Jason M. Sansone and Bermans J. Iskandar
Advances in endoscopic technology have afforded the neurosurgeon new avenues in the treatment of hydrocephalus, rendering many patients independent of shunts, thus averting shunt complications and failure. Cerebral aqueductoplasty has gained popularity as an effective treatment for membranous and short-segment stenoses of the sylvian aqueduct. Traditionally, this procedure has been performed via a coronal approach, passing through the lateral ventricle, foramen of Monro, and third ventricle into the aqueduct. The authors report on the success of a novel technique for this operation, in which they use a suboccipital foramen magnum trans—fourth ventricle approach.
A retrospective chart review was performed to document the success of cerebral aqueductoplasty procedures via the foramen magnum trans—fourth ventricle approach in patients who had membranous or short-segment stenosis of the cerebral aqueduct. Nine patients underwent 11 cerebral aqueductoplasty procedures. At a mean of 21 months of postoperative follow up, all patients demonstrated resolution of their preoperative symptoms. The only surgical complication was transient vertical diplopia or upgaze weakness in two patients. There was no permanent morbidity. Recurrent aqueductal stenosis developed in one patient twice, requiring the placement of an aqueductal stent via the same approach.
The authors state that in their experience, performing cerebral aqueductoplasty via the foramen magnum trans—fourth ventricle approach is both effective and safe. They advocate the use of this technique, if performed by an experienced neuroendoscopist, for select cases involving membranous or short-segment stenosis of the cerebral aqueduct, a trapped fourth ventricle, or aqueductal stent placement.
Bermans J. Iskandar and Victor Haughton
Measurements of cerebrospinal fluid (CSF) velocities in the foramen magnum are used to determine the functional significance of Chiari malformation Type I (CM-I). Significantly higher peak velocities are found in adult patients with CM-I than in adult control participants. In addition, it appears that higher CSF velocities are found in pediatric patients with CM-I than in adult patients. Variations in CSF velocities across age groups in healthy individuals, however, have not been systematically studied.
Phase-contrast magnetic resonance imaging was performed in 10 pediatric patients after induction of anesthesia to evaluate conditions thought not to affect CSF flow in the foramen magnum. The peak systolic and diastolic velocities were plotted with respect to age and compared with velocities obtained in a group of 10 healthy adult volunteers. Differences between the adult and pediatric groups were tested for significance by using the Student t-test.
Peak velocities ranged from 1.9 to 19.9 cm/second in the pediatric group and from 1.2 to 4.5 cm/second in the adults. A trend line fitted to the data showed a decrease in velocity with age in the first two decades of life, and little change thereafter. Differences in the pediatric and adult groups were significant at a level of 0.05.
Peak CSF velocities vary significantly with age. To determine the normalcy of a CSF flow measurement, it must be compared with age-appropriate normative data.
Brandon G. Rocque, Samir Lapsiwala, and Bermans J. Iskandar
The clinical diagnosis of cerebrospinal fluid (CSF) shunt malfunction can be challenging. In this prospective study, the authors evaluated a common method of interrogating shunts: the shunt tap; specifically, its ability to predict proximal malfunction.
The authors performed standardized shunt taps in a consecutive series of cases involving children with suspected or proven shunt malfunction, assessing flow and, when possible, opening pressure. Data were collected prospectively, and results analyzed in light of surgical findings.
A shunt tap was performed prior to 68 operative explorations in 51 patients. Of the 68 taps, 28 yielded poor or no CSF flow on aspiration. After 26 of these 28 procedures, proximal catheter obstruction was identified. After 28 taps with good CSF return and normal or low opening pressure, 18 shunts were found to have a proximal obstruction, 8 had no obstruction, and 2 had a distal obstruction. Another 12 taps with good CSF flow had high opening pressure; subsequent surgery showed distal obstruction in 11 of the shunts, and proximal obstruction in 1. The positive predictive value of poor flow was 93%, while good flow on shunt tap predicted adequate proximal catheter function in only 55% of cases.
Poor flow of CSF on shunt tap is highly predictive of obstruction of the proximal catheter. Because not all patients with good flow on shunt tap underwent surgical shunt exploration, the specificity of this test cannot be determined. Nonetheless, a shunt tap that reveals good flow with a normal opening pressure can be misleading, and management of such cases should be based on clinical judgment.
Bermans J. Iskandar, Mark Quigley, and Victor M. Haughton
Object. The Chiari I malformation presents significant challenges to clinicians because its pathophysiology is not well understood. In conducting cerebrospinal fluid (CSF) flow studies, investigators have attempted to correlate the clinical severity of these lesions with general flow velocity or bulk flow at the foramen magnum; however, these techniques have not allowed consistent prediction of symptomatology, explanation of the presence of syringomyelia, or the assessment of the hydrodynamic characteristics of the decompression. The authors used temporally and spatially resolved flow analyses to assess the characteristics of CSF flow in children with Chiari I malformation and the changes in these flow characteristics that occur after suboccipital decompression.
Methods. The authors studied eight children with symptomatic Chiari I malformation with or without syringomyelia and two children without Chiari I malformation. All patients underwent phase-contrast magnetic resonance imaging before and after posterior fossa decompression. Velocity plots were displayed for each voxel. Several indices of CSF flow were developed to characterize the flow patterns associated with Chiari I malformation.
In children with symptomatic Chiari I malformation, even though bulk flow or velocity is often normal, there was marked heterogeneity of flow at the foramen magnum. This was evident for several reasons: 1) an increase in cephalad and caudad peak velocities; 2) spatial inhomogeneity in velocities; 3) simultaneous bidirectional flow; and 4) substantial net craniad or caudad flows within particular voxels and subregions during the cardiac cycle. After posterior fossa decompression, the severity of these flow abnormalities decreased.
Conclusions. Foramen magnum CSF flow in children with symptomatic Chiari I malformations is spatially and temporally heterogeneous, and this heterogeneity improves postoperatively. The authors propose that relying on mean flow parameters in patients with Chiari I malformation is no longer sufficient; instead, more elaborate techniques to analyze foramen magnum CSF flow have become necessary.
Mark R. Kraemer, Carolina Sandoval-Garcia, Taryn Bragg, and Bermans J. Iskandar
The authors conducted a survey to evaluate differences in the understanding and management of shunt-dependent hydrocephalus among members of the American Society of Pediatric Neurosurgeons (ASPN).
Surveys were sent to all 204 active ASPN members in September 2014. One hundred thirty responses were received, representing a 64% response rate. Respondents were asked 13 multiple-choice and free-response questions regarding 4 fundamental problems encountered in shunted-hydrocephalus management: shunt malfunction, chronic cerebrospinal fluid (CSF) overdrainage, chronic headaches, and slit ventricle syndrome (SVS).
Respondents agreed that shunt malfunction occurs most often as the result of ventricular catheter obstruction. Despite contrary evidence in the literature, most respondents (66%) also believed that choroid plexus is the tissue most often found in obstructed proximal catheters. However, free-text responses revealed that the respondents’ understanding of the underlying pathophysiology of shunt obstruction was highly variable and included growth, migration, or adherence of choroid plexus, CSF debris, catheter position, inflammatory processes, and CSF overdrainage. Most respondents considered chronic CSF overdrainage to be a rare complication of shunting in their practice and reported wide variation in treatment protocols. Moreover, despite a lack of evidence in the literature, most respondents attributed chronic headaches in shunt patients to medical reasons (for example, migraines, tension). Accordingly, most respondents managed headaches with reassurance and/or referral to pain clinics. Lastly, there were variable opinions on the etiology of slit ventricle syndrome (SVS), which included early shunting, chronic overdrainage, and/or loss of brain compliance. Beyond shunt revision, respondents reported divergent SVS treatment preferences.
The survey shows that there is wide variability in the understanding and management of shunt-dependent hydrocephalus and its complications. Such discrepancies appear to be derived partly from inconsistent familiarity with existing literature but especially from a paucity of high-quality publications.
Harold L. Rekate
Aaron F. Struck, Michael J. Murphy, and Bermans J. Iskandar
✓ Arachnoid cysts are commonly thought to arise from either congenital defects or trauma. In this article the authors report the spontaneous development of a suprasellar third ventricular arachnoid cyst whose origin was not clearly congenital or traumatic. At the age of 4 months, the patient presented with hypertonia, and a magnetic resonance (MR) imaging study showed no abnormalities. At the age of 2 years, the boy presented with headaches and projectile eme-sis, symptoms that prompted further imaging studies. An MR image of the brain revealed a suprasellar cyst and obstructive hydrocephalus. The cyst was endoscopically fenestrated, which led to long-term symptom resolution.