A case of mitral regurgitation due to bilateral undifferentiated papillary muscles with detailed preoperative diagnosis of associated morphological abnormalities.

Incomplete differentiation of the mitral valve structures during fetal life results in the papillary muscles and tendon cords becoming hypoplastic, a condition termed undifferentiated papillary muscles (UDPM). This fetal abnormality causes a group of diseases that cause mitral valve dysfunction in adult life. Here, we report a case of UDPM centered on the medial posterior apex in which detailed morphological abnormalities were diagnosed preoperatively using echocardiography and three-dimensional computed tomography (3DCT) analysis, contributing to plastic surgery.The patient was a 64-year-old man who was followed up for several years for atrial functional mitral regurgitation (MR), ultimately developing heart failure. His MR was severe, and he was referred for surgery.Echocardiography revealed restrictive tendon cords primarily in the posterior apex, abnormal muscle bundles in the lower part of the valve, and findings indicative of UDPM; this was considered the main cause of MR. The patient had surgery findings similar to the preoperative diagnosis, which greatly aided the surgery. Postoperatively, the MR was well-controlled and mild.UDPM may present as various morphologic and functional abnormalities, including partial club-shaped tendinous MR and rheumatoid mitral stenosis, which are rarely accurately diagnosed preoperatively. Detailed analysis of morphological abnormalities using 3DCT or other methods may be beneficial for a successful plasty.