Steven D. Ham

Value of Overnight Monitoring of Intracranial Pressure in Hydrocephalic Children

Objective: Exaggerated nocturnal intracranial pressure (ICP) dynamics are commonly observed in hydrocephalic children with a compromise of CSF compensatory reserve capacity. Successful shunting restores this cerebrospinal reserve. We used ICP overnight monitoring combined with positional maneuvers in complex hydrocephalic children with a suspected shunt malfunction for the assessment of shunt function. Methods: In 32 hydrocephalic children, we performed 65 computerized overnight recordings and 25 positional maneuvers. Baseline ICP was considered abnormal if it exceeded the operating pressure of the shunt by more than 2.5 mm Hg. The maximum ICP (normal = <25 mm Hg), RAP coefficient (the correlation coefficient between pulse amplitude and mean intracranial pressure, which indicates pressure volume compensatory reserve; normal = <0.6), magnitude of slow waves (SLOW) and ICP pulse amplitude (AMP) were calculated for each night. Results: Using baseline ICP, maximum ICP and RAP, 19 recordings were classified as ‘normal’ (group 1), 13 as ‘questionable’ (group 2), and 33 as ‘pathological’ (group 3) indicating shunt dysfunction or active hydrocephalus. ICP, AMP, RAP and SLOW were significantly different between groups and significantly elevated in group 3 compared to group 1. Positional tests identified shunt overdrainage in 5 of 25 occasions. In patients of group 1, who underwent revision, shunts turned out to be functional. All patients of group 3 eventually underwent shunt revision with improvement of symptoms thereafter. Conclusion: Computerized ICP monitoring can benefit the assessment of shunt function, and can accurately characterize the status of CSF compensation in shunted children with a complex presentation.

Effects of hydrocephalus and ventriculoperitoneal shunt therapy on afferent and efferent connections in the feline sensorimotor cortex.

OBJECT The authors of previous studies have suggested that connectivity within the cerebral cortex may be irreversibly altered by hydrocephalus. To examine connectivity-related changes directly, the authors conducted a study in which they used an axonal tracer in an animal model of infantile hydrocephalus. METHODS In five hydrocephalic kittens low-pressure ventriculoperitoneal (VP) shunts were placed 10 to 14 days after induction of hydrocephalus by intracisternal kaolin injections. Wheat germ agglutinin-conjugated horseradish peroxidase was injected laterally into the motor cortex in hydrocephalic animals 9 to 15 days after kaolin injection, and 1, 2, and 4 weeks after VP shunt insertion in shunt-treated animals, and in age-matched controls. Reduction of antero- and retrograde labeling was most profound within the contralateral cortex and portions of the midbrain. Thalamic nuclei exhibited reductions in anterograde and retrograde labeling. Labeling within cell bodies of the ventral tegmental area decreased greatly in animals with untreated hydrocephalus, in which retrograde labeling was reduced in the locus coeruleus but did not affect the raphe nucleus. Shunt treatment increased both antero- and retrograde labeling of contralateral motor cortex to near-normal levels. Thalamic relay nuclei recovered antero- and retrograde labeling, although not to levels exhibited in controls. Shunt therapy restored cellular labeling within the ventral tegmental area and locus coeruleus. Recovery of labeling occurred as early as 7 days after shunt insertion. CONCLUSIONS Collectively, analysis of these data indicates the following. 1) Cortical connectivity involving both afferent and efferent pathways was impaired in untreated hydrocephalic animals. 2) Shunt therapy improved both cortical afferent and efferent connectivity. 3) Complete reestablishment of the cortical efferent pathways, however, did not occur. Cortical pathway dysfunction, if permanent, could cause many of the motor and cognitive deficits seen clinically in children with hydrocephalus.

Frontal and occipital horn width ratio for the evaluation of small and asymmetrical ventricles.

The aim of this study was the introduction of a new linear ventricular measurement which has a better correlation with ventricular volume than the commonly used linear measurements, especially in chronically shunted patients with small and/or asymmetrical ventricles. Ventricular volume, brain volume, Evans ratio, Schierman index, cella media index and frontal and occipital horn ratio were measured from CT scans of 57 shunted hydrocephalic patients and 20 normal control children. Four groups of patients were identified with regards to the ventricular size and symmetry (small, large, symmetrical and asymmetrical). A new linear measurement was defined as half of the ratio of the frontal and occipital ventricular width to that of the skull (frontal and occipital horn width ratio; FOHWR) and compared to other linear measurements in different patient groups. FOHWR showed better correlation with ventricular size and ventricular brain ratio than the ventricular linear measurements currently in use, especially in chronically shunted patients with small and/or asymmetrical ventricles.

Cerebral Anomalies and Chiari Type 1 Malformation

Objective: To analyze the association of diverse cerebral anomalies in a series of pediatric patients with cerebellar tonsillar ectopia. Methods: We reviewed the medical records of 60 children diagnosed with Chiari type 1 malformation (CM1), of these, 20 patients (11 boys and 9 girls; mean age 7.2 years, range 2–16 years) had an associated cerebral anomaly. Symptoms of tonsillar ectopia evolved over a mean of 12 months (range 3 months to 4 years). Syringomyelia was present in 5 cases. All patients underwent a posterior fossa decompression. Results: Disclosed anomalies included: congenital hydrocephalus (n = 11), cervicomedullary kinking (n = 5), focal cerebral heterotopia with epilepsy (n = 4), partial agenesis of the corpus callosum (n = 4), hypoplastic brain stem (n = 2), holoprosencephaly (n = 1), and subcortical dysplasia in the context of neurofibromatosis type 1 (n = 1). Other malformations included: subcortical hamartoma associated with neurofibromatosis type 1, craniofacial dysmorphism secondary to Noonan syndrome, congenital occipital plagiocephaly, os odontoideum, craniofacial cleft, juvenile rheumathoid arthritis with platybasia, and osteogenesis imperfecta with bathrocephaly and scoliosis. Conclusion: Craniocerebral anomalies in children treated for CM1 may be found consistently. The association of hydrocephalus, which was the most common anomaly in this cohort, with cerebellar tonsillar ectopia may contribute to a poor outcome in regard to tonsillar herniation symptoms.

Useful components of the shunt tap test for evaluation of shunt malfunction

Results of shunt tap were studied in 224 clinically or radiologically suspected instances of shunt malfunction. In 130 retrospectively studied patients the results of the tap had reported the opening pressure and ease of aspiration. In 94 prospectively studies instances the shunt tap parameters described were (i) the opening pressure, (ii) the drip interval, i.e., the interval between the drops of cerebrospinal fluid when the open end of the butterfly used for tapping was placed 5 cm below the level of the valve, and (iii) the closing pressure. The efficacy of the aspiration procedure for proximal malfunction was 40.3%, compared with the efficacy of drip interval which was 95.1%. For distal malfunction, the efficacy of measurement of opening pressure was 54.3% whereas that of closing pressure was 60.6%. An in vitro model of a functioning shunt showed that the opening and the closing pressures were related to the flow rate and the level of the distal catheter tip with respect to the valve, whereas the drip interval was linearly related to the flow through the proximal catheter and was independent of the distal catheter position. The opening pressure, closing pressure, and the drip interval recorded at surgery were not significantly different from the values obtained by shunt tap. The results suggested that shunt tap accurately provides information otherwise obtained at surgery and the drip interval is most useful for evaluating a proximal malfunction. The subjective impression of the distal flow may be more helpful in diagnosing distal malfunction rather than the absolute level of opening or closing pressures.

Pure endoscopic removal of pineal region tumors

PurposeEndoscopic resection of pineal tumors using an endoscope with a mounted rigid suction that allows bimanual handling of the tumor for resection. This contrasts to the established method of biopsy of pineal tumors through intraventricular approach.MethodsTwo patients, one with a cystic lesion in the pineal region and one with a large pineal tumor, were operated in sitting position through a subtorcular approach. Endoscope was held in the left hand with suction tip extending beyond the tip through its instrument channel. Regular microsurgical instrumentation/CUSA/Nico Aspirator was used with the right hand for dissection, cutting, and removing the tumor under endoscopic vision.ResultSurgeon comfort was superior to when microscope is used in sitting position. Complete resection was achieved in all cases.ConclusionThe two-handed endoscopic technique using a mounted suction on the endoscope as described is a safe and effective strategy for resecting pineal region tumors.

Complications of bioresorbable fixation systems in pediatric neurosurgery.

ObjectiveBioresorbable devices are an attractive alternative to metal instrumentation for internal fixation of bone, and have been used extensively in orthopedic and craniofacial surgery. In neurosurgery, the reported literature is predominantly confined to pediatric craniofacial procedures, with encouraging results and minimal complications. We have used bioreabsorbable plates and screws in cranial and spinal pediatric neurosurgery procedures. We report four complications related to their usage.Materials and methodsBioabsorbable instrumentation was used in pediatric patients for fixation of bone after cranial or spinal procedures.ResultsFour patients developed complications related to the instrumentation: 2 following cranial surgery for epilepsy, 1 after correction of a growing skull fracture, and 1 after laminotomy for an intramedullary tumor. Two patients had fibrous encapsulation with granuloma formation and 2 patients had osteolysis following the fixation.ConclusionBioabsorbable fixation devices for the stabilization of bone following craniotomy and laminotomy in pediatric patients may be associated with complications, including granuloma formation and osteolysis.

Evaluation of Shunt Malfunction Using Shunt Site Reservoir

Objective: To determine the usefulness of a separate reservoir placed at the site of the shunt in evaluation of shunt malfunction. Methods and Materials: A ventricular catheter was placed alongside the proximal catheter of the shunt and connected to a subgaleal reservoir in 17 patients, in 9 a double-lumen catheter with integrated reservoir and in 13 patients a dual catheter with a double-port reservoir was used. At presentation of suspected shunt malfunction, a standard shunt function evaluation using shunt tap, CT scan or shunt injection was performed, and subsequently, the pressure from the tap of the reservoir was obtained. Results: Thirty-three patients presented with symptoms of malfunction at an interval of 2.3 ± 3 months (range 2–429 days). The pretest probability of shunt malfunction in this population was 73%. Posttest probability of shunt malfunction was 82.5% with standard evaluation and improved to 100% by the separate reservoir tap pressure measurement. In 4 patients in whom the shunt tap was dry, shunt infection was diagnosed prior to revision using CSF obtained at the reservoir tap. In 5 patients with proximal malfunction and bradycardia, the reservoir tap allowed early ventricular decompression. Conclusion: This study shows that a reservoir placed at the site of the shunt remains patient even when the shunt malfunctions, suggesting that flow rather than catheter position is important in proximal malfunction. It is superior to shunt tap for detection of shunt malfunction and infection, and it allows early ventricular decompression in a sick patient awaiting surgery for shunt revision.

Postural changes in intracranial pressure in chronically shunted patients

A subset of hydrocephalic patients with indwelling shunts become symptomatic when they are upright and active. Intracranial pressure (ICP) measurements in these patients have shown a significant drop in pressure when the patient is upright with return to normal levels when the patient is supine. In 20 chronically shunted hydrocephalic patients who previously had no siphon protection devices, ICP changes in supine and upright position were studied at the time when the patient had external ventriculostomy for treatment of shunt infection. Our hypothesis was that these patients might display rapid changes in ICP from fluid shifts occurring in non-CSF compartments. To minimize the effects of hysteresis, drift and zero-point error, measurements were made using a fluid manometer rather than a strain gauge pressure transducer. The pressure-volume index was estimated using the standard technique of bolus injection. Intracranial CSF volume was estimated on CT scans. The fluid shift was calculated using a mathematical model of the CSF compartment that incorporates negative pressure and volume components that permits simulation of siphoning. Sixteen patients had small, slit ventricles; 3 patients had moderate-sized ventricles and in 1 patient the ventricular size was normal. The average intracranial CSF volume estimated on CT scan was 12 cm3. There was a mean drop in ICP in the upright position of 159 mm H2O. The mean PVI of 42 ml suggested a volume displacement out of proportion to the available intracranial CSF volume. Based on these findings, we conclude that even in the absence of drainage through the shunt, chronically shunted patients still display a fall in ICP when assuming the upright position. This raises the possibility of fluid shifts other than of CSF through nonshunt pathways. Possible mechanisms involving altered CSF-venous system interaction are discussed.

Effect of molding helmet on head shape in nonsurgically treated sagittal craniosynostosis: Clinical article

OBJECT Sagittal craniosynostosis is traditionally considered to be a surgical condition. Poor results of simple suturectomy follow from early reclosure of the suture. A wider craniectomy or use of interposing materials has not improved the outcome. However, endoscopic suturectomy supplemented with postoperative use of a molding helmet has shown good results. Because suturectomy reunites within 8-12 weeks of surgery, the authors questioned if the improved outcome was primarily related to use of the helmet. METHODS In 4 patients whose families opted for calvarial reconstruction when the infant was 4-6 months old, instead of endoscopic suturectomy, a molding helmet was used to minimize compensatory changes in the interim. Patients underwent 3D CT scanning to confirm craniosynostosis. Follow-up visits were made at intervals of 4 weeks for adjustment of the helmet, head circumference measurements, clinical photographs, and cranial index measurement. RESULTS There was significant improvement in the head shape within 6 weeks of use of the molding helmet. The cranial index score improved from a mean (± SD) of 67% ± 3% to 75% ± 2%. CONCLUSIONS These cases demonstrate that molding helmets improve head shape even without a suturectomy in patients with sagittal craniosynostosis, challenging the traditional view.