Is the distance between mammillary bodies predictive of a thickened third ventricle floor?

Advances in the ETV technique have been based on a detailed understanding of third ventricular anatomy, surgical trajectories, and improved instrumentation.Knowledge of third ventricle anatomy is essential for the safety and reliability of intraventricular endoscopic procedures. Many anatomical variants or anomalies can complicate the ETV procedure and compromise the surgical results for example, thickening of the TVF, which disturbs the usual anatomical orientation and can render perforation of the floor technically difficult; a narrow foramen of Monro; or the so-called upward ballooning phenomenon, in which, after perforation of the TVF and withdrawal of a Fogarty catheter, the floor herniates into the third ventricle, hindering the endoscopic view. The operative results mainly depend on the selection of suitable hydrocephalic patients; therefore, specific MR imaging findings in the evaluation of the pathophysiological and anatomical prerequisites are a fundamental part of preoperative planning. Unfortunately, the consistency of the TVF cannot be adequately determined preopera-tively based on MR images, even with an advanced MR imaging protocol and 3D reconstruction. However, the distance between MBs, the fundamental anatomical landmarks for ETV, is a linear measure readily assessable on axial MR images and can provide indirect information about the conformation of the TVF. A thorough search of the medical literature failed to reveal any systematic MR imaging evaluation of this particular measure in healthy persons or in an ETV study. Because in neuroendoscopic studies variable IMDs and a thickened TVF have been commonly observed, we retrospectively evaluated the IMDs on routine MR images both in 23 patients with hydrocephalus who had undergone ETV and in 120 healthy persons to define normal values of the IMD, which to our knowledge has never been reported, and to assess the possible correlation between such preoperative measures and the thickness of the TVF in patients with hydrocephalus.