Assessment of ventricular reconfiguration after third ventriculostomy: what does shape analysis provide in addition to volumetry?

PURPOSE From neuroradiologic experience, it is evident that the adaptation of the ventricular system secondary to pathologic processes or surgery is not uniform. To describe changes entirely, one must consider, in particular, information about volume and shape. In this study, we address specifically the information encoded in the change of shape. To exemplify the technique, we used time-series MR imaging examinations of patients with surgically treated chronic or acute occlusive hydrocephalus. METHODS Preoperative and postoperative MR imaging at different time-steps was performed in 2 patients with occlusive hydrocephalus with a different time course of ventricular enlargement. The third and lateral ventricles were segmented with an automated classification scheme. Ventricular surfaces were binarized, mapped to a spheric coordinate system, and modeled by harmonic-basis functions. This approach allows simplification of the complex shape by stepwise filtering of the details that form the surface. The ventricles can be directly compared on the level of the simplified shape. RESULTS Although the relative volumetric change was comparable between patients, analysis of shape revealed notable regional differences in the pattern of adaptation. Comparing subacute and chronic hydrocephalus, the analysis reflected fundamental differences in the pattern of ventricular enlargement. CONCLUSION In addition to the mere volumetric description, this approach identifies regions that re-adjust differently to the altered pressure. The pattern of re-adaptation depends on the time course and history of the hydrocephalus. Furthermore, the different patterns of ventricular adaptation in patients with chronic or subacute hydrocephalus suggest a contiguity with properties of the surrounding parenchymal tissue.