THE TRANSCALLOSAL INTERFORNICEAL APPROACH TO THE 3RD VENTRICLE - ANATOMIC AND MICROSURGICAL ASPECTS

OBJECTIVE: The ability to visualize median-sagittal brain structures b y magnetic resonance imaging improves planning for surgery to treat le sions of the third ventricle. The most appropriate path to the third v entricle is the transcallosal approach. The present study was undertak en to describe the surgical anatomy and landmarks encountered during t his approach. METHODS: The transcallosal-interforniceal approach was u ndertaken in 30 formalin-fixed brains using an operating microscope. T he surface landmarks for the approach pathway were the two points, P5 and P7, located 5 and 7 cm anterior to the central sulcus, respectivel y. Using these two points on the cortical surface as references, a var iety of measurements were made to provide quantitative information abo ut distances between brain structures that are encountered during the surgical approach. Measurements that were made include the following: 1) the distance between P5 and the cingulate sulcus, 2) the distance b etween the cingulate sulcus and the corpus callosum, 3) the height of the corpus callosum, 4) the distance between the anterior commissure a nd the foramen of Monro, and 5) the distance between the lower margin of the corpus callosum and the fornix. RESULTS: Mean values for these key measurements were as follows: 1) 23.96 mm (range, 15.0-32.0 mm); 2 ) 13.50 mm (range, 8.0-20.0 mm) with reference to P5 and 12.73 mm (ran ge, 6.0-18.0 mm) with reference to P7; 3) 6.12 mm (range, 4.0-8.0 mm) with reference to P5 and 6.60 mm (range, 4.0-9.0 mm) with reference to P7; 4) 4.96 mm (range, 2.5-10.0 mm), independent of P5 and P7; and 5) 8.46 mm (range, 3.0-16.0 mm) with reference to P5 and 11.04 mm (range , 6.0-22.0 mm) with reference to P7. CONCLUSION: The detailed quantita tive information obtained in this study about the interforniceal appro ach permitted definition of surgical approach pathways that preserve i mportant anatomic structures, such as the motor strip, genu of the cor pus callosum, fornical commissure (hippocampal commissure), anterior c ommissure, and fornical columns. The approach through this surgical co rridor can easily be planned and performed in individual cases using m edian-sagittal magnetic resonance imaging scans.