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Answers to Illuminations questions

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(1) True, (2) False, (3) True, (4) False, (5) True, (6) False, (7) True, (8) False.

The image shows herniation of the cerebellar tonsils below the foramen magnum, with effacement of CSF spaces at the craniocervical junction. On the complete MR scan, the right cerebellar tonsil extended 17 mm below the foramen magnum, and the left 10 mm. Subjectively, the posterior fossa looks normal in size and there was no other intracranial abnormality. The answer to Question 3 may therefore be true or false, depending on how you interpret the question.

In Chiari I (sometimes called Arnold-Chiari I) malformation, the cerebellar tonsils protrude or herniate below the foramen magnum (the craniocervical …

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  • Competing interests None declared.

  • Provenance and peer review Commissioned; internally peer reviewed.