Enigma of raised intracranial pressure in patients with complex craniosynostosis: the role of abnormal intracranial venous drainage

Hominid evolution of the arteriovenous system through the cranial base and its relevance for craniosynostosis

OBJECTIVE

This paper discusses how the evolving hominid architecture of the arteriovenous system through the cranial base diverted foreseeable pathology in the human brain.

MATERIALS AND METHODS

Bipedal upright posture was an early adaptation in mosaic morphological pattern changes in hominid evolution; a key feature, the ability of blood to flow either to vertebral or internal jugular venous systems. Encephalization punctuated hominid evolution, its vulnerable feature, a lower threshold for thermal damage. Comparative analysis of ape and human skulls show "fingerprint" structures, revealing big changes in pattern complexity of the cranial vascular tree. Clues to structural/functional changes span data for apes, humans, and hominid fossils. Here, the increasing vascular network, Australopithecus to Homo sapiens, necessitated changes in the blood flow patterns. The transverse-sigmoid (T/S) and occipital-marginal (O/M) venous networks accommodated hydrostatic changes of blood flow, regulating temperature uniquely: the O/M system enlarged, allowing blood to flow straight down into the vertebral plexus without cooling, and added a vast network of emissary/diploic veins, acting as a brain cooling "radiator." This O/M system was fixed in the Australopithecus robustus lineage, p = 0.000001; high frequencies of emissary foramen were selected for over time. Ontologically, the human neonatal O/M system is fully developed; emissary/diploic veins are established by age 5, setting conditions for selective brain cooling.

CONCLUSION

The Radiator Theory is the evolution of the functionally efficient brain cooling system, fixed in the A. robustus lineage, tying hydrostatic consequences of bipedalism with release of a "thermal constraint" on the encephalizing brain, and reflected in our own ontogeny.

Morphometric analysis of untreated adult skulls in syndromic and nonsyndromic craniosynostosis

The aim of this study was to perform a morphometric analysis of untreated adult skulls displaying syndromic and nonsyndromic craniosynostosis. We analyzed, in detail, 42 adult craniosynostoses (18 scaphocephaly, 11 anterior plagiocephaly, 2 trigonocephaly, 9 oxycephaly, and 2 brachycephaly) from archeological (three skulls) and pathoanatomical samples (39 skulls). The univariate and bivariate measurements from the pathological skulls were compared with 40 anatomical skulls with normal cranial vault morphology. Bony signs of chronic elevated intracranial pressure (ICP) are (1) diffuse beaten copper pattern, (2) dorsum sellae erosion, (3) suture diastasis, and (4) abnormalities of venous drainage that particularly affect the sigmoid-jugular sinus complex. The mean cranial length was significantly greater in scaphocephaly than in anatomical skulls (20.3 vs 18.0 cm), and the sagittal suture was also longer (14.3 vs 11.8 cm). There were three types of suture course in the bregma region in scaphocephaly: anterior spur (28%), normal configuration (61%), and posterior spur (11%). The plagiocephaly measurements showed nonsignificant differences, and there was no correlation between the length of the anterior and middle skull base (ipsilateral anterior-posterior shortening of the skull) and incomplete or complete suture synostosis. Bony signs of chronic elevated ICP were found in 82% of cases of oxycephaly and brachycephaly. In three such cases of oxycephaly, we found a marked (1.8-2.1 cm) elevation of bregma region. One skull (Saethre-Chotzen syndrome) yielded human DNA sufficient for polymerase chain reaction (PCR)-based amplification procedures. Mutation analyses in the FGFR3 gene revealed nucleotide alterations located in the mutational hot spot at amino acid residue 250 (g.C749). The mean cranial length in adult scaphocephaly was 12% greater than anatomical skulls. A unilateral complete or incomplete coronal synostosis can be found with or without plagiocephalic deformation. Elevation of the bregma region is a bony sign of chronic elevated ICP. These data on adult craniosynostosis could be of interest for physicians dealing with craniosynostotic children.

Vein of galen aneurysmal malformations

Different types of malformations share a dilated vein of Galen, but only one of them is a true vein of Galen aneurysmal malformation (VGAM). The optimal window of opportunity for treatment is between 4 and 5 years of months [corrected], because this allows the child to grow and mature. Heart failure and hydrocephalus respond favorably to embolization. Cerebrospinal fluid ventricular shunting, if needed, should be performed after the embolization. The transvenous approach carries significantly elevated morbidity and mortality and is rarely indicated. Anatomic cure of the VGAM is not the main goal of treatment; the ultimate goal is control of the malformation to allow the brain to mature and develop normally.

Anomalous venous drainage preventing safe posterior fossa decompression in patients with chiari malformation type I and multisutural craniosynostosis. Report of two cases and review of the literature

The authors report on two children in whom an anomalous posterior fossa venous drainage pattern prevented safe posterior fossa decompression. Both patients had Chiari malformation Type I, multisutural craniosynostosis, and crowded posterior fossa structures. Both patients had been treated with ventriculoperitoneal shunts for hydrocephalus. Pfeiffer syndrome had been diagnosed in one of the patients, and the other was suspected to have osteogenesis imperfecta. Although both patients were believed to have symptoms resulting from brainstem compression, posterior fossa decompression was not offered due to profound venous anomalies noted on imaging studies that greatly increased the expected risks associated with surgery. These cases are presented to alert neurosurgeons to carefully evaluate the posterior fossa venous anatomy prior to considering posterior fossa decompression with or without occipitocervical fusion or calvarial vault remodeling procedures in patients with multisutural craniosynostosis.

The management of vein of Galen aneurysmal malformations

OBJECTIVE

The vein of Galen aneurysmal malformation (VGAM) is a choroidal type of arteriovenous malformation involving the vein of Galen forerunner. This is distinct from an arteriovenous malformation with venous drainage into a dilated, but already formed, vein of Galen. Reports of endovascular treatment of VGAM in the literature approach the disease from a purely technical viewpoint and often fail to provide satisfactory midterm results. To focus the therapeutic challenge to a strictly morphological goal overlooks the fundamental aspects of neonatal and infant anatomy and fluid physiology. During the past 20 years, our approach to VGAM has remained the same. Our experience, based on 317 patients with VGAM who were studied in Hospital Bicêtre between October 1981 and October 2002, allows us to describe the angioarchitecture, natural history, and management of VGAM in neonates, infants, and children.

METHODS

Of our cohort of 317 patients, 233 patients were treated with endovascular embolization; of these, 216 patients were treated in our hospital. The treatment method of choice was a transfemoral arterial approach to deliver glue at the fistulous zone.

RESULTS

Of 216 patients, 23 died despite or because of the embolization (10.6%). Twenty out of the 193 (10.4%) surviving patients were severely retarded, 30 (15.6%) were moderately retarded, and 143 (74%) were neurologically normal on follow-up.

CONCLUSION

Our data demonstrate that most treated children survive and undergo normal neurological development; an understanding of the clinical, anatomical, and pathophysiological features of VGAM has, therefore, reversed the former poor prognosis. Our level of understanding about the lesion allows us to predict most situations and remedy them by applying a strict evaluation protocol and working within an optimal therapeutic window. Patient selection and timing remain the keys in the management of this condition. It is more important to restore normal growth conditions than a normal morphological appearance, with the primary therapeutic objective being normal development in a child without neurological deficit.

Prevalence of Abnormal Pattern Reversal Visual Evoked Potentials in Craniosynostosis

BACKGROUND

The purpose of this study was to examine the prevalence and type of changes observed in the pattern reversal visual evoked potentials recorded at the first assessment of children with craniosynostosis.

METHODS

Visual evoked potentials were recorded from 114 patients with craniosynostosis. Eighty-one patients were syndromic and 33 were nonsyndromic. No patient had received any craniofacial surgical intervention. At the time of the test, 22 of 40 patients were aged 6 months and younger, and 18 patients were between 6 months and 1 year of age. Pattern reversal visual evoked potentials were recorded from a midoccipital electrode positioned 3 cm above the inion. The pattern reversal visual evoked potentials elicited to 50' checks with three reversals per second viewed with both eyes were analyzed for n80-p100 amplitude, p100 latency, and breadth of waveform.

RESULTS

Sixty percent of patients had abnormal pattern reversal visual evoked potentials to 50' checks. This did not show a significant association with age, or classification of craniosynostosis.

CONCLUSIONS

The high prevalence of abnormal pattern reversal visual evoked potentials to a robust stimulus suggests that visual pathway dysfunction, as measured electrophysiologically, can affect a majority of patients with craniosynostosis. This study indicates that a baseline evaluation of all children with craniosynostosis at their first presentation is essential if subsequent electrophysiologic visual pathway monitoring is to take place.

Intracranial pressure monitoring in children with single suture and complex craniosynostosis: a review

INTRODUCTION

One third of patients with craniofacial dysostosis syndromes and about 15-20% of children with single suture craniostenosis have a documented increase in intracranial pressure (ICP). The early detection of intracranial hypertension is important in order to reduce the risks for brain development and visual function. However, in children with craniosynostosis, the clinical manifestations of abnormally increased ICP are difficult to detect, as the majority of patients may have neither warning signs nor symptoms for a long period of time.

REVIEW

Moreover, data from the literature suggest that neither fundoscopic nor radiological findings are necessarily related to intracranial pressure recordings in this type of pathology. In this context prolonged ICP monitoring seems actually to be the most valuable diagnostic tool. Extradural, subdural, and intraparenchymal devices have been used, and different softwares have been employed for PC storage and analysis of the data obtained. Most recent series consider mean ICP combined with plateaux waves as the most sensitive indicators in the final evaluation of the results.

CONCLUSIONS

The analysis of the literature demonstrates a significant difference in the prevalence of raised ICP preoperatively between non-syndromic and syndromic patients. Among the non-syndromic children, a direct relation between the number of sutures involved and raised ICP is documented. The analysis of plateaux waves seems to be particularly important in children with borderline mean ICP values. Persistent postoperative raised ICP has been described in 6-15% of patients with craniofacial dysostosis. It must be related to the multifactorial etiology of increased ICP in these patients, which includes cerebral venous congestion, upper airway obstruction, and hydrocephalus.

Skull base growth in craniosynostosis

INTRODUCTION

The interrelationship of skull base growth and craniosynostosis is one that is not often taken into account in the clinical management of patients with craniofacial disorders by neurosurgeons and craniofacial surgeons. Very early on in our medical training we are taught the anatomical differences between the calvarial unit and skull base portion of the skull. The inherent differences in both underlying tissue components and the different growth characteristics of these two uniquely different structures are critical in understanding skull base growth in craniosynostosis and the inherent potential craniofacial growth in these unique children.

REVIEW

This paper will review some of the basic anatomy of these zones of growth plus review some of the prevalent theories of the effect of skull base growth on craniosynostosis and the converse.

CONCLUSION

While the theories of these growth patterns have yet to be finalized an understanding of their potential influences and abnormal growth patterns remain key to providing a good surgical outcome in surgery for craniosynostosis.

Hydrocephalus in craniosynostosis: a review

INTRODUCTION

Ventricular dilatation in the presence of primary craniosynostosis is a unique condition with respect to pathogenesis, clinical significance, and morphological appearance. It is rarely observed in nonsyndromic craniosynostosis, and in these cases usually attributable to coincidental disorders. Conversely, it is a common feature of syndromic craniosynostosis, affecting at least 40% of patients with Crouzon's, Pfeiffer's or the Apert syndrome. Shunt-dependent hydrocephalus is predominantly associated with Crouzon or Pfeiffer syndrome while in the Apert syndrome the usual finding is nonprogressive ventriculomegaly which, however, may also occur in some cases of Crouzon syndrome.

PATHOGENESIS

The pathogenesis of progressive hydrocephalus remains somewhat obscure, a hypoplastic posterior fossa and a venous outlet occlusion at the skull base being the main causative factors discussed in literature. Ventriculomegaly may reflect primary brain maldevelopment or in some cases even a compensated state of increased cerebrospinal fluid (CSF) outflow resistance. CLINICAL EVALUATION: Clinical evaluation is mainly aimed at identifying progressive hydrocephalus, but diagnosis is hampered by the fact that classical clinical signs may be absent, and that ventricular dilatation will often become evident only after decompressive cranial surgery. Moreover, mild ventriculomegaly may in some cases coexist with intracranial hypertension from craniostenosis. Therefore, careful monitoring of intracranial pressure and ventricular size in the pre- and postoperative period is a diagnostic mainstay.

CONCLUSION

In true hydrocephalus ventriculo-peritoneal shunting is currently the single promising mode of treatment.

Chiari malformation in craniosynostosis

INTRODUCTION

Chiari malformation (CM) is a frequent finding in multisutural and syndromic craniosynostosis, occurring in 70% of patients with Crouzon's syndrome, 75% with oxycephaly, 50% with Pfeiffer's syndrome and 100% with the Kleeblattschädel deformity. The pathogenesis of this condition and rationale for treatment are still controversial.

DISCUSSION

Since its first description in 1972, several factors have been cited to play a role in inducing CM. In the light of recent publications, the roles of premature fusion of cranial vault and cranial base sutures, of congenital anomalies of the cerebellum and brain stem, of raised intracranial pressure, of venous hypertension and of hydrocephalus are reviewed. Evaluation and management of CM are also discussed.

CONCLUSION

Chiari malformation appears to be an acquired and progressive condition that develops in the first months of life, because of a disproportion between hindbrain growth and an abnormally small posterior fossa, a consequence of the premature fusion of lambdoid and cranial base sutures. Venous hypertension caused by stenosis of the jugular foramen can also be present in these patients, resulting in intracranial hypertension and/or hydrocephalus. Careful MRI evaluation is recommended for the forms of craniosynostosis at a high risk of developing hindbrain herniation. The selection of posterior cranial vault expansion as the first surgical procedure is advocated. In selected cases, treatment of the posterior cranial deformity by occipital vault remodelling and treatment of the Chiari-like deformity by suboccipital decompression can be carried out using the same surgical procedure.

Venous hypertension and craniosynostosis

INTRODUCTION

This article addresses the relevance of venous hypertension to children born with, in particular, the "syndromic" forms of craniosynostosis. The development of the human cerebral venous system is summarised and the patterns of anomalous venous drainage seen in children with complex forms of craniosynostosis associated with raised intracranial pressure are described.

AETIOLOGY

The aetiology of these abnormal patterns is discussed under the general headings of "The constriction theory", "A primary role for FGFR mutations" and "Persistence of the foetal pattern of intracranial venous drainage."Venous hypertension (along with hydrocephalus, cranio-cerebral disproportion and airway obstruction) has an important role in the aetiology of raised intracranial pressure in severely affected children.

TREATMENT

The inter-relationship between these factors is explained and then the treatment of those children whose raised intracranial pressure is considered to be due predominantly to venous hypertension is described.

FGFR3 P250R mutation increases the risk of reoperation in apparent 'nonsyndromic' coronal craniosynostosis

Many patients with a clinical diagnosis of "nonsyndromic" coronal craniosynostosis have been found to be heterozygous for the fibroblast growth factor receptor 3 (FGFR3) mutation Pro250Arg. The phenotype associated with this mutation is variable and lacks highly distinctive features, so it is difficult to diagnose on clinical examination alone. The authors present a retrospective study of 76 patients with isolated coronal synostosis who were operated on in a single dedicated craniofacial unit over 25 years. The authors investigated whether any single factor, including the presence of a FGFR3 Pro250Arg mutation, predisposed to an increased transcranial reoperation rate. Eight patients had repeat transcranial surgery for a functional indication. Heterozygosity for the FGFR3 Pro250Arg mutation, present in 29 patients in the cohort, was the only factor found to have a significant association (P=0.048) with the transcranial reoperation rate. Six patients (20.7%) with the mutation underwent reoperation on the basis of raised intracranial pressure, as compared with two patients (4.3%) without the mutation. This highlights the need for genetic analysis and long-term clinical follow-up in apparently "isolated" coronal synostosis.

Adenoid-tonsillectomy to treat visual dysfunction in a child with craniosynostosis

We report a child with isolated saggital synostosis where a gradual deterioration of the P100 component of the pattern reversal visual evoked potential recorded during the day was associated with episodes of upper airway obstruction during sleep that correlated with periods of ICP spiking. Adenoid-tonsillectomy reversed this deterioration with coincident increase in SaO2 and decreased sleep apnoea.

Cranial venous outflow obstruction and pseudotumor Cerebri syndrome

The pathophysiology of PTS including idiopathic intracranial hypertension or 'BIH', remains controversial. The older literature frequently referred to pathology in the cerebral venous drainage but more modern imaging techniques (CT and early MR) failed to reveal gross venous pathology. The role of impaired cranial venous outflow has recently been re-examined in the light of new methods of investigation (advanced MR venography and direct microcatheter venography with manometry) and of treatment (venous sinus stenting). Venous sinus obstruction in PTS is a more common factor in the pathogenesis of the condition than previously recognised. Venous obstruction may be primary, that is, it is the underlying aetiological factor in PTS. Venous sinus obstruction may also be secondary to raised CSF pressure which may exacerbate problems with intracranial compliance and raised CSF pressure. Early experience with venous stenting suggests that it may be a helpful treatment for patients with PTS but more experience and longer follow-up is required to define the subgroups of patients for whom it is most appropriate.

The effects of craniosynostosis on the brain with respect to intracranial pressure

Intracranial pressure (ICP) and skull volume are intricately related. Craniosynostosis alters skull volume, and the many forms of craniosynostosis complicate the relationship to ICP even further. Patients with single-suture synostosis are less likely to experience elevated ICP than patients in whom multiple sutures, craniofacial syndromes, or both are involved. Among patients with more than one suture involved, the multifactorial mechanisms underlying elevated ICP include cephalocranial disproportion and venous outflow obstruction. Direct monitoring of ICP for at least 24 hours can aid in the diagnosis and decision making process. The management of craniosynostotic patients is diverse and necessitates a long-term plan for follow-up.

Visual Loss in Syndromic Craniosynostosis With Papilledema But Without Other Symptoms of Intracranial Hypertension

Four children with syndromic craniosynostosis (Crouzon's syndrome and Apert syndrome) developed irreversible visual loss. Apart from papilledema, there were no other clinical symptoms of intracranial hypertension. Ventriculomegaly or hydrocephalus was present in all cases. Two children were known to have obstructive sleep apnea syndrome. These cases are reported to inform specialists involved in follow-up of children with syndromic craniosynostosis that visual loss can develop suddenly without other symptoms of intracranial hypertension. To prevent visual loss, papilledema should be detected at an early stage and intervention should be instituted promptly. Therefore, periodic funduscopy should be performed in children at risk, such as children with syndromic craniosynostosis and additional hydrocephalus or obstructive sleep apnea syndrome.

Intracranial Pressure Changes in Craniosynostotic Rabbits

Cranial vault and brain deformities in individuals with craniosynostosis are thought to result, in part, from changes in intracranial pressure, but clinical findings are still inconclusive. The present study describes intracranial pressure changes in a rabbit model with naturally occurring, uncorrected coronal suture synostosis. Longitudinal and cross-sectional intracranial pressure data were collected from 241 New Zealand White rabbits, divided into four groups: normal controls (n = 81); rabbits with delayed-onset coronal suture synostosis (n = 78); rabbits with early-onset unilateral coronal suture synostosis (n = 32); and rabbits with early-onset bilateral coronal suture synostosis (n = 50). Epidural intracranial pressure measurements were obtained at 10, 25, 42, and 84 days of age using a NeuroMonitor microsensor transducer. Normal rabbits and rabbits with delayed-onset coronal suture and early-onset unilateral coronal suture synostosis showed a similar oscillating pattern of age-related changes in normal and head-down intracranial pressure from 10 to 84 days of age. In contrast, rabbits with early-onset bilateral coronal suture synostosis showed markedly elevated normal and head-down intracranial pressure levels from 10 to 25 days and showed a different pattern through 84 days. Results from one-way analysis of variance revealed significant (p < 0.01) group differences only at 25 days of age. Rabbits with early-onset bilateral coronal suture synostosis had significantly (p < 0.05) greater normal and head-down intracranial pressure (by 42 percent) than the other three groups. These results showed differing intracranial pressure compensations in rabbits with uncorrected multiple-suture synostosis compared with normal rabbits or rabbits with uncorrected single-suture synostosis, possibly through progressive cerebral atrophy and decreased intracranial volume, abnormal intracranial vascular patterns and blood volume, and/or differing cranial vault compensatory changes.

Neonatal venous cerebral hemorrhage

Intracranial pathological changes can occur as a result of impaired craniocervical venous return. Thrombosis of central venous access catheters was demonstrated in two neonates born at 38 and 27 weeks' gestation. Neither infant developed hemorrhage of prematurity as confirmed on cranial ultrasonography. Clinical evidence of vena cava thrombosis and associated spontaneous intraventricular hemorrhage developed on Day 24 and 36, respectively, and these findings were confirmed on imaging studies. In one infant the hemorrhage was accompanied by communicating hydrocephalus.

The cause of the intracranial disease was attributable to the retrograde cerebral venous congestion. This, together with the primitive venous bed developing in the periventricular region, was associated with the spontaneous hemorrhage in the region of the foramen of Monro.

To the authors' knowledge, this is the first report in the English-language literature of spontaneous neonatal intra-cerebral hemorrhage, due to thrombosis of the superior or inferior vena cava.

The natural history of this condition is resolution without sequelae after appropriate therapeutic intervention for the vena cava thrombosis.

Venous variations of the brain and cranial vault

Vascular anomalies involving both intra- and extra-cranial structures are more common than previously thought. It is important to evaluate the brain and its coverings carefully when imaging cervicofacial vascular malformations. Scientific knowledge regarding developmental mechanisms responsible for blood vessel formation is increasing rapidly and, hopefully, will contribute to better understanding of these clinical and imaging "patterns."

The craniofacial surgeon as amateur geneticist

Craniofacial surgeons, by nature and training, focus on how to correct anomalies rather than on why they occur. Surgeons often leave diagnosis and etiopathogenic speculation to geneticists. Craniofacial surgeons should cross over the specialty line and learn to think like geneticists. This article reviews definitions of basic words in the genetic language and emphasizes the three diagnostic levels, phenotypic, pathogenic, and genetic, for the principal categories of craniofacial anomalies. Whenever possible, examples are given to illustrate how genetic knowledge can influence surgical strategy. As a member of the perinatal team, the craniofacial surgeon must be "cyber-savvy" to counsel parents and communicate with geneticists.

Stenting of a venous stenosis in vein of galen aneurysmal malformation. A case report

SUMMARY

The vein of Galen aneurysmal malformation (VGAM) is a high flow arteriovenous shunt at the choroidal level. In the neonatal period, it typically presents with cardiac failure. Venous stenoses, occlusions and anomalies are often present. In the absence of adequate venous outflow pathways, severe, irreversible cerebral parenchymal damage may occur due to intracranial venous hypertension, altered hydrodynamics and ischaemia. We present a case of deployment of a stent across a focal superior jugular bulb stenosis in an effort to avert this outcome.