The Yin Yang Sign is a radiological sign that is found on an Abdominal CT scan after injection of the product of contrast or Doppler Ultrasound [1]. Also assimilated to the PEPSI LOGO, It looks like the ancient Chinese Symbol Yin-Yang representing two opposing forces (Star and Arrow) interdependent and interconnected (Figure 1).

In CT Imaging, it corresponds to a mass well -defined round or oval made of two parts, one of which hyper dense and another hypodense. The sign of Yin Yang is useful for recognizing true arterial or pseudo aneurysms partially thrombosed aneurysms. At CT scan with injection of the contrast medium, the hyper dense portion (Arrow white) represents the still circulating permeable light and the hypodense portion (black arrow) indicates the presence of intramural thrombus (Figure 2).

On Doppler Ultrasound, The Yin Yang Sign indicates a flow bidirectional due to the vortex of the blood in the right or the wrong aneurysm. His differential diagnosis is a fistula arteriovenous. The presence of this sign everywhere on the body human suggests partially thrombosed aneurysm but it is very evocative mainly in abdominal imagery and often concerning aorta vessel [2].

Figure 1: Yin -Yang symbol.

Figure 2: Abdominal CT scan, axial plan showing an aortic aneurysm partially thrombosed illustrated by the presence of the Yin-Yang Sign characteristics.

1.       Reddy S, Khashram M, Wicks K. The Yin –Yang Sign: A Contrast Enhancement Pattern Indicating a Partial Thrombosed Aneurysm: A Case Report. J  Radiology Diagnostic Imaging. 2014; 2: 3-4.

2.       Lupattelli T. The Yin-Yang Sign. Radiology. 2006; 238: 1070-1071.