On the assessment of ventricular reconfiguration after intracranial pressure relief. What information is encoded in size and form?

Objective: In pathologic conditions such as occlusive hydrocephalus, the alteration of ventricular size and shape is not uniform. The aim of this study is to visualise and quantify the dynamics of parenchymal and ventricular adjustment in patients who underwent third ventriculostomy for the treatment of occlusive hydrocephalus. A statistical group analysis of the ventricular deformation allows one to mimic the pattern of parenchymal and ventricular adaptation.

Material and Methods: 3D T1w volume datasets of 5 patients were obtained prior to surgery and at different time points within 8 months after surgery. In an off-line analysis the datasets were mapped onto each other which allowed the assessment of the temporally varying brain morphology by a 3D non- linear deformation analysis. A statistical approach to the deformation renders the comparison of local volume changes at each voxel possible. Furthermore, a continuous parametric representation of the ventricular system allows to quantify shape differences.

Results: Dynamic adaptations of the ventricles to the altered pressure condition take place in all parts of the ventricular system and in the surrounding parenchyma: regions that primarily shrink are neighboured by others that even expand. The adjustment of the tissue and ventricular system to the intracranial pressure relief is more pronounced in the later postoperative course. The combination of a deformation-based analysis with parametric shape modelling of the periventricular structure expresses the interaction between volume and shape differences yielding a better group discrimination and an improved understanding of morphologic differences.

Conclusion: A novel technique allows a 3D visualisation and a quantitative assessment of the dynamics of structural tissue change. Parametric modelling suggests that there is new information in shape not represented in size, a property that might improve our understanding of tissue adaptation. These findings contribute to a theoretical concept of brain reconfiguration after intracranial pressure relief.