Syringosubarachnoid Shunt Research Articles

A lumped-parameter model of the cerebrospinal system for investigating arterial-driven flow in posttraumatic syringomyelia

Fluid transport in syringomyelia has remained enigmatic ever since the disease was first identified some three centuries ago. However, accumulating evidence in the last decade from animal studies implicates arterial pulsations in syrinx formation. In particular, it has been suggested that a phase difference between the pressure pulse in the spinal subarachnoid space and the perivascular spaces, due to a pathologically disturbed cerebrospinal fluid (CSF) or blood supply, could result in a net influx of CSF into the spinal cord (SC). A lumped-parameter model is developed of the cerebrospinal system to investigate this conjecture. It is found that although this phase-lag mechanism may operate, it requires the SC to have an intrinsic storage capacity due to the collapsibility of the contained venous reservoir. This net flux is associated with a higher mean pressure in the SC than the SSS which is maintained in the periodic steady state. According to our simulations the mechanical perturbations of arachnoiditis exacerbate the phase-lag effect, which may be partially alleviated by the presence of a posttraumatic syrinx and more completely by a syringo-subarachnoid shunt.

Syringosubarachnoid shunt for syringomyelia associated with Chiari I malformation

An 11-year-old girl with Chiari I malformation presented with a large cervico-thoracic syrinx (Fig. 1). There was poor clinical improvement 4 months after foramen magnum decompression. Subsequently, syringosubarachnoid shunting was performed, resulting in complete resolution of the syrinx and marked clinical improvement. The shunt was seen as a small tubular structure on MRI, with prominent flow artifact within the thecal sac near the shunt opening (Fig. 2). Syringomyelia associated with Chiari I malformation can be treated by foramen magnum decompression, syringosubarachnoid shunting and syringoperitoneal shunting [1, 2]. Syringosubarachnoid shunting is a safe, effective and techni-

Polytetrafluoroethylene sponge syringosubarachnoid shunt.

Syringomyelia is condition in which a cyst or cavity forms inside the spinal cavity. Its management always remains a difficult. A variety of surgical techniques have been used in management of syringomyelia. Syringosubarachnoid shunt remains an effective method in management of syringomyelia. Shunt tube obstruction remains an important complication of shunt procedure. We describe a novel technique of use of polytetrafluoroethylene sponge shunt for syringosubarachnoid shunt in patient with large syrinx and Chiari 1 malformation. Polytetrafluoroethylene sponge is a non irritant material with multiple porosities that is less susceptible to blockages or kinking. It could provide a good alternative technique in syringosubarachnoid shunting.

Clinical Significance and Prognosis of Idiopathic Syringomyelia

Retrospective case series. To determine the clinical significance and prognosis of idiopathic syringomyelia. With the widespread use of magnetic resonance imaging, cases of syringomyelia are found occasionally. However, the clinical significance and optimum treatment strategy for idiopathic syringomyelia remain unclear, because there are few reports on details of this condition. The clinical records and magnetic resonance images of 15 patients with idiopathic syringomyelia were reviewed to determine the changes in patient's neurologic status assessed by the Japanese Orthopedic Association scores for cervical myelopathy and the distribution of the syringomyelia on magnetic resonance imaging. Twelve cases were treated conservatively (conservative group) and syringo-subarachnoid shunt was performed in the remaining 3 cases (surgical group). The follow-up period ranged from 7 to 20 years (mean: 10.5 y). The localized type of idiopathic syringomyelia, which extended under 3 vertebras (mean: 2.1 vertebras), was observed in the 12 patients of the conservative group. There were no significant changes in either the size of the syringomyelia or the severity of the neurologic deficits during the follow-up period (mean: 10 y). In contrast, the extended type, which distributed over 4 or more vertebras (mean: 10.2 vertebras), was observed in the 3 patients of the surgical group. Because of severe and progressive neurologic deficits, syringo-subarachnoid shunt was performed and the surgery successfully prevented further neurologic deterioration. The mean Japanese Orthopedic Association score of the surgical group was significantly lower than that of the conservative group, both at the time of the initial examination and at the final follow-up. There are 2 types of idiopathic syringomyelia. One is a "localized" type, which might represents congenital enlargement of the central canal of the spinal cord, and can be managed conservatively. The other is an "extended" type, which causes progressive neurologic dysfunction, and should be treated surgically to prevent further neurologic deterioration. Further study should be needed to clarify the mechanism of the extended type of idiopathic syringomyelia.

Factors contributing improvement of syringomyelia and surgical outcome in type І Chiari malformation

The aim of our study was to compare pre- and postoperative radiologic data of posterior fossa and the improvement of syringomyelia after posterior fossa decompression (PFD) with and without tonsillar management in Chiari type capital I, Ukrainian malformation (CM-I). A retrospective analysis was made of all patients who underwent PFD between Oct 1991 and March 2007 for CM-I. Fifty-seven patients treated for CM-I at a single institution were included in the study. Patients were divided into two groups according to the procedures used during their PFD: PFD vs. PFD with tonsillar management. To determine whether the tonsillar management or changes of posterior fossa volume relate with surgical outcome, we measure posterior fossa size and syringomyelia pre- and postoperatively using magnetic resonance imaging. Forty patients (70.2%) received PFD and 17 patients (29.8%) received PFD with tonsillar management. The length of syringomyelia affected improvement of syringomyelia (alteration rate, A-rate). Clinical symptoms, craniectomy size, syringomyelia type, and the surgeon's specialty did not affect A-rate. Tonsillar management has no significant effect on improvement of syringomyelia. Four patients need repeated surgery due to recurrence. We have shown that tonsillar management do not lead to improve A-rate, and the radiologic changes of posterior fossa volume do not relate with radiologic improvement of syringomyelia. PFD without tonsillar management is sufficient to improve syringomyelia. The longer syrinx, the more A-rate improve in our study. However, a wider craniectomy is unrelated to A-rate. In cases of recurrent patients, we obtained good results with tonsillar management or syringosubarachnoid shunt.

CEREBROSPINAL FLUID-RELATED COMPLICATIONS WITH AUTOLOGOUS DURAPLASTY AND ARACHNOID SPARING IN TYPE I CHIARI MALFORMATION

Although there is a current consensus that Type I Chiari malformations (CM-I) should be treated only in the setting of symptomatic disease, significant controversy surrounds the most appropriate surgical procedure. Recent enthusiasm for osseous decompression without duraplasty is supported by the purportedly lower morbidity of this approach. Precise rates of morbidity with duraplasty, however, have not been reported. This study is intended to assess the cerebrospinal fluid-related morbidity associated with a patient population treated uniformly with autologous duraplasty for symptomatic CM-I. A review of one surgeon's practice (MMS) from 1997 to 2007 identified patients treated for symptomatic CM-I with osseous decompression and autologous duraplasty. A retrospective chart review was then performed for these patients with an emphasis on cerebrospinal fluid-related complications. Forty patients were treated for CM-I with decompression and autologous duraplasty. Twenty-four patients presented with a preoperative syrinx. The mean age was 13.3 years, and the median age was 12.9 years (range, 3.3-45.8 yr). The mean follow-up period was 11.4 months (range, 1-101 mo). There was no mortality associated with the procedure. Clinical response was observed in 91.8% of patients, with 70.2% experiencing complete symptomatic resolution and 21.6% experiencing partial improvement. Two patients (5.4%) had persistent symptomatic syringomyelia requiring syringosubarachnoid shunting. There was an overall morbidity rate of 2.5% due to one pseudomeningocele treated with a single percutaneous tap. There were no incidences of cerebrospinal fluid leak, meningitis, or postoperative hydrocephalus. The cerebrospinal fluid-related morbidity associated with autologous duraplasty for CM-I in a uniformly treated population is negligible. These results challenge the current rationale for a less aggressive surgical approach to CM-I.

MINIMALLY INVASIVE INSERTION OF SYRINGOSUBARACHNOID SHUNT FOR POSTTRAUMATIC SYRINGOMYELIA

Symptomatic posttraumatic syringomyelia affects up to 10% of patients with spinal cord injuries and manifests in a delayed manner as progressive sensorimotor changes below the level of the syrinx. Syrinx shunting, and in particular syringosubarachnoid shunting (SSAS), provides neurological improvement or stabilization in at least 50% of these patients. Given the debilitated condition of many of these patients, a minimally invasive approach to the insertion of these devices is desirable. We provide the first report of an SSAS inserted in a minimally invasive fashion through a tubular retractor. A 27-year-old woman presented 4 years after C6 to C7 fracture dislocation and incomplete spinal cord injury with increasing pain and spasticity below the midthoracic region. Magnetic resonance imaging scan revealed a midthoracic syrinx that had enlarged on serial imaging. SSAS was inserted using a minimally invasive technique via the X-Tube retractor (Medtronic Sofamor Danek, Memphis, TN). Through a 2.5-cm incision, hemilaminotomy was performed, and a midline durotomy and myelotomy were opened for SSAS insertion under microscopic visualization. Intraoperative ultrasonography revealed successful syrinx decompression after SSAS insertion. The operative time was 150 minutes and estimated blood loss was less than 100 mL. The patient was mobilized on postoperative Day 1 and was discharged 38.5 hours after surgery with resolution of her preoperative symptoms. Postoperative magnetic resonance imaging scan revealed excellent decompression of the syrinx, and through 1 year of follow-up, the patient has had no recurrence of her syrinx-related symptoms. This is the first report of minimal-access insertion of an SSAS. The minimally invasive technique appears to be a safe and effective means of implanting an SSAS. This approach allows for diminished blood loss and early mobilization and transfer to rehabilitation units for these patients.

Electrophysiologic and clinical data support the use of dorsal root entry zone myelotomy in syringosubarachnoid shunting for syringomyelia

Background The objectives of this study were to correlate preoperative changes in SEPs with clinical sensory dysfunction and to establish their importance in planning the microsurgical approach, either by DM myelotomy or by DREZ myelotomy, for patients with syringomyelia. Methods In addition to conducting clinical sensory examination, we evaluated the N13 potential after median nerve stimulation and CPs after tibial nerve stimulation intraoperatively before performing myelotomy on patients with syringomyelia (N = 14). Results Eleven patients with intact DS presented with unilateral PTD, and 9 had distressing unilateral dermatomal pain. Deep sensibility was affected in 3 patients (bilaterally in 1 patient) without PTD. Patients with PTD were likely to have spontaneous pain ( P = .005). A significant correlation between preoperative PTD and the absence of the N13 potential was demonstrated on the right ( P = .015) and left ( P = .004) sides. In patients with PTD, DREZ myelotomy on the symptomatic side is suggested as the treatment of choice, whereas DM myelotomy might be superior in patients without PTD. Conclusions Absence of pain or temperature sensation in patients with syringomyelia is usually accompanied by same-sided loss of the N13 potential, suggesting damage to the DH gray matter. Deep sensibility is typically normal, and DREZ myelotomy with preservation of DCs is proposed as the treatment of choice. Conducted potentials are usually distorted in patients with normal pain or temperature sensation and affected vibration and posture sensation, suggesting damage to DCs and making DM myelotomy the treatment of choice. Electrophysiologic and clinical data support the use of DREZ myelotomy in syringosubarachnoid shunting for syringomyelia in patients whose DCs have an intact function.

A modified technique for syringo-subarachnoid shunt for treatment of syringomyelia

Syringo-subarachnoid shunting is a well-established procedure for the treatment of syringomyelia. However, the standard surgical procedure requires a laminectomy and posterior midline myelotomy, which have potential complications. In this study, we describe our clinical experience with a modified technique for syringo-subarachnoid shunt insertion in eight patients between 1998 and 2002. The technique comprises a limited hemilaminectomy, a 2 mm myelotomy at the site of dorsal root entry zone, introduction of a 1.5 mm thick catheter into the syrinx and placement of the distal tip of the catheter in the anterolateral subarachnoid space. Using this technique there was no operative morbidity or mortality. Collapse of the syrinx, in the first post-operative month, was demonstrated by MRI in all cases. There were no relapses in the follow-up period. Although our experience is limited and the results preliminary, this technique is less invasive than commonly used techniques and the results are favorable.

Rapid expansion of a ventral arachnoid cyst after syringo-subarachnoid shunting in the thoracic spinal cord: case report

Background Intradural spinal arachnoid cysts have rarely been reported in association with intramedullary cysts. These associated lesions most commonly occur in the thoracic spine. Case Description We reported an unusual balance of cerebrospinal fluid dynamics between an initially occult arachnoid cyst and syringomyelia. The arachnoid cyst was not allowed to express itself until the syrinx was decompressed with a syringo-subarachnoid shunt. Conclusion Only one other report in the literature described a similar case; however, our case is the first to be confirmed by intraoperative ultrasound.

Clinical features and pathomechanisms of syringomyelia associated with spinal arachnoiditis

Background Syringomyelia is a common intramedullary lesion associated with spinal arachnoiditis and obstruction of the foramen magnum such as in Chiari's malformation. Disturbance of cerebrospinal fluid flow around the spinal cord has an important role in the development of syringomyelia due to spinal arachnoiditis; however, the exact mechanisms have not been clarified. The purpose of this retrospective study is to understand the clinical features and pathomechanisms of syringomyelia secondary to spinal arachnoiditis and to provide the current choice of surgical treatment in this difficult clinical entity. Methods Clinical and radiological findings in 15 patients with syringomyelia associated with spinal arachnoiditis who underwent surgical treatment in our institutes between 1982 and 2000 were reviewed. All patients presented with paraparesis or tetraparesis on admission. Results Magnetic resonance imaging (MRI) or computed tomography-myelography revealed that the syrinx predominantly existed at the thoracic levels. Five patients showed complete block of the thoracic subarachnoid space by conventional myelography. T2-weighted MRI showed diffuse intramedullary hyperintensity at the level of arachnoiditis. As the first surgical treatment, 10 patients underwent syringo-peritoneal shunt placement. Three patients were treated with a syringo-subarachnoid shunt, and 2 patients were treated with a ventriculoperitoneal shunt. Eight patients required further shunting operations for syringomyelia 2 months to 12 years after the first surgery. Neurologic improvement was obtained in 9 patients (60%) with decreased size of the syrinx. One patient remained stable; 5 patients showed gradual deterioration. Conclusions The syrinx originated from the thoracic levels where severe adhesion of the subarachnoid space was present. The mechanisms of syrinx formation may be based on the increased interstitial fluid in the spinal cord. Shunting procedures were effective in some population of the patients. Decompression procedures of the spinal subarachnoid space may be an alternative primary surgical treatment except for patients with longitudinally extensive arachnoiditis.

Theoretical analysis of the pathophysiology of syringomyelia associated with adhesive arachnoiditis

Objective: To apply a theoretical model to analyse the derangement of cerebrospinal fluid (CSF) dynamics in syringomyelia associated with adhesive arachnoiditis. Methods: An electrical circuit model of CSF dynamics in...

Subdural Hematoma Caused by Intracranial Hypotension After Syringosubarachnoid Shunting-Case Report-

A 32-year-old man developed an extremely rare subdural hematoma after syringosubarachnoid shunting for syringomyelia. He presented with a 4-year history of neck pain and spastic paraparesis resulting from T-7 and T-8 vertebral body fracture suffered in a traffic accident at age 22 years. Magnetic resonance imaging revealed syringomyelia between the craniocervical junction and the T-10 level. The symptoms were slowly progressive, and a syringosubarachnoid shunting was performed. His spasticity improved after surgery, but he developed orthostatic headache 7 days after surgery. Magnetic resonance imaging of the brain demonstrated a thin subdural hematoma over the right cerebral convexity. The subdural hematoma resolved spontaneously within a week with conservative treatment. Vigorous cerebrospinal fluid outflow observed during surgery presumably lowered the pressure in the syrinx cavity, leading to significant but transient intracranial hypotension and consequently the formation of subdural hematoma.

Terminal Syringomyelia: Is It As Innocent As It Seems?-Case Report-

A 5-day-old newborn girl presented with cutaneous signs of hypertrichosis, skin dimple, and subcutaneous lipoma in the lumbar region. Magnetic resonance (MR) imaging of the thoracolumbar spine demonstrated spinal dermal sinus, type II split cord malformation, and tethered cord. A small terminal syringeal cavity was also present. Five months after the diagnosis, weakness in dorsal flexion of the bilateral feet and toes was detected. Surgery to untether the cord was performed. Her deficits resolved completely. Nearly 4 years later, she was admitted with weakness in dorsal flexion of the right foot and toe. MR imaging of the spine showed holocord syringomyelia, postoperative changes, and tethered cord. No Chiari malformation was seen. Syringosubarachnoid shunt placement was performed. Terminal syringomyelia is common in cases of occult spinal dysraphism, but the natural history and management remain unclear. Progression, regression, or persistence of terminal syringeal cavity can occur whether untethering is performed or not. Progression of the terminal syrinx occurred after tethered cord release and the enlargement of the cavity involved the entire spinal cord in the present case. Terminal syringomyelia requires close follow up for a long time even in asymptomatic cases. Surgical treatment should be considered in symptomatic cases.

Progression of terminal syrinx in occult spina bifida after untethering.

The association of spinal dysraphism and terminal syringomyelia is a well-known entity, and untethering with or without syrinx drainage is usually the surgery of choice. However, progression of the previously existing syrinx after an untethering procedure is an uncommon course. The objective of this study was to discuss the diagnostic, surgical, and follow-up consequences of such an occurrence. Four children with occult spina bifida associated with terminal syrinx at the time of initial presentation are included in this study. After the primary releasing procedure, all developed enlargement of the syrinx. Two of them were operated on for placement of a syringo-subarachnoid shunt, while the other two were followed up conservatively. One of the shunted patients also had a second releasing procedure. Progression of the pre-existing terminal syrinx after the primary untethering procedure should be kept in mind even in the absence of overt neurological progression.

Syringomyelia associated with foramen magnum arachnoiditis.

Syringomyelia is often linked to pathological lesions of the foramen magnum. The most common cause is hindbrain herniation, usually referred to as Chiari I or II malformation. Foramen magnum arachnoiditis without either Chiari I or II malformation is a rare cause of syringomyelia. The authors undertook a retrospective analysis of 21 patients with foramen magnum arachnoiditis (FMA) and syringomyelia treated between 1978 and 2000 to determine clinical course and optimum management. In the review of records, 21 patients with FMA and syringomyelia were documented. A stable clinical course was demonstrated in three patients in whom surgery was not performed, and one patient refused surgical intervention. Seventeen patients underwent 23 operations to treat progressive neurological disease. Of these 23 operations, 18 involved opening of the foramen magnum, arachnoid dissection, and placement of a large dural graft. One patient underwent insertion of a ventriculoperitoneal shunt for treatment of accompanying hydrocephalus, one patient received a cystoperitoneal shunt for an accompanying arachnoid cyst; two syringoperitoneal and one syringosubarachnoid shunts were also inserted. Hospital and outpatient files, neuroimaging studies, and intraoperative photographic and video material were analyzed. Additional follow-up information was obtained by telephone interview and questionnaires. Standard and cardiac-gated magnetic resonance imaging studies are the diagnostic procedures of choice in these patients. Sensory disturbances, dysesthesias, and pain were the only symptoms likely to improve after foramen magnum surgery. Motor weakness and gait disturbances, which were severe in a considerable number of patients, and swallowing disorders tended to remain unchanged. As a consequence of the rather severe arachnoid lesions in most patients, clinical recurrences were observed in 57% over a 5-year period. Surgery for FMA and syringomyelia has to provide clear cerebrospinal fluid pathways between the cerebellopontine cisterns, spinal canal, and fourth ventricle. If this can be achieved successfully, the syrinx decreases in size and the clinical course of the patient may even improve. In patients with severe and widespread areas of arachnoiditis, however, multiple operations may be required at least to stabilize the clinical course.

Surgical treatment of post-traumatic myelopathy associated with syringomyelia.

Retrospective review. Evaluate the clinical outcome of surgical intervention for post-traumatic syringomyelia. Progressive post-traumatic cystic myelopathy (PPCM), or syringomyelia, can occur after spinal cord injury. The authors present their surgical treatment protocol and treatment outcome of a series of patients with post-traumatic syringomyelia. The medical records of 53 patients with PPCM undergoing surgical treatment were reviewed. Laminectomies and intraoperative ultrasonography were performed. For patients with no focal tethering and only a confluent cyst on ultrasonography, a syringosubarachnoid shunt (stent) was inserted. For patients with both tethering and a confluent cord cyst, an untethering procedure was performed first. When a cyst showed significant size reduction (>50%) after untethering, no shunt was placed. When the cyst size persisted on ultrasonographic images, a short syringosubarachnoid shunt was used. The mean follow-up was 23.9 months for the 45 patients available for follow-up (range 12-102 months). The interval between the causative event and the operation was from 5 months to 37 years (mean 6.5 years). Pain was the most frequent manifestation, followed by motor deterioration and spasticity. Postoperative improvements in >50% of the patients were noted in those presenting with worsening motor function or spasticity. In 19 of 28 patients with associated tethered spinal cord, untethering alone caused significant collapse of the cyst. Postoperative MRI demonstrated cyst collapse in 95% of the patients with untethering alone and 93% of the patients with a syringosubarachnoid shunt. Post-traumatic syringomyelia can occur with or without cord tethering. Untethering alone for patients with cord tethering and cyst formation can reduce cyst size and alleviate the symptoms and signs of syringomyelia in the majority of these cases. Untethering with expansion of subarachnoid space with an expansile duraplasty may be a more physiologic way of treating a tethered cord with associated syringomyelia, i.e., treating the cause rather than the result.

Syringosubarachnoid shunt for syringomyelia associated with Chiari I malformation

The authors describe the surgical procedures for placing syringosubarachnoid shunts and the results of surgery, as well as the prevention of shunt malfunction. The series consisted of 59 patients with syringomyelia associated with Chiari I malformation in whom syringosubarachnoid shunts were placed. Their ages ranged from 4 to 62 years (median 28 years). The follow-up period ranged from 13 to 219 months. The authors principally implanted the shunts in patients with large-sized syringes. Neurological improvement was satisfactory, and postoperative magnetic resonance imaging demonstrated that the syringes had resolved or decreased in size in all patients. Reoperation was necessary in 10 patients who were treated before 1993. To prevent shunt malfunction, both dorsal root entry zone myelotomy and placement of the syringosubarachnoid shunt tube into the ventral subarachnoid space are useful.

CHIARI I MALFORMATION

The Chiari I malformation (CMI) is a caudal displacement of the cerebellar tonsils into the cervical spinal canal. It is generally agreed that CMI is defined by tonsillar herniation more than 5 mm below the plane of the foramen magnum. The disorder affects children and adults and may be congenital or acquired. Although advances in magnetic resonance (MR) imaging have significantly enhanced our ability to diagnose CMI, management of this condition remains controversial. In patients with CMI, the most common presenting symptom is pain. Presenting signs include brainstem, cerebellar, and spinal cord dysfunction. The widespread use of MR imaging has led to CMI being diagnosed with increased frequency earlier in a patient’s life and sometimes even prior to the onset of symptoms. Despite advances in neuroimaging, major questions about CMI remain unanswered. What are the indications for surgery? What type of operation should be performed? Should patients with significant hydrosyringomyelia be treated differently? How should patients with asymptomatic CMI be managed? In this issue of Neurosurgical Focus, we explore the complexities of CMI with a diversity of reports that answer some of the aforementioned questions and pose new ones. Leading off is Bejjani with a discussion of the adult CMI. The author provides a historical review of CMI, beginning with the earliest descriptions of the disorder in the nineteenth century and ending with a detailed account of the radiological criteria in the modern MR imaging era. Alden and colleagues discuss the clinical presentation of CMI and review the evolution of different surgical approaches. These authors then present their clinical experience and provide an algorithm, which suggests that the surgical approach be tailored to treat the predominant clinical problem. Next, Alzate, et al., review a series of 66 consecutive patients with CMI who underwent surgical decompression of the craniovertebral junction. More than half the patients in this series had hydrosyringomyelia, and the authors recommend placing a syringosubarachnoid shunt at the time of foramen magnum decompression if there is a large symptomatic syrinx. Although patients in this series had an excellent outcome, the authors call for further studies to determine whether or when a shunt should be placed. Pandey and coworkers report on a subset of children with symptomatic CMI who presented with so-called “cerebellar fits.” Preoperatively, these children had a fulminant course with drop attacks, abnormal posturing, and varying degrees of respiratory compromise. Recognition of this entity is important because the diagnosis can be confused with cardiogenic syncope or cortical epilepsy, and patients recover promptly following foramen magnum decompression. In Menick’s paper on phase-contrast MR imaging he examines the use of preand postoperative noninvasive real-time imaging to look at cerebellar tonsillar motion at the craniovertebral junction. This technique provides information about the physiological status of the subarachnoid space at the foramen magnum and may be of predictive value in patients with hydrosyringomyelia. Along the same lines, Alperin and colleagues use phase-contrast MR imaging to evaluate blood and cerebrospinal fluid flow before and after surgery in patients with CMI. They found a markedly abnormal intracranial volume change waveform in patients with symptomatic CMI and suggest that MR imaging measurement of hemodynamic and hydrodynamic changes may provide useful information for guiding therapy. The final paper by Hida and Iwasaki describe the treatment of patients with CMI and hydrosyringomyelia by syringosubarachnoid shunt placement without foramen magnum decompression. This work will probably be judged as controversial because the authors have gone against the mainstream approach of foramen magnum decompression for symptomatic CMI. Their results were generally good, although 17% of patients in their series required repeated surgery. Of interest is the authors’ suggestion for improving the patency of syringosubarachnoid shunts by placing the proximal catheter into the ventral subarachnoid space. We hope you will find this issue of Neurosurgical Focus to be informative and provocative and that it will serve as a stimulus for further investigation. Alan R. Cohen, M.D., Rainbow Babies & Children’s Hospital, Cleveland, Ohio Sarah J. Gaskill, M.D., Pediatric Neurosurgery of South Texas, San Antonio, Texas

Treatment of Chiari type I malformation in patients with and without syringomyelia: a consecutive series of 66 cases

The authors describe the results of performing a standard posterior craniovertebral decompression and placement, if indicated, of a syringosubarachnoid shunt for the treatment of patients with Chiari I malformation with and without syringomyelia. This is a retrospectively analyzed consecutive series of 66 patients (mean patient age 15 years, range 1-53 years). The uniform posterior craniovertebral decompression consisted of a small suboccipital craniectomy, a C-1 laminectomy, microsurgical reduction of the cerebellar tonsils, and dural closure with a synthetic dural graft to increase the cerebrospinal fluid space at the craniocervical junction. The presence of a large syrinx, with significant thinning of the spinal cord tissue and obliteration of the spinal subarachnoid space, particularly when combined with syrinx-related symptoms, was an indication for the placement of a syringosubarachnoid shunt. In 32 patients Chiari I malformation alone was present, and 34 in patients it was present in combination with syringomyelia. Clinical findings included pain, neurological deficits, and spinal deformity. The presence of syringomyelia was significantly associated with the presence of scoliosis (odds ratio 74.4 [95% confidence interval 8.894-622.4]). All patients underwent a posterior craniovertebral decompression procedure. In 22 of the 34 patients with syringomyelia a syringosubarachnoid shunt was also placed. The mean follow-up period was 24 months (range 3-95 months). Excellent outcome was achieved in 54 patients (82%) and good outcome in 12 (18%). In no patient were symptoms unchanged or worse at follow-up examination, including four patients who initially required a second operation for persistent syringomyelia. Pain was more likely to resolve than sensory and motor deficits after decompressive surgery. Radiological examination revealed normalization of tonsillar position in all patients. The syrinx had disappeared in 15 cases, was decreased in size in 17, and remained unchanged in two. Posterior craniovertebral decompression and selective placement of a syringosubarachnoid shunt in patients with Chiari I malformation and syringomyelia is an effective and safe treatment. Primary placement of a shunt in the presence of a sufficiently large syrinx appears to be beneficial. The question of if and when to place a shunt, however, requires further, preferably prospective, investigation.