3-dimensional magnetic resonance imaging modeling of the pelvic floor musculature in classic bladder exstrophy before pelvic osteotomy.

PURPOSE We provide a 3-dimensional (3D) model of the pelvic floor musculature in patients with classic bladder exstrophy using magnetic resonance imaging (MRI). MATERIALS AND METHODS Five male infants 1 day to 12 months old underwent MRI of the pelvis, which was compared to pelvic MRI of 1 male infant without pelvic floor abnormalities. Of the patients 3 were studied before primary closure and 2 before reclosure. None of the patients had a prior pelvic osteotomy. While the entire pelvic floor was imaged, special attention was paid to the contours of the levator ani muscle group which were drawn on T1-weighted axial and coronal images. The overlap of contours in these 2 planes was used to construct a 3D model of this muscle group. The diastasis of the pubic symphysis was also measured for all patients on a plain pelvic radiograph. RESULTS The levator ani muscle group conformed to an elliptical dome shape in the control. For the patients the 3D shape was somewhat irregular with an apparent kink in the ellipse. The elliptical shape of the group was described by a shape factor, s, which equals the ratio of the maximum height-to-the length of the base of the ellipse. The shape factor was equal to 0.176 in the control compared to a mean of 0.448 for the patients. There was no relationship between diastasis of the pubic symphysis and the extent of disproportionate curvature of the levator group. CONCLUSIONS To our knowledge this is the first qualitative description of the pelvic floor anatomy in bladder exstrophy using MRI. Our model gives further insights into the true pelvic floor anatomy in exstrophy cases and is the first to suggest that abnormalities in the pelvic floor may not correlate with abnormalities of the bony pelvis.