Usefulness of silicone elastomer drains in endoscopic treatment of arachnoid cysts – preliminary report

Introduction
Arachnoid cysts (AC) are collections of liquid biochemically resembling cerebrospinal fluid within the arachnoid membrane, usually of congenital origin. They derive from cleft or doubling of the arachnoid meninx [1, 2] and arise in locations similar to natural arachnoid cisterns [1-5]. From five to fifty per cent of AC are asymptomatic and are discovered only accidentally [5]. Some of them can manifest with symptoms of brain compression, which appear after cessation of skull growth or result in hypoplasia of neighbouring neural structures [6]. Haemorrhages to the AC lumen have been described as well as cases of spontaneous cyst resolution [7, 8]. Increasing accessibility of neuroimaging studies results in much more frequent diagnosis of AC than in previous decades. Since the first description of the cyst by Bright, their treatment has been a source of controversy regarding indications for surgery and choice of treatment method [6, 9-15]. Among recommended surgical procedures are endoscopic cystocisternostomy and cystoventriculostomy [13, 16-21]. Long-term patency of such a stoma and its functional effectiveness are debatable.
Aim
The aim of the study is to present early and long-term results of endoscopic cystocisternostomy and cystoventriculostomy with their functional effec-tiveness secured with a silicone elastomer drain. This method has never been a topic of a separate publication.
Material and methods
Thirteen patients with AC were treated with endoscopy and implant in the last 8 years. There were 7 women and 6 men, aged 21-45 years (mean 29.6 years). In all patients diagnosis was made with ambulatory computed tomography (CT) or mag-netic resonance imaging (MRI) of the head. Symptoms found on admission are shown in Table I. Duration of the symptoms varied from 6 months to 8 years and 2 patients could not define when their symptoms had started. In 7 patients the cyst was located in a lateral fissure of the brain and in 6 on the convexity of the brain. The majority of the lateral fissure cysts fitted into the 2nd and 3rd group of Galassi classification [22].
Qualification for surgery was based on meticulous analysis of clinical symptoms and radio-logical pictures. Patients scheduled for surgery suffered from symptoms of increased intracranial pressure or from epilepsy resistant to standard pharmacological treatment. Other symptoms were at first ambulatory-observed to make sure they were not cyst-independent. A small increase in the size of a cyst was found in only one patient.
The goal of the endoscopic procedure was to join the AC lumen with one of the natural cisterns of cerebrospinal fluid by the shortest route possible. Surgical access was planned with the cistern aimed at on a single line with the trepanation bore. This line was also intended as an endoscope track. In two cases of convexity cysts, a TatraMed stereotactic frame was applied to ensure precise aim localization. All patients were operated on in the supine position with appropriate head rotation. To stabilize the head during the whole procedure, it was fixed in a Mayfield clamp. The procedures were performed with rigid GAAB, FRAZEE and CHAVANTES-ZAMORANO Karl Storz Endoscope instruments. Major differences as to the size of working channel and instrumental equipment exist between different endoscope models. Due to its length, the CHAVANTES-ZAMORANO endoscope was used for procedures with a stereotactic frame. Visualization of the operative field was secured with a digital camera and high-definition monitor integrated with a visual track. The endoscope was inserted into the skull via a 10-15 mm trepanation bore, the location of which was first planned in detail. After incision of the dura mater the external wall of the cyst was coagulated and cut. The endoscope was introduced into the cyst and its inside was inspected ‘freehand’. This stage was accomplished with exchangeable 30 and 70° angular optics. The field was continually rinsed with warm Ringer solution to secure clear sight. This procedure also prevented excessive loss of cerebrospinal fluid, which prevented a collapse of the cyst walls. Final location of the cyst and natural cerebrospinal cistern stoma was chosen after endoscopic exploration. The AC of the lateral fissure of the brain was drained into the cistern of the optical chiasma, the carotid artery cistern or the prepontine cistern with cystocis-ternostomy. Cystoventriculostomy of AC located on the convexity of the brain was performed with the lateral ventricle. Basic endoscopic tools were used. The cyst wall was blunt-punctured and the fenestration was widened with a Fogarty no. 3 balloon catheter. When the wall was too thick, it was cut with scissors after coagulation of small superficial vessels. In neither of the cases did anatomical limitations allow for formation of a stoma wide enough to secure long-term effective patency. Hence, it was secured with a silicone elastomer Integra NeuroSciences umbrella drain. The umbrella not only prevented obturation of the opening, but stabilized the position of the drain within fluid collections as well. The drain was introduced via the working channel of the endoscope or outside the endoscope (next to it) under visual guidance. In patients with a lateral fissure cyst the umbrella tip of the drain was implanted into an arachnoid cistern and the free tip floated inside the cyst. In brain convexity cysts, two connected drains were placed in such a manner that one umbrella remained inside the cyst while the other was set inside the lateral ventricle (Figure 1). Thorough flushing of blood clots off the surgical field finished the procedure. Dura mater hole was filled with Tach^oComb. Meticulous suture of soft tissues covering the skull prevented cerebrospinal fluid collection below the periosteum immediately after the surgery.
Results were assessed both clinically and radio-logically. Neurological examination was conducted according to the protocol of the department. Radiological studies included CT or MRI of the head and were assessed by the same team. The first control examination was performed 48 h after surgery, then a month, 3 months, 6 months and a year after the procedure and annually later on. This scheme could be tailored to the clinical situation and was not always strictly adhered to. Resolution of increased intracranial pressure symptoms and remission or reduction of previously seen symptoms were considered significant clinical improvement. Patients with minimal improvement had a small clinical benefit when compared to the pre-operative period. Reduction of AC size by 20% was a radiological criterion of successful surgery. The measurement used was the sum of the largest dimensions obtained in 3 different planes. Ambulatory follow-up was 2.5-6 years (mean 34 months).
Results
Immediate and long-term results of AC ac-cording to adopted assessment criteria are show in Tables II and III. Clinical improvement was observed in 11 patients (84.6%) and reduction of cyst size in 12 patients (92.3%). Signs of increased intracranial pressure, blurred vision and balance disturbances resolved in all patients. Six patients showed improvement of intellectual function. Pyramidal symptoms resolved in 3 patients and decreased in the remaining patients. In 3 epilepsy patients symptoms receded in the immediate post-op period until month 16, when one of these patients had a relapse without any sign of radiological deterio-ration. In 2 patients headache returned, but dif-ferent in character and without any signs of the cyst rebuilding in CT. Hence, headache of other than AC origin was diagnosed. A significant radiological improvement was noted in all younger patients with a cyst on the convexity, and a lesser one with lateral fissure cysts. No deterioration of neurological status, infectious complications, drain migration or death was seen. Peri-cerebral haematoma with shrinking of the cyst was seen in 2 patients with lateral fissure AC treated with cystocisternostomy and drain implantation. Both were asymptomatic and no surgery was necessary. Their resorption was monitored with CT. One patient suffered from cerebrospinal fluid collection below the epicranial aponeurosis early post surgery, yet it resolved spontaneously within a few weeks (Figures 2A-C, 3A-B).
Discussion
Patients with diagnosed AC are not uncommon in neurological clinics, yet the literature lacks clear-cut qualification criteria for surgical treatment of this condition. In the presented, highly-selected group of patients these seemed obvious. Gaab et al. suggest surgical treatment of all symptomatic and asymp-tomatic cysts in young patients with mass effect on CT or MRI. When no correlation of clinical and radiological picture can be found, they propose observation and intracranial pressure monitoring [23]. Beltramello and Mazza broaden the spectrum of indications for symptomatic cysts with increased intracranial pressure, regardless of existing communication of the cyst with a natural cerebrospinal fluid cistern [8]. No consensus of management of asymptomatic AC has been worked out so far. A chance to improve intellectual performance speaks in favour of surgical treatment, especially in younger patients [16]. Glassi thinks grade 2 and 3 (according to his own classification) asymptomatic lateral fissure cysts should only be treated with surgery after lack of their communication with arachnoid cisterns has been confirmed [22]. Risk of complications exceeding the potential risk of cyst growth and cases of spontaneous cyst resolution should also be considered when evaluating indications for surgery [8].
The problem of endoscopic AC treatment in adults is not extensively discussed in the literature. Thorough planning of operative access and drainage point of the cyst into the natural cerebrospinal fluid cistern is a key to successful surgery. The possibility of such stoma formation from anatomical and technical points of view ought to be analyzed, regarding aberrant, as a result of cyst, intracranial anatomy. Complete MRI allows for three dimensional assessment of the cyst, its wall thickness, content and relations to arachnoid cisterns and the ventricular system. The adopted method of localizing the trepanation bore and the cistern aimed at on the same line perpendicular to the bore, extracerebral access and minimization of intervention into the brain structure confirmed its usefulness in all cases. Application of the stereotactic frame was necessary for finding optimal access to a narrow lateral ventricle. However, due to disfigurement of anatomical structures from the cyst, various neuronavigation systems ought to be used [24, 25].
Rigid neuroendoscopes seem superior in surgical application to flexible ones. They have a better optical system, allow easier orientation in the operative field, and more instruments can be used with them [16, 18, 20, 21, 23, 26].The intra-operative situation is always decisive for the point of AC wall fenestration into a natural cerebrospinal fluid cistern. Proper orientation in the operative field is crucial for this stage of surgery. Identification of the frontal lobe, temporal lobe, lesser wing of sphenoid bone, petrosphenoid fold, veins of the lateral fissure and middle cerebral artery make it easier in the case of a lateral fissure cyst. Thickening and cloudiness of the cyst wall from previous bleedings can make orientation much more difficult [7, 26]. Our experience shows that a basic endoscopic tool set is sufficient for performing fenestration [27]. Edges of the opening can be coagulated to make them contract. This is especially recommended when a valve mechanism is seen in the cyst wall [3, 16]. Adequate size of fenestration, guaranteeing its long-term functionality, ought to be 10-15 mm. It can rarely be done with lateral fissure cysts. Hence, whenever there is a risk of obstruction of the stoma, a few smaller holes to adjacent natural cerebrospinal fluid cisterns can be formed [20, 21, 26]. Bleeding from bridging veins within the cyst during surgery or iatrogenic injury to blood vessels can also affect fenestration patency [7, 16]. Post-haemorrhagic fluid contains more cells and proteins, which potentially promote adhesions of the arachnoid, resulting in closure of a created stoma. Continual rinsing with warm Ringer solution and bipolar coagulation usually allow effective control of minor bleeding.
The authors secured functional effectiveness of cystocisternostomy and cystoventriculostomy with silicone elastomer drainage. Such a procedure was recommended by Schroeder et al. [20, 23]. Regardless of location of the AC, its additional benefit is prevention of closure of the fenestration due to decrease of pressure within the cyst and receding of the cyst walls. In the case of cystoventriculostomy, the distance from the cyst of the brain convexity and lateral ventricle is significant and drainage placement ensures communication. Introduction of the drain is not always possible and safe because of the proximity of important neurovascular structures and should never be forced. Kim and Paladino et al. adopted a similar treatment scheme, observing satisfactory results, although in only a few patients and without approaching cysts of the brain convexity [21, 28].
Cases of patients who had only minor im-provement after surgery or no improvement at all suggest another undiagnosed reason, unrelated to the presence of the AC. According to Bidziński, neurological symptoms and epilepsy in cysts are caused by two factors: compression on the brain structures and gliosis in the immediate proximity, which can explain treatment failures [29].
No radiological improvement with neurological betterment comes from lesser elasticity of the brain in adult patients and from aforementioned gliosis [7, 20, 30]. Greenfield et al. believe that in lateral fissure cysts remission of symptoms is more likely than reduction of the cyst size [3]. Improvement of clinical status in such cases can be explained by equalization of pressure on both sides of the fenestration. Schroeder et al. point to this phenomenon in cysts with a valve mechanism in the wall [31]. However, according to Roszkowski, the pressure gradient across fluid compartments is unpredictable, con-sidering pulse-dependent phases of intracranial pressure fluctuation and the resultant direction of cerebrospinal fluid flow [18].
Due to its safety, repeatability, effectiveness and small number of complications, application of a si-licone elastomer drain seems a promising option in endoscopic treatment of selected arachnoid cyst cases.
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