Pedunculated Chiari 3 malformation with proatlas defect.

Chiari III malformation is considered to be a rare congenital abnormality in human with very high mortality rates. Seventy percent of Chiari III is found to be associated with C1 arch defect as reported by Cakirer (Clin Imaging 27:1-4, 2003). The herniation of posterior fossa elements or dysplastic neural tissue is a must to stamp it as Chiari 3 malformation. The malformation is a result of the abnormal development of craniovertebral junction (CVJ). The CVJ developed from the occipital somites and the first spinal sclerotome. The major role in the development of the CVJ is played by the fourth occipital somite, which is otherwise known as "proatlas." The Chiari III anomalies are due to a result of proatlas defect, which results from failures of segmentation, failures of fusion of different components of each bone, or hypoplasia and ankylosis. We are presenting a case of a 1-year 4-month-old female child who presented with pedunculated swelling at the suboccipital region. The swelling was cystic and with pulsation. On evaluation, we found Chiari III anomaly with C1 posterior arch deficiency (proatlas defect). He was surgically managed. The outcome of the patient was good. Despite literature concluding Chiari 3 malformation with an unfavorable outcome, however, meticulous management and good pre- and postoperative care, physical therapy, and follow-up are necessary for good outcome.

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