Water dissection technique of Toth for opening neurosurgical cleavage planes

1. Introduction 

One of the least known and most elegant techniques in microneurosurgery is the use of WDT. Water dissection technique, using the separating effect of injected low gentle pressure physiological saline, was introduced by Toth et al [18] in early 1980s and published in 1987 (Fig. 1). It is a simple method to cautiously open natural preformed cleavage planes such as the sylvian fissure or the interhemispheric space, and the interfaces between the cortex and extraparenchymal lesions such as meningiomas, aneurysms, and AVMs. The aim of the present technical report is to present our long-term experience with the low-pressure water dissection technique as an adjunct to everyday microneurosurgical practice. An early comparison of microsurgery with and without WDT was done by Toth et al [18], but no randomized trial has been conducted comparing the pros and cons of the technique.

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Fig. 1. Principle of WDT.

In the original article by Toth, the method was called “water jet dissection technique.” However, in later publications on a method called “water jet resection technique,” using high pressure, the tissue incision in experimental conditions appeared [5], [7], [10], [11], [17], and it has also been introduced into the clinical field, for example, cornea [3], liver [6], [19], and kidney [1], [15] surgery. Frankly, these two are completely different methods indeed. Toth water dissection is a gentle microsurgical method, but the water jet resection works more like a “destructive knife.”

2. Neurosurgical cleavage planes 

A microneurosurgeon faces many cleavage planes to be gently opened, thus avoiding damage to the brain tissue by compression. These cleavage planes include (a) natural but adherent spaces such as the sylvian fissure in front of middle cerebral artery aneurysms and insular tumors, the interhemispheric space above falcine or third ventricle tumors and distal anterior cerebral artery aneurysms, the space between the tonsils and medulla behind posterior inferior cerebellar artery aneurysms, and the way into the fourth ventricle; and (b) interfaces formed between brain tissue and solid extraparenchymal masses, and so on. Meningiomas and large/giant aneurysms, which grow in eloquent cortical or deep areas, may push these areas to unexpected directions or bury them into the cleavage plane. After widening the cleavage planes with WDT, the microsurgical methods to separate cleavage planes include classic sharp opening of arachnoidal adhesions and dissection of vessels and nerves with intermittent use of bipolar or jeweller forceps, suction, microscissors, and surgical pads to make the way. In our current practice, we avoid the use of retractors as much as possible [8].

We provide the water jet by a 20- to 50-mL syringe with a blunt steel needle or a plastic flexible needle (Fig. 2A), but an irrigating balloon is also feasible. The irrigation pressure is hand-controlled according to the microscopical view of the ongoing dissection, and consequently it requires learning the feasible applications (Fig. 2B). This technique does not need special equipment, and it is easily adapted to everyday microsurgical practice. We do not find constant pressure irrigation provided by a pump or a pressurized cuff on a saline bag practical because the jet pressure cannot be adopted according to the anatomical findings.

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Fig. 2. A: Simple syringe. B: Intraoperative picture demonstrates the separation effect of low-pressure WDT under microscope.

3. Cleavage planes of meningiomas, giant aneurysms, and AVMs 

Meningiomas usually rather compress than infiltrate the adjacent cortex or cranial nerves (Fig. 3A and B). The tumor-cortex interface is crossed by varying numbers of small feeding arteries and veins to be interrupted, nonfeeding arteries, sometimes embedded in meningioma tissue, and veins to be preserved. Benign meningiomas may partially disrupt the arachnoidal and pial layers, which combined with softened, gliotic, and edematous cortex, make the true arachnoidal cleavage plane hard to maintain [16]. Genuine infiltration of the brain, seen at least in grade III tumors [9], also makes the surgical cleavage uncertain. High-quality magnetic resonance imaging and computed tomography may give valuable data on the cleavage plane, infiltration of the cortex, vascular supply, and encasement vessels [2], [4], [13], [14], [16]. In large/giant aneurysms that may be filled with thrombus, previously incompletely coiled or otherwise indicating reconstruction of its neck, it may be necessary to dissect the sac loose from the adjoining brain tissue and arteries before resection of the sac and clipping the neck or reconstruction of the parent vessel. In AVMs, enlarged and convoluted vessels and the nidus need to be carefully separated from adjacent, possibly eloquent areas using their gliotic cleavage (see Video 1).

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Fig. 3. Convexity meningioma and its delicate separation from eloquent cortex with WDT at the beginning (A) and lost stage (B) of surgery (cf Video 1).

4. Opening the sylvian fissure 

We usually approach nearly all middle cerebral artery aneurysms directly by opening the fissure laterally, beginning with jeweller forceps and then continuing with water dissection [12]. Even in acute subaracnoid hemorrhage, in most cases enough space can be obtained by patiently removing cerebrospinal fluid after the fissure is first open. If the brain is very edematic and swollen and the fissure very tight, cerebrospinal fluid can be first removed by opening the frontobasal cisterns, or more effectively, the lamina terminalis, or both. Gentle injection of fluid into the sylvian fissure helps tremendously in its opening. Once enough room is achieved, the lateral dissection is carried deeper into the fissure, and 1 of the distal MCA branches is followed to the aneurysm. Many times, the sylvian fissure is opened straight over the aneurysm. Usually, at this stage of dissection the need for lobe retraction is minimal and is achieved with small cotton patties (see Video 2).

5. Discussion 

In 1987, Toth et al [18] published their original article on 3-year clinical experience on WDT, injection of body-temperature physiological saline by a handheld syringe with blunt needle or by an irrigating balloon, in the microsurgical dissection of intracranial meningiomas. The technique has proven to be a safe and a practical adjunct in careful separation of tumor tissue from the adjacent cortex, vessels, and cranial nerves. Since 1984, 3 senior authors (SzT, JV, and JH) have extensively used WDT in thousands of microsurgical cases, mainly meningiomas, aneurysms, and AVMs. Water dissection is aimed to improve (a) cautious opening of the cleavage plane, (b) avoidance of damage to the adjacent, possibly eloquent cortex, (c) preservation of nonfeeding cortical arteries and veins, and (d) avoidance of the use of retractors.

In most extraparenchymal lesions, cleavage planes are under pressure by the mass effect. Water dissection technique should not be used alone against this pressure, and it is recommended to apply after extensive debulking of the lesion. The proper management of the cleavage planes using low-pressure water is then combined with the routine microsurgical separation of structures, like pulling arachnoid edges adhered to the lesion along the pial vessels in the typical triangle fashion.

Limitations of the WDT may arise from firm adhesions in cleavage spaces or tumor infiltration of the surrounding and softened brain tissue. Potential hazards of the technique include (a) infusion of saline into brain tissue by using too high or inappropriately directed pressure; (b) increased pressure in the cleavage space because of insufficient outflow of the fluid—the surgeon should provide and secure sufficient outflow while maintaining adequate separating pressure; (c) abrupt loss of control of irrigation pressure because of air in the syringe; and (d) creating a false cleavage plain. It is very important to avoid infusion into brain tissue, for example, with meningiomas hiding and compressing eloquent cortical areas or breaking the pia-arachnoid layer (malignant meningiomas). All of the previously mentioned mainly theoretical complications may be avoided by using careful caution, and in fact, in our experience, there have not been any such complications. We recommend the water dissection technique as an asset of microsurgery for neurosurgeons already in training.

6. Conclusions 

Hand-controlled WDT, using the separating property of the fluid, is a safe, very inexpensive, and effective aid (a) in the microsurgical removal of solid extraparenchymal space-occupying lesions and (b) opening of cleavage planes created by the nature such as the sylvian fissure or the interhemispheric space. We recommend WDT for widespread use in microneurosurgery. After experience with thousands of patients, a randomized study seems as unnecessary as comparing 2 different microinstruments. Most small microsurgical steps and tricks have taken their stable places without such studies.