Inferior Left Atrial Diverticulum Communicating with the Right Atrium or Inferior Vena Cava: Prevalence and CT Features

Purpose: To evaluate the prevalence and cardiac CT features of inferior left atrial diverticula (ILAD) communicating with the right atrium (RA) or inferior vena cava (IVC), a novel type of interatrial communication. Materials and Methods: This retrospective study included 11,512 consecutive patients who underwent cardiac CT. CT features and prevalence of ILAD communicating with the RA or IVC were analyzed. Shunts were defined as anatomical defects between the two structures with or without visible contrast flow. In a subset of the patients we compared interatrial septal aneurysm (n = 20) and ILAD without shunt (n = 66), assessing the involvement of a wedge-like fatty space bordered by both atria, IVC and coronary sinus. Results: There were 33 patients (19 males and 14 females; aged 59.8 ± 11.2 years; age range, 18–87 years) with ILAD with shunts (ILADSs). The prevalence of ILADSs was 4.2% (33/783) among ILAD and 0.3% (33/11,512) among all patients. Maximal dimensions of ILAD were 17.6 ± 9.9 mm (range, 5.3–41.0 mm). Mean ostial diameters of ILAD and mean sizes of shunts were 6.2 ± 5.6 mm and 3.2 ± 2.9 mm, respectively. Shunts were larger than 5 mm in 6 patients (15.2%) and larger than 3 mm in 10 patients (30.3%). In 30 patients who underwent transthoracic echocardiography, ILADSs were not identified at echocardiography. CT showed involvement of the wedge-like fatty space for all ILAD and for no cases with interatrial septal aneurysm. Conclusions: Cardiac CT enables detection of incidental ILADSs unrecognized at echocardiography.