CLINICAL ARTICLE Morphometric analysis of foramen magnum dimensions and intracranial volume in pediatric Chiari I malformation Sunil V. Furtado & Darpan J. Thakre & Prasanna K. Venkatesh & Kalyan Reddy & A. S. Hegde Received: 23 April 2009 / Accepted: 25 July 2009 / Published online: 12 August 2009 # Springer-Verlag 2009 Abstract Purpose Foramen magnum dimensions and intracranial volume in Chiari I malformations in children were studied, and the statistical relationship between patient demographics, radiological features and foramen mag- num morphometry was investigated. Methods Linear measurements were used to calculate the intracranial volume using preoperative magnetic resonance images and computed tomogram images. The area of the foramen magnum was obtained independently using com- puter imaging software and a regression formula. The result of 21 pediatric patients was compared with a matched control group. Results The area of the foramen magnum was within the range of the expected value deduced using a formula based on the intracranial volume. There was no statistical difference in the area and linear dimensions of the foramen magnum in the study and control groups. Six patients (28%) had a foramen magnum in close proximity to a spherical shape. Conclusion The authors provide a simple, accurate and reproducible method of estimating foramen magnum area in the pediatric Chiari I group. The irregular shape of the foramen magnum is accentuated by developmental bony and soft tissue anomalies at the cranio-vertebral junction in Chiari malformation. Consequently, an individualized cross-sectional assessment of the foramen magnum in relation to the hindbrain tissue in the same plane is required to study the initiation and propagation of the Chiari I symptomatology. Keywords Chiari I malformation . Foramen magnum area . Intracranial volume . Pediatric . Posterior fossa . Syringomyelia Introduction Hans Chiari described different variations in hindbrain malformations, based on a series of autopsy studies between 1891 and 1896 [12]. Two types of Chiari malformation are most common, of which Type I Chiari malformation (CMI) is characterized by the descent of cerebellar tonsils into the cervical canal. The first two occipital sclerotomes form the basiocciput; the third sclerotome is responsible for the exoccipital bone [16]. A small posterior fossa is caused by improper development of occipital somites from paraxial mesoderm [3, 18, 20, 23, 24]. The resultant overcrowding is ascribed to push the cerebellar tonsils caudally [9, 20, 23]. There is a wide variation in the anatomical configuration of the foramen magnum in various individuals [8, 19, 31]. To investigate the syndrome of CMI in children, we studied the intracranial volume (ICV) and foramen magnum (FM) dimensions in a group of 21 patients matched with an equal number of controls. We evaluated whether the FM area in CMI patients is significantly different for a given ICV. This is the first study to analyze the cross-sectional area at the S. V. Furtado (*) : D. J. Thakre : P. K. Venkatesh : A. S. Hegde Department of Neurosurgery, Sri Satya Sai Institute of Higher Medical Sciences, EPIP Area, Whitefield, Bangalore 560066 Karnataka, India e-mail: sunilvf@gmail.com K. Reddy Department of Radiology, Sri Satya Sai Institute of Higher Medical Sciences, EPIP Area, Whitefield, Bangalore 560066 Karnataka, India Acta Neurochir (2010) 152:221–227 DOI 10.1007/s00701-009-0480-5