Over the last 3 decades, the endoscope has become a highly valued visualization tool in neurosurgery, applicable to a broad range of neurosurgical procedures. Following the pace of technological innovations, the quality of the instrumentation has greatly improved along with the status of endoscopy in the neurosurgical field. The use of the endoscope in interdisciplinary extended transnasal approaches revolutionized skull-base surgery.1 Transcranial neurosurgery took advantage of the endoscope for inspection, endoscope-assisted, and endoscope-controlled procedures, although the main visualization tool during these interventions remains the operating microscope.
At present, endoscopy has applications in a variety of neurosurgical procedures including transnasal approaches for pituitary and other skull-base tumors, third ventriculostomy, and resection of intraventricular tumors. The range of application is expanding to include extracranial procedures such as peripheral nerve and spine surgery.
Hopf and Perneczky2 defined the terminology regarding endoscopic procedures and divided them into 3 categories:
Pure endoscopic neurosurgery, ie, procedures performed through working channels under complete endoscopic visualization and with endoscopic instrumentation (Figure 1).3
Endoscope-controlled microsurgery, ie, operations performed with standard microsurgical instruments under endoscopic visualization—the microscope is not used (Figure 2).
Endoscope-assisted neurosurgery, ie, the use of both microscope and endoscope during the same intervention. In endoscopic inspection the endoscope is solely used as an adjunctive tool for visualization and not for surgical manipulations.
Enhanced area and surgical dissection
Technical innovations are probably the major reason for the growing role of endoscopy in neurosurgery over the last 3 decades.4 High-definition imaging, neuronavigation, new instruments, an interdisciplinary approach mostly with ear, nose, and throat (ENT) surgeons, and detailed anatomic studies led to the breakthrough of endoscopic endonasal extended approaches in skull-base surgery.5
These endoscopic techniques allow the neurosurgeon to optimize tumor resection, increasing the area of surgical dissection without increasing the size of the surgical approach, thereby limiting perioperative morbidity due to surgical manipulation of eloquent brain structures. Endoscopy offers direct illumination of the operative field, magnification, and the ability to look around corners with angled optics.
However, while angled endoscopic optics provide various visual perspectives, the surgical issue is not only to see but also to work on and around remote structures. Microsurgical endoscope-assisted manipulations require optimal working angles that are guaranteed only by a sufficiently large craniotomy. As an example, a dissection study by Chaynes et al6 highlights that a craniotomy that is too narrow often hinders a sufficient exploration of the entire cerebellopontine angle. Most neurosurgeons are familiar with the operating microscope. The microscopic field of inspection is 3-dimensional (3D) and of high quality. However, the light stream is straight and thus limited in the narrow and angled corridor of the cerebellopontine angle or in the perimesencephalic cisterns. In these situations, the angled optic of the endoscope offers the advantage of being able to look around the corner with the appropriate amount of direct illumination.7