Swiss cheese appearance | Radiology Signs

Answer:

The Swiss cheese septum is the perforated appearance produced by multiple defects in the muscular (trabecular) interventricular septum, most of them in the apical and mid-muscular portions. On two-dimensional imaging the trabeculated apical septum looks fenestrated, and colour Doppler resolves several discrete left-to-right jets, which is what confirms the appearance as true defects rather than deep intertrabecular recesses. A characteristic feature is that a single defect often has a single left ventricular orifice and several right ventricular orifices, because the right side of the septum is coarsely trabeculated; this serpiginous course is why the surgical count regularly exceeds the echocardiographic count and why the right ventricular approach is unreliable. Haemodynamic significance is judged by the combined shunt rather than by any one defect: a Qp:Qs above 1.5 to 2.0, left atrial and left ventricular dilatation, and pulmonary arterial pressure determine whether intervention is needed and how urgently. Many small muscular defects close spontaneously in infancy, so a small shunt is followed rather than treated. When closure is needed the options are hybrid perventricular device closure, pulmonary artery banding as a staging procedure, or apical left ventriculotomy with a single patch, and cardiac MRI or ECG-gated CT is used to map defect number, size and position when the echocardiographic window is inadequate. The main mimic is a prominent trabecular recess or an aneurysmal septum without flow, which is excluded by the absence of a colour jet.

Why is it called so?

The septum appears riddled with holes on cross-sectional imaging, like a slice of Emmental or Swiss cheese.

Pathophysiology

Muscular septal defects arise from failure of coalescence and excavation of the trabecular component of the ventricular septum during embryogenesis rather than from malalignment of the conal septum, which is why they are not associated with the outflow anomalies that accompany perimembranous and doubly committed defects. Because the trabecular septum thickens and its trabeculations grow after birth, small defects can close spontaneously by muscular apposition. Sustained left-to-right shunting increases pulmonary blood flow, produces volume loading of the left atrium and left ventricle, and if uncorrected leads to pulmonary vascular remodelling and eventual shunt reversal.

Alternative names: Swiss cheese septum; multiple muscular ventricular septal defects

Other associated named signs: Goose neck deformity of an atrioventricular septal defect and the egg on a string appearance of transposition are the other classic shape signs of septal and conotruncal anomalies

References

1. Capelli H, Andrade JL, Somerville J. Classification of the site of ventricular septal defect by 2-dimensional echocardiography. Am J Cardiol. 1983;51(9):1474-80. PMID: 6846180.