Annals of the Royal College of Surgeons of England (I98I) vol. 63 Chronic herniation of the hindbrain Bernard Williams MD chM FRCS Neurosurgeon, Midland Centre for Neurosurgery and Neurology, Smethwick, Warley, West Midlands Key words: ARNOLD-CHIARI DEFORMITY; CEREBELLAR DISEASES; CEREBROSPINAL FLUID; INTRACRANIAL PRESSURE; SPINA BIFIDA; SYRINGOMYELIA Summary disease is arrested. Operative techniques for hind- Herniation of the hindbrain occurs when the brain 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 fourth ventricle 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