Pressure Inside the Neuroendoscope

Introduction

Endoscopy allows direct vision of brain structures without the need for large cranial openings. Neuroendoscopic transcortical intraventricular approach, adopted in the early 1920s thanks to Walter Dandy among all, has permitted neurosurgeons to access deep structures within both the cranial and spinal compartments thanks to its panoramic views, proximity to the surgical target, and minimization of tissue retraction and brain manipulation.

The development of microneurosurgery in the 1960s initially limited the widespread use of the endoscopic technique, because of its then inferior quality of vision as compared to the microscope, which has consistently provided high magnification and adequate illumination while maintaining stereoscopic visualization. Endoscopic imaging reached an incredible high quality standard only 20 years ago. From then neuroendoscopy has become a subspecialty in neurosurgery; it has developed as a result of the versatility and applicability of the neuroendoscope to a multitude of neurosurgical approaches. One of the main limitations to its widespread use in neurosurgery still stems from drawbacks due to handling of the endoscope, cumbersomeness related to the camera and light cable connections, and manoeuvrability inside the skull.

Indications and Procedures

From a clinical standpoint, intraventricular neuroendoscopy was vitalized by popularity of the endoscopic third ventriculostomy (ETV) for the treatment of obstructive hydrocephalus (HD), endoscopic marsupialization of arachnoid cysts, and/or colloid cyst resection inside the third ventricle. Neuroendoscopy has also shown great utility in different areas of the brain, outside of the ventricular system. At the present time, it is used for neurosurgical treatment of many diseases, including skull base tumors, vascular lesions, spine and peripheral nerve pathology, and craniosynostosis, because the endoscope has offered the great advantage of reaching deep areas and bringing the surgeon’s eyes close to the relevant anatomy, while minimizing brain manipulation and retraction.

Intraventricular neuroendoscopic biopsy has a very good diagnostic yield and reasonably low complication rate and has become the first-line modality for this procedure. Neuroendoscopy seems most advantageous for the diagnosis of intraventricular lesions where cerebrospinal fluid (CSF) diversion is an additional therapeutic requirement. These conclusions are supported by a meta-analysis by Somji et al. A total of 30 studies with 2069 performed biopsies were included; remarkably, these biopsies were performed concurrently with at least 1 other procedure in 82.7% (n = 1252/1513) of procedures. Germ cell tumors [26.6% (n = 423)], astrocytomas [25.5% (n = 406)], and nonneoplastic lesions [12.4% (n = 198)] accounted for most of the reported intraventricular lesions. The combined major morbidity of 17 studies reporting 592 total biopsies was 3.1% [95% confidence interval (CI) 1.9–5.1%]. The combined mortality of 22 studies reporting 991 total biopsies was 2.2% (95% CI 1.3–3.6%).

Intraventricular tumors may present technical challenges because of their deep location and proximity to critical neurovascular structures. Microsurgery remains the gold standard for the resection of intravascular tumors, but purely neuroendoscopic gross total resection of this type of tumors has been shown to be an effective surgical approach in carefully selected cases. They often cause CSF pathway obstruction, resulting in ventricular dilation, which provides sufficient space for maneuvering with the endoscope. The general principle of the endoscopic removal of intraventricular tumors is interruption of the blood supply to the tumor and subsequent tumor debulking.

In pineal region tumors, which cause occlusive HD due to aqueductal compression, third ventriculostomy as well as tumor biopsy are required.

ETV has a high success rate and is becoming the treatment of choice for noncommunicating HD. When indicated, a ventriculocisternostomy is done to communicate the lateral ventricles and the third ventricle to the cisterns and the subarachnoid spaces. A hole is made in the lamina quadrigemina at the floor of the third ventricle where it directly communicates with the interpeduncular cistern, and a Fogarty is passed through the hole to build a permanent communication. Probably there is a subset of patients with idiopathic normal pressure HD with a high-grade stenosis at the aqueduct of Silvius and differences between the outflow resistances measured above and below the aqueduct that can benefit from ETV.

Neuroendoscopy has also been used to review malfunctioning shunts, to treat infective HD secondary to tuberculous meningitis and intraventricular hemorrhage. Other interventions include endoscopic removal of intraventricular nontumoral lesions such as neurocysticercosis, hematomas, and hypothalamic hematomas, and choroid plexus cauterization.