalmologic exam: check for gliosis of the optic nerve head
- Pay careful attention to presence of ptosis, proptosis, or limitations of extra-ocular muscle movement
- Carefully review orbital MRI scans to document fusiform enlargement of the optic nerve, as well as lateral oblique views with fat suppression
- To visualize tumor progression radiographically along optic tracts and radiations, consider use of specialized MRI sequences (i.e., fluid attenuated inversion recovery or diffusion tensor imaging)
Special Equipment
- Diamond bit high-speed drill
- Narrow malleable retractors
- Narrow curved Leksell rongeurs
♦ Intraoperative
Unilateral Medial-Frontal Approach
- Appropriate for medial-apical pathology
- For tumors of the optic nerve
- Patient supine, head directly midline
- May be accomplished by a coronal incision (scalp and galea are incised as one) with an osteoplastic flap or a Fraser incision and free bone flap including the orbital rim
- Pericranium should be cut 1 cm above the orbital rim to minimize postoperative lid edema
- If the frontal sinus is entered, it must be repaired by exenterating the mucosa
Tumor Resection
- A linear horizontal incision is made in the dura
- A malleable retractor is placed to reveal the perichiasmatic cistern and allow release of cerebrospinal fluid; minimal retraction is required
- The intracranial optic nerve is inspected to prove the presence of the tumor and note proximity of the tumor to the chiasm
- Intracranial sectioning of the nerve may be performed once the tumor is seen
- Once the optic nerve is seen to be clearly abnormal, the nerve is cut anterior to the chiasm with scissors
- The frontal retractor is then removed and placed in the epidural space to protect the olfactory nerve and frontal lobe
- The orbital roof is then perforated extradurally with a diamond bit high-speed drill
- Perforation is further expanded with the rongeurs, exposing and opening the optic canal
- The periorbita is exposed on unroofing of the orbit and canal; the frontalis nerve should be visible, demarcating the location of the levator and superior rectus muscles
- Periorbita is incised medial to the levator and superior rectus muscle complex
- Malleable retractors and Cottonoids are used in directly approaching the tumor capsule through the orbital fat
- The levator and superior rectus muscles are laterally retracted
- The medial rectus and superior oblique muscles are medially retracted
- Orbital fat is retracted anteriorly toward the globe (it must not be dissected because it protects nerves and vessels hidden from view)
- The levator and superior rectus muscles are laterally retracted
- The optic nerve can be divided anteriorly after the tumor capsule is exposed
- If the tumor is large, it must be debulked through an incision in the capsule
- The optic nerve is then doubly clamped directly behind the globe and sectioned between the clamps
- If the tumor is large, it must be debulked through an incision in the capsule
- The linear periorbital incision is continued through the canalicular dura; as a result, the levator origin will be sectioned because of its medial origin at the annulus
- The optic nerve is then dissected from the annulus of Zinn, and the specimen is removed in one piece
- Hemostasis of the ophthalmic artery is methodically achieved with bipolar cautery
- The levator origin is reattached to the annulus with fine suture in a figure-eight stitch
- The cruciate incision of the periorbita is closed with interrupted suture; Gelfoam is placed over the defect
- The orbital roof can be bridged with a small piece of curved titanium mesh; take care not to constrict the orbit with a flat construct as proptosis will result
- The orbital bridge is covered with Gelfoam and held in place by tenting the dura
- The dura is then closed in a watertight fashion
- Gelfoam is placed over the dural suture line
- A temporary tarsorrhaphy should be placed to protect the cornea from abrasion
- A pressure dressing is used for 3 to 4 days to reduce postoperative proptosis and swelling
- The orbital roof can be bridged with a small piece of curved titanium mesh; take care not to constrict the orbit with a flat construct as proptosis will result
♦ Postoperative
- Once swelling has subsided, the temporary tarsorrhaphy may be removed
- Begin steroid taper on postoperative day 3
- Antibiotics continued for 24 hours
- A postoperative MRI with and without contrast should be obtained within 48 hours for documentation of tumor resection and subsequent response to adjuvant therapy if significant residual tumor is left at the cut terminal margin
- Visual fields assessed in the contralateral eye
- Extraocular muscles can be tested through the closed lid
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