horseshoe kidney

horseshoe kidney

horseshoe kidneys
transverse and coronal views through the fetal abdomen reveal a mass of tissue crossing the midline and bridging the lower poles of the kidneys. this isthmus is isoechoic to the renal parenchyma and is symmetrical in shape. the kidneys are rotated anteriorly and their lower poles are more medial than usual. mild pelviectasis is noted in both kidneys.

description

this abnormality occurs at approximately 4 to 6 weeks gestation after the ureteral bud meets the metanephric blastema, before ascent and rotation.the kidneys are joined at the lower pole by a parenchymatous or a fibrous isthmus.the isthmus is usually located adjacent to the third or fourth lumbar vertebra just below the junction of the inferior mesenteric artery and aorta and is almost always anterior to the aorta. the amount of tissue on each side is equivalent and the ureters generally do not cross the midline before entering the renal pelves. this condition occurs in approximately 1/400 births and is more common in males.

diagnosis

the diagnosis of horseshoe kidney should be considered if the kidneys appear fused with equal amounts of tissue bilaterally. the calyces usually point posteriorly and the pelvic axis is vertical. hydronephrosis is the most frequently associated genitourinary anomaly and is present in approximately 45% of cases. other genitourinary anomalies include hypospadias and cryptorchidism. there may be ureteral duplication. there have also been occasional reports of bicornuate uterus, undescended testes and vesicoureteral reflux (vur). the adrenal glands are usually of normal appearance, although there have been reports of malformed adrenals associated with horseshoe kidney. approximately 1/3 of individuals with horseshoe kidney have other anomalies, including congenital heart defects (chd), skeletal, central nervous, and anorectal malformations.

differential diagnosis

the fused pelvic kidney is an irregular mass of renal tissue in the midline with two or less pelves and a variable number of ureters: this is frequently of unusual shape with unequal distribution of tissue on either side and the area of fusion is frequently not obvious. tumours may mimic a horseshoe kidney if located between two normal kidneys which are then displaced posteriorly.

sonographic features

kidney fused at midline – equal amounts of tissue on each side

lower poles displaced anteriorly

renal pelvis located anteriorly and may be dilated

normal bladder

normal amniotic fluid volume

associated syndromes

  • caudal dysplasia
  • fanconi pancytopenia
  • fetal alcohol syndrome (fas)
  • roberts
  • thanatophoric dysplasia
  • trisomy 18
  • turner

references

  1. stevenson r, hall t, goodman r in: human malformations and related anomalies vol ii oxford u press: new york, p501
  2. chervenak fa, issacson gc, campbell s in:ultrasound in obstetrics and 足球世界杯赛程2022赛程表 vol i little, brown & co: boston, p256
    romero r,pilon g, jeanty p, ghidini a, hobbins j in: prenatal diagnosis of congenital anomalies appleton & lange: norwalk, p336
  3. julia p, hanotel mc, ghalayin b, fabian jd abdominal aortic aneurysm associated with horseshoe kidney and duplication of the inferior vena cava ann vasc surg 7:587-9
  4. crawfurd m. d’a in: the genetics of renal tract disorders oxford u press: oxford, p553
  5. fleischer ac, romero r, manning fa, jeanty p, james ae jr in: the principles & practice of ultrasonography in obstetrics & 足球世界杯赛程2022赛程表 4th ed appleton & lange: norwalk, p 256
  6. warkany j in: congenital malformations, notes and comments year book: chicago, p429
  7. fleischer a, romero r, manning f, jeanty p, james jr a in: the principles and practice of ultrasonography and obstetrics and 足球世界杯赛程2022赛程表 , 4th edition appleton & lange. norwalk, p429