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Carolina Martins, Eduardo Carvalhal Ribas, Albert L. Rhoton Jr. and Guilherme Carvalhal Ribas

Three-dimensional images have become an important tool in teaching surgical anatomy, and its didactic power is enhanced when combined with 3D surgical images and videos. This paper describes the method used by the last author (G.C.R.) since 2002 to project 3D anatomical and surgical images using a computer source. Projecting 3D images requires the superposition of 2 similar but slightly different images of the same object. The set of images, one mimicking the view of the left eye and the other mimicking the view of the right eye, constitute the stereoscopic pair and can be processed using anaglyphic or horizontal-vertical polarization of light for individual use or presentation to larger audiences. Classically, 3D projection could be obtained by using a double set of slides, projected through 2 slide projectors, each of them equipped with complementary filters, shooting over a medium that keeps light polarized (a silver screen) and having the audience wear appropriate glasses. More recently, a digital method of 3D projection has been perfected. In this method, a personal computer is used as the source of the images, which are arranged in a Microsoft PowerPoint presentation. A beam splitter device is used to connect the computer source to 2 digital, portable projectors. Filters, a silver screen, and glasses are used, similar to the classic method. Among other advantages, this method brings flexibility to 3D presentations by allowing the combination of 3D anatomical and surgical still images and videos. It eliminates the need for using film and film developing, lowering the costs of the process. In using small, powerful digital projectors, this method substitutes for the previous technology, without incurring a loss of quality, and enhances portability.

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Arthur J. Ulm, Antonino Russo, Erminia Albanese, Necmettin Tanriover, Carolina Martins, Robert M. Mericle, David Pincus and Albert L. Rhoton

Object

The aim of this study was to determine the anatomical limitations of the transcallosal transchoroidal approach to the third ventricle.

Methods

Twenty-six formalin-fixed specimens were studied. Sagittal dissections were used to determine the anatomical relationships of the foramen of Monro, the angle of approach to landmarks, and placement of a callosotomy. Lateral ventricular dissections were performed to quantitate the forniceal anatomy.

Results

The foramen of Monro was found 1.07 ± 0.11 cm superior and slightly anterior to the mammillary bodies, 1.48 ± 0.16 cm posterosuperior to the optic recess, and 2.26 ± 0.16 cm anterosuperior to the aqueduct. Relative to the genu, a callosal incision 2.64 ± 0.53 cm long and angled 37 ± 4.3° anterior was needed to access the aqueduct, and an incision 4.92 ± 0.71 cm long and angled 49 ± 7.4° posterior was needed to access the optic recess. The fornix progressively widened within the lateral ventricle, from 1.25 ± 0.63 mm at the foramen of Monro to > 7 mm at 2 cm behind the foramen. Three zones of exposure were identified, requiring unique craniotomies, callosotomies, and angles of approach. The major limiting factors in the approach included the columns of the fornix anteriorly, the width of the fornix posteriorly, and the draining veins of the parietal cortex. The choroidal fissure opening was limited to 1.5 cm posterior to the foramen of Monro; this limited opening created an aperture effect that required an anterior-to-posterior angle, an anterior craniotomy, and an anteriorly placed callosotomy to access the posterior landmarks. In contrast, a posterior-to-anterior angle, posteriorly placed craniotomy, and posteriorly placed callosotomy were required to access anterior landmarks.

Conclusions

The transcallosal transchoroidal approach was ideally suited to access the foramen of Monro and the middle and posterior thirds of the third ventricle. Exposure of the anterior third ventricle was limited by the columns of the fornix and by the presence of parietal cortical draining veins.