Devoted to diagnostic and interventional spine imaging and therapeutics

Library

Chiari III: Two Cases Spanning the Spectrum 2013

Category General Spine Mina Lotfi, Medical Student
David C. Keyes
Purpose Chiari III is an extremely rare congenital condition originally described as herniation of posterior fossa contents through a high posterior cervical spina bifida. The original definition has been expanded and now includes low occipital encephaloceles with characteristics of Chiari II, including small posterior fossa, cervicomedullary kinking, herniation of cerebellar tonsils into the foramen magnum, tectal beaking, corpus callosum dysgenesis, and hydrocephalus [1].  McLone and Knepper proposed a theory to describe the malformations of Chiari II, which is also applicable to the pathogenesis of Chiari III as there are shared features. Leakage of CSF through neural tube defects causes failure of the cerebral ventricles to expand resulting in hypogenesis of the posterior fossa and herniation of posterior fossa contents [2].  We present two cases on various ends of the Chiari III spectrum. Case 1 A 54 yo male with LUE pain and limited ROM and history of metastatic breast cancer had been diagnosed with Chiari I based on imaging in 2008 and 2010.  MRI images of the cervical spine in the sagittal and axial planes were obtained with and without gadolinium.  A soft tissue tract extended from the cervicomedullary junction to the posterior margin of the thecal sac.  Incomplete posterior fusion of C1 was noted with a sinus tract that extended from the cervicomedullary junction to the cutaneous surface.  The cerebellar tonsils were abnormally low-lying and the fourth ventricle elongated.  These findings were unchanged compared to studies dating back to 2007.  The results were discovered to be consistent with a tethered variant of Chiari III due to the high cervical spine defects in addition with the abnormal posterior fossa development.  Despite the findings, the patient did not exhibit signs and symptoms specific to the Chiari spectrum of malformations. Case 2 A male infant of a 17 year old G1P0 mother diagnosed in utero with occipital encephalocele and ventriculomegaly was delivered at term via C section due to congenital anomaly. The infant had APGAR scores of 8 and 9. On exam a 5cm posterior encephalocele covered with intact, epithelialized skin was observed.  The day after delivery, cerebral MRI with and without 0.3 cc Gadavist was performed.  MRI revealed a 9.3 x 5.5 cm suboccipital encephalocele. The posterior fossa was diminutive in size with herniation of cerebellar tissue into the encephalocele.  Additionally, absence of the falx and beaking of the posterior midbrain were observed.  The diagnosis of Chiari III was made based on the MRI findings.  Three days after birth he underwent surgical repair and had an uncomplicated recovery. Materials & Methods NA Results NA Conclusion NA References 1.            Smith, A.B., et al., Diagnosis of Chiari III malformation by second trimester fetal MRI with postnatal MRI and CT correlation. Pediatr Radiol, 2007. 37(10): p. 1035-8. 2.            Barkovich, A.J., Pediatric neuroimaging. Contemporary neuroimaging. 1990, New York: Raven Press. xi, 355 p.