M.A. Poca

Posterior fossa reconstruction: a surgical technique for the treatment of Chiari I malformation and Chiari I/syringomyelia complex--preliminary results and magnetic resonance imaging quantitative assessment of hindbrain migration.

Experimental models have shown that Chiari I malformation is a primary paraaxial mesodermal insufficiency occurring after the closure of the neural folds takes place. According to these hypotheses, a small posterior fossa caused by an underdeveloped occipital bone would be the primary factor in the formation of the hindbrain hernia. The main objective in the surgical treatment of Chiari I malformation and related syringomyelia is directed to restore normal cerebrospinal fluid dynamics at the craniovertebral junction. The most widely accepted surgical approach is to perform a craniovertebral decompression of the posterior fossa contents with or without a dural graft. It has been emphasized that suboccipital craniectomy should be small enough to avoid downward migration of the hindbrain into the craniectomy. This slump of the hindbrain has been verified by studies using postoperative assessment by magnetic resonance imaging. Our aim in this study is to present a modification of the conventional surgical technique, which we have called posterior fossa reconstruction (PFR). Ten patients were operated on using this technique and compared with a historical control group operated on with the classic approach of making a small suboccipital craniectomy, opening the arachnoid, and closing the dura with a graft. To evaluate the morphological results in both groups objectively, preoperative and postoperative measurements of the relative positions of the fastigium and upper pons above a basal line in the midsagittal T1-weighted magnetic resonance images were obtained. In those cases with syringomyelia, syringo-to-cord ratios were calculated. The mean age of the PFR group was 35 +/- 16 years (mean +/- SD); in the control group it was 35.2 +/- 12 years. In the PFR group, the formation of an artificial cisterna magna was observed in every case; it was observed in only one case in the control group. An upward migration of the cerebellum was seen in all cases in the PFR group, with a mean ascent of the fastigium of 6.2 mm. A significant downward migration of the cerebellum was observed in seven cases in the control group. No significant differences were found in both groups when comparing syringo-to-cord ratios. This leads us to conclude that PFR is more effective than conventional surgical approaches in restoring the normal morphology of the craniovertebral junction. This allows cranial ascent of the hindbrain verified by magnetic resonance imaging and good short-term clinical results. Because PFR is mainly an extraarachnoidal approach, complications related to surgery using this technique can be kept to a minimum.

Reappraisal of the intracranial pressure and cerebrospinal fluid dynamics in patients with the so-called “Normal pressure hydrocephalus” syndrome

SummaryFifty-four shunt-responsive patients were selected from a prospective protocol directed to study patients with suspected normal pressure hydrocephalus (NPH). Patients with gait disturbances, dementia, non-responsive L-Dopa Parkinsonism, urinary or faecal incontinence and an Evans ratio greater or equal to 0.30 on the CT scan were included in the study.As a part of their work-up all patients underwent intracranial pressure monitoring and hydrodynamic studies using Marmarous bolus test. According to mean intracranial pressure (ICP) and the percentage of high amplitude B-waves, patients were subdivided in the following categories: 1) Active hydrocephalus (mean ICP above 15 mmHg), which is in fact no tone normal pressure hydrocephalus; 2) Compensated unstable hydrocephalus, when mean ICP was below 15 mmHg and B-waves were present in more than 25% of the total recording time and 3) Compensated stable hydrocephalus when ICP was lower or equal to 15 mmHg and beta waves were present in less than 25% of the total recording time.The majority of the patients in this study (70%) presented continuous high or intermittently raised ICP (active or unstable compensated hydrocephalus group). Mean resistance to outflow of CSF (Rout) was 38.8 mm Hg/ml/min in active hydrocephalus and 23.5 mm Hg/ml/min in the compensated group (Students t-test, p < 0.05). Higher resistance to outflow was found in patients with obliterated cortical sulci and obliterated Sylvian cisterns in the CT scan.No statistically significant correlation was found when plotting the percentage of beta waves against pressure volume index (PVI), compliance or Rout. An exponential correlation was found when plotting beta waves against the sum of conductance to outflow and compliance calculated by PVI method (r=0.79).Patients with the so-called normal pressure hydrocephalus syndrome have different ICP and CSF dynamic profiles. Additional studies taking into consideration these differences are necessary before defining the sensitivity, specificity and predictive value of ICP monitoring and CSF studies in selecting appropriate candidates for shunting.

Influence of APOE polymorphism on cognitive and behavioural outcome in moderate and severe traumatic brain injury

Aim: To analyse the influence of apolipoprotein (APOE) ε4 status on the cognitive and behavioural functions usually impaired after moderate and severe traumatic brain injury (TBI). Methods: In all, 77 patients with TBI selected from 140 consecutive admissions were genotyped for APOE. Each patient was subjected to neuropsychological and neurobehavioural assessment at least 6 months after injury. Results: Performance of participants carrying the ε4 allele was notably worse on verbal memory (Auditory Verbal Learning Test), motor speed, fine motor coordination, visual scanning, attention and mental flexibility (Grooved Pegboard, Symbol Digit Modalities Test and part B of the Trail Making Test) and showed considerably more neurobehavioural disturbances (Neurobehavioral Rating Scale—Revised) than the group without the ε4 allele. Conclusions: In particular, performance on neuropsychological tasks that are presumed to be related to temporal lobe, frontal lobe and white matter integrity is worse in patients with the APOE ε4 allele than in those without it. More neurobehavioural disturbances are observed in APOE ε4 carriers than in APOE ε2 and ε3 carriers.

Posterior Fossa Reconstruction

Experimental models have shown that Chiari I malformation is a primary paraaxial mesodermal insufficiency occurring after the closure of the neural folds takes place. According to these hypotheses, a small posterior fossa caused by an underdeveloped occipital bone would be the primary factor in the formation of the hindbrain hernia. The main objective in the surgical treatment of Chiari I malformation and related syringomyelia is directed to restore normal cerebrospinal fluid dynamics at the craniovertebral junction. The most widely accepted surgical approach is to perform a craniovertebral decompression of the posterior fossa contents with or without a dural graft. It has been emphasized that suboccipital craniectomy should be small enough to avoid downward migration of the hindbrain into the craniectomy. This slump of the hindbrain has been verified by studies using postoperative assessment by magnetic resonance imaging. Our aim in this study is to present a modification of the conventional surgical technique, which we have called posterior fossa reconstruction (PFR). Ten patients were operated on using this technique and compared with a historical control group operated on with the classic approach of making a small suboccipital craniectomy, opening the arachnoid, and closing the dura with a graft. To evaluate the morphological results in both groups objectively, preoperative and postoperative measurements of the relative positions of the fastigium and upper pons above a basal line in the midsagittal T1-weighted magnetic resonance images were obtained. In those cases with syringomyelia, syringo-to-cord ratios were calculated. The mean age of the PFR group was 35 +/- 16 years (mean +/- SD); in the control group it was 35.2 +/- 12 years. In the PFR group, the formation of an artificial cisterna magna was observed in every case; it was observed in only one case in the control group. An upward migration of the cerebellum was seen in all cases in the PFR group, with a mean ascent of the fastigium of 6.2 mm. A significant downward migration of the cerebellum was observed in seven cases in the control group. No significant differences were found in both groups when comparing syringo-to-cord ratios. This leads us to conclude that PFR is more effective than conventional surgical approaches in restoring the normal morphology of the craniovertebral junction. This allows cranial ascent of the hindbrain verified by magnetic resonance imaging and good short-term clinical results. Because PFR is mainly an extraarachnoidal approach, complications related to surgery using this technique can be kept to a minimum.

Cognitive changes after cerebrospinal fluid shunting in young adults with spina bifida and assumed arrested hydrocephalus

OBJECTIVES To establish whether surgery can improve the neuropsychological functioning of young adult patients with spina bifida and apparent clinically arrested hydrocephalus showing abnormal intracranial pressure. METHODS Twenty three young adults with spina bifida and assumed arrested hydrocephalus (diagnosed as active or compensated by continuous intracranial pressure monitoring) underwent surgery. All patients received neuropsychological examination before surgery and 6 months later. Neuropsychological assessment included tests of verbal and visual memory, visuospatial functions, speed of mental processing, and frontal lobe functions. RESULTS Shunt placement in this subgroup of patients improves neuropsychological functioning, especially in verbal and visual memory and attention and cognitive flexibility. CONCLUSIONS Young adults with spina bifida and suspected non-functioning shunt or non-shunted ventriculomegaly should be carefully monitored to identify those who could benefit from shunting.

Fiberoptic intraparenchymal brain pressure monitoring with the Camino V420 monitor: reflections on our experience in 163 severely head-injured patients.

To assess the safety and accuracy of the Camino intraparenchymal sensor, we prospectively evaluated hemorrhagic complications, zero-drift, infection, and system malfunction in 163 patients monitored after a severe head injury. Mean duration of intracranial pressure (ICP) monitoring was 5 +/- 2.2 days (range: 12 h to 11 days). Of the 141 patients with a control CT scan, four showed a 1-2-cc collection of blood at the catheters end. When removed, the sensors underread the true ICP value (negative zero-drift) in 80 of the 126 sensors evaluated (63.5%). Fourteen sensors showed no zero-drift, and 32 sensors overread the true ICP value (positive zero-drift) (median: -1 mm Hg; interquartile range: -4 to +1 mm Hg). No significant relationship was found between zero-drift, the surgeon who implanted the sensor, intracranial hypertension, or duration of ICP monitoring. No clinical infections could be attributed to the devices. Sixteen patients (9.8%) required more than one ICP sensor due to malfunctioning of the system. In conclusion, continuous ICP monitoring using the Camino intraparenchymal sensor has a low complication rate. However, this sensor may underread the real ICP values in a high number of patients. The lack of correlation between duration of ICP monitoring and zero-drift suggests that, contrary to the recommendations of other reports, the intraparenchymatous Camino sensor can provide reliable readings after the fifth day of use.

Does an Increase in Cerebral Perfusion Pressure Always Mean a Better Oxygenated Brain? A Study in Head-Injured Patients

The adequate management of cerebral perfusion pressure (CPP) continues to be a controversial issue in head-injured patients. The purpose of our study was to test two hypotheses. The first was that in patients with a CPP below 70 mm Hg, oxygen delivery is compromised and that therefore signs of tissue hypoxia would be reflected in low PtiO2 measurements. The second hypothesis was that manipulating mean arterial blood pressure to increase CPP improves oxygen delivery, particularly in patients with a CPP below 70 mm Hg. Twenty-five moderately or severely head-injured patients were included in the study. In all of them PtiO2 was monitored in the non-injured hemisphere using the Licox system (GMS, Kiel-Mielkendorf, Germany). Arterial hypertension was induced with phenylephrine 29 times. To quantify the effect of increasing mean arterial blood pressure (MABP) on oxygen delivery to the brain, the PtiO2-BP index was calculated (PtiO2-BP index = delta PtiO2/delta MABP). In 16 tests (55%) baseline CPP was above or equal to 70 mm Hg and in the remaining 13 (45%) it was below 70 mm Hg. Mean increase in MABP after phenylephrine was 23.7 +/- 10.2 mm Hg. Mean PtiO2 was 29.5 +/- 14.7 mm Hg in patients with a basal CPP of below 70 mm Hg and 28.9 +/- 10.6 mm Hg in patients in the high CPP group. These differences being not statistically significant. The PtiO2-BP index was 0.29 +/- 0.23 in patients with a basal CPP of below 70 mm Hg and in patients with a CPP of above 70 mm Hg this index was 0.16 +/- 0.11 Hg. These differences were not statistically significant (Students t-test, P = 0.09). In our study a low PtiO2 was not observed in patients with marginally low CPPs (48-70 mm Hg) and readings below 15 mm Hg were observed in cases with both normal or supranormal CPPs. We conclude that episodes of low PtiO2 could not be predicted on the basis of CPP alone. On the other hand, raising CPP did not increase oxygen availability in the majority of cases, even if the CPP was markedly improved.

Early ischaemia after severe head injury. Preliminary results in patients with diffuse brain injuries.

SummaryIschaemic brain lesions still have a high prevalence in fatally head injured patients and are the single most important cause of secondary brain damage. The present study was undertaken to explore the acute phase of severely head injured patients in order to detect early ischaemia using Robertsons approach of estimating cerebral blood flow (CBF) from calculated arterio-jugular differences of oxygen (AVDO2), lactates (AVDL), and the lactate-oxygen index (LOI).Twenty-eight cases with severe head injury were included (Glasgow Coma Scale Score below or equal to 8). All patients but one had a non-missile head injury. All the patients had a diffuse brain injury according to the admission CT scan. ICP measured at the time of admission was below 20 mmHg in 17 cases (61%). All patients were evaluated with the ischaemia score (IS) devised in our center to evaluate risk factors for developing ischaemia. Mean time from injury to the first AVDO2/AVDL study was 23.9±9.9 hours.According to Robertsons criteria, 13 patients (46%) had a calculated LOI (-AVDL/AVDO2) value above or equal to 0.08 and therefore an ischaemia/infarction pattern in the first 24 hours after the accident. Of the 15 patients without the ischaemia/infarction pattern, in three cases the CBF was below the metabolic demands and therefore in a situation of compensated hypoperfusion. No patient in our series had hyperaemia. Comparing different variables in ischaemic and non-ischaemic patients, only arterial haemoglobin and ischaemia score (IS) was significantly different in both groups. The ischaemia score had mean of 4.3±1.7 in the ischaemic group and 2.7±1.4 in non-ischaemic patients (p=0.01). It is concluded that ischaemia is highly prevalent in the early period after severe head injury. Factors potentially responsible of early ischaemia are discussed.

Arterio-jugular differences of oxygen (AVDO2) for bedside assessment of CO2-reactivity and autoregulation in the acute phase of severe head injury

SummaryAutoregulation and CO2-reactivity can be impaired independently of each other in many brain insults, the so-called ‘dissociated vasoparalysis’. The theoretical combination of preserved CO2-reactivity and impaired or abolished autoregulation can have many clinical implications in the daily management of brain injured patients. To optimize their treatment, a bedside assessment of autoregulation and CO2-reactivity is desirable. When cerebral metabolic rate of oxygen is constant, changes in arterio-jugular differences of oxygen (AVDO2) reflect changes in CBF. In these situations relative changes in AVDO2 can be viewed as inverse changes in CBF and used as an evaluation method of CO2-reactivity and autoregulation. In 39 consecutive severe head injury patients with a mean age of 28±17 years and a diffuse brain injury, cerebrovascular response to changes in pCO2 was tested in the acute phase after injury (18±8 hours). In 28 of those cases autoregulation was also assessed. A relative CBF value (1/AVDO2) was calculated from baseline AVDO2 and was expressed as 100%. Changes in 1/AVDO2 after inducing pCO2 changes give a good estimate of changes in global CBF. Two different indexes were calculated for CO2-reactivity: 1) absolute CO2-reactivity (CO2RABS) and 2) percentage reactivity (CO2R%). CO2R% was used to separate patients with impaired/abolished CO2-reactivity from those with preserved CO2-reactivity. Patients with CO2R% above 1% were considered in the intact CO2-reactivity group and patients in whom CO2R% was below or equal to 1 % were included in the impaired/abolished CO2-reactivity group. Only five cases (12.8%) presented an impaired/abolished CO2-reactivity. AVDO2 response to induced hypertension was studied in a subset of 28 patients. Phenylephrine was used to increase MABP about 25%. All AVDO2 values were corrected for changes in pCO2. Patients with changes in 1/AVDO2 less than or equal to 20% were included in the intact autoregulation group. Patients with estimated CBF changes above 20% were classified as having an impaired autoregulation (impaired/abolished). In 12 patients (43%) autoregulation was intact. In the remaining 16 patients (57%) autoregulation was impaired. Of the 28 cases, CO2-reactivity was impaired in only five cases. All patients with an impaired CO2-reactivity also had an impaired autoregulation. Moni toring relative changes in AVDO2 permits a reliable study of CO2-reactivity and autoregulation at the bedside. Introducing these variables into the day-to-day management should be considered in treatment protocols.

Decompressive craniectomy in traumatic brain injury after the DECRA trial. Where do we stand

Purpose of reviewThe results of the multicentre, randomized, controlled trial to test the effectiveness of decompressive craniectomy in adults with traumatic brain injury and high intracranial pressure (Decompressive Craniectomy, DECRA) were published in 2011. DECRA concluded that decompressive craniectomy decreased intracranial pressure (ICP) but was associated with more unfavourable outcomes. Our review aims to put the DECRA trial into context, comment on its findings and discuss whether we should include decompressive craniectomy in our clinical armamentarium. Recent findingsThe key message that DECRA conveys is that decompressive craniectomy significantly lowers ICP and shortens the length of the stay in the ICU. However, neither mortality nor unfavourable outcome was reduced when adjusting the significant baseline covariates. SummaryThe claim that decompressive craniectomy increases unfavourable outcome is overstated and not supported by the data presented in DECRA. We believe it premature to change clinical practice. Given the dismal outcome in these patients, it is reasonable to include this technique as a last resort in any type of protocol-driven management when conventional therapeutic measures have failed to control ICP, the presence of operable masses has been ruled out and the patient may still have a chance of a functional outcome. The main lesson to be learned from this study is that an upper threshold for ICP must be used as a cut-off for selecting decompressive craniectomy candidates.