Basilar Impression and Arnold-Chiarimalformation
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J. Neurol. Neurosurg. Psychiat., 1968, 31, 596-605 Basilar impression and Arnold-Chiari malformation A study of 66 cases1 M. CAETANO DE BARROS, W. FARIAS, L. ATAIDE, AND S. LINS From the Institute of Neurology and Neurosurgery, Medical School, Federal University ofPernambuco, Brazil We have been interested for a long time in the Fischgold, David, and Bregeat (1952) described problem of the deformation of the base of the skull two lines, both of them drawn in anteroposterior known as basilar impression and described by the view of the skull. The first joining the tips of the anatomists since 1790 (Ackermann), although only mastoid processes usually passes at the level of the recently recognized from the clinical point of view. atlanto-occipital joints and to 3 mm above or This condition has attracted our attention partic- below the tips of the odontoid process. In patients ularly because of its high incidence in the North- with basilar impression the atlanto-occipital joints east of Brazil and has given rise to other papers and the odontoid process are clearly above this line. written by one of us (de Barros, 1957, 1959). The second line drawn between the two digastric The possibility of precise pre-operative diagnosis grooves passes well above the tip of the odontoid has been established by Chamberlain's paper (1939). process in normal skulls (Fig. 2). As routine for the This author described a line in plain radiograph of radiological diagnosis of basilar impression we use the skull which permits recognition of the mal- the Chamberlain's and Fischgold's lines taken in formation under discussion. Chamberlain's line is plain views or in tomographs of the skull (Fig. 3). that which in a lateral view of the skull goes from Basilar impression may be acquired, the deform- the dorsal lip of the foramen magnum to the dorsal ation of the skull deriving from a systemic osseous margin of the hard palate and in normal individuals disease like Paget's disease, osteoporosis, rickets, passes above the atlas and the tip of the odontoid hyperparathyroidism, osteochrondro-dystrophy, etc., process. When a basilar impression is present, these or-as is more frequent-it may be primary, a structures are above this line. congenital malformation. Phillips (1955) considers as arbitrary any definition We believe that in its primary form basilar of basilar impression based on Chamberlain's line, impression derives from an embryonic disturbance. although admitting that it exists when the tip of the Such an assertion is supported by its frequent odontoid process is found more than 5 mm above association with other anomalies of the skeleton this line. To McRae (1953) the limit would be only such as morphological alteration of the foramen 3 mm. magnum (narrow, asymmetrical, shaped like hearts As it is not always easy to draw Chamberlain's of playing cards), hypoplasia of the atlas, Klippel- line in a plain radiograph of the skull, one can resort Feil anomaly, spina bifida, etc. to the tomograph or to other referencial lines. A frequent operative finding is an association of McGregor's line (1948) connects the dorsal rim of basilar impression with a displacement of the the hard palate to the lowest point of the occipital odontoid process. Another frequent association is bone. In normal individuals this line almost super- with the Arnold-Chiari malformation. This latter imposes that of Chamberlain, whereas in people condition was classified by Chiari (1896) into three having basilar impression it tends to be separate types: from it. Bull (1946) and Bull, Nixon, and Pratt (1955) I-Cerebellar tonsils and lower part of the point out that the planes passing by the hard palate medulla below the foramen magnum, without dis- and by the atlas are parallel or they slightly intersect, placement of the 4th ventricle. this relation being altered when there is basilar II-Caudal migration of the lower part of the impression (Fig. 1). cerebellum still more pronounced, associated with downward displacement of the 4th ventricle which and with its foramina 'Lecture given at the Institute of Neurology, National Hospital, appears lengthened opening Queen Square, London, on 25 May 1967 by M. Caetano de Barros. into the spinal subarachnoid spaces. 596 Basilar impression and Arnold-Chiari malformation 597 _6 _ v -4-- FIG. 1. Basal angle: AB-Chamberlain's line. CD- Bull's line. FIG. 2. Basilar impression. Fischgold's lines: AB- Bi-digastric line. CD-Bi-mastoid line. III-Cerebellum and medulla displaced into the cervical spinal canal within a meningocoele. From these three types only those of type I and exceptionally some of type II reach adult age and are the subject of this paper. Patients classified as belonging to type III and a great majority of those of type II do not survive, as has been well demonstrated by Russell (1949). MATERIAL AND METHODS Our material is represented by 66 patients examined in the Institute of Neurology and Neurosurgery, Medical School of the University of Pernambuco, Brazil, and in private practice until 1964. Since then we have operated upon 15 further cases, giving a total of 71 cases. Some of these have already been discussed in previous papers (de Barros, 1957; de Barros, Pernambucano, Hazin, Maia, and Ataide, 1957; de Barros, 1959). In the present study we include only those patients whose clinical manifestations were caused by the malformations under discussion. We put to one side another group, perhaps larger, in which the diagnosis of FIG. 3. Basilar impression. Lateral planigraphy: AB- basilar impression was suspected by the morphology of Chamberlain's line. the head and confirmed by radiological studies but whose 598 M. Caetano de Barros, W. Farias, L. Ataide, and S. Lins very heterogeneous complaints had nothing to do with the danger of bleeding from puncture of large veins that the osseous anomaly. All patients were born in the sometimes exist on the dorsal aspect of these tonsils, as North-east of Brazil, 52 were male and 14 female we have quite often seen during operation. We recognize (Table I). This marked preponderance of the male sex in that the number of cases in which these anomalies were our series could perhaps be partially explained by the found separately is very small, but as already emphasized fact that we dispose of a greater number of beds for men by one of us (de Barros, 1959) in a previous paper we than for women in our wards. have found it possible to make the pre-operative differential diagnosis on clinical grounds. TABLE I ANALYSIS OF THE MATERIAL AND COMMENTS SEX DISTRIBUTION Sex Group I 1i Ftpi AGE We had no cases in the first decade, only two Male 25 27 in the fifth, and four cases in the sixth decade. The Female 8 6 greatest incidence was in the third decade (24 cases) followed by the second and fourth decades with As to the racial type, 35 patients were white, 29 18 and 17 cases respectively (Table III). mulattoes and only two were negroes (Table II). The population ofthe North-east of Brazil is formed by a little more than 50% of mulattoes and about 2% of negroes, TABLE III the rest being white. The lowest social and economic AGE OF PATIENTS classes are predominantly represented by mulattoes and Age (yr) Group I Group II our Service admits only poor patients. Even so the majority of the cases in our series are white. 10-19 11 7 20-29 8 16 30-39 11 6 40-49 2 TABLE II 50-59 3 RACIAL TYPE Racial Type Group I Group II AGE OF ONSET OF SYMPTOMS The clinical history of White 18 these patients usually dates back several years, with Mulatto 14 insidious symptoms and an evolution needing a very Negro careful inquiry to pinpoint the appearance of the It should be noted that the North-east of Brazil had same which, in the majority of cases, was already been occupied by the Dutch in the 17th century for forgotten. 34 years and it has been said that basilar impression is This makes it difficult to establish with certainty a common condition in the Netherlands. It may be that the age at which complaints begin. The analysis of there is some connexion between these facts. Table IV permits us to place the appearance of the The cases are separated into two equal groups of 33 symptoms, in the great majority of cases, in the patients. Group I consists of cases verified by surgery second and third decades (24 and 26 cases respect- (32 cases) or by necropsy (one case). This group includes ively). However, they may appear early in the first 22 cases of basilar impression associated with Arnold- decade (five cases) or late (three cases in the sixth Chiari malformation operated on, and one case verified by necropsy; seven cases of pure basilar impression decade). We had seven patients whose complaints operated on; three cases of pure Arnold-Chiari mal- started in the fourth decade and in only one of our formation also operated on. patients the complaints came from the fifth decade Group II consists of patients with a diagnosis of basilar (Table IV). impression associated or not with Arnold-Chiari syndrome but for several reasons not operated on. TABLE IV Every patient, apart from the neurological examination, according to the routine of the Service, had a radiograph ONSET OF SYMPTOMS of the skull taken in four positions (P.A., lateral, Hirtz, Age (yr) Group I Group II and Towne). Some of them also had tomographs. The 0-9 5 diagnosis was established through Fischgold's and 10-19 12 12 Chamberlain's lines.