Table 2.

Organ system-based guidelines for imaging of conjoined twins

General imaging guidelines	• Twins should have the same orientation during all imaging investigations • CT is performed by using multislice thin section machines • The dose of contrast agent is calculated according to the combined weight by using pump injector (contrast dose and iodine concentration may vary by institution) • Each twin should be injected on a separate day. Twins with limited pelvic fusion (as pygopagus twins) may undergo CT with simultaneous contrast injection • The images are transmitted into the workstation for additional post-processing and multiplanar reconstruction • MRI usually needs general anesthesia (General anesthesia is better than deep sedation) • Two anesthesia teams should be available throughout the study • A phased array surface coil is used to cover both twins during MRI examination
Twins with fusion of the cranium and vertebral column	Imaging aims for evaluation of the central nervous system • Non-contrast CT with 3-D reconstruction of the bony calvarium and vertebral column • CT cerebral arteriography and venography • MRI standard sequences in addition to high resolution, 3-D heavily T2-WI volumetric sequences of the brain and spinal cord • Non-contrast MR arteriography and venography • Dynamic post-contrast MR angiography of the cerebral circulation • Functional MRI and Diffusion tensor imaging
Twins with thoracic fusion`	Imaging aims for evaluation of the cardiac and pulmonary systems • Dynamic post-contrast study in the arterial and venous phases • ECG-gated post-contrast CT for cardiac anomalies • 3-D reconstruction of the thoracic cage
Twins with abdominal fusion	Imaging aims for evaluation of the hepatobiliary and gastrointestinal systems and kidneys • Post-contrast study in arterial and venous phases for demonstration of shared arteries, or veins and demonstration of the surgical plane of hepatic separation • MRCP and HIDA scan: to rule out biliary fusion if suspected • Upper gastrointestinal series and follow through
Twins with fusion of the pelvis and perineum	Imaging aims for evaluation of the urogenital systems, distal gastrointestinal system and perineum • Post contrast study in arterial and venous phases with acquisition of multiple delayed phases to demonstrate urologic anomalies especially of the urinary bladder and ureters • 3-D reconstruction of the bony pelvis • High resolution T2-weighted image in axial and coronal planes with and without fat suppression for demonstration of the associated genital, urologic anomalies, and pelvic floor anatomy • Distal loopogram (if colostomy is present) for demonstration of anorectal anomalies (e.g., rectourethral fistula) • Micturating cystourethrography demonstrate of reflux and other associated renal anomalies especially if there is urinary tract dilatation (detected by ultrasound)

CT computed tomography; ECG electrocardiogram, HIDA hepatobiliary iminodiacetic acid, MRCP magnetic resonance cholangiopancreatography, MRI magnetic resonance imaging, 3-D, three-dimensional