Variations in levator ani volume and geometry in women: the application of MR based 3D reconstruction in evaluating pelvic floor dysfunction.

OBJECTIVE: We report on the comparative 3-dimensional (3D) living female pelvic floor geometry in five women, comparing the volume, morphology, and integrity of the levator sling, and pelvic anatomic relationships among study subjects. METHODS: Five women of varying ages, parity, continence, and prolapse status were studied. Two-dimensional (2D) imaging of the pelvic floor organs was performed on each subject in the supine position. Manual segmentation techniques and solid modeling software was used to build 3D models of each patient's pelvic floor structures, which could then be viewed and measured on the computer screen. We measured levator muscle volume, posterior urethro-vesical angle, distance from the urethra to pubo-coccygeal line, and the levator plate angle. The integrity of pubo-coccygeal attachments was also recorded. RESULTS: Levator muscle volume ranged from 68 ml in the nulliparous female, to 26 ml in the grand multipara with severe prolapse and mild genuine stress incontinence (GSI). The second lowest volume (30 ml) was in the multipara with GSI. Volumes in the parous subjects without stress urinary incontinence or pelvic organ prolapse were 36 and 39 ml. Pubo-coccygeal attachments were found to be torn in the 2 symptomatic subjects, and were intact in all 3 asymptomatic subjects. CONCLUSION: MR based 3D modeling is feasible and can be used in a research setting to evaluate complex anatomic relationships which may accompany pelvic floor dysfunction. The technique can also be used to evaluate levator muscle morphology and volume, as well as pelvic floor support integrity and its possible role in GSI and prolapse. We are currently conducting a larger study to validate our technique, and to better define the relationship between pelvic floor geometry and pelvic floor dysfunction.

Anatomical analysis and preoperative planning of correctional osteotomies: slipped capital femoral epiphysis (SCFE).

SCFE is defined as the slippage of the femoral head relative to the femoral neck along the proximal femoral growth plate. The femoral head shifts and rotates along the proximal end of the femoral neck, usually posteriorly and interiorly. The pathoanatomical findings are characterised by the changed relationship between the femoral head and femoral metaphysis, and between the femoral head and the acetabulum. A reduced femoral anteversion, a varus deformity of the femur, a shortening of the femoral metaphysis and an anterior metaphyseal prominence are also regularly observed. This may lead to impingement between the femoral metaphysis and the acetabular rim. Potential consequences of this complex 3D deformity are pain, a reduced range of hip motion and an early degenerative joint disease. In moderate and severe cases a redirectional femoral osteotomy is recommended. Different techniques, such as subcapital, base-of-neck, intertrochanteric and subtrochanteric osteotomies, have been described. These correctional osteotomies aim towards a reconstruction of the hip joint geometry, to prevent early arthritic degeneration. Currently, the planning of surgical treatment in these cases is based on measurements on antero-posterior and lateral plain radiographs. The relevant angle for planning of correctional osteotomies is the physis-shaft angle, determined in both plains. These angles describe the degree of slippage, thereby helping the surgeon to indicate and plan a correctional osteotomy. However, plain radiographs are projectional images and therefore carry inaccuracies caused by the overlay of anatomical structures and an incorrect positioning of the patient. 3D reconstructions are more accurate and provide substantial additional information for the surgeon, such as, for example, the anteversion of the acetabulum. We have developed interactive 3D software to measure projected angles, to analyse the geometry of the proximal femur and to determine the orientation of the acetabulum based on 3D reconstructions of CT data-sets. A program was also developed to simulate different techniques of osteotomies and to evaluate the postoperative range of hip motion and the hip-joint geometry. Accurate 3D measurements, additional anatomical information, simulations of different techniques of osteotomies and the evaluation of simulated postoperative results enables the surgeon to determine the best surgical treatment, based on the clinical findings.

Image-guided therapy and intraoperative MRI in neurosurgery.

Computer-assisted 3D planning, navigation and the possibilities offered by intra-operative imaging updates have made a large impact on neurological surgery. Three-dimensional rendering of complex medical image information, as well as co-registration of multimodal sources has reached a highly sophisticated level. When introduced into surgical navigation however, this pre-operative data is unable to account for intra-operative changes, ('brain-shift'). To update structural information during surgery, an open-configured, intra-operative MRI (Signa SP, 0.5 T) was realised at our institution in 1995. The design, advantages, limitations and current applications of this system are discussed, with emphasis on the integration of imaging into procedures. We also introduce our integrated platform for intra-operative visualisation and navigation, the 3D Slicer.