Exam AB-Abdomen Topic 1 Question 62 Discussion

The ultrasound image labeled "SAG RUQ KIDNEY" demonstrates a midline sagittal view showing a renal parenchymal structure that extends across the midline anterior to the aorta and vertebral bodies, suggesting the presence of a horseshoe kidney.
A horseshoe kidney is a congenital renal anomaly in which the lower poles of both kidneys are fused across the midline by a parenchymal or fibrous isthmus. This isthmus typically lies anterior to the aorta and inferior vena cava and can be seen as a hypoechoic band of tissue crossing the midline on ultrasound.
Ultrasound findings characteristic of a horseshoe kidney:
* Abnormally low position of the kidneys in the abdomen
* Renal tissue (isthmus) bridging the lower poles anterior to the great vessels
* Renal axes may be more horizontal than usual
* Kidneys may appear closer together or "kissing" the spine anteriorly
Differentiation from other options:
* A. Duplicated collecting system: Manifests as two separate collecting systems within one kidney, often with a central renal sinus split into two - not typically midline bridging.
* B. Crossed renal ectopia: Involves one kidney crossing midline and fusing with the other on the opposite side, but they do not form a midline isthmus.
* D. Pelvic kidney: A single kidney located in the pelvis due to failed ascent - it does not appear as midline fusion of two kidneys.
References:
Rumack CM, Wilson SR, Charboneau JW, Levine D. Diagnostic Ultrasound. 5th Edition. Elsevier, 2018.
Chapter: Urinary Tract, pp. 215-218.
American Institute of Ultrasound in Medicine (AIUM). Practice Parameter for the Performance of an Ultrasound Examination of the Abdomen and/or Retroperitoneum. 2020.
Radiopaedia.org. Horseshoe kidney: https://radiopaedia.org/articles/horseshoe-kidney