The optimal treatment for arachnoid cysts is controversial. Cyst-ventricle stent as primary or salvage treatment for posterior fossa arachnoid cysts

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1 J Neurosurg Pediatrics 7: , 7: , 2011 Cyst-ventricle stent as primary or salvage treatment for posterior fossa arachnoid cysts Clinical article Daniel H. Fulkerson, M.D., 1 Todd D. Vogel, M.D., 1 Abdul A. Baker, M.D., 2 Neal B. Patel, M.D., 1 Laurie L. Ackerman, M.D., 1 Jodi L. Smith, M.D., Ph.D., 1 and Joel C. Boaz, M.D. 1 1 Department of Neurosurgery, Division of Pediatric Neurosurgery, Indiana University School of Medicine, Goodman Campbell Brain and Spine, Indianapolis, Indiana; and 2 Department of Neurosurgery, University of Louisville, Kentucky Object. The optimal treatment of symptomatic posterior fossa arachnoid cysts is controversial. Current options include open or endoscopic resection, fenestration, or cyst-peritoneal shunt placement. There are potential drawbacks with all options. Previous authors have described stenting a cyst into the ventricular system for supratentorial lesions. The current authors have used a similar strategy for posterior fossa cysts. Methods. The authors performed a retrospective review of 79 consecutive patients ( ) with surgically treated intracranial arachnoid cysts. Results. The authors identified 3 patients who underwent placement of a stent from a posterior fossa arachnoid cyst to a supratentorial ventricle. In 2 patients the stent construct consisted of a catheter placed into a posterior fossa arachnoid cyst and connecting to a lateral ventricle catheter. Both patients underwent stent placement as a salvage procedure after failure of open surgical fenestration. In the third patient a single-catheter cyst-ventricle stent was stereotactically placed. All 3 patients improved clinically. Two patients remained asymptomatic, with radiographic stability in a follow-up period of 1 and 5 years, respectively. The third patient experienced initial symptom resolution with a demonstrable reduction of intracystic pressure. However, he developed recurrent headaches after 2 years. Conclusions. Posterior fossa cyst ventricle stenting offers the benefits of ease of surgical technique and a low morbidity rate. It may also potentially reduce the incidence of shunt-related headaches by equalizing the pressure between the posterior fossa and the supratentorial compartments. While fenestration is considered the first-line therapy for most symptomatic arachnoid cysts, the authors consider cyst-ventricle stenting to be a valuable additional strategy in treating these rare and often difficult lesions. (DOI: / PEDS10457) Key Words arachnoid cyst stent ventricle posterior fossa The optimal treatment for arachnoid cysts is controversial. Accepted options include observation, open or endoscopic fenestration, and shunt placement. Most cysts occur in the supratentorial space where they are anatomically amenable to fenestration into a cisternal, ventricular, or subdural space. Resection or fenestration of posterior fossa arachnoid cysts may be more challenging, as the cysts may have complex relationships to the brainstem, vasculature, and cranial nerves. Although previous authors have reported excellent initial results with surgical treatment, there is the potential for complications and/or cyst recurrence. Abbreviation used in this paper: ICP = intracranial pressure. J Neurosurg: Pediatrics / Volume 7 / May 2011 Shunting a cyst to an extracranial location is another standard option. While the operative morbidity rate is low, there is a potential for all the significant long-term problems associated with shunts. Anecdotally, we have noted that patients with cyst-peritoneal shunts often suffer intractable headaches. We speculate, along with previous authors, that shunting creates unnatural pressure gradients between the cyst cavity and the intracranial contents. The effects of these gradients may be magnified in the restricted space of the posterior fossa. Therefore, we explored the stenting of posterior fossa cysts to the supratentorial ventricular system. This allows for drainage of the cyst while normalizing the pressure between the cyst and both the supra- and infratentorial intracranial space. 549

2 D. H. Fulkerson et al. Stenting or shunting of an arachnoid cyst to the ventricular system has been described primarily for supratentorial cysts. 3,4,9,26,29 There are few reports describing this technique for posterior fossa cysts. In this article, we describe 3 cases in which this procedure was performed. In 2 patients, the procedure was performed after clinical and radiographically documented cyst recurrence following an open surgical fenestration. In the third, the anatomy of the cyst was favorable to a stereotactic, minimally invasive stent placement. The results of these cases and a review of the literature are provided. Methods We performed a retrospective chart review of all patients surgically treated for an arachnoid cyst at the Riley Hospital for Children from Relevant clinical, operative, and radiographic notes were reviewed. Patients with the diagnosis of Dandy-Walker syndrome or variant were excluded. The project began after approval from the local institutional review board. Decision for Surgery Clinical and imaging factors were used to determine which patients required surgery. Indications for surgery included the radiographic progression of a cyst and findings of elevated ICP (papilledema). Patients with medically intractable headaches alone were considered for surgery only after all other potential causes were evaluated and excluded. Surgical Technique Surgery involved one of two strategies. Cases 1 and 2 demonstrate the strategy of placing a valveless system connecting a posterior fossa cyst to a supratentorial ventricle. A ventricular catheter is placed in both the cyst and the ventricle. The catheters are cut to the appropriate length and affixed to individual reservoirs. The 2 reservoirs are then connected with an intervening piece of shunt tubing (see Fig. 3). Case 3 shows a strategy that we have used with both supratentorial and posterior fossa cysts. A single catheter is placed with stereotactic navigation. The trajectory of the catheter is planned to enter both the cystic and ventricular space with one pass (see Fig. 5). The catheter is connected to a reservoir. Results We identified 79 consecutive patients treated surgically for intracranial arachnoid cysts over the study period. Open or endoscopic fenestration was the initial surgical therapy (50 [63.3%]). Cyst-peritoneal shunt placement was performed initially in 25 patients (31.6%). Thirty (38.0%) of the 79 cysts occurred in the posterior fossa. We performed cyst-ventricle stenting in a total of 8 patients. Supratentorial stents were placed in 5 patients. Three patients had posterior fossa cysts and these cases represent the focus of the article. The demographics and clinical courses of these patients are shown in Table 1. TABLE 1: Study patient demographics and outcomes* Age (yrs), Sex Presentation Comorbidities Cyst Location Ops Op Complications Outcome Case No. none headaches resolved after stent placement; stable at 1 yr FU 1 16, M intractable headaches none pst fossa 8/07: open fenestration/resection of cyst walls; 6/09: pst fossa lateral ventricle stent placement none continued headaches at 1.5-yr FU pst fossa 2/03: open fenestration/resection of cyst walls; 5/07: placement of cyst catheter; 8/07: placement of ventricular catheter for cyst-ventricle stent; 1/09: placement of cyst-peritoneal shunt psychiatric disorder; seizures 2 11, M behavior problems; intractable headaches; radiographic cyst enlargement clinically stable w/ radiographic decrease in cyst size at 5-yr FU small area of wound dehiscence requiring extra sutures but not affecting implant 5/05: resection of encephalocele; 5/05: stereotactic placement of cyst-ventricle stent atretic encephalocele ambient & suprasellar cistern, w/ extension into middle cranial fossa 3 8 mos, M enlarging occipitofrontal circumference; plagiocephaly; torticollis * FU = follow-up; pst = posterior. 550 J Neurosurg: Pediatrics / Volume 7 / May 2011

3 Posterior fossa arachnoid cyst ventricular stent Case 1 Illustrative Cases Examination. This otherwise healthy 16-year-old boy presented with severe, medically refractory headaches. The results of the patient s neurological examination were normal. A CT scan demonstrated a cm retrocerebellar paramidline posterior fossa arachnoid cyst, with scalloping of the adjacent occipital skull (Fig. 1A). Operation. The patient was taken to the operating room for an open, suboccipital craniectomy with fenestration of the cyst. Intraoperatively, the cyst contents were found to be under high pressure. We performed a wide fenestration into the subarachnoid space to the foramen magnum, and resected the dural part of the cyst wall. Pathological examination of the wall confirmed the diagnosis of arachnoid cyst. Stenting. The patient s headaches improved for approximately 1 year. His headaches returned and again became refractory to medical therapy. Imaging showed that the cyst was unchanged in size compared with the preoperative MR imaging (Fig. 1B). A cyst-ventricle stent was placed. The construct consisted of 2 proximal ventricular catheters attached to reservoirs, with an intervening segment of connective tubing (Fig. 1C). Follow-Up. The patient s headaches resolved completely after the procedure. He has not had recurrence of his symptoms in over 1 year of follow-up. Case 2 Examination and Operation. This 11-year-old boy presented with intractable headaches. His medical history included seizures and psychiatric problems. Imaging studies showed a large, midline, retro- and supracerebellar arachnoid cyst (Fig. 2A and B) that had enlarged compared with earlier imaging studies. We performed a posterior fossa craniotomy with wide fenestration and resection of the posterior wall of the cyst. The pathological analysis confirmed the diagnosis. Stenting. The patient clinically improved after surgery. Follow-up MR imaging at 2 years showed that the cyst s size was similar to that before prior to surgery (Fig. 2C). Four years after his surgery, he developed symptoms of neck pain, stiffness, and a troublesome popping sensation on turning his head. We placed a cyst-catheter to allow access to the intracystic space for pressure measurements and potential aspiration. The patient again improved immediately after surgery. However, his symptoms quickly recurred. The reservoir was tapped twice. Both times, the opening pressure was well over 20 cm H 2 O. His symptoms improved immediately after withdrawal of fluid. The patient was taken back to the operating room for placement of an additional catheter into the lateral ventricle and creation of a cyst-ventricle stent. Postoperative CT scanning showed that the cyst size was stable to decreased (Fig. 2D). The construct is shown in Fig. 2E and in an artist s rendering in Fig. 3. Follow-Up and Shunting. The patient s symptoms completely resolved. However, he returned 2 years later with recurrent headaches but without the neck stiffness and pain. The reservoir was subsequently tapped. The opening pressure was low, but he did feel better with withdrawal of fluid. Therefore, a cyst-peritoneal shunt was placed with a programmable valve and antisiphon device. Unfortunately, he continued to have headaches and dizziness. His valve was reprogrammed on 6 occasions without improvement. His headaches were not consistent or stereotypical; he had some headaches suggestive of low ICP and others more indicative of high ICP. A shunt tap was performed and his opening pressure was less than 15 cm H 2 O. A shunt revision was performed to remove the antisiphon device. Unfortunately, he continues to suffer from headaches. Case 3 Examination. This 8-month-old boy initially presented to the neurosurgery clinic for occipital plagiocephaly and torticollis. Magnetic resonance imaging demonstrated a large arachnoid cyst extending in both the middle and posterior cranial fossae (Fig. 4A and B). There was moderate mass effect on the midbrain and dilation of the lateral ventricles. The physical examination was significant for macro- Fig. 1. A: Sagittal T2-weighted MR image obtained at diagnosis. The patient underwent an open fenestration for a posterior fossa arachnoid cyst. B: The cyst remained radiographically stable 2 years after fenestration, but the patient suffered recurrence of his symptoms. C: Lateral scout view of the CT scan after placement of a cyst-ventricle stent. J Neurosurg: Pediatrics / Volume 7 / May

4 D. H. Fulkerson et al. Fig. 2. A and B: Sagittal and axial T2-weighted MR images demonstrating a large posterior fossa cyst. C: The cyst remained stable 2 years after fenestration. The patient initially had a cyst catheter placed. This was converted to a cyst-ventricle stent. D: The cyst size decreased slightly. E: The construct is shown on a lateral radiograph. cephaly and a small, raised lesion on the vertex consistent with an atretic encephalocele. Evaluation of his growth curves showed that his occipitofrontal circumference was crossing expected growth lines. Fig. 3. Artist s rendering of the cyst-ventricle stent described in Case 2 based on MR imaging source images. The blue represents the ventricular system and the purple represents the arachnoid cyst. Used with permission from the Trustees of Indiana University. Operation. The patient was taken to the operating room for stereotactic placement of a single-catheter cystventricle stent attached to a reservoir (Figs. 4C and 5). There were no complications with surgery except a slight wound dehiscence. This was treated successfully with local debridement and an additional suture. Follow-Up. The patient has undergone follow-up for 5 years. He has remained neurologically stable, although he is slightly delayed on his milestones. A CT scan performed 2 years after surgery showed a decrease in both cyst and ventricle size compared with preoperative studies (Fig. 4D and E). An artist s rendering based on the MR source images is shown in Fig. 5. Discussion The optimal treatment for intracranial arachnoid cysts is controversial. While some authors argue for aggressive surgical treatment of cysts, others recommend a more conservative approach. While the choice of whom to treat is difficult, the choice of how to treat also remains controversial. Arachnoid cysts are considered predominantly congenital lesions arising at or soon after birth. The prevailing theory is that cysts form from an anomalous splitting of the endomeninx during the folding of the neural tube. Many cysts remain asymptomatic. Others may become symptomatic in childhood or may lie quiescent until adulthood. The most common presenting symptom is headache. 18 Other symptoms are location specific and include seizures, endocrinopathies, bobble-head doll 552 J Neurosurg: Pediatrics / Volume 7 / May 2011

5 Posterior fossa arachnoid cyst ventricular stent Fig. 4. A and B: Axial and sagittal MR images of a large quadrigeminal cyst extending into the posterior and middle cranial fossa. C: A cyst-ventricle stent was placed. D and E: Axial CT scans comparing an immediately postoperative image (D) and a similar cut at the tip of the catheter 2 years later (E), showing improvement in both cyst and ventricle size. Fig. 5. Left and Right: Artist s renderings of the cyst-ventricle catheter with the ventricular (blue) and cyst (purple) anatomy in sagittal and coronal planes representing Case 3. The illustrations are rendered off the source images of the MR images. Used with permission from the Trustees of Indiana University. J Neurosurg: Pediatrics / Volume 7 / May 2011 syndrome for suprasellar cysts, failure to thrive, and hydrocephalus. A small percentage present with hemorrhage, with an annual risk estimated at 0.1% per year. 31 In children, cysts may present in with an elevation in ICP. 28 There is a consistent predilection for males. 28 In our series, 38.0% of all surgically treated arachnoid cysts occurred in the posterior fossa. Posterior fossa cysts comprise roughly 5% 10% of cysts in previously published series. 18 Presenting symptoms of posterior fossa cysts may include brainstem compression, ataxia, headache, trigeminal hypoesthesia, psychomotor delay, tinnitus, cranial nerve abnormalities, progressive spastic quadriparesis, or hydrocephalus. 10,34 The patient described in Case 3 presented with a rapidly increasing occipitofrontal circumference, torticollis, and subsequent positional plagiocephaly. While most cysts will remain stable in size, some enlarge. Theories on a mechanism for enlargement include the following: 1) a 1-way-valve connection with the subarachnoid space, allowing CSF to enter the cyst but not to exit; 5,36,37 2) fluid shifts via an osmotic gradient; and 3) active secretion by the cyst wall. Berle et al. 2 studied the cyst fluid obtained in 15 adult patients with temporal arachnoid cysts. They found that the composition of the fluid differed from CSF in levels of phosphate, total protein, ferritin, and lactate dehydrogenase; their findings support the theory of active transport/secretion of fluid from the cyst walls. 2 Treatment options include open or endoscopic resection, fenestration of the cyst into a ventricular or subarachnoid space, and cyst shunting. Frazier 11 was one of the first to advocate open surgery for arachnoid cysts. Most cysts are supratentorial and relatively amenable to surgical access. Direct surgical treatment of posterior fossa cysts may be more difficult, as the cyst may have a complex relationship with cranial nerves, major vessels, or the brainstem. Resection of the cyst or fenestration into an existing CSF space may be accomplished using open or endoscopic techniques. Surgical techniques and results for supratentorial cysts have been well described. 3,4,8,9,21,23,26,30,32 Several authors have also reported excellent clinical and surgical outcomes in treating posterior fossa cysts. 5,6,10,19,27,29,34,39 While most surgically treated patients do well, there is a definite recurrence rate of both clinical symptoms and radiographic findings. Oberbauer et al. 28 reported on a cooperative study of 285 children treated from 1980 to 1988 in Europe. In their survey of neurosurgeons, the most common procedure was open surgery (43.3%) that entailed fenestration and/ or excision. There was a need for a subsequent surgical procedure in 25.8%. Helland and Wester 18 reported fail- 553

6 D. H. Fulkerson et al. ure after surgery in 15 of 156 adult patients. The risk of failure in this study was related to cyst location (temporal) and a minimalist initial approach. Our strategy with resection or fenestration is to widely remove the dural wall of the cyst, assuming that a wider fenestration reduces the risk of recurrence. We agree with other authors that aggressive peeling of the cyst away from neural structures is an unnecessarily risky maneuver. Despite this technique, the patients in Cases 1 and 2 experienced recurrence of symptoms and the continued radiographically documented presence of a cyst. Another surgical option is cyst shunting. While shunting is a technically simple procedure, it subjects the patient to all the potential device-related problems. Similar to ventricular shunts, cyst shunts have the potential for failure and infection. Patients are at risk for the complications of overshunting, including slit-ventricle syndrome, craniosynostosis, and subdural hygromas/hematomas. 1,14,20,24,25,35,38 In a series of 37 cyst shunt treated patients by Martínez-Lage et al., 25 7 patients (18.9%) developed severe neurological manifestations of excessive CSF drainage. There is a high rate of shunt malfunction. In the European Cooperative study, 30% of shunt-treated patients required multiple procedures. 28 In our experience, patients with cyst shunts commonly have shunt-related headaches. This seems to be more common in cases involving posterior fossa cysts. We also have noted that some patients with relatively small cysts will have severe symptoms that are relieved with treatment. This is shown in Case 1, which also demonstrates that relatively small cysts may have a high intracystic pressure. The local pressure differences may contribute to patients symptoms. Helland and Wester 17 have statistically correlated intracystic pressure to symptoms in 38 adult patients. A simple connection or stent from an arachnoid cyst to an existing CSF space may allow drainage of cyst contents while normalizing local pressure gradients. 26 This has been described for supratentorial cysts. McBride et al. 26 reported the outcomes of 10 patients with cystventricle shunting. All patients improved symptomatically. The cyst decreased in size in 6 patients. Four patients required subsequent surgery, leading to the authors calculation of a risk of return to surgery of 5% per year. 26 Other authors have described stenting or shunting a cyst into the subdural space. 16,40 Stenting to an intracranial space may lessen the pressure differential of a cyst to extracranial (peritoneal) shunt. Stenting a posterior fossa lesion to the supratentorial ventricles has been described for the trapped fourth ventricle. In this condition, a pressure gradient between a shunted supratentorial ventricular system combined with outlet obstruction of the foramina of Luschka and Magendie collapses the cerebral aqueduct. The fourth ventricle progressively dilates. Shunting the dilated fourth ventricle has a high complication rate. Approximately 40% of these shunts will require revision by 1 year. 12,22 A pressure gradient between the supra- and infratentorial space may potentially cause downward herniation symptoms. Therefore, previous authors have explored aqueductal stenting to the supratentorial ventricular system. 7,12,13,15,33 With stenting, the fourth ventricle may drain without creating potentially dangerous pressure gradients. While there are reports of cyst-ventricle fenestration or stenting for the trapped fourth ventricle or cysts associated with Dandy-Walker malformation, there are few reports describing this technique for arachnoid cysts. King et al. 21 reported on 3 patients with endoscopic ventriculocystostomy combined with third ventriculostomy or shunt placement in patients with retrocerebellar cysts associated with Dandy-Walker complex. In one of the patients the procedure was performed after an attempted open fenestration. All patients improved clinically and radiographically. 21 The series reported by McBride et al. 26 did include 2 patients with posterior fossa cysts, including 1 cyst that enlarged despite endoscopic fenestration. The cysts decreased in size in both cases, with no subsequent shunt malfunctions, although the follow-up duration was not specified. There are 3 potential benefits to cyst-ventricle stenting. First, the procedure is minimally invasive and technically simple. Connecting a posterior fossa cyst to a supratentorial ventricle can be accomplished with 1 well-planned catheter or with 2 connected proximal catheters. When using a single catheter (Case 3), it is important to ensure that the tubing holes will span both the cyst and the ventricle. We have used custom cyst-puncture catheters with holes up the catheter side for this purpose (Fig. 5). There are a number of surgical options for the patient in Case 3. Certainly, one could fenestrate this cyst via an open or endoscopic approach, but placement of a single catheter simplifies this procedure and still accomplishes the fenestration. Leaving a stent in place may also reduce the risk of cyst recurrence with fenestration alone, as the catheter provides a tract even if the cyst collapses. Second, the addition of a reservoir allows the surgeon to access the cyst fluid percutaneously. The ability to tap the reservoir, both for diagnostic and therapeutic reasons, may be helpful. While the tap will not distinguish pressure from either the cyst or the ventricular system (ideally, they are the same), it is clinically germane if the pressure is inordinately high. The third and possibly most important advantage is the consideration that connecting the cyst to the ventricular space minimizes or eliminates local pressure gradients that may arise with shunting to an extracranial compartment. In severe forms, these pressure differences may lead to severe consequences of over-shunting as described above. More commonly, they may lead to intractable shunt-related headaches. Measuring outcome is somewhat problematic in the treatment of arachnoid cysts. Clinical outcome does not necessarily correlate with radiographic outcome. 16,18,28 In our series, 2 of 3 patients had clinical resolution of their symptoms. The patient in Case 1 had resolution of his headaches and the lesion has remained radiographically stable. The head growth stabilized in the patient in Case 3 and his cyst is smaller radiographically. Case 2 illustrates the difficulty in treating these patients. The patient s headaches did resolve for 2 years after surgery. There was also a demonstrable decrease in intracystic pressure after stenting. The patient underwent placement of a cyst catheter 554 J Neurosurg: Pediatrics / Volume 7 / May 2011

7 Posterior fossa arachnoid cyst ventricular stent with a reservoir after fenestration failed. This reservoir was tapped twice. Both times, the intracystic pressure was over 20 cm H 2 O, indicating a high local pressure. After placing a stent to the ventricle, the pressure normalized. Although the pressure normalized, his headaches returned without the previous neck pain. We placed a cyst-peritoneal shunt. However, his headaches, if anything, intensified. Despite maneuvers to lower, raise, and prevent siphoning, the patient continues to have symptoms. Conclusions Posterior fossa arachnoid cysts are relatively rare lesions that engender much debate in the neurosurgery community. Established methods of surgical treatment include open or endoscopic fenestration and cyst-peritoneal shunting. Cyst-ventricle stenting offers the advantages of being technically easy and safe to perform, minimally invasive, and may theoretically lessen some of the problems associated with cyst-peritoneal shunting. A stent may be placed stereotactically with one catheter as in Case 3 or in a construct as in Cases 1 and 2. All of our patients had clinical benefits after this procedure. Its long-term efficacy is still a matter of study, as 1 of the 3 patients did have recurrence of symptoms 2 years later. While open or endoscopic fenestration may still be the initial procedure of choice, we consider cyst-ventricle stenting to be a valuable option, either as a primary or a salvage treatment, in this difficult and often frustrating condition. Disclosure The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper. Author contributions to the study and manuscript preparation include the following. Conception and design: Fulkerson, Boaz. Acquisition of data: Fulkerson, Vogel, Baker, Patel, Boaz. Analysis and interpretation of data: Fulkerson, Vogel, Patel, Smith, Boaz. Drafting the article: Fulkerson, Vogel, Baker, Patel, Ackerman, Smith. Critically revising the article: Fulkerson, Patel, Ackerman, Smith, Boaz. Reviewed final version of the manuscript and approved it for submission: all authors. Study supervision: Fulkerson. Acknowledgments The authors thank Sharon Teal and the Indiana University School of Medicine s Office of Visual Media for the graphics in Figs. 3 and 5. References 1. Aoki N, Sakai T, Umezawa Y: Slit ventricle syndrome after cyst-peritoneal shunting for the treatment of intracranial arachnoid cyst. Childs Nerv Syst 6:41 43, Berle M, Wester KG, Ulvik RJ, Kroksveen AC, Haaland OA, Amiry-Moghaddam M, et al: Arachnoid cysts do not contain cerebrospinal fluid: A comparative chemical analysis of arachnoid cyst fluid and cerebrospinal fluid in adults. 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8 D. H. Fulkerson et al. 26. McBride LA, Winston KR, Freeman JE: Cystoventricular shunting of intracranial arachnoid cysts. Pediatr Neurosurg 39: , Mohindra S, Gupta SK, Chhabra R, Gupta R, Kumar A, Radotra BD: Ventrally placed craniovertebral junction arachnoid cysts in children: a report of 2 cases and literature review. Surg Neurol 68:85 88, Oberbauer RW, Haase J, Pucher R: Arachnoid cysts in children: a European co-operative study. Childs Nerv Syst 8: , Oertel JM, Baldauf J, Schroeder HW, Gaab MR: Endoscopic cystoventriculostomy for treatment of paraxial arachnoid cysts. Clinical article. J Neurosurg 110: , Oertel JM, Wagner W, Mondorf Y, Baldauf J, Schroeder HW, Gaab MR: Endoscopic treatment of arachnoid cysts: a detailed account of surgical techniques and results. Neurosurgery 67: , Parsch CS, Krauss J, Hofmann E, Meixensberger J, Roosen K: Arachnoid cysts associated with subdural hematomas and hygromas: analysis of 16 cases, long-term follow-up, and review of the literature. Neurosurgery 40: , Rappaport ZH: Suprasellar arachnoid cysts: options in operative management. Acta Neurochir (Wien) 122:71 75, Sagan LM, Kojder I, Poncyljusz W: Endoscopic aqueductal stent placement for the treatment of a trapped fourth ventricle. J Neurosurg 105 (4 Suppl): , Samii M, Carvalho GA, Schuhmann MU, Matthies C: Arachnoid cysts of the posterior fossa. Surg Neurol 51: , Sandberg DI, Souweidane MM: Endoscopic-guided proximal catheter placement in treatment of posterior fossa cysts. Pediatr Neurosurg 30: , Santamarta D, Aguas J, Ferrer E: The natural history of arachnoid cysts: endoscopic and cine-mode MRI evidence of a slitvalve mechanism. Minim Invasive Neurosurg 38: , Schroeder HW, Gaab MR: Endoscopic observation of a slitvalve mechanism in a suprasellar prepontine arachnoid cyst: case report. Neurosurgery 40: , Sunami K, Saeki N, Sunada S, Hoshi S, Murai H, Kubota M, et al: Slit ventricle syndrome after cyst-peritoneal shunting for temporal arachnoid cyst in children a clinical entity difficult to detect on neuroimaging study. Brain Dev 24: , Tsuboi Y, Hamada H, Hayashi N, Kurimoto M, Hirashima Y, Endo S: Huge arachnoid cyst in the posterior fossa: controversial discussion for selection of the surgical approach. Childs Nerv Syst 21: , Wester K: Arachnoid cysts in adults: experience with internal shunts to the subdural compartment. Surg Neurol 45:15 24, 1996 Manuscript submitted October 14, Accepted February 22, Address correspondence to: Daniel H. Fulkerson, M.D., Department of Neurosurgery, Indiana University School of Medicine, Goodman Campbell Brain and Spine, Riley Hospital for Children, 702 Barnhill Drive #1134, Indianapolis, Indiana dfulkers@iupui.edu. 556 J Neurosurg: Pediatrics / Volume 7 / May 2011