ª Springer Science+Business Media New York 2015

Abdominal Imaging

Abdom Imaging (2015) DOI: 10.1007/s00261-015-0393-0

The yin–yang sign Melanie P. Caserta,1 Raymond B. Dyer2 1

Department of Radiology, Mayo Clinic, 4500 San Pablo Road, Jacksonville, FL 32224, USA Department of Radiology, Wake Forest Baptist Medical Center, Wake Forest University School of Medicine, Medical Center Blvd., Winston-Salem, NC 27157, USA 2

The yin and the yang are typically shown as an interweaved symbol in Chinese philosophy with the intent of indicating how contrary forces are complementary and interconnected (Fig. 1) [1]. At ultrasound imaging, this classic appearance can also be seen in a pseudoaneurysm (PSA) (Fig. 2) [2]. The PSA, also known as ‘‘false aneurysm,’’ occurs when there is a dilation of an artery due to disruption of one or more arterial layers. This is most commonly due to arterial trauma, but may occur in contained rupture of a true aneurysm [2]. Diagnosis of PSA is most commonly made with ultrasound, and Doppler ultrasound is essential. On grayscale imaging, PSAs are often unilocular with the appearance of a cyst or fluid collection. A well-defined neck connecting the collection to an arterial structure may be identified [2, 3]. Color Doppler imaging will demonstrate internal blood flow in a PSA distinguishing it from a cyst (Fig. 3 A, B) [3]. Color Doppler imaging will often show a well-defined swirl pattern due to turbulent internal flow giving rise to the namesake ‘‘yin–yang sign.’’ Spectral Doppler analysis of a well-defined neck in a PSA will demonstrate a diagnostic ‘‘to and fro’’ pattern of flow (Fig. 4). This occurs due to blood flowing into the collection during systole and out of the collection during diastole. Identification of the ‘‘to and fro’’ pattern of flow in the neck of a PSA helps identify the point of communication with the artery, which is useful in treatment planning [4].

Correspondence to: Melanie P. Caserta; email: [email protected] mayo.edu

Fig. 1. Chinese yin–yang www.clker.com Free Clipart).

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Fig. 2. Color Doppler US image of a transplant kidney demonstrates the characteristic ‘‘yin–yang’’ appearance in this large pseudoaneurysm (arrow).

M. P. Caserta, R. B. Dyer: The yin–yang sign

Fig. 3. A Longitudinal images of a renal transplant in a 30year-old male with history of prior biopsy. Gray-scale ultrasound image demonstrates two adjacent simple appearing cystic structures (arrows). B Color Doppler imaging reveals

flow in one of the lesions with the ‘‘yin–yang’’ sign of a pseudoaneurysm (arrow). The other lesion is a simple cyst. This case highlights the importance of using color Doppler imaging.

References 1. Dixon A, Bashir O. (2014) Yin yang sign. www.Radiopaedia.org. http://radiopaedia.org/articles/yin-yang-sign-1. Accessed 18 Dec 2014. 2. Jung J, Kirby CL (2007) 2006 SRU cases of the day, case 5, diagnosis: lymph node mistaken as a partially thrombosed pseudoaneurysm. Ultrasound Q 23:76–78 3. Middleton WD, Dasyam AD, Teefey SA (2005) Diagnosis and treatment of iatrogenic femoral artery pseudoaneurysms. Ultrasound Q 21:3–17 4. Abu-Yousef MM, Wiese JA, Shamma AR (1988) The ‘‘to and fro’’ sign: duplex Doppler evidence of femoral artery pseudoaneurysm. Am J Roentgenol 150:632–634

Fig. 4. Same patient as Fig. 2. Spectral Doppler interrogation of the neck of the pseudoaneurysm demonstrates the diagnostic ‘‘to and fro’’ pattern of pseudoaneurysm with a short phase of antegrade systolic flow followed by more prolonged retrograde diastolic flow.

The yin-yang sign.

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