ONG debulking surgery can thus be limited to the orbital component of the glioma, leaving a minimal portion of the tumor in the most posterior apex (if necessary) to minimize risk of postoperative cranial nerve injury (with the exception of the optic nerve itself). We have approached surgery via a standard lateral orbitotomy. This involves a modified eyelid crease incision to the lateral canthus, allowing for good exposure of the lateral orbital rim. The malar surface of the zygoma and orbital rim is incised superiorly and inferiorly and reflected laterally (Fig. 3). This allows for adequate exposure of the orbit. The periosteum is incised and the lateral rectus is retracted, exposing the ONG within the orbit. The tumor is lysed from the posterior globe surface leaving a small (approximately 2 mm) stump of tumor attached to the posterior sclera. The ONG is carefully dissected posteriorly and the tumor is lysed at the orbital apex taking care to leave a small portion of the nerve (if present) at the annulus of Zinn, which is the common tendinous ring surrounding the optic nerve at its entrance at the apex of the orbit. Care is made to preserve dissection over the posterior lateral rectus to prevent an injury to the ciliary ganglion, which can injure the nerves innervating the cornea. In our experience to date in five cases of ONG debulking via a lateral orbitotomy approach alone, we have experienced no complications, with the exception of one case of postoperative esotropia, which resolved within 6 months. Despite the lysis of the ophthalmic artery within the ONG, there were no cases of ocular ischemia, due to the additional blood supply to the eye via the anterior ciliary arteries. All of our five patients to date experienced a significant reduction in relative proptosis, with resolution of pain and improvement in cosmesis (Fig. 2).
The management of ONGs remains challenging and our understanding of their behavior continues to evolve. Treatment is unnecessary for those sporadic and NF1-related ONGs that have not caused vision loss. When children manifest a decline in visual acuity, visual field or significant radiologic progression, chemotherapy with vincristine/carboplatin remains first-line. Fortunately, newer molecularly-target therapies such as MEK inhibitors and bevacizumab show promise in refractory cases and may become more widely used as ongoing phase 2 and 3 trials are completed. Radical surgical resection and radiotherapy, though successful in the past, are associated with high morbidity and should be reserved as a last resort. Debulking surgery can be safe and effective in cases where mass effect causes pain and disfigurement and vision is already limited. As our knowledge and experience with molecularly targeted therapies improves, hopefully the long-term impact and visual morbidity will be reduced for these children.
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