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Pelvic kidney

Published:September 07, 2021DOI:https://doi.org/10.1016/j.ajog.2021.06.047

      Introduction

      A pelvic kidney is the most common type of renal ectopia and occurs in 1 in 700 live births.
      • Caiulo V.A.
      • Caiulo S.
      • Gargasole C.
      • et al.
      Ultrasound mass screening for congenital anomalies of the kidney and urinary tract.
      Pelvic kidneys are usually smaller than expected for gestational age and have an aberrant blood supply. Most of these kidneys are malrotated on their vertical axis, with the hilum facing anteriorly instead of medially toward the spine.

      Definition

      A pelvic kidney is one located below the aortic bifurcation in the presacral area. The pelvic location results from failure of renal ascent in early embryonic development.

      Ultrasound Findings

      A pelvic kidney is usually discovered when an empty renal fossa prompts a thorough search for the absent kidney. Demonstration of a kidney within the pelvis can be challenging because of bowel and acoustic shadowing from the iliac wings.
      • Meizner I.
      • Yitzhak M.
      • Levi A.
      • Barki Y.
      • Barnhard Y.
      • Glezerman M.
      Fetal pelvic kidney: a challenge in prenatal diagnosis?.
      Furthermore, the small kidney size, diagonal or horizontal orientation, and anteriorly facing the hilum make the visualization of the kidney more challenging. Frequently, dilation of the renal collecting system and cystic dysplasia further confound the ultrasonographic diagnosis because of distortion of normal anatomy. However, a reniform structure between the iliac vessels on the coronal view or adjacent to the bladder suggests a renal pelvic location, even if the appearance is somewhat atypical (Figure 1). Color Doppler tracing of the blood supply from the distal aorta, aortic bifurcation, or an aberrant pelvic vessel to the renal hilum may provide further supportive evidence for the presence of a pelvic kidney. Not infrequently, a follow-up examination is helpful in visualizing the ectopic kidney, as bowel echogenicity changes with gestational age.
      Figure thumbnail gr1
      Figure 1Pelvic kidney between iliac bones (calipers)
      Society for Maternal-Fetal Medicine. SMFM Fetal Anomalies Consult Series #4. Am J Obstet Gynecol 2021.
      Occasionally, the absence of the kidney from the renal fossa is overlooked because loops of bowel can be mistaken for a kidney. However, close inspection in the transverse and parasagittal views will reveal the absence of the slit-like renal pelvis and the lack of hypoechoic medullary pyramids converging toward the hilum. Other clues of an empty renal fossa are loss of the boomerang shape of the adrenal gland, which may appear flattened, elongated, and “lying down” in the parasagittal plane (Figure 2), and the inability to demonstrate a renal artery in the coronal plane using color Doppler.
      • Hoffman C.K.
      • Filly R.A.
      • Callen P.W.
      The “lying down” adrenal sign: a sonographic indicator of renal agenesis or ectopia in fetuses and neonates.
      ,
      • Majmudar A.
      • Cohen H.L.
      “Lying-Down” adrenal sign: there are exceptions to the rule Among fetuses and neonates.
      Figure thumbnail gr2
      Figure 2Empty renal fossa with a “lying-down” adrenal sign (arrow)
      Society for Maternal-Fetal Medicine. SMFM Fetal Anomalies Consult Series #4. Am J Obstet Gynecol 2021
      The contralateral kidney, bladder, and genitalia should be carefully assessed as well. Rarely, both kidneys are located in the pelvis.

      Associated Abnormalities

      Nearly 50% of pelvic kidneys are affected by hypoplasia, dysplasia, or hydronephrosis.
      • Batukan C.
      • Yuksel A.
      Prenatal diagnosis and postnatal outcome of pelvic kidneys.
      However, these conditions rarely correlate with an adverse prognosis for the fetus.
      • Batukan C.
      • Yuksel A.
      Prenatal diagnosis and postnatal outcome of pelvic kidneys.
      Although vesicoureteral reflux is identified in 80% of contralateral kidneys during childhood, it usually resolves over time with conservative management.
      • Batukan C.
      • Yuksel A.
      Prenatal diagnosis and postnatal outcome of pelvic kidneys.
      ,
      • Arena F.
      • Arena S.
      • Paolata A.
      • Campenni A.
      • Zuccarello B.
      • Romeo G.
      Is a complete urological evaluation necessary in all newborns with asymptomatic renal ectopia?.
      Dysplasia affects the contralateral kidney in 4% of cases.
      • Guarino N.
      • Tadini B.
      • Camardi P.
      • Silvestro L.
      • Lace R.
      • Bianchi M.
      The incidence of associated urological abnormalities in children with renal ectopia.
      Contralateral hydronephrosis requiring surgical intervention, such as that caused by ureteropelvic junction (UPJ) obstruction, is uncommon, occurring in 5% of cases.
      • Arena F.
      • Arena S.
      • Paolata A.
      • Campenni A.
      • Zuccarello B.
      • Romeo G.
      Is a complete urological evaluation necessary in all newborns with asymptomatic renal ectopia?.
      Coexisting single umbilical artery and cardiac and intracranial anomalies have been reported.
      • Batukan C.
      • Yuksel A.
      Prenatal diagnosis and postnatal outcome of pelvic kidneys.
      Hypospadias and cryptorchidism in males and genital anomalies affecting females seem to be slightly increased in pediatric series.
      • Batukan C.
      • Yuksel A.
      Prenatal diagnosis and postnatal outcome of pelvic kidneys.
      • Arena F.
      • Arena S.
      • Paolata A.
      • Campenni A.
      • Zuccarello B.
      • Romeo G.
      Is a complete urological evaluation necessary in all newborns with asymptomatic renal ectopia?.
      • Guarino N.
      • Tadini B.
      • Camardi P.
      • Silvestro L.
      • Lace R.
      • Bianchi M.
      The incidence of associated urological abnormalities in children with renal ectopia.

      Differential Diagnosis

      Other pelvic masses, including teratoma, neuroblastoma, supernumerary pelvic kidney, and ovarian or mesenteric cysts, should be considered. An empty renal fossa is associated with renal agenesis in 47% of cases and an ectopic kidney in 42% of cases, usually in the pelvis.
      • Chow J.S.
      • Benson C.B.
      • Lebowitz R.L.
      The clinical significance of an empty renal fossa on prenatal sonography.
      In some cases, the missing kidney may be fused to the contralateral kidney or in an unusual location if other anomalies (eg, diaphragmatic hernia) are present.
      • Chow J.S.
      • Benson C.B.
      • Lebowitz R.L.
      The clinical significance of an empty renal fossa on prenatal sonography.

      Genetic Evaluation

      Chromosomal anomalies are rare with an isolated pelvic kidney. If no further abnormalities are noted on ultrasound and the family history is unremarkable, no genetic evaluation beyond standard aneuploidy screening is typically recommended. If additional nongenitourinary anomalies are present, amniocentesis and chromosomal microarray analysis (CMA) should be offered. Syndromic conditions, such as VACTERL (vertebral defects, anal atresia, cardiac defects, tracheoesophageal fistula, renal anomalies, and limb abnormalities) and CHARGE (coloboma, heart defects, atresia choanae [choanal atresia], growth restriction, genital anomalies, and ear anomalies), should be considered in the presence of multiple anomalies.
      • Sahay M.
      Congenital anomalies of kidney and urinary tract (CAKUT).
      ,
      • Wellesley D.
      • Howe D.T.
      Fetal renal anomalies and genetic syndromes.
      If there are additional anomalies, consanguinity, or a family history of a specific condition, gene panel testing or exome sequencing is sometimes useful because CMA does not detect single-gene (Mendelian) disorders. If exome sequencing is pursued, appropriate pretest and posttest genetic counseling by a provider experienced in the complexities of genomic sequencing is recommended. After appropriate counseling, cell-free DNA screening is an option for patients who decline diagnostic evaluation, particularly if a common aneuploidy is suspected.

      Pregnancy and Delivery Management

      A detailed anatomic survey focusing on the genitourinary and cardiovascular systems should be performed to exclude associated anomalies. A fetal echocardiogram should be considered if a cardiac anomaly is suspected. A follow-up ultrasound examination in the third trimester of pregnancy to assess for late development of hydronephrosis is warranted, and consultation with pediatric urology or nephrology specialists can be helpful to review childhood follow-up. The finding of a pelvic kidney in the absence of other anomalies should not affect timing and mode of delivery, which should be based on the usual obstetrical indications.

      Prognosis

      The prognosis of a pelvic kidney is favorable in most cases, although renal function in the affected kidney is usually reduced.
      • van den Bosch C.M.
      • van Wijk J.A.
      • Beckers G.M.
      • van der Horst H.J.
      • Schreuder M.F.
      • Bökenkamp A.
      Urological and nephrological findings of renal ectopia.
      Generally, vesicoureteral reflux involving either the pelvic or contralateral kidney improves with conservative management.
      • Batukan C.
      • Yuksel A.
      Prenatal diagnosis and postnatal outcome of pelvic kidneys.
      Surgical intervention for hydronephrosis in the contralateral kidney (eg, UPJ obstruction) is needed in 5% of cases.
      • Arena F.
      • Arena S.
      • Paolata A.
      • Campenni A.
      • Zuccarello B.
      • Romeo G.
      Is a complete urological evaluation necessary in all newborns with asymptomatic renal ectopia?.
      Although there is no evidence for an increased incidence of hypertension, follow-up until young adulthood is recommended.
      • van den Bosch C.M.
      • van Wijk J.A.
      • Beckers G.M.
      • van der Horst H.J.
      • Schreuder M.F.
      • Bökenkamp A.
      Urological and nephrological findings of renal ectopia.
      An increased incidence of urinary tract infections and nephrolithiasis is reported in adults.
      • Singer A.
      • Simmons M.Z.
      • Maldjian P.D.
      Spectrum of congenital renal anomalies presenting in adulthood.

      Summary

      The diagnosis of pelvic kidney relies on a high index of suspicion on recognizing an empty renal fossa. Direct visualization of a kidney within the pelvis requires focused gray scale and color Doppler examination due to challenges posed by the fetal bowel and pelvic bones and, occasionally, atypical anatomic appearance. Amniocentesis and CMA are warranted only when additional, extragenitourinary malformations are present. Obstetrical management should not be altered, and the prognosis is generally good.

      References

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        Urological and nephrological findings of renal ectopia.
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