Spontaneous resolution of Chiari malformation Type I in monozygotic twins.

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, approximately 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.