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Contributed from the case records of the
Indiana University Department of Radiology

History: Boy with seizures.

Click these images to enlarge them.

Which choice best localizes the salient abnormality?

Temporal lobe.Orbit.Thalamus.Posterior fossa.Optic nerve.

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Two key images are again shown below. Click to enlarge.

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Given that this is the only significant CNS finding, which choice is the most likely diagnosis?

Chiari I malformation.Chiari II malformation.Chiari III malformation.Chiari IV malformation.

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Findings: There is caudal protrusion of the cerebellar tonsils through the foramen magnum.

Differential diagnosis:

Diagnosis: Chiari I malformation

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Key points:

Chiari I malformation occurs when a normal sized cerebellum tries to fit in an underdeveloped posterior fossa.
The cerebellar tonsils protrude inferiorly through the foramen magnum.
There can be obstruction of CSF flow at the foramen magnum.
In children, tonsillar protrusion > 7mm is abnormal. In adults, 5mm is abnormal.
In contrast to Chiari II, Chiari I is not associated with myelomeningocele or any midline abnormality.
Patients with Chiari I may experience symptoms associated with obstructed CSF flow such as headache and syncope.
Treatment is aimed at restoring and maintaining CSF flow and involves surgical decompression.

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