Juxtaposition of the morphologically right atrial appendage in solitus and inversus atria: a study of 35 postmortem cases.

Juxtaposition of the atrial appendages has previously been classified positionally, left sided being more frequent than right sided. In our study of 35 postmortem cases, juxtaposition was analyzed morphologically for the first time. Juxtaposition of the morphologically right atrial appendage (JRAA) was always left sided with solitus atria (34 cases) but was right sided with inversus atria (1 case), the latter patient being the first documented case of JRAA with atrial inversion. Thus in patients with JRAA, the sidedness of the juxtaposition depends on the type of atrial situs that coexists. Frequent associated malformations included tricuspid valve anomalies (21 [60%] of 30), hypoplasia of the right ventricular sinus (26 [74%] of 35), and an abnormal conus (subaortic or bilateral) in 100%. Hypoplasia of the right ventricular sinus, plus malformation of the conus, appears to be important in the morphogenesis of JRAA.