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An 11-year-old male child presented with worsening vision in his left eye. Examination and imaging revealed a left optic nerve tumour causing mass effect and optic neuropathy, without systemic evidence of neurofibromatosis. In view of the significant risk to visual acuity, a biopsy was deferred and chemotherapy was commenced. After initial stability, continued visual decline necessitated incisional biopsy. Surgical navigation was used to facilitate minimal access surgery avoiding bone removal. The system also precluded biopsy of cystic parts of the tumour, allowing successful intraoperative frozen-section confirmation of lesional tissue. Our case report serves to highlight specific circumstances where surgical navigation may be a useful tool for the orbital surgeon.
An 11-year-old male child presented with a 3-month history of blurred vision in his left eye. He had no other visual or systemic symptoms. His medical history was unremarkable. He had an ocular history of bilateral optic disc drusen (Fig. 1A) that had remained stable with no effect on visual acuity or optic nerve function on previous reviews. On this examination, his vision was 20/20 right eye and 20/50 left eye. He had loss of color vision and an inferior visual field defect in the left eye on automated testing. He also had a left relative afferent pupillary defect with 2 mm of proptosis by Hertel exophthalmometery. Fundus examination showed severe edema of the left optic nerve (Fig. 1B). An urgent magnetic resonance imaging (MRI) was performed on the day of presentation and revealed a heterogeneously enhancing mass involving the intraorbital left optic nerve with minimal extension to the intracanalicular and prechiasmatic segments (Fig. 2A). Based on typical imaging features, a presumptive diagnosis of optic nerve glioma was made. Orbital biopsy was discussed between the patient, parents, and multidisciplinary team, but deferred because of the significant risk of iatrogenic worsening of vision in the affected eye.
The patient was started on vinblastine and followed closely. For 5 months, the patient’s visual acuity and field remained stable and the optic nerve edema steadily improved. Six months after starting treatment, the patient noted a decrease in his vision. Examination revealed a 2-line loss of visual acuity, worsening of the visual field loss, and recurrence of the optic nerve edema. There was enlargement of the tumour on MRI with more posterior extension. The chemotherapeutic regimen was changed to vincristine and carboplatin.
In the 3 months after the change of chemotherapy, the patient’s visual function continued to progressively decline, eventually reaching 20/1250, with severe, generalized loss of visual field. Repeat MRI showed a significant increase in the size of the prechiasmatic/chiasmatic component of the tumour with patchy T2/FLAIR nonenhancing hyperintensities extending into the bilateral optic tracts, hypothalamus, and internal capsules (Fig. 2B). The patient also developed a temporal visual field defect in the previously unaffected right eye.
On account of the worsening of visual function and enlargement on MRI, an orbital biopsy of the tumour was arranged. This was performed through a transconjunctival medial approach via an intraconal route; however, it was nondiagnostic as the tissue sample was found to contain only thickened dura with no lesional tissue. A further multidisciplinary meeting, including neurosurgery, oncology, and ophthalmology, concluded that a combined-approach tumour resection would present considerably morbidity to the patient and risk vision damage in the contralateral eye. It was agreed that a diagnostic incisional biopsy via a lateral orbitotomy with bone removal would allow further management options to be considered. At this point, consideration was given to the use of surgical navigation available within the unit.
The Medtronic Stealthstation S7® Surgical Navigation System uses an electromagnet placed in close proximity to the site of surgery that calibrates using a tracker in relation to preuploaded patient computed tomography (CT) and MRI images. This tracker can also be used intraoperatively to ascertain position within the surgical field. We used a lower eyelid swinging approach and, by use of surgical navigation, were able to avoid bone removal and visualize the optic nerve tumour (Fig. 3). Furthermore, the use of the tracking system allowed us to avoid cystic parts of the tumour (Fig. 4A) and biopsy solid lesional tissue (Fig. 4B). Neurosurgical forceps and scissors were used for incisional biopsy. Intraoperative frozen section confirmed that we had a true biopsy and the surgical site was close with minimal postoperative morbidity to the patient. Histopathology demonstrated a low-grade astrocytoma that was glial fibrillary acidic protein (GFAP) and neurofilament (NF) stain positive but BRAF negative, the latter precluding the use of currently experimental chemotherapy. Unfortunately, postbiopsy, the patient’s vision declined to no perception of light in the affected eye. This was most likely from anticipated biopsy trauma to the compromised optic nerve. The patient continues to be managed on a combined chemotherapy regimen with no further surgery currently planned.
Computer-assisted surgery (CAS) or surgical navigation was developed at the turn of the century and is now in widespread use in many surgical disciplines. It is based on accurate image-based modeling of the patient usually through CT, MRI, or ultrasound. These images are processed and allow preoperative planning as well as surgical simulation. Certain systems allow the use of a probe intraoperatively to provide correlation between anatomical sites and preoperative imaging. The addition of robotic surgery to this concept allows for novel uses such as remote surgery and minimally invasive surgery.
The use of CAS for the surgical management of deep orbital apex tumours has been described in the literature.
Neuronavigation has been translated from specialties such as ENT surgery and neurosurgery and applied to patients requiring orbital decompression, sphenoid wing meningioma excision, and frontoethmoidal osteoma sino-orbital approaches.
The key benefits are preoperative planning through systems that simulate surgical approaches, improving safety when performing surgery near critical structures and ensuring intraoperative surgical targets (such as required depth of decompression or relationship to tumour margins). Lee et al. describe 2 patients in whom CAS complimented the surgical approach in providing optimal surgical access, minimal tissue manipulation, and safe execution of the procedure.
The latter was particularly evident in a patient requiring orbital decompression as it allowed safe maximal removal of bone through a posterolateral approach. They comment on how the use of CAS may be particularly valuable to the surgeon beginning to perform deep posterolateral orbital decompression in enhancing surgeon confidence that adequate bone removal has been achieved. They describe the initial transition from frame-based to frameless systems allowing better access to surgical sites. There are now a variety of systems available providing different advantages such as reduced setup time, less interference with other instrumentation/devices within the operating room, and better user interface.
Intraconal orbital lesions may remain undetected until growth causes compromise of critical adjacent structures such as the optic or other cranial nerves, or sufficiently noticeable globe displacement. Incisional or excisional biopsy is also hampered by this relationship and the risk of inadvertent damage to these structures. Certain tumours may also have ill-defined margins and distort normal local anatomy. Bruneau et al. described a mirroring technique using navigation guidance whereby the side of normal anatomy is projected intraoperatively to the operated side, allowing delineation of likely similar relationships.
This could be a useful guide in cases of suspected altered anatomy. Meningioma is the most common tumour entity in the skull base region and complete resection remains the most important therapeutic step to avoid recurrence. CAS can help achieve this main goal of surgery while preserving important neurological function.
In our case, CAS precluded the need for bone removal during lateral orbitotomy while ensuring that cystic areas of the tumour were avoided at incisional biopsy.
We describe the feasibility and success of CAS as a tool in improving the management of specific orbital pathology. It would be prudent for surgeons not to become reliant on this potentially expensive and extraneous technology, but rather consider it an option for complex cases with abnormal anatomy or increased morbidity to the patient.
The authors have no proprietary or commercial interest in any materials discussed in this article.