Automated Posterior Cranial Fossa Volumetry by MRI: Applications to Chiari Malformation Type I

Abstract

BACKGROUND AND PURPOSE Quantification of PCF volume and the degree of PCF crowdedness were found beneficial for differential diagnosis of tonsillar herniation and prediction of surgical outcome in CMI. However, lack of automated methods limits the clinical use of PCF volumetry. An atlas-based method for automated PCF segmentation tailored for CMI is presented. The method performance is assessed in terms of accuracy and spatial overlap with manual segmentation. The degree of association between PCF volumes and the lengths of previously proposed linear landmarks is reported. MATERIALS AND METHODS T1-weighted volumetric MR imaging data with 1-mm isotropic resolution obtained with the use of a 3T scanner from 14 patients with CMI and 3 healthy subjects were used for the study. Manually delineated PCF from 9 patients was used to establish a CMI-specific reference for an atlas-based automated PCF parcellation approach. Agreement between manual and automated segmentation of 5 different CMI datasets was verified by means of the t test. Measurement reproducibility was established through the use of 2 repeated scans from 3 healthy subjects. Degree of linear association between PCF volume and 6 linear landmarks was determined by means of Pearson correlation. RESULTS PCF volumes measured by use of the automated method and with manual delineation were similar, 196.2 ± 8.7 mL versus 196.9 ± 11.0 mL, respectively. The mean relative difference of −0.3 ± 1.9% was not statistically significant. Low measurement variability, with a mean absolute percentage value of 0.6 ± 0.2%, was achieved. None of the PCF linear landmarks were significantly associated with PCF volume. CONCLUSIONS PCF and tissue content volumes can be reliably measured in patients with CMI by use of an atlas-based automated segmentation method.

Chiari type I malformation with high foramen magnum anomaly

“…One case and no control is a major limitation. Recently, morphometric studies have clearly shown significantly smaller volume or underdeveloped bony parts of the PCF in adults [1][2][3]5]. A significant smaller basiocciput in CMI group was demonstrated by Noudel et al [8], but no significant difference was found in the length of the supraocciput and FM.…”

“…Bagci et al [2] used 9 CMI patients for an atlas-based automated PCF parcellation approach as manually delineated PCF. PCF volumes measured by use of the automated method and with manual delineation were found to be similar, 196.2 ± ± 8.7 vs. 196.9 ± 11.0 cm 3 , respectively.…”

“…3. Tonsillar herniation measured from the McRae line to tip of the cerebellar tonsil [2,11]. The diagnosis of CMI was based on the determination of a cerebellar tonsillar herniation of at least 5 mm below the FM [3].…”

“…Posterior cranial fossa (PCF) abnormality of the skull is a developmental disorder and its variations have widely been reported in the literature [2,4,9]. Chiari malformations, Dandy Walker malformations, spina bifida and craniovertebral junction disorders are the common forms of the structural abnormality [1,7].…”

Magnetic resonance imaging–based measures predictive of short-term surgical outcome in patients with Chiari malformation Type I: a pilot study

“…Posterior cranial fossa volumetry was performed by using a previously described automated method. 12 With this method, the PCF, hindbrain, and fourth ventricle volumes were quantified using automated segmentation guided by a CM-I-specific brain atlas. These data provide a measure of hindbrain crowdedness as the ratio of hindbrain/PCF volume.…”