Spontaneous resolution of Chiari malformation Type I in monozygotic twins

Report of 2 cases

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The spontaneous resolution of isolated tonsillar ectopia in Chiari malformation Type I (CM-I) is a known and reported entity in 2 previous single study case reports. However, it has not been previously described in monozygotic twins. Two children, ~ 1 year of age with CM-I and presumed episodes of pallid syncope or breath-holding spells presented for neurosurgical evaluation. Although Chiari decompression was considered, the authors decided to proceed with conservative management with close follow-up due to the uncertain nature of these episodes. Approximately 4 years later, both children's symptoms had resolved. Repeated MR imaging examinations also showed spontaneous resolution of the malformation in both girls. These cases emphasize that when patients with CM-I present with atypical symptoms, spontaneous resolution or improvement is possible, which may influence the decision to pursue a trial of nonsurgical management. The possible pathophysiological mechanisms and genetic influences of CM-I are also briefly discussed.

Abbreviations used in this paper: CM-I = Chiari malformation Type I; EEG = electroencephalography.

Article Information

Address correspondence to: David D. Limbrick Jr., M.D., Ph.D., One Children's Place, St. Louis, Missouri 63110-1077. email: limbrickd@nsurg.wustl.edu.

© AANS, except where prohibited by US copyright law.

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    Case 1. Sagittal T1-weighted MR images obtained when the patient was 1 year of age (left) and 5 years of age (right). The initial MR imaging shows the cerebellar tonsils to be elongated and peg-shaped. They were measured to symmetrically extend ~ 12 mm beyond the margin of the foramen magnum. The followup MR image shows interval ascension of the cerebellar tonsils to a position ~ 6 mm beyond the foramen magnum. In addition, the tonsils appeared more rounded and less elongated.

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    Case 2. Sagittal T1-weighted MR images obtained when the patient was 1 year of age (left) and 5 years of age (right). The initial MR imaging study shows the cerebellar tonsils to be elongated and peg-shaped. They were measured to symmetrically extend ~ 10 mm beyond the margin of the foramen magnum. The follow-up MR image demonstrates interval ascension of the cerebellar tonsils to a position ~ 3 mm beyond the foramen magnum. In addition, the tonsils appeared more rounded and less elongated

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