Annals of the Royal College of Surgeons of England (I98I) vol. 63

Chronic herniation of the

Bernard Williams MD chM FRCS Neurosurgeon, Midland Centre for Neurosurgery and Neurology, Smethwick, Warley, West Midlands

Key words: ARNOLD-CHIARI DEFORMITY; CEREBELLAR DISEASES; ; INTRACRANIAL PRESSURE; SPINA BIFIDA; SYRINGOMYELIA Summary disease is arrested. Operative techniques for hind- Herniation of the hindbrain occurs when the herniation are discussed. lowest parts of the cerebellum and sometimes Chiari Type II deformity is probably respon- part of the medulla are moved downwards sible for the progression of hydrocephalus after through the foramen magnum, a pressure differ- birth in the majority of babies with spina bifida. ence acting across the foramen magnum mould- Measurement of pressure in the cerebrospinal ing the tissues into a plug. It is suggested that fluid above and below the foramen magnum the clinical course in both adults and babies shows that intermittent pressure difference is with spina bifida may be explained by the hind- commonly present at times of neurological de- brain hernia acting as a valve. terioration. Surgical decompression of the hernia The term 'Chiari Type I deformity' is com- in adults allows correction of the valvular effect, monly used for an abnormality in which the which may be monitored by pressure measure- tonsils and lowermost parts of the cerebellar ments. In babies the associated hydrocephalus hemispheres are prolapsed through a normal is usually so gross that it requires separate treat- foramen magnum. Acute herniation may occur ment, but pressure monitoring may be of value as a result of space-occupying lesions. Chronic in assessing the state of the disease. herniation may be morphologically identical Introduction although it tends to be more severe. Some- times it will produce few symptoms which often In discussing herniation of the hindbrain two may be delayed so that the original causative age groups must be considered. Herniation in lesion may not be apparent. Causes include infants with spina bifida is more gross than the bone softening, tumour, or previous meningitis. herniation formed in adults and is often labelled Birth injury is probably the commonest cause a 'malformation'. The resemblances between of the deformity, which presents clinically in the infantile and adult forms have sometimes adults. In infants with severe forms of spina bifida a hindbrain herniation is present. This abnor- mality may be called 'Chiari Type II deformity' or Arnold-Chiari deformity and is an intra- uterine abnormality in which the and medulla are grotesquely herniated before they are properly developed and the foramen magnum is enlarged. The commonest clinical presentation of Chiari Type I deformity is syringomyelia, which is usually not diagnosed until adult life. Other presentations include syringobulbia, headache, oscillopsia, attacks of giddiness, lower cranial nerve palsies, and ataxia. Particularly character- istic are cough headache and cough syncope. Syringomyelia and syringobulbia in particular .:: - i ... w::. g ... wu....g may be irreversible by the time they are di- FIG. I Acute brain hernias resulting from a supra- agnosed. Nevertheless, surgical decompression tentorial glioma (above). There is a hernia of the may be successful in relieving symptoms of head- uncus (top arrow) pushing a part of the temporal ache, cough syncope, and long-tract compres- lobe through the incisura and a hindbrain hernia sion; mnost cases of syringomyelia show some im- (bottom arrow) due to the downward displacement provement and in others progression of the from the tumour. Based on an Arris and Gale Lecture given in Birmingham on 27th February I980 Io Bernard Williams to the subject by Mr Jack Small, of the Midland Centre for Neurosurgery and Neurology, who has built up a large personal series, thoroughly investigated and documented, which has pro- vided clinical material. Herniation of the lower part of the cerebellum through the foramen magnum is the simplest form of hindbrain herniation and is commonly caused by space-occupying lesions (Figs I and 2). There is little difference between the tonsils engaged in the foramen magnum as the result of an acute event such as a tumour and the ton- sils which are deeply engaged in the upper part of the spinal canal as a result of a long-standing -^ 4 - w,- .. herniation (Fig. 3). In the latter case the mould- FIG. 2 Acute hindbrain hernia dissected from be- ing is commonly greater and the tonsils may hind in a patient who died of an untreated cere- extend downwards as far as the upper border of bellar haemangioblastoma (Chiari Type I). the axis. The patients with the most severe led to the assumption that the adult chronic herniation are those in whom the deformities herniation is also a 'malformation'. have come on during fetal development. In Interest in the hindbrain hernias of adults newborn babies with spina bifida the herniation has been stimulated by the realisation that syrin- of the cerebellum may extend down as far as gomyelia in adults is usually accompanied by hindbrain hernia, that the commonest chronic presentation of herniation in adults is syringo- myelia, and that operations on the posterior fossa may produce remarkable benefit (I). Both Eric Newton, who gave his Hunterian Lecture II vears ago, and I were introduced

FIG. 3 Chronic hindbrain herniation in a patient FIG. 4 Sagittal section through the chronic hindbrain who presented with cough headache 27 years after hernia associated with severe meningocele (Chiari precipitate labour. The limited normal operative Type II). The upper arrow shows the moulding of exposure to decompress the tonsils is shown. Note the midbrain by the cerebral hemispheres and the that there is no morphological difference between lower arrow shows the overfolding of the medulla. this case and Fig. 2 apart from the fixation shrink- The fourth ventricle and lower parts of the cere- age in the patient who died contrasted with the tight bellum are elongated, deformed, and herniated down impaction during life. to the level of the body of C6. Chronic herniation of thIe hindbrhain I I the thloracic spine; appearances as shown in raised intracranial pressure with papilloedema Figure 4 are common. inay come on in the course of chronic hindbrain The deformities of adult life are so different herniation, sometirnes precipitated by investiga- from those in infants that Chiari divided the tion, bout patients with papilloedema and head- cerebellar herniation into two types and this ache usually have space-occupying lesions. division remains convenient for discussion. The Cranial nerve symptoms, particularly deafness term Arnold-Chiari malformation has passed and diplopia, are common and patients some- into common usage although it lacks a precise times complain of oscillopsia. More common is definition. Chiari's classification seems prefer- nystagmus, often with vertical or rotatory com- able; his Type I occurs in adults and Chiari ponents. Ataxia is most troublesome when it Type II refers to the severe deformities found affects stance and gait. in infants with spina bifida. Attacks of unconsciousness may occur; syn- cope produced by coughing, laughing, or some Clinical course other form of straining is the characteristic find- ADULTS ing. It comes on a few seconds after the strain Clinical presentation may be divided into two and the patient usually recovers in a minute or groups, syringomyelia and posterior fossa so. Death may occur from lower cranial nerve symptomatology. Many patients have both; dysfunction, dysphagia and associated respir- some patients with brainstem features suggesting atory distress, or syncope which passes into respir- a posterior fossa presentation may have syrin- atory arrest. Occasionally in patients present- gobulbia. Both kinds of patient may have long- ing with cough headache alone the symptom tract signs from compression of the upper spinal may remit, either spontaneously or following an cord, particularly of the posterior columns, by event such as a sudden jerk or a pneumo- the herniated cerebellar tonsils. encephalogram. It is probable that most cases of posterior fossa presentation progress to death if Syringomyelia Syringomyelia is a well-recog- not treated. nised symptom complex and identifies a use- ful subdivision of patients with chronic hindbrain INFANTS hernia for such purposes as enquiry about In newborn children with spina bifida the aetiological factors or correlations with changes neurological and orthopaedic deficits associated in the ventricles. There are of course other with the spinal lesion dominate the presentation. causes of syringomyelia such as spinal tumours Of those severely affected, with the spinal cord or cystic cavities above a paraplegia and there- everted on to the surface, around 95%o will fore it is necessary to note that 'syringomyelia' in develop progressive hydrocephalus. The child- this paper refers only to cases associated with ren are usually born normally because the head chronic hindbrain herniation. This type, some- is not enlarged and there is little external evi- times called 'communciating syringomyelia', dence of hydrocephalus. There are some ex- accounts for the biggest group of patients pre- ternal signs: the ears seem low on the head, senting with clinical evidence of cord cavities the forehead may protrude, and the occiput seems and it is also the commonest and most severe large and overhangs the back of the neck. The presentation of chronic adult hindbrain hernia. internal morphology of the cerebrospinal fluid When syringomyelia presents with dissociated (CSF) pathways is grotesquely deformed in sensory loss or a Charcot joint it is readily re- such infants. The are large, cognised. The earliest symptom, however, is unequal, and fused in the middle, and the occi- usually pain, which commonly takes the patient pital horns are blended in with the enlarged to an orthopaedic surgeon or a physician. The bodies. The frontal horns and temporal horns stigmata of syringomyelia and a review of the appear to be in competition with each other for presenting features, including a discussion on space, and a patient with large frontal horns the origins of the pain, have been presented else- may have small temporal horns and vice versa. where (2). The is small and deformed, hav- ing been compressed from side to side by the Posterior fossa presentation Posterior fossa pre- enlarging lateral ventricles. The massa inter- sentation may be of several kinds. Headaches, media is large and may obliterate part of the particularly occipital or nuchal, may be ex- third ventricle. The foramina of Monro are acerbated by coughing; in these cases surgical elongated and slit-like from front to back as a treatment is likely to be successful. Many result of compression. The aqueduct is usually patients have headache related to exertion which narrowed from compression by the lateral is overshadowed by other complaints. Acutely ventricles or the suprapineal recess and may be 1 2 Bernard Williams elongated as the fourth ventricle is displaced The commonest cause of herniation is an downwards through the foramen magnum. The abnormality in the head pushing the brain out, fourth ventricle and lowest part of the cerebel- such as a space-occupying lesion of the type lum are sometimes so far herniated through the shown in Figures I and 2; such cases are most enlarged foramen as to be unrecognisable. commonly acute. In patients with no space- The choroid plexus is concealed in a mass of occupying lesion and a chronic hernia hydro- enlarged veins and such structures as the cere- cephalus was implicated by Chiari. Studies of bellar tonsils have not been formed. The patients with syringomyelia, however, have foramina of Magendie and Luschka are deep in shown that only 29% have even mild hydro- the cervical canal and not identifiable. cephalus (3), while in those with posterior fossa The cortical mantle may show microgyria, the presentation the proportion with hydrocephalus cortex having become corrugated and compressed is similar. It seems probable that the hindbrain owing to the hydrocephalus. Many morpho- hernia causes the hydrocephalus rather than the logical changes may be due to hydrocephalus other way round. and those that cause narrowing of the CSF path- With Chiari Type I herniation it is commonly ways may in turn aggravate it; thus the hydro- not possible to determine the cause. It seems cephalus may become progressive and irrevers- likely that birth injury is much the commonest ible. Clinically these babies are compensated at cause and comparison with a control series sup- birth and the external circumference of the ports this contention (4). Compression of the head may be normal or less than normal. They bones of the vault may cause downward dis- then become progressively decompensated with- placement of the brain and, particularly if as- in a few weeks after birth; in many cases re- sociated with tentorial tears, may cause herni- moval of a meningocele and closure of the back ation of the hindbrain (5). Local compression defect seems to hasten the onset of the hydro- of the bones of the base by the expulsive force cephalus. The typical case with severe myelo- of the uterus or obstetric forceps may cause meningocele therefore has a biphasic course, the fracture or greenstick deformity of the occipital second episode being brought on at birth or bone. Local haemorrhage around the cisterna immediately afterwards. mnagna, brain swelling due to anoxia, and tran- In cases in which the hydrocephalus compen- sient hydrocephalus may all play a part in sates early the patient may survive. Such starting off the hernia. patients may have mild forms of spina bifida The Chiari Type II malformation of infancy and be prone to syringomyelia or posterior fossa is an intrauterine abnormality, but the aetiology presentation of chronic hindbrain hernia in later is as obscure as that of the spina bifida. The life. simplest explanation would seem to be that the mesodermal abnormalities of spina bifida Aetiology are primary and that when the ectodermal tube Mlost hernias seem to be due to failure of the fails to close the pressure in the spine remains orifice to hold the contents. Femoral, inguinal, low compared with that in the head. A similar and incisional hernias are examples in which the explanation was proposed by Cameron (6). Cer- contents of the hernia are initially normal, the tainly the brain tissues seem almost to have extruding force is the increase in pressure which flowed down into the spine (Fig. 4). It is not accompanies the normal events of life, and the necessary to postulate a primary high pressure essential cause is weakness of the orifice. The in the head; the embryo is a high-pressure pul- situation at the foramen magnum might be sating system and a breach in its coverings and thought to be quite different because only in resultant low pressure may produce widespread Chiari Type II is the foramen magnum common- abnormality. ly enlarged and that is most probably a response to the tissue jammed in it during development Mechanism of advance in hindbrain of the skull. herniation Perhaps because of the use of the term Both the adult and the infantile herniation 'Arnold-Chiari malformation' the idea has be- therefore show a stable period sometimes followed come widespread that the Chiari Type I defor- by exaggeration of the hernia symptoms and mity is also a 'malformation' and that it reflects even death. an intrauterine pathological process. Uusually, Why does the hindbrain recommence herni- however, a deformity is either Type I or Type II ation or even continue to herniate through a and it seems that the milder deformity is later normal orifice when the brain is free of hydro- in its onset and occurs after the cerebellum is cephalus or space-occupying lesions? It might fully formed. be thought that the brain does not move in and Chronic herniation of the hindbrain I 3 out of the foramen magnlum and could not be the ventricular pressure from that in the lumbar exposed to such pressures as those in the abdo- sac. Figure 5 shows an abnormal result in a men for instance. A fundamental principle of patient with severe basilar impression, head- neurosurgery is that the total contents of the ache, ataxia, and oscillopsia. The pressure dif- intact skull inust be constant at all times be- ference after a single cough took about 25 s to cause of the incompressibility of the brain and disappear. its associated fluids. When a person coughs, for In most cases of chronic hindbrain herniation example, CSF moves sharply upwards through in adults a valvular action can be detected. It the foramen magnum and then rebounds down- is almost always of the 'baseline equality with xvards to return to normal. This is because the valvular effect' type; the baselines have only epidural veins around the spinal theca become been separated in 3 recordings out of I68 and distended when the thoracoabdominal pressure no case of total dissociation has been seen in is raised. During Valsalva's manoeuvre, for adults. Another example is given in Figures 6 example, the CSF pressure is equal in the head and 7, taken from a patient who presented with and the spine, but the veins in the spinal canal a sudden onset of diplopia caused by a syringo- are distended, the CSF is partly displaced into bulbia. There were long-standing changes of the head, and veins within the head are com- syringomyelia and radiographic signs of hind- pressed. The jugular and facial veins are dis- brain hernia with arachnoiditis due to birth tended not only because of damming back of injury. blood from the thoracoabdominal cavity but also because the diploic veins draining the intra- Thus it can be seen that the valvular action to the extracranial tissues are of the chronic hindbrain hernia has a high cranial system value for several associated clinical fully open. explanatory features. Firstly, the maintenance and pro- Recording intracranial and initraspinal press- gression of the morphological deformity of the uLres simultaneously in patients with hindbrain hindbrain hernia itself: the moulding provided hernia may show a pressure difference between by the pressure difference between the spine the head and the spine which may be per- and the head causes downward moulding of the inanent or transitory. This is called craniospinal lower cerebellum and makes it fit more closely pressure dissociation (7). Observations may be made easily on babies with spina bifida. A Lumbar meningocele may be slack and subject only to 30- atmospheric pressure at the time when the fonta- nelle is tense. If a meningocele is squeezed the 15- fluid from it may be displaced into the head and then be greatly delayed in its return to the 0- spine (8). The measurement of such pressure Ventricular changes by electrical methods allows classification 30- of Chiari Type II malformations into four groups. In the normal group the pressures are 15-A in the head and the In the equal spine. second, 0- with mild impaction of the hernia, the pressures are equal at rest, but delayed equalisation indi- Difference cates a valvular effect. In the next worse group 10- the baseline (resting) pressures are unequal, the 0- pressure in the head being higher, but valvular action is still detectable. In the most severely -15- impacted group the pressures are entirely dis- sociated so that pressure events in the spine and Time in seconds the head are independent. Once the record- FIG. 5 Pressure traces from a patient with valvular ings become abnormal there is a tendency for effect from a hindbrain hernia showing the effect of the situation to grow worse and for the patients a single cough. When the differential trace is dis- to move into the entirely dissociated group, in placed downwards-that is, below zero-there is a which there is progression of the hydro- downward force acting across the foramen magnum. cephalus (9). Reading the trace from left to right, for 7 s after the trace begins only cardiac pulsation is seen, then In adults craniospinal pressure dissociation a cough produces a pressure pulse up to 30 mm Hg may be recorded in the sitting position with a (4 kPa) in the lumbar sac which does not go so ventricular and lumbar puncture needle and high in the head. There is a downward force present differential manometry performed by subtracting thereafter for some 25 s. 14 Bernard Williams

Airway thus causing exacerbation of the hydrocephalus. When the meningocele 40 - is closed by surgical repair the pressure swings in the spine in re- sponse to crying are higher because the damp- 0- ing effect of the meningocele has been removed LumbaQr (9,Io), causing impaction of the hernia to be speeded up. 20 - Operative treatment 0- Although treatment of a hernia by making the Ventricutar rim of the orifice larger might seem contrary to surgical principles, this is the basis of cranio- 20- vertebral decompression. Part of the occipital boine is removed from the back of the foramen 0- as also is the arch of the atlas. The exposed dura is removed the Di fference and impacted tissues de- 10- compressed. The wound is closed leaving the dura widely open. If a free flow of CSF is re-established, then the pressure difference is -10 - abolished (Fig. 7) and the intermittent force -20 - ...... moulding the hindbrain is removed. Relief of Time in seconds downward dislocation may alleviate traction on cranial nerves or pain-sensitive structures; simi- FIG. 6 Effects of blowing for I2 S to a height of larly the foramen of Magendie may be de- mm trace ex- 40 Hg (5.3 kPa). The top shows the and pressure piratory effort and provides a guide to the abdomino- compressed may be taken off the thoracic pressure. After the blow is over a post- cord if the tonsils have been compressing it Valsalva rebound occurs which is confined to the directly. head. The downward force across the foramen mag- The hindbrain is suspended in CSF of almost num is in excess of 25 mm Hg (3.3 kPa). This is severe dissociation. Airway into the foramen in both adults and babies with 40 spina bifida. Secondly, the downward traction provides an 0 explanation for the progressive cranial nerve deformities and the pain which accompanies the Lumbar maximum pressure dissociation in patients with 20 - cough headache. Thirdly, the filling of syringomyelia may be 0- explained on the basis of a communication be- tween the fourth ventricle and the inside of the Ventricular spine. Such a communication is commonly pre- sent as the central canal which, although of small 20 size, can be expected to transmit increments of fluid under the influence of pressures such as 0- those shown in Figures 5 and 6 thoughout a Diff erence lifetime. Because the transient pressure increase 10 - above the hernia is equally Li I-LU 1 a a 1 dispersed through I ri-Iri-i-i-,-Itttttt,-YIIIl4?tttttttttftl. all compartments of the head there is no ten- dency to hydrocephalus. -14 Finally, the relapse of compensated hydro- cephalus after birth is almost certainly related Time in seconds to the onset of FIG. 7 Same case as in Fig. 6 after operative de- respiration, crying, sucking, and compression of the hindbrain hernia. Note that the so on producing an increase in the ebb and flow post-Valsalva rebound is shared equally between the through the foramen magnum. If the valvular head and the spine and that the differential trace action causes the hernia to become forced down shows little deviation from zero compared with Fig. into the foramen and upper spine this constricts 6. The trace is indistinguishable from normal and and compresses the exit of the fourth ventricle, was accompanied by an excellent clinical result. Chlronic herniation of the hindbrain 1m

FIG. 8 Drawings made from lateral radiographs of a patient before and after a generous de- compression of the tonsils. The cerebellum has slumped badly into the decompression and car- ried the brainstem down with it producing postoperative head- ache.

the same density, the cerebellum is held on to terventions and this is at present the preferred the brainstem by the cerebellar peduncles, and policy. if the decompression is modest the remaining parts of the occipital squamous bone support Results the lateral parts of the cerebellum. If the de- ADULTS compression is too large or if craniospinal pres- Operative treatment of hindbrain hernia in sure dissociation is still occurring, then the hind- adults has been encouraging. My personal series brain may 'slump' into the decompression, pro- of 53 cases of chronic hindbrain hernia in adults ducing a worse hernia than the original lesion. is broadly in line with the experience of others An example is given in Figure 8 of a case de- (I4-20). The most impressive results have been scribed elsewhere (ii). Because of the possibility with posterior fossa presentations such as cough that free egress of CSF from the head to the headache, but 42%' of patients with syringomy- spine may not be re-established it is tempting elia have shown unequivocal improvement after to open the foramen of Magendie widely and operation and in others the progression of the hold it open. This may be done by making a slit disease has seemed to be arrested or delayed. in the tonsils and sucking out the contents, Clinical improvement may be pleasing; all suturing the pia together so that the tonsils are symptoms may be abolished without perfect cor- plicated, and taking the sutures upwards and rection of craniospinal pressure dissociation. outwards and fastening them to the dura. The complications of decompression of adult Alternative schemes include the insertion of a Chiari deformity for syringomyelia have been tube to hold the foramen of Magendie open commoner in patients who had hydrocephalus, (I2). A series of soft pliable funnels have been syringobulbia, or arachnoiditis around the herni- made from woven silicone rubber (I3). The ated tissues (I 1,I4,59). In such patients posterior funnel is cut into petal-like flanges and is put fossa operations may be avoided. A ventriculo- in upside down with the hollow stem holding atrial shunt for hydrocephalus may help not open the foramen of Magendie. The petals are only posterior fossa types of presentation but bent back and sutured to the dural edges so as also syringomyelia (I I,20). to support the lower edge of the cerebellum. This prosthesis has not been successful, the post- BABIES operative course usually being stormy. One The hernia seems likely to be the cause of the patient died from an associated tumour and ne- exacerbation of the hydrocephalus in babies and cropsy showed that the funnel had caused in- although attempts to control it by hindbrain flammatory reaction and fibrosis with dense decompression have been made, failure has been blockage of both the tube and the foramen of almost universal. The rewards of allowing the Magendie. normal pathways to open would be considerable. it is to evacuate The arachnoid villi make a more satisfactory Although possible the bulk absorptive mechanism than any mechanical of the tonsils and suture them back without valve. If the head could develop normally for causing any neurological deficit, there is some- a few months the normal pathways might be times a difficult postoperative period, particu- remoulded to limit dependence on any foreign larly if the brainstem has been manipulated. The device. results after decompressing the craniovertebral A small series of cases has been treated in junction seem as good as after more radical in- conjunction with monitoring of craniospinal i 6 Bernard Williams pressure dissociation using hindbrain decompres- If babies after difficult labour develop sion and insertion of a valved shunt, developed hydrocephalus or a cisternal haematoma it by Eric Turner, posing no resistance and allow- would seem sensible to image the tonsils by ing fluid to move from the head to the cervical Amipaque. If the tonsils are herniated, then subarachnoid space. This, it was hoped, would pressure recordings from the ventricles and the prevent the development of craniospinal pres- spine simultaneously are easy to carry out in sure dissociation and reverse the trend to hind- the first year, using the anterior fontanelle. brain impaction. Although some of the results If craniospinal pressure dissociation can be were initially encouraging, the immediate mor- demonstrated in conjunction with chronic hind- bidity and complication rate was higher than brain hernia, then surgical correction may be for ventriculoatrial shunting and the method advisable in childhood. Even if surgery is has been abandoned. thought inadvisable it would seem sensible to follow up such children carefully as outpatients. Future developments There is a need for research into chronic hind- The treatment of chronic hindbrain hernia at brain hernia. Although there is a clear asso- present is frequently beset by the difficulty that ciation with difficult birth a proportion of when the diagnosis is made in the adult the hernias have no known aetiology. It may be damage continues to progress inexorably despite that the desire to explain deformity in terms of the apparently successful correction of the hind- pressure is unduly simplistic and that teratogenic brain hernia. This is particularly true of factors are at work in the hindbrains of many syringomyelia. Emphasis therefore should be up- persons who present with mild forms of the on prevention and earlier diagnosis of hindbrain Chiari deformities in adult life. In many cases, herniation. however, the pressure disturbances seem to be If, as seems probable, difficult birth is the important and indicate the opportunity for mini- commonest aetiological factor, then it does not mising a deal of suffering, provided that the give any cause for complacency that obstetrics lesions are promptly recognised. is advancing and the perinatal mortality rate is falling. The perinatal mortality rate in England References and Wales has not improved as well as in other I Gardner WJ. Hydrodynamic mechanism of developed countries (5). Perhaps more import- syringomyelia: its relationship to myelocele. J ant is the consideration that as neonatal inten- Neurol Neurosurg Psychiat I965;28:247-59. sive care units become more successful, so does 2 Williams B. Orthopaedic features in the present- the number of children at risk who survive in- ation of syringomyelia. J Bone Joint Surg [Br] crease. The most spectacular increase in survival I976;16I :314-23. has been seen in infants with birth weights of 3 West RJ, Williams B. Radiographic studies of I500 g or less and it is this group which is par- the ventricles in syringomyelia. Neuroradiology ticularly prone to neurological sequelae such as I980;20: 5-I6. spastic diplegia, hydrocephalus, epilepsy, and 4 Williams B. Difficult labour as a cause of com- mental retardation. Thus it seems unlikely that municating syringomyelia. Lancet 1977;2:5I-3. the occurrence of a group at risk can be lessened, 5 Pape K, Wigglesworth JS. Haemorrhage, ischae- short of euthanasia for low-birth-weight infants. mia and the perinatal brain. Clinics in develop- The hindbrain hernia is usually silent for many mental medicine, 69-70. London: Heinemann years and it is perhaps advisable to use modern Medical, 1979. techniques to screen babies who have been at 6 Cameron AH. The Arnold-Chiari and other risk. neuro-anatomical malformations associated with Lateral skull radiographs of newborn infants spina bifida. Journal of Pathology and Bacterio- may show occipital bone fracture. It may be logy 1957;73:195-211. possible to decide whether basilar invagination 7 Williams B. Cerebrospinal fluid pressure changes can occur as part of moulding during birth. in response to coughing. Brain 1976;99:33I-46. Computer-assisted tomographic scanning gives 8 Van Houweninge Graftdijk CJ. Hydrocephalus. more information: intraventricular, paraventricu- Thesis, University of Leiden, I1932. lar, and subarachnoid haemorrhage may be 9 Williams B. Cerebrospinal fluid pressure gra- seen Transient hydrocephalus is likely to be dients in spina bifida cystica, with special refer- (5). ence to the Arnold-Chiari malformation and common in infants after difficult birth with hind- Child Neurol 1975 brain hernia. It is possible that in the majority aqueductal stenosis. Dev Med [Supp 35]:138-50. of cases of hindbrain hernia which become 1o Williams B. A demonstration analogue for ven- chronic a hydrocephalus is present in the early tricular and intraspinal dynamics (DAVID). J stages which may later become compensated. Neurol Sci 1974;23: 445-6I. Chronic herniation of the hindbrain I 7

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