CTICasesSigmoid Septum with Systolic Anterior Motion of the Mitral Valve
Imaging findings
Cardiac MRI (cine three-chamber view) demonstrates systolic anterior motion (SAM) of the mitral valve anterior leaflet and chordae tendineae, which are drawn into the left ventricular outflow tract (LVOT). This causes a high-velocity dephasing jet and severe dynamic LVOT obstruction. There is mild thickening of the basal anterior septum (15-16 mm), characteristic of a sigmoid septum, without late gadolinium enhancement or scarring.
Key takeaways
A "sigmoid septum" is a benign, age-related conformational change of the basal interventricular septum that can narrow the LVOT and lead to severe systolic anterior motion (SAM) of the mitral valve and dynamic obstruction. Pathological analysis of myomectomy specimens in these patients reveals histologically normal myocytes without the myofiber disarray characteristic of genetic hypertrophic obstructive cardiomyopathy (HOCM).
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