Chiari Malformation Presenting as Cerebellar Degeneration Maj Vinay Maurya", Col Hariqbal Singh" MJAFI 2003; S9: 147·148
Key Words: Chiari malfonnatioo; Cerebellar degeneration
Introduction
C
omputed tomography (CT) is the primary imaging modality in the investigation of suspected cerebellar degeneration. A case is presented in which an inaccurate clinical and radiological diagnosis of cerebellar degeneration resulted from CT imaging demonstrating loss of cerebellar substance. Subsequent clinical recognition of down beat nystagmus led to MR examination and a diagnosis of Chiari malformation was made. Visualization of the loss of cerebellar substance should not be considered to exclude Chiari malformation.
Case Report A 34 year old right handed male, not on any antiepileptics. presented with feeling of imbalance and tendency to fall since (alit three years. Onset was insidious with slowly progressive course . There was no history of alcohol abuse or any other substance. seizure. trauma, toxic exposure or surgery. There was no family history of similar complaints.
General examination was unremarkable. Fundus examination was normal. Initial neurological examination revealed horizontal and rotatory nystagmus on lateral gaze
Fig , I : CT showing cercbcll ur degeneration with prominent pericerebcllar cisterns
with mild dysarthria. Gait was ataxic and wide based with inability to do tandem walking. Motor and sensory systems were normal. Routine laboratory investigations were within normal limits. CT head revealed generalized atrophy of cerebellum with prominent folia. Left hemisphere was affected more than the right with vermis also showing atrophic changes. There was prominence of pericerebellar cisterns more so on the left side (Fig I). Further testing showed subtle down beat nystagmus. Down beat nystagmus, however, a type of central vestibular nystagmus frequently found in lesions near cervicomedullary junction II J. prompted a search for a Chiari malformation . MR examination confirmed cerebellar degeneration (Fig 2) and also revealed tonsillar descent below the foramen magnum (Fig 3). There was no syringohydromyelia or any other brain anomaly confirming the diagnosis of Chiari type I malformation with cerebellar degeneration.
Discussion The prevalence of the Chiari type I lesion in the normal population was formerly grossly overestimated but is probably under 1% [2]. It is also becoming clear that it is an acquired deformation, the mechanism often seeming to be the posterior fossa growing at a slower
Fig. 2 : MRI TI W axial sect ion confirms the finding s seen in Fig . I.
'Graded Specialist (Radiology). Military Hospital. Jodhpur- 342010. •Senior Advisor (Radiology). Command Hospital (Western Command J. Chandimandir.
Maurya and Singh
148
type I, but shows a caudally displaced pons and medulla oblongata with an elongated fourth ventricle and, almost always, some type of meningocele. In type III, there is displacement of the medulla oblongata, fourth ventricle. and cerebellum into an occipitocervical encephalomeningocoele.
Fig.3: MRI TI W saggital image showing tonsillar descent into the spinal canal
rate than the hindbrain; it is now documented that all the elements of the type I lesion may develop postnatally [3J. It also occurs in association with raised intracranial venous pressure, craniosynostosis and basilar invagination. Although the diagnosis of Chiari malformation on CT is difficult, the relationship between loss of cerebellar substance and this malformation has not been stressed. In fact, previous publications appear to suggest that visualizing loss of cerebellar substance provides evidence against the diagnosis of Chiari malformation [4J. A case is presented in which this inaccurate conclusion was made and the diagnosis of Chiari malformation delayed. Chiari malformations represent a group of abnormalities characterized by dislocation of the hindbrain into the spinal canal. Three types are well known. Type I shows only varying degree of caudal displacement of the cerebellar tonsils and inferior cerebellum into the spinal canal.Type II is similar to
Loss of cerebellar substance. easily determined by CT. is not generally considered a manifestation of Chiari malformation [4). Diffuse cerebellar ischaemia from chronic compression provides a speculative etiology for our patient's loss of cerebellar substance. No evidence of acute or subacute ischemic brain injury was noted on CT or MR. These findings are not surprising. as the ischemic injury would be expected to arise from previous chronic compression of small vessels [5J. Clinical presentations of mild degrees of Chiari malformations are usually confusing. Only by meticulous neurological testing was downbeat nystagmus, a significant finding suggestive of Chiari malformation appreciated. This led to a definitive diagnosis. Chiari malformation should be included in the differential diagnosis of loss of cerebellar substance to increase both clinical and neuroradiologic vigilance regarding this potentially treatable disease. References I.
Baloh RW, Spooner JW. Downbeat nystagmus: a type of central vestibular nystagmus. Neurology (Minneap)1981 ;31:304-10.
2. Savy L, Stevens JM, Taylor DJ. Apparent cerebellar ectopia: a reappraisal using volumetric MRI. Neuroradiology 1994;6:360-3. 3. Huang PP. Constantine S. Acquired Chiari I malformations. J Neurosurg 1994;80: 1099-1102. 4. Naidich TP. Pudlowski RM, Naidich JB. CT signs of Chiari malformations, Part I, II and III. Radiology 1980;134:65-71, 391-8,657-63. 5. Gebarski SS. Greenberg HS. Chiari malformation presenting as loss of cerebellar substance on CT. Surg Neurol 1984;21:562-4.
MJAFI. Vol. 59. No.2. 2003
Key Words: Chiari malfonnatioo; Cerebellar degeneration
Introduction
C
omputed tomography (CT) is the primary imaging modality in the investigation of suspected cerebellar degeneration. A case is presented in which an inaccurate clinical and radiological diagnosis of cerebellar degeneration resulted from CT imaging demonstrating loss of cerebellar substance. Subsequent clinical recognition of down beat nystagmus led to MR examination and a diagnosis of Chiari malformation was made. Visualization of the loss of cerebellar substance should not be considered to exclude Chiari malformation.
Case Report A 34 year old right handed male, not on any antiepileptics. presented with feeling of imbalance and tendency to fall since (alit three years. Onset was insidious with slowly progressive course . There was no history of alcohol abuse or any other substance. seizure. trauma, toxic exposure or surgery. There was no family history of similar complaints.
General examination was unremarkable. Fundus examination was normal. Initial neurological examination revealed horizontal and rotatory nystagmus on lateral gaze
Fig , I : CT showing cercbcll ur degeneration with prominent pericerebcllar cisterns
with mild dysarthria. Gait was ataxic and wide based with inability to do tandem walking. Motor and sensory systems were normal. Routine laboratory investigations were within normal limits. CT head revealed generalized atrophy of cerebellum with prominent folia. Left hemisphere was affected more than the right with vermis also showing atrophic changes. There was prominence of pericerebellar cisterns more so on the left side (Fig I). Further testing showed subtle down beat nystagmus. Down beat nystagmus, however, a type of central vestibular nystagmus frequently found in lesions near cervicomedullary junction II J. prompted a search for a Chiari malformation . MR examination confirmed cerebellar degeneration (Fig 2) and also revealed tonsillar descent below the foramen magnum (Fig 3). There was no syringohydromyelia or any other brain anomaly confirming the diagnosis of Chiari type I malformation with cerebellar degeneration.
Discussion The prevalence of the Chiari type I lesion in the normal population was formerly grossly overestimated but is probably under 1% [2]. It is also becoming clear that it is an acquired deformation, the mechanism often seeming to be the posterior fossa growing at a slower
Fig. 2 : MRI TI W axial sect ion confirms the finding s seen in Fig . I.
'Graded Specialist (Radiology). Military Hospital. Jodhpur- 342010. •Senior Advisor (Radiology). Command Hospital (Western Command J. Chandimandir.
Maurya and Singh
148
type I, but shows a caudally displaced pons and medulla oblongata with an elongated fourth ventricle and, almost always, some type of meningocele. In type III, there is displacement of the medulla oblongata, fourth ventricle. and cerebellum into an occipitocervical encephalomeningocoele.
Fig.3: MRI TI W saggital image showing tonsillar descent into the spinal canal
rate than the hindbrain; it is now documented that all the elements of the type I lesion may develop postnatally [3J. It also occurs in association with raised intracranial venous pressure, craniosynostosis and basilar invagination. Although the diagnosis of Chiari malformation on CT is difficult, the relationship between loss of cerebellar substance and this malformation has not been stressed. In fact, previous publications appear to suggest that visualizing loss of cerebellar substance provides evidence against the diagnosis of Chiari malformation [4J. A case is presented in which this inaccurate conclusion was made and the diagnosis of Chiari malformation delayed. Chiari malformations represent a group of abnormalities characterized by dislocation of the hindbrain into the spinal canal. Three types are well known. Type I shows only varying degree of caudal displacement of the cerebellar tonsils and inferior cerebellum into the spinal canal.Type II is similar to
Loss of cerebellar substance. easily determined by CT. is not generally considered a manifestation of Chiari malformation [4). Diffuse cerebellar ischaemia from chronic compression provides a speculative etiology for our patient's loss of cerebellar substance. No evidence of acute or subacute ischemic brain injury was noted on CT or MR. These findings are not surprising. as the ischemic injury would be expected to arise from previous chronic compression of small vessels [5J. Clinical presentations of mild degrees of Chiari malformations are usually confusing. Only by meticulous neurological testing was downbeat nystagmus, a significant finding suggestive of Chiari malformation appreciated. This led to a definitive diagnosis. Chiari malformation should be included in the differential diagnosis of loss of cerebellar substance to increase both clinical and neuroradiologic vigilance regarding this potentially treatable disease. References I.
Baloh RW, Spooner JW. Downbeat nystagmus: a type of central vestibular nystagmus. Neurology (Minneap)1981 ;31:304-10.
2. Savy L, Stevens JM, Taylor DJ. Apparent cerebellar ectopia: a reappraisal using volumetric MRI. Neuroradiology 1994;6:360-3. 3. Huang PP. Constantine S. Acquired Chiari I malformations. J Neurosurg 1994;80: 1099-1102. 4. Naidich TP. Pudlowski RM, Naidich JB. CT signs of Chiari malformations, Part I, II and III. Radiology 1980;134:65-71, 391-8,657-63. 5. Gebarski SS. Greenberg HS. Chiari malformation presenting as loss of cerebellar substance on CT. Surg Neurol 1984;21:562-4.
MJAFI. Vol. 59. No.2. 2003
