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Definition/Background
Chiari I malformation is defined as downward displacement of
the peg-shaped cerebellar tonsils, and sometimes the inferior vermis, through
the foramen magnum into the upper dorsal cervical canal.
Characteristic
Clinical Features
Headaches (often worsened by physical stress), ocular disturbances,
dizziness, and tremors are common presenting features. When associated with
syringohydromyelia, a sensory level can be elicited. Other associated findings
include abnormal reflexes and weakness of the extremities.
Characteristic
Radiologic Findings
Inferiorly displaced (≥5 mm), peg-shaped cerebellar tonsils,
Compression of the cerebellar cisterns. Anterior displacement of the cerebellum.
Reduced length of the clivus.
Less Common
Radiologic Manifestations
Hydrocephalus, Syringohydromyelia, Basilar invagination, Klippel-Feil
anomaly
Primary Differential
Diagnoses
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Downward Displacement of the Tonsils
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Mass Lesion
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Syringohydromyelia (Possible Etiologies)
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Chiari I Malformation
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Chiari II Malformation
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Trauma
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Intramedullary Tumors
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Idiopathic
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Infective Lesions, Including Arachnoiditis
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Compressive Lesions of the Cord
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Multiple Sclerosis
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Communicating Hydrocephalus
Discussion of
Differential Diagnoses
Mass Lesion: The
intracranial mass lesion responsible for the downward displacement of the
tonsils will be easily identified. Also, the downward displacement of the
tonsils will not demonstrate the typical peg-shape seen in Chiari malformation.
Syringohydromyelia:
It is critical to evaluate the underlying etiology of the syrinx. The
associated findings with each of the above processes help in determining the
cause of the syrinx.
The patient is a 22-year-old man with weakness of the extremities.
Sagittal T1WI demonstrates a syrinx extending from the craniocervical junction up to the upper thoracic spine.
Sagittal T2WI demonstrates downward displacement of peg-shaped tonsils. The classic haustral pattern of the syrinx can be appreciated. Diagnosis: Chiari I malformation with syringohydromyelia.
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Labels: Brain, Congenital Anomalies
