Peter W. Carmel and James Drake
James M. Drake
✓The tethered spinal cord is a fascinating yet controversial condition seen frequently in neurosurgical practice. Treatment decision making is made difficult by the variety of lesions and clinical presentations comprised by this condition and the absence of high-quality clinical outcome data to provide guidance. Clinical presentations may be divided into four general categories or typical scenarios: 1) significant dysraphic abnormality, clear clinical deterioration; 2) significant dysraphic abnormality, clinically normal or stable deficit; 3) incidentally discovered abnormality, other problem; and 4) tethered spinal cord symptomatology, normal imaging. The author provides case examples to illustrate potential treatment approaches and suggests balancing the risks and benefits for each general category.
Clearer diagnostic and treatment strategies for the tethered spinal cord will only result from high-quality clinical and basic research. Until the results of such research are available, surgeons should endeavor to maximize benefit and reduce risk for patients who may have a tethered spinal cord, walking the fine line between over- and undertreatment.
John R. W. Kestle, D. Douglas Cochrane, and James M. Drake
The potential for increased complications related to the arrival of new residents in July each year has not previously been demonstrated in the neurosurgical literature. The authors investigated this phenomenon in children undergoing cerebrospinal fluid shunt surgery.
Data were obtained from a multicenter hydrocephalus clinical trials database and from hospital admission records in English-speaking Canada. Data pertaining to patients treated in July and August were compared with those pertaining to patients treated during the remainder of the year. The incidence of shunt failure, shunt infection, neurological deficits, wound infection, technical errors, and death were compared using a chi-square test for categorical outcomes, means for continuous outcomes, and survival analysis for time-dependent outcomes.
In the hydrocephalus clinical trials database, 138 of 737 patients were treated in July and August. The median duration of shunt lifespan (hereafter referred to as “shunt survival”) was 1.7 years for patients treated during the summer months and 2.4 years for those treated throughout the rest of the year (p = 0.10); for shunt infection the figures were 13.8 and 8.8% (p = 0.08) of the total number of cases, and for wound dehiscence they were 2.9 and 0.7% (p = 0.05), respectively. When all shunt procedures were included, an examination of shunt survival and infection incidence rates recorded in the Canadian Hospital Discharge Database seemed to imply a significant advantage to having surgery between September and June (log-rank statistic = 7.10, p = 0.008).
The data suggest a “July effect” on some outcomes related to shunt surgery, but the effect was small. Nonetheless, the potential morbidity of shunt failure, infection, and the cost of treatment indicate that continued vigilance and appropriate supervision of new staff by attending surgeons is warranted.
Yuzuru Tashiro and James M. Drake
Intellectual impairment has been related to alteration of neuronal innervation in the following regions: cholinergic basal forebrain nuclei (Ch1–Ch6, learning and memory), dopaminergic ventral tegmental area (emotional control), and noradrenergic locus ceruleus (cognition). Recent studies have implicated neuronal injury in the pathogenesis of hydrocephalus.
Object. The authors used immunohistochemical techniques to investigate functional injury in these regions in animals with progressive hydrocephalus, following shunt placement for cerebrospinal fluid (CSF) drainage.
Methods. Hydrocephalus was induced in 20 Wistar rats by intracisternal injection of 0.05 ml of 25% kaolin solution. Four control animals (Group 1) received the same volume of saline. Ventriculoperitoneal shunts were inserted in eight rats at 2 and 4 weeks after kaolin injection and the animals were killed at 8 weeks (Group 2). The other 12 hydrocephalic animals were killed at 2, 4, and 8 weeks without undergoing shunt placement (Group 3). Immunoreactive (IR) neurons to choline acetyltransferase (ChAT) in Ch1–Ch6, tyrosine hydroxylase (TH) in the ventral tegmental area, and dopamine B-hydroxylase (DBH) in the locus ceruleus, as well as IR projection fibers in the terminal areas, were compared between groups. The number of ChAT- and TH-IR neurons in rats with and without shunt placement was counted for quantitative analysis. The number of ChAT-IR neurons was progressively reduced during the development of hydrocephalus in Ch1, Ch2, Ch3, and Ch4 (p < 0.05). Tyrosine-hydroxylase-immunoreactive neurons were also reduced in number, and demonstrated decreased projection fibers and terminals. Early shunting (at 2 weeks) restored ChAT and TH immunoreactivity to control levels, but late shunting (at 4 weeks) did not (p < 0.05). The DBH—IR neurons in the locus ceruleus were remarkably compressed by the dilated fourth ventricle, and diminished immunoreactivity was observed in the terminal areas. Shunt placement for CSF also restored the immunoreactivity in this system.
Conclusions. These findings indicate that a progressive functional injury occurs in the cholinergic, dopaminergic, and noradrenergic systems as a result of hydrocephalus. This may contribute to intellectual impairment and might be prevented by early treatment with shunt placement.
James M. Drake
The author describes the paucity of information known about occult tethered cord syndrome and summarizes the argument for using a nonsurgical approach in these cases.
A review of what we do and do not know about this syndrome is provided. Surgical procedures to divide the terminal filum in patients with symptoms of tethered spinal cord without the imaging correlates are said to result in clinical improvement, yet there is little physiological evidence to support the surgical release of the filum in the absence of other anatomical lesions. Validated diagnostic and outcome measures are also lacking, which makes the interpretation of reported results exceedingly difficult. Finally, reports used to support surgical intervention are limited by small size, the absence of control groups, and observer bias.
Without conclusive clinical evidence, the arguments supporting surgery for occult tethered cord syndrome must be viewed cautiously.
Roland N. Auer, James Budny, Charles G. Drake, and Melvyn J. Ball
✓ A 15-year-old youth presented with a history and computerized tomography picture of subarachnoid hemorrhage. Conservative management was undertaken after failure to demonstrate an aneurysm. Reevaluation and operation 15 months later disclosed a firm leathery schwannoma intimately related to the frontal lobe and extending into the cortex in the Virchow-Robin spaces.
Abhaya V. Kulkarni, James M. Drake, and Maria Lamberti-Pasculli
Object. Hydrocephalus is a common condition of childhood that usually requires insertion of a cerebrospinal fluid (CSF) shunt. Infection is one of the most devastating complications that may arise from the presence of CSF shunts. In this study, the authors prospectively analyzed perioperative risk factors for CSF shunt infection in a cohort of children.
Methods. Between 1996 and 1999, 299 eligible patients underwent CSF shunt operations (insertions and revisions) that were observed by a research nurse at a tertiary care pediatric hospital. Several perioperative variables were recorded. All cases were followed postoperatively for 6 months to note any development of CSF shunt infection. A Cox proportional hazards model was used to analyze the relationship between the variables and the development of shunt infection.
Thirty-one patients (10.4%) experienced shunt infection. Three perioperative variables were significantly associated with an increased risk of shunt infection: 1) the presence of a postoperative CSF leak (hazard ratio [HR] 19.16, 95% confidence interval [CI] 6.96–52.91); 2) patient prematurity (< 40 weeks' gestation at the time of shunt surgery: HR 4.72, 95% CI 1.71–13.06); and 3) the number of times the shunt system was inadvertently exposed to breached surgical gloves (HR 1.07, 95% CI 1.02–1.12).
Conclusions. Three variables associated with an increased incidence of shunt infection have been identified. Changes in clinical practice should address these variables, as follows. 1) Great care should be taken intraoperatively to avoid a postoperative CSF leak. 2) Alternatives to placement of a CSF shunt in premature infants should be studied. 3) Surgeons should minimize manual contact with the shunt system and consider the use of double gloves.
Yuzuru Tashiro, Shushovan Chakrabortty, James M. Drake, and Toshiaki Hattori
✓ The authors investigated functional neuronal changes in experimental hydrocephalus using immunohistochemical techniques for glutamic acid decarboxylase (GAD) and two neuronal calcium-binding proteins: parvalbumin (PV) and calbindin D28K (CaBP).
Hydrocephalus was induced in 16 adult Wistar rats by intracisternal injection of a kaolin solution, which was confirmed microscopically via atlantooccipital dural puncture. Four control rats received the same volume of sterile saline. Immunohistochemical staining for GAD, PV, and CaBP, and Nissl staining were performed at 1, 2, 3, and 4 weeks after the injection. Hydrocephalus occurred in 90% of kaolin-injected animals with various degrees of ventricular dilation. In the cerebral cortex, GAD-, PV-, and CaBP-immunoreactive (IR) interneurons initially lost their stained processes together with a concomitant loss of homogeneous neuropil staining, followed by the reduction of their total number. With progressive ventricular dilation, GAD- and PV-IR axon terminals on the cortical pyramidal cells disappeared, whereas the number of CaBP-IR pyramidal cells decreased, and ultimately in the most severe cases of hydrocephalus, GAD, PV, and CaBP immunoreactivity were almost entirely diminished. In the hippocampus, GAD-, PV-, and CaBP-IR interneurons demonstrated a reduction of their processes and terminals surrounding the pyramidal cells, with secondary reduction of CaBP-IR pyramidal and granular cells. On the other hand, Nissl staining revealed almost no morphological changes induced by ischemia or neuronal degeneration even in the most severe cases of hydrocephalus.
Hydrocephalus results in the progressive functional impairment of GAD-, PV-, and CaBP-IR neuronal systems in the cerebral cortex and hippocampus, often before there is evidence of morphological injury. The initial injury of cortical and hippocampal interneurons suggests that the functional deafferentation from intrinsic projection fibers may be the initial neuronal event in hydrocephalic brain injury. Although the mechanism of this impairment is still speculative, these findings emphasize the importance of investigating the neuronal pathophysiology in hydrocephalus.