Rajesh Krishnamurthy MD, Presenter: Research support, Koninklijke Philips Electronics NV

1) Clarify concept of situs, and define heterotaxy. 2) Describe the segmental approach to evaluating visceral and cardiovascular anatomy in the setting of heterotaxy. 3) Provide an overview of visceral, vascular, and cardiac manifestations of heterotaxy, and their clinical significance. 4) Describe Cross-sectional Imaging protocols and pitfalls for delineating morphology and function in heterotaxy.

Situs refers to position of the atria and the abdominal viscera relative to the midline. There are three types: solitus, inversus, and ambiguous. Heterotaxy is synonymous with situs ambiguous. It is not a specific disease, but a constellation of cardiac, vascular, and visceral abnormalities, characterized by situs ambiguous of the viscera, abnormal lung and atrial appendage symmetry, anomalous systemic and pulmonary venous return, and characteristic intracardiac defects. There is a tendency towards syndromic clustering of defects like asplenia and polysplenia, which is helpful for teaching purposes, but a high number of exceptions to the rule results in poor clinical utility. An independent assessment of organ systems regardless of syndromic classification, based on the segmental approach by Van Praagh, is required to do justice to the Pandora's box that heterotaxy represents. MRI and CT play an important role in the diagnostic work-up of heterotaxy syndrome in the preoperative and postoperative periods, and provide information on visceral status, airways, extracardiac vasculature, complex intracardiac anatomy, ventricular and valvular function, and vessel-specific flow quantification. Choosing the appropriate imaging modality, familiarity with the anatomy prior to planning the study, careful choice of dynamic phases on MRA and CTA, use of 3D post-processing, and an obsessive compulsive attitude are required to avoid the numerous pitfalls in imaging in this setting.

Krishnamurthy, R, Visceral Heterotaxy Syndromes.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9000074.html