Chiari malformation type I: A new MRI classification

Magnetic

Imaging, Vol. 15. No. 4. pp. 397-403, 1997 Copyright 0 1997 Elsevier Science Inc. Printed in the USA. All rights reserved 0730-725X/97 $17.00 + .OO

PI1 SO730-725X( 96)00383-9

ELSEVIER

l

Resonance

Original Contribution CHIARI

MALFORMATION TALAL

TYPE

I: A NEW

A. AMER AND OMRAN

MRI

CLASSIFICATION

M. EL-SHMAM

Mansoura Faculty of Medicine, Egypt, and Dr. Ali Omar Askar Neurosurgery Center. Tripoli, Libya Thirty patients with Chiari I malformation were examined by MRI over 2-year period. All patients underwent MRI scan before and after surgical decompression of the posterior fossa. Images of the craniocervical junction confirmed tonsillar herniation in all cases and allowed the definition of two anatomically distinct types of Chiari malformation. Twenty-one of the 30 patients (70%) had concomitant syringomyelia and were classified as type A, while the remaining 9 patients (30% ) had evidence of frank herniation of the cerebellar tonsils below the foramen magnum without evidence of syringomyelia and were labeled type B. Type A patients had a predominant central cord symptomatology; type B patients exhibited signs and symptoms of brain stem or cerebellar compression. The concomitant cord cavitary lesions (syringomyelia) were noncommunicating (isolated syrinxes), which were separated from the fourth ventricle by a syrinxfree segment of normal spinal cord. Holocord hydromyelic cavities were seen in 8 out of 21 patients with syringomyelia, isolated cervical cavities were seen in 4 patients, while combined cervical and thoracic cavities were seen in 9 patients. Kinking of the medullocervical junction and brain stem was seen in 20 out of 30 patients (67% ). MRI has proved to be an excellent, noninvasive means of studying of the craniocervical anatomy; it has allowed a classification of Chiarl malformation based on objective anatomic criteria with prognostic and clinical relevance. 0 1997 Elsevier Science Inc. Keywords:

Chiari malformation;

MRI scan.

INTRODUCTION

both before and after surgery and has allowed the correlation of these findings with the clinical presentation and response to therapeutic intervention.3 The aim of this work is to review the neurodiagnostic findings in Chiari I malformation using MRI, and to use MRI criteria in their classification into anatomic and pathologic types that has definite correlation with the clinical presentation.

The initial description by Chiari of the malformation that bears his name is commonly interpreted to suggest at least two distinct types of hind brain pathology usually designated types I and II. Although both types are associated with a structurally small posterior fossa and tonsillar herniation, the Chiari II malformation exhibits, in addition, a downward displacement of the medulla and fourth ventricle, a younger age of presentation, and an association with myelodysplasia and hydrocephalus.’ Chiari I malformations is a relatively simple anomaly that is unassociated with other congenital brain malformation. However, spinal cord, skull base and spine lesions are common in this disorder. An additional clue to the diagnosis would be the presence of hydromyelia, seen in up to 75% of Chiari I patients.’ Magnetic resonance imaging (MRI) has provided an excellent noninvasive means of studying the anatomy of this malformation in sagittal and axial planes

A total number of 30 patients with Chiari malformation type I based on the MRI criteria were selected during the routine work in the MRI Department, Dr. Ali Omar Askar, Neurosurgery Center, Tripoli, Libya, in the period from May, 1994 to May, 1996. They were 19 male and 11 female patients ranging in age from 6 to 50 years (mean age of 29.1 years). The main clinical presentations were headache, neck pain, and varying degrees of weakness or spasticity of the extremities. All patients had progressive symptoms

7131196; ACCEPTED 10/24/96. Address correspondence to Talal A. Amer, Lecturer of

Diagnostic Radiology, Mansoura Faculty of Medicine, Mansoura, Egypt.

MATERIAL

RECEIVED

391

AND

METHODS

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Magnetic ResonanceImaging l Volume 15, Number 4, 1997

Fig. 1. Chiari type B-malformation. Sagittal TlWI (SE, TR = 520, and TE = 25) demonstrating tonsillar hemiation without syringomyelia. There is no kinking of the medullocervical junction.

Fig. 2. Chiari type A-malformation. Sagittal Tl WI (SE, TR = 560, and TE = 30). demonstrating extensive syringomyelia involving the whole spinal cord, tonsillar hemiation, and mild kinking of the medullocervical junction.

over 4 or more months before diagnosis. The clinical features of these 30 patients are detailed in Table 2. All patients had undergone one or more MR examination of the brain and cervical spine. Seventeen patients with syringomyelia extending below the cervical level underwent combined head, cervical, and thoracic spine MRI. Imaging was performed with head coil for brain and surface coil for the spinal cord using OST Phillips Gyroscan T5-11 Machine. Sagittal and axial spin-echo images were done, utilizing a repetition time (TR) of 500 to 750 ms and echo time (TE) of 15 to 30 ms to obtain Tr-weighted image, while T,-weighted image utilized a TR of 2,000 to 2,500 ms and a TE of 90 to 120 ms. All patients underwent surgical treatment for progressive symptoms. Many surgical procedures were used including ( 1) posterior fossa decompression alone in 22 patients, (2) decompression of the posterior fossa and shunting of the syrinx to the spinal subarachnoid space (syringospinal shunt) in 3 patients, and (3) posterior fossa decompression and shunting from the

syrinx to the cistema magna or cerebellopontine angle cistern (syringocistemostomy) in the last 5 patients.

RESULTS The criteria used for the diagnosis of Chiari I malformation are the same criteria used by Aboulezz et a1.4and Elster and Chen’ are as follows: (a) hemiation of at least one cerebellar tensil 5 mm or more below

Table 1. The degree of tonsillar hemiation by MRI in patients with and without syringomyelia (30 patients) Tonsillar hemiation level *Foramen magnum to Cl level *Cl C2 level *Below C2 level Total

Syringomyelia or type A = 21

No syringomyelia or type B = 9

11 10 21

2 6 1 9

399

Chiari malformation type I l T.A. AMER AND 0. EL-SHMAM

Table 2. The clinical presentationsin 30 patientswith chiari I malformation Clinical presentation *Pain Headache Neck pain Back pain Girdle pain *Weaknessof one or more limbs *Numbnessof one or more limbs *Muscle atrophy *Loss of temperaturesensationand painlessbums *Unsteadiness *Diplopia *Ptosis *Vomiting *Dizziness *Epilepsy *Nystagmus *Hyperasthesia *Hypoasthesia *FIappy tremors *Hyperreflexia *Absent anklejerk *Kyphoscoliosis *Urine incontinence *Neck stiffness *Exophthalmos *Bilateral papilloedema

No. of patients 14 3 1 1 19 1 8 2 2 1 1 4 5 1 2 1 1 1 1 1 7 1 1 1 1

* Most of the patients had multiple symptoms.

the plane of foramen magnum as defined on sagittal T,-weighted image, the plane of foramen magnum was defined by Aboulezz et a1.,4as a line drawn between the inferior margin of the basion and the opisthion; (b ) hemiation of both cerebellar tonsils 3 - 5 mm below the foramen magnum if accompanied by other definite features consistent with a Chiari malformation, i.e., syrinx or cervicomedullary kinking; (c) no clinical history of myelomeningocele or radiologic evidence of Chiari II malformation; (d) no prior cervical or cranial

surgery; and (e) tonsillar herniation appears to be a primary dysplasia and not secondary to cerebral mass lesion. Also, ail patients had pointed or peg-like configuration of the tonsils.

MRI Classification

of Chiari I Malformation

MRI scan of the spinal cord allowed the identification of hydromyelic cavities in 21 of 30 patients (70%). Based on the presenceor absenceof associated syringomyelia on MRI scans, patients were classified into two groups. Type A (patients with syringomyelia) and type B (patients without syringomyelia). The degree of tonsillar hemiation on MRI scan was significantly greater in type B patients than in type A patients (Table 1). The clinical presentations (signs and symptoms) of our 30 patients with Chiari I malformation were variable, where type A patients (with syringomyelia) were more likely to have a central cord syndrome, and type B patients (without syringomyelia) had mainly a cerebellar syndrome or a foramen magnum compression syndrome. There are multiple MRI findings in Chiari I malformations that are illustrated in Table 3. The concomitant cord cavitary lesions (syrnigomyelia) were noncommunicating (isolated) syrinxes that were separatedfrom the fourth ventricle by a syrinxfree segmentof normal spinal cord that varied in length from one to four levels. Holocord hydromyelic cavities were seen in eight patients, isolated cervical cavities were seen in four patients, while combined cervical and thoracic cavities were seen in nine patients. The locations of syrinx in different spinal cord regions are illustrated in Table 4.

DISCUSSION Several authors have interpreted the first type of malformation described by Chiari as tonsillar hemiation without concomitant brain stem hemiation.6 Others stated that the original description includes distal

Table 3. The different MFU findingsin 30 casesof chiari malformation,type A and type B Finding Small posteriorfossa Tonsillar herniation Pointed (peg-like) tonsils Obliteration of the subarachnoidspaces& cisternsof posteriorfossa Syringomyelia Medullocervical kinking Supratentorialhydrocephalus Kyphoscoliosis Partial agenesisof the corpuscallosum Completeagenesisof’ the corpuscallosum Posteriorfossaarachnoidcyst

Type A = 21

Type B = 9

Total

21 21 21 21 21 13 2 7 1

9 9 9 9 7 2

30 30 30 30 21 20 4 7

-

1 1 1

1

1

-

Magnetic ResonanceImaging 0 Volume 15, Number 4, 1997

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Table 4. The locations and extent of syrinxes in type A patients (2 1 patients) No. of cases

Location & extent of syrinx *Holocord cavities *Cervical syrinxes C2-C6 c3-c7 C4-C6 U-C7 *Combined cervical & dorsal syrinxes C2-D2 C2-DlO C2-Dll C3-D2 C&D1 Total

displacement

and flattening

8 4 1 1 1 1 9 1 3 3 1 1 21

of the medulla. Further-

more, the clinical relevance of differentiating adult cases into two different types based on brain stem descent has never been demonstrated due to overlap

Fig. 4. Chiari type A-malformation. Sagittal TlWI (SE, TR = 560, and TE = 30) demonstrating mild downward tonsillar herniation with pointed (peg-like appearance) of the tonsils and syringomyelia.

in presenting symptomatology.7.8 MRI with an objective and accurate demonstration of the craniovertebral anatomy and syrinx detection has allowed a simple

classification of Chiari malformation in adults with clinical and prognostic significance.3 The presence or absence of associated syringomyelia seemed to be the main determinant of clinical presentation and strongly influenced the surgical outcome. Based on these observations, we propose the classification

of patients

with

Chiari

malformation

solely on the basis of the presence (type A) or absence (type B ) of associated syringomyelia. This differentiation is easy to delineate by MRI scan and avoids any confusion

about extent and significance

of associated

brain stem hemiation.3 We agree with the last authors who had examined 35 patients with Chiari I malformation by MRI and found syringomyelia in 20 patients

Fig. 3. Chiari type A-malformation. Sagittal Tl WI (SE, TR = 560, and TE = 30) demonstrating, lobulated syringomyelia of the cervical cord, downward tonsillar herniation, mild and medullocervical kinking. The fourth ventricle appears normal.

(57%) and 15 patients without syringomyelia (43%). In our series we have nearly similar results where type A was seen in 70% and type B in 30%. The detection of associated syringomyelia with ar-

nold Chiari has been hindered in the past by the available imaging modalities like myelography, and computed tomographic scans with metrizamide; syringo-

myelia has often been missed by these studies.’ In a

Chiari malformation type IO T.A. AMER .~ND 0. EL-SHMAM

401

more recent study’ showed that one-third of the syrinxes demonstrated by MRI were either not adequately visualized or missed by myelography. According to Aboulezz et al? and Spinos et al.” syringohydromyelia is present in 20 to 70% of Chiari I malformation cases, depending upon the series. Also, Forbes and Isherwood” stated that hydromyelia is seen in 75% of Chiari I malformation patients. In our series we have similar results, where syringomyelia is seen in 21 out of 30 cases (70%). The location and extent of syringomyelia were variable in our series (Table 4). Holocord hydromyelic cavities were seen in 8 out of 21 patients (38%)) the cervical cord was involved alone in 4 patients, while combined cervical and thoracic cord cavities were seen in 9 patients. Isolated thoracic syrinxes were not seen. The mean length of the syrinx was 11 vertebral segments (range from 3 -2 1) . Pillay et a1.3 had nearly similar results in a series of 35 patients, where holocord was seen in 6 out of 20 patients with syringomyelia (30%)) isolated cervical

(4

(W Fig. 6. Chiari type A malformation with short cervical syrinx. Sagittal TlWI (SE, TR = 650, TE = 30) showing; downward tonsillar herniation with pointed edges and a short syrinx opposite C6 and C7 vertebral bodies, (B) Axial TlWI (SE, TR = 560, and TE = 30) showing the syrinx. Fig. 5. Chiari type A-malformation after posterior fossa decompression. Sagittal TlWI (SE, TR = 500, and TE = 25) demonstrating mild downward tonsillar hemiation with rounded inferior edge of the tonsils and slight collapse of the cervical syringomyelia.

cord syrinxes were seen in 12 patients, and also there was no isolated thoracic cord cavities. According to Milhorat et al.,” this is explained by the fact that

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the lumbar and thoracic segments of the central spinal canal are frequently obliterated during the middle years of adult life by proliferation of the ependymal cells. In our series the neurodiagnostic findings depicted by MRI in Chiari I malformation were multiple; small posterior fossa, tonsilar hemiation, and pointed or peglike tonsils were found in all cases of type A and type B. Supratentorial hydrocephalus was seen in four cases (13%): two cases of type A, and two cases of type B. According to Longue and Edwardi hydrocephalus is seen in 3%. Forbes and Isherwood, ” stated that hydrocephalus is variable and ranges from O-40%. Latchow et a1.14stated that usually there is no hydrocephalus or very mild ventricular enlargement secondary to slight elongation of the fourth ventricle and aqueduct with tissue compaction at the foramen magnum preventing free flow of C.S.F. Cervicomedullary “kink” was said to be absent in the original series of Chiari I malformation.6 However, it has been found in 12% of patients at time of surgery’ and in 7 1% of all Chiari I patients imaged with MRI and in 90% of those patients who had syringomyelia lo that such high incidence in patients imaged by MRI is probably due to the ability to image the craniocervical junction in sagittal view in a noninvasive way.13 Another explanation was stated by Welch et al., I5 who stated that kinking is present but obscured by the more obvious cerebellar tonsillar descent. In our series medullocervical kinking was seen in 20 patients out of 35 (67%), it was seen in 13 patients of type A and 7 patients of type B. In our series type B patients have better surgical outcome than type A patients after posterior fossa decompression. This is explained by Milhorat et al., l6 who stated that certain cavitary patterns, in particular extracanalicular syrinxes and the paracentral dissections of the central canal syrinxes, produce irreparable damage of the spinal nuclei and tracts. These lesions have definite prognostic implications and their pathological consequences may explain why certain patients do not improve following surgery, despite MR evidence of collapse or disappearance of the syrinxes postoperatively. CONCLUSION Finally we come to the conclusion that Chiari I malformation is a simple anomaly that consists mainly of downward tonsillar herniation and pointed or peg-like appearance of the cerebellar tonsils. Other associated lesions may be present and the commonest are syringomyelia (70%)

and kinking

of the craniocervical junction. MFU

is a noninvasive simple means of studying of this malfor-

mation and has allowed the correlation of these findings with the clinical presentation. Based on the presence or absence of syringomyelia, this anomaly can be classified into type A (with syringomyelia), and type B (with no syringomyelia) . Type A patients had predominantly central cord symptoms, while type B patients had signs and symptoms of brain stem or cerebellar compression. Kinking of the medullocervical junction is more with type B. Also, type B patients had better surgical outcome after posterior fossa decompression.

REFERENCES 1. Chiari, H. Concerning alterations in the cerebellum resulting from cerebral hydrocephalus. Pediatr. Neurosci. 13:3-s; 1987. 2. Osbom, E.G.C. Disorders of neural tube closure. In: E.G. Osbom (Ed). Diagnostic Neuroradiology, 1st ed. St. Louis, MO: Mosby Year Book Company; 1994: p. 15. 3. Pillay, P.K.; Awad, I.A.; Little, J.R.; Hahn, J.F. Symptomatic Chiari malformation in adults: A new classification based on Magnetic Resonance Imaging with clinical

and prognostic significance. Neurosurgery 28:639-645; 1991. 4. Aboulezz, A.O.; Sartor, K.; Geyer, C.A.; Gado, M.H. Positions of the cerebellar tonsils in the normal population and in patients with Chiari malformation: A quantitative approach with MR imaging. J. Comput. Assist. Tomogr. 9: 1033- 1036; 1985. 5. Elster, A.D.; Chen, M.Y.M. Chiari I malformation: Clinical and Radiologic Reappraisal. Neuroradiology 183: 347-353; 1992. 6. Cannel, P.W.; Markesbery, W.R. Early descriptions of the Arnold-Chiari malformation. The contribution of John Cleland. J. Neurosurg. 37:543-547; 1972. 7. Levy, W.J.; Mason, L.; Hahn, J.E. Chiari malformation presenting in adults: A surgical experience in 127 cases. Neurosurgery 12:377-390; 1983. 8. Paul, K.S.; Lye, R.H.; Strang, F.A.; Dutton, J. AmoldChiari malformation. Review of 71 cases. J. Neurosurg. 58:183-187; 1983. 9. Wilberger, J.E.; Maroon, J.C.; Prostoko, E.R.; Baghai, P.; Beckman, I.; Deeb, Z. Magnetic Resonance Imaging and intraoperative neurosonography in syringomyelia. Neurosurgery 20:599-605; 1987. 10. Spinos, E.; Faster, D.W.; Moody, D.M.; Ball, M.R.; Witcofski, R.L.; Kelly, D.L., Jr. MR evaluation of Chiari I malformation at 0.15 T. AJNR 6:203-208; 1985. 11. Forbes, W.S.; Isherwood, I. Computed tomography in syringomyelia and the associated Arnold-Chiari type I malformation. Neuroradiology 15:73-78; 1978. 12. Milhorat, T.H.; Johnson, W.D.; Miller, J.I.; Bergland, R.M.; Hollenberger-Sher, J. Surgical treatment of syringomyelia based on Magnetic Resonance Imaging criteria. Neurosurgery 31:231-245; 1992. 13. Longue, V.; Edwards, M.R. Syringomyelia and its surgical treatment: An analysis of 75 patients. J. Neurol.

Chiari malformation type I l T.A. AMER AND 0. EL-SHMAM

Neurosurg.Psychiatry 44:273-284; 1981. 14. Latchaw, R.E.; Haaga,C.T.; Bainter, N.D. Congenital anomaliesof the brain. In: R.E. Latchaw (Ed). MR and CT Imagingof the Head, Neck and Spine,2nd. ed. St. Louis, MO: Mosby Year Book Company; 1991:p. 756. 15. Welch, K.; Shillito, J.: Strand,R.; Fisher,E.G.; Winston,

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K.R. Chiari I malformation: An acquired disorder.J. Neurosurg.55:604-609; 1981. 16. Milhorat, T.H.; Capocell, A.L.; Anzil, A.P.; Kotzen, R.M.; Milhorat, R.H. Pathologicalbasisof spinalcord cavitation in syringomyelia: Analysis of 105 outpsy cases.J. Neurosurg.82:802-812; 1995.