• Neuro-Ophthalmology/Orbit

    Investigators have shown that using intraoperative computed tomography (iCT) can improve control of tumor excision, allowing a maximal safe resection, especially in patients with osseous tumor parts and masses within the orbit.

    Neuronavigation system (NNS) guided neurosurgery has shown great success in optimizing surgical approach planning and increasing the amount of resection in patients with skull-based tumors. In other parts of the cranium, the addition of intraoperative CT scanning (iCT) has demonstrated increased precision and safety by quickly and accurately aligning the NNS spatial model with the patient’s anatomy when they are on the surgical table, and updating after position-dependent brain shift. The authors evaluated this combination approach in 23 patients with skull-based tumors involving the orbit, sphenoid wing or cavernous sinus.

    Pre-surgical imaging, either contrast-enhanced, high resolution cranial MRIs (performed the day before surgery when possible) or a DOTATOC-PET scan (for cases of extensive and/or recurrent meningioma) were uploaded into the NNS software. In the operating room, a iCT scanner took baseline images to coordinate the navigation to the patient. After initial resection, a second intraoperative iCT was performed to determine if further removal of tumor tissue was necessary.

    The authors found that intraoperative imaging changed the surgical approach in more than half (12/23) of the patients, leading to removal of more tumor tissue than a standard approach. In 6 cases, the second iCT revealed remaining tumor tissue not seen in situ, and in 3 cases tissue was discovered that had been hidden by overlay of osseous tumor. In instances of intraorbit tumor, iCT after insertion of a contrast-agent soaked cotton pad helped localize the mass and define previously unseen margins. In addition, a second iCT led to better decompression the optic nerve for 5 patients.

    Histopathological examination of the masses showed meningioma in the majority (82.6%) of patients, followed in prevalence by sarcoma (8.7%), chondrosarcoma (4.3%) and neurinoma (4.3%). Surgical complications were minimal: 2 patients developed subgaleal CSF requiring intervention, and no new cranial nerve or oculomotor deficits were observed.

    Two patients, both with meningioma WHO Grade I, have required subsequent removal surgery 4.5 and 4.9 years after initial operation. Initially, 9 of the 23 (39%) patients had undergone at least 1 operation for recurrent tumor growth.

    Postoperatively, visual acuity and/or visual field defects remained stable or improved in 83% of patients. Exophthalmos resolved or was significantly reduced in 11 of the 13 patients who presented with it.

    The current results indicate these technologies may increase the extent of maximal safe resection for complicated cases that previously carried high risk of morbidity, such as skull base tumors involving bone, dura mater and the orbital system. The authors propose further studies to determine if NNS/iCT guided surgery significantly reduces complications and rates of recurrence in a larger cohort.