Diagnostic Ultrasound - Abdomen and Pelvis

Horseshoe Kidney
Diagnoses: Urinary Tract
TERMINOLOGY
• Congenital anomaly in which kidneys are fused at their
lower poles in midline
○ In contradistinction to crossed fused ectopia, where both
kidneys are located on 1 side
IMAGING
• Kidneys on opposite sides with lower poles fused in midline
• Presence of isthmus is defining feature; crosses midline
anterior to spine and aorta, but posterior to inferior
mesenteric artery
• Cross-sectional imaging (CT or MR) to define vascular
anatomy and can be used to visualize associated
complications such as malignancy
TOP DIFFERENTIAL DIAGNOSES
• Renal ectopia
• Paraaortic lymphadenopathy/retroperitoneal mass
KEY FACTS
PATHOLOGY
• Proposed theory of fusion of nephrogenic blastomas at 4
weeks gestational age when still located in pelvis,
preventing appropriate ascent
• Numerous associated abnormalities and congenital
disorders
CLINICAL ISSUES
• Complications include obstruction, infection,
nephrolithiasis, and malignancy
• Prognosis is good in absence of associated abnormalities
(Left) Graphic shows a
horseshoe kidney with the
isthmus ſt anterior to the
aorta and inferior vena cava.
Note the additional renal
arteries arising from the
common iliac arteries st.
(Right) Transverse ultrasound
in the midline shows a
horseshoe kidney. The isthmus
of the horseshoe kidney
lies anterior to the aorta ſt
and inferior vena cava st. The
isthmus is composed of
functioning renal tissue.
(Left) In this longitudinal
ultrasound, note the
boomerang configuration of
the left kidney, with the lower
pole ſt obscured as it bends
away from the transducer.
(Right) Axial CECT in the same
patient demonstrates
horseshoe kidney st draped
over the aorta ſt in the lower
abdomen. The inferior
mesenteric artery prevents
ascent of the kidney in utero.
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