A 59-year-old woman with non-ischaemic dilated cardiomyopathy and severe mitral regurgitation was referred for mitral valve repair. Intraoperative transoesophageal echocardiography (TOE) performed before cardiopulmonary bypass (CPB) showed normal mitral leaflets with increased mitral valve tenting area and posterior mitral leaflet tethering; no masses were seen within the left atrium. After ring annuloplasty and during weaning from CPB, repeat TOE was performed, disclosing a new 27×13 mm mass within the left atrium with a “crooked finger” appearance and a hinge-type motion. The mass appeared to be attached to the left lateral wall of the left atrium above the mitral annulus, and prolapsed into the mitral valve (fig 1, panel A, arrows, and video 1). The normal left atrial appendage (LAA) could not be visualised. With filling of the heart, the mass suddenly disappeared and a normal LAA became clearly evident (fig 1, panel B and video 2), confirming the diagnosis of inverted LAA. Only minimal residual mitral regurgitation was seen after the procedure, and the patient’s postoperative course was uneventful.

During cardiac surgery, the LAA may invert as a result of the negative pressure that occurs during placement of the left atrial vent catheter or during the de-airing manoeuvres before discontinuing CPB. Inverted LAA often everts spontaneously while the heart is being filled during weaning from CPB. However, sometimes it fails to evert, particularly if the base is narrow. If routine intraoperative TOE is not performed, an inverted LAA may go unnoticed and may be later on misdiagnosed as an atrial tumour or clot.

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Figure 1 (A) Transoesophageal echocardiography disclosing a mass within the left atrium (arrows) that appeared to be attached above the mitral annulus, and prolapsed into the mitral valve. (B) With filling of the heart a normal left atrial appendage can be seen.