Abstract
Advances in optics, computing, and imaging have encouraged the application of intraventricular neuroendoscopy to a variety of neurosurgical procedures as transcortical third ventriculostomy, biopsy, or tumor retrieval. The advantages include accurate localization of lesions usually inaccessible to conventional surgery, less trauma to healthy brain, blood vessels and nerves, shorter operating time, reduced blood loss, and early recovery and discharge. Although neuroendoscopic procedures are considered minimally invasive, at times it may lead to life-threatening complications and one should be aware of them. Intracranial pressure monitoring and an arterial line are needed to detect and avoid potentially harmful high intracranial pressure secondary to intraoperative intraventricular rinsing. Anesthesia goals remain the same: careful preoperative assessment and planning and meticulous cerebral hemodynamic control to ensure adequate cerebral perfusion pressure. The degree of postoperative care depends on patient factors, intraoperative events, local practice, and postoperative brain imaging.
Keywords
Anesthesia, Cardiovascular complications, Intracranial pressure monitoring, Intracranial surgery, Minimally invasive neurosurgery, Neuroendoscopy, Surgical complications, Transcranial doppler
Keywords
Anesthesia, Cardiovascular complications, Intracranial pressure monitoring, Intracranial surgery, Minimally invasive neurosurgery, Neuroendoscopy, Surgical complications, Transcranial doppler
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.
How Do Neurosurgeons Perform an Intraventricular Endoscopic Procedure?
Careful preoperative planning is needed to assure access to the target while protecting neural structures; for example, a trajectory to a third ventricle lesion must consider both the position of the lesion and access into the third ventricle through the intraventricular foramen without damage to the fornix.
The patient position is usually supine with slight flexion of the neck, or with head up tilt ranging from 45° to 90°. The cranium is fixed in a head frame as a 3-point skull-pin holder. Through a coronal burr hole, the endoscope is introduced into the ventricular system via the frontal horn. This standard approach may not be appropriate when targeting lesions that are located in the atrium or posterior or temporal horns of the ventricles. In unilateral HD caused by obstruction of one foramen of Monro, the burr hole is placed more laterally to get good access to the foramen for biopsy and to the septum for septostomy. When the tumor arises in the anterior part of the third ventricle, the burr hole is made at the coronal suture. When the tumor is located in the posterior part, the entry point is selected more anteriorly to pass the foramen of Monro in a straight line. Many neuronavigation systems provide a method for registering the endoscope as a navigable instrument to facilitate the procedure.
Rigid or flexible endoscopes can be used; they may have a channel for aspiration and a working channel through which a variety of instruments can be passed. Depth of the peel-away introducer is adjusted to the ependyma and confirmed by withdrawing the endoscope. The diameter of the scope versus the diameter of the foramen of Monro must be considered as the size and shape of the foramen of Monro depends on the ventricular caliber and the extent and duration of HD. One of the most important considerations is the maintenance of adequate visualization, so good irrigation is needed to facilitate removal of blood and debris and maintain a clear medium of image transmission and ventricular patency.
The rinsing can be done via a syringe attached to the endoscope channel, or by using a peristaltic pump or a more complex system like a modified centrifugal pump. Irrigation can be crucial in facilitating successful endoscopy, but can be a cause for complications; we must keep in mind that an adequate ventricular outflow is mandatory. Otherwise, an iatrogenic elevation of intracranial pressure (ICP), potentially harmful if not recognized, will occur. Intraoperative visual signs of increased ICP include pale appearance of the parenchyma and loss of pulsation, which can present earlier than the hemodynamic signs. There are different outflow methods including use of a ventricular catheter that is open to drain, use of a sheath that is larger than the endoscope, use of one of the endoscope working channels as an outflow port, or allowing backflow of irrigation.
A variety of techniques can be used to control bleeding, but the most important factor is the maintenance of visualization with adequate and safe irrigation. If bleeding cannot be brought under control, then the surgical team must be prepared to abort the procedure and leave an external ventricular drain or to convert to an open craniotomy.
Warmed lactated Ringer, normal saline, or Hartmann solution are the frequently used irrigation fluids.
These solutions have quite similar osmolality but differences in pH and electrolytic composition with respect to CSF, as depicted in Table 27.1 . Meningeal reactions have been recorded previously secondary to saline solution irrigation. The use of normal saline as a rinsing solution produced significant changes in CSF composition in a reported study ; they found a significant correlation between changes in CSF composition and the total volume of irrigation solution used, but no correlation with the duration of neuronavigation. A cutoff point of 500 mL saline irrigation solution was associated with a reduction in CSF pH of greater than 0.2. Unfortunately, similar studies have not been performed with Ringer or Hartmann solution.
| Parameter (Units) | Normal Theoretical Values | Preneuroendoscopy Values | Normal Saline | Ringer Solution | Cerebrospinal Fluid-Like |
|---|---|---|---|---|---|
| pH | 7.28–7.32 | 7.44 ± 0.09 | 6 | 6.5 | 7.4 |
| P O 2 (mmHg) | 40–44 | 147.80 ± 31.20 | — | — | — |
| P CO 2 (mmHg) | 44–50 | 34.10 ± 22.20 | — | — | — |
| Standard bicarbonate (mEq L −1 ) | 20–25 | 23.80 ± 3.00 | — | — | 11 |
| Base excess (mmol L −1 ) | — | −1.70 ± 3.90 | — | — | — |
| Ionized calcium (mmol L −1 ) | — | 0.80 ± 0.06 | — | — | — |
| Total calcium (mEq L −1 ) | 2.1–2.7 | 2.12 ± 0.5 | — | 2.7 | 2.37 |
| Glucose (g L −1 ) | 0.5–0.8 | 0.67 ± 0.12 | — | — | — |
| Sodium (mEq L −1 ) | 135–145 | 148.70 ± 3.53 | 154 | 130 | 142.6 |
| Potassium (mEq L −1 ) | 2.6–3 | 2.35 ± 0.24 | — | 4 | 3.09 |
| Magnesium (mEq L −1 ) | 3.5–4.4 | 3.14 ± 0.44 | — | — | 2.36 |
| Proteins (g L −1 ) | 15–45 | 26.15 ± 22.90 | — | — | — |
| Chlorine (mEq L −1 ) | 118–130 | 126.44 ± 1.60 | 154 | 109 | 136.6 |
| Osmolality (mOsm Kg −1 ) | 280–310 | 297.10 ± 20.27 | 308 | 273 | 280 |
Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
