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2006-03-27-16 Pyelectasis © Malkomes www.thefetus.net/


Pyelectasis

Paulo Malkomes, MD

Unimed Hospital, Departamento de Ginecologia e Obstetricia, Capivari, Sao Paulo, Brasil

Synonyms: Mild hydronephrosis, pelviectasis

Definition: Pyelectasis is a pelvicaliceal dilatation. Fetal pyelectasis can be classified accordingly to the gestational age:

  • Between 15 and 20 weeks: greater or equal to 4mm
  • Between 20 and 30 weeks: greater or equal to 5mm
  • Between 30 and 40 weeks: greater or equal to 7mm

Persistent fetal pyelectasis is defined as >7 mm in the third trimester (1).

Incidence: Abnormalities of the urinary tract can be found in up to 5% of newborns. They account for 25% of all prenatally congenital defects and contribute to 4% of the perinatal mortality (24). The most common sonographic abnormality found in the fetal urinary tract is collecting system dilatation, accounting for 4.5% of all examinations (3). Pyelectasis is more likely to be bilateral (57%) (7), and is more common in the left kidney (11).

Prevalence: The prevalence of fetal pyelectasis during an anomaly scan in a low-risk population is not high (1.25%) (7).

Sex ratio: Male fetuses exhibit a significantly increased frequency of renal pelvis dilatation compared with female fetuses (3:1) (14).

Etiology: The maternal hydration influences fetal renal pelvic diameter. The effects of maternal hydration on amniotic fluid volume are partially mediated via fetal urine production (6). The fetal anteroposterior renal diameter increases with maternal hydration in both normal fetuses and in those with pyelectasis and is independent of the state of the fetal bladder (16).
Maternal high level progesterone seems to influence the fetal and mother ureter smooth muscle. There is a statistically significant association between maternal and fetal collecting system dilatation during pregnancy (19).
Isolated pyelectasis can be a sign of the presence of vesicoureteral reflux (3), which is frequent in neonates with urinary tract infection. It is often a cause of moderate dilatation of the fetal renal pelvis (20) but antenatal ultrasound has a poor sensibility for vesicoureteral reflux detection (10). Fluctuation, defined as size of renal pelvis changing by more than 4 mm during the course of prenatal or postnatal scans, is strongly associated with high-grade vesicoureteral reflux (17). Antenatal isolated pelvis dilatation is a weak predictor of vesicoureteral reflux (21). Ureteropelvic junction obstruction perhaps is the most important etiology of fetal pyelectasis. Prenatal ultrasound has led to earlier diagnosis of ureteropelvic junction obstruction, allowing earlier repair (22). In some series, dilatation of the renal pelvis was caused by primary ureteropelvic junction obstruction in 65.6%.

Sonographic findings: Diagnosis is made by the measure of the renal pelvic anteroposterior diameter. There is a positive correlation between gestational age and renal pelvic anteroposterior diameter (15). The size of the fetal renal collecting system is highly variable over the course of a two hour period. Significant caution should be used when considering the implications of renal collecting system dilatation based upon a single anteroposterior measurement (18).

Differential diagnosis: The differential diagnoses include other causes of dilatation of the renal pelvis like multicystic kidney disease, duplex system, ureterovesical junction obstruction, and posterior urethral valves.

Associated anomalies: Mild pyelectasis is a common finding which is often incidental, with no significant long term sequelae. However, there is a small association with aneuploidy, in particular the trisomy 21 and postnatal renal pathology (4). The presence of isolated pyelectasis had 9.09% sensitivity, 97.6% specificity, 0.33% positive predictive value, and 99.9% negative predictive value to detect fetuses with trisomy 21 (8). The incidence of Down syndrome is 3.3% when fetal pyelectasis is present, but 25% of fetuses with trisomy 21 have pyelectasis (12).

Prognosis: Most pyelectasis resolve spontaneously in the first year of life and invasive procedures are not required. Adequate monitoring of these children can avoid urinary tract infections and their sequelae (2). Unilateral prenatal lesions are less common than bilateral, but they have a significant postnatal pathology in 47 and 26 per cent, respectively. Postnatal follow-up is required for persistent pyelectasis (9). Fetal pyelectasis of 8 mm was 91% sensitive and 72% specific in predicting subsequent hydronephrosis (11). Urological tests are performed when the prenatal renal pelvic diameter is larger than 10 mm (10). Neonatal surgery is recommended when the anteroposterior, transverse, and longitudinal renal pelvic diameters during the prenatal period are at least 20, 25, and 26 mm, respectively. Surgery is not necessary when the diameters are less than 20 mm (13). Reflux is frequent in neonates with urinary tract infection (20).

Recurrence risk: Compared with normal fetuses, mothers with fetal pyelectasis in the first pregnancy have a relative risk of 6.1 to have a recurrence of this finding in their next pregnancy. These results suggest a predisposition for pyelectasis that may be influenced by genetic and/or environmental factors (5).

Management: Data suggest that the risk of aneuploidy associated with isolated fetal pyelectasis is low, that it should not be an indication for invasive prenatal karyotyping (7)(8). The risk of chromosomal anomalies increases when the pyelectasis is diagnosed in older pregnant women (>35 years of age) or if it is associated with other sonographic markers of chromosomal anomalies (choroids plexus cysts, cystic hygroma etc.) (7).The likelihood ratio of trisomy 21 in the group of fetuses with isolated pyelectasis is 3.79. Among fetuses with pyelectasis and other associated markers/structural anomalies the likelihood ratio for trisomy 21 is 19.2 (8), which justify the performance of an amniocentesis.

 

References

  1. Ahmad G, Green P. Outcome of fetal pyelectasis diagnosed antenatally. J Obstet Gynaecol. 2005 Feb;25(2):119-22
  2. May Llanas ME, Moreira Echeverria A, Garcia Boente CV, Comesias Gonzalez MJ, Filloy Lavia AC, Hernandez Sanchez JL, Gomez de la Cruz A. Prenatal hydronephrosis: incidence, management and final diagnoses in 2003 An Pediatr (Barc). 2004 Dec;61(6):499-501
  3. Ismaili K, Hall M, Avni FE. [Management of isolated fetal dilatations of the kidney pelvis Rev Med Brux. 2003 Feb;24(1):29-34
  4. Chudleigh T. Mild pyelectasis.Prenat Diagn. 2001 Nov;21(11):936-41
  5. Degani S, Leibovitz Z, Shapiro I, Gonen R, Ohel G. Fetal pyelectasis in consecutive pregnancies: a possible genetic predisposition.Ultrasound Obstet Gynecol. 1997 Jul;10(1):19-21.
  6. Babcook CJ, Silvera M, Drake C, Levine D. Effect of maternal hydration on mild fetal pyelectasis. J Ultrasound Med. 1998 Sep;17(9):539-44; quiz 545-6.
  7. Havutcu AE, Nikolopoulos G, Adinkra P, Lamont RF. The association between fetal pyelectasis on second trimester ultrasound scan and aneuploidy among 25,586 low risk unselected women. Prenat Diagn. 2002 Dec;22(13):1201-6.
  8. Coco C, Jeanty P. Isolated fetal pyelectasis and chromosomal abnormalities. Am J Obstet Gynecol. 2005 Sep;193(3):732-8.
  9. Wilson RD, Lynch S, Lessoway VA. Fetal pyelectasis: comparison of postnatal renal pathology with unilateral and bilateral pyelectasis.Prenat Diagn. 1997 May;17(5):451-5.
  10. Podevin G, Levard G, Marechaud M, Girault F, Barret D.  Post-natal diagnostic strategy of urinary tract malformations detected by prenatal screening. Arch Pediatr. 1997 May;4(5):411-5
  11. Ouzounian JG, Castro MA, Fresquez M, al-Sulyman OM, Kovacs BW. Prognostic significance of antenatally detected fetal pyelectasis.Ultrasound Obstet Gynecol. 1996 Jun;7(6):424-8.
  12. Benacerraf BR, Mandell J, Estroff JA, Harlow BL, Frigoletto FD Jr. Fetal pyelectasis: a possible association with Down syndrome.Obstet Gynecol. 1990 Jul;76(1):58-60.
  13. Gotoh H, Masuzaki H, Fukuda H, Yoshimura S, Ishimaru T. Detection and assessment of pyelectasis in the fetus: relationship to postnatal renal function.
     Obstet Gynecol. Aug;92(2):226-31.
  14. Wax JR, Cartin A, Pinette MG, Blackstone J. Does the frequency of soft sonographic aneuploidy markers vary by fetal sex? J Ultrasound éd. 2005 Aug;24(8):1059-63.
  15. Odibo AO, Marchiano D, Quinones JN, Riesch D, Egan JF, Macones GA. Mild pyelectasis: evaluating the relationship between gestational age and renal pelvic anterior-posterior diameter. Prenat Diagn. 2003 Oct;23(10):824-7.
  16. Robinson JN, Tice K, Kolm P, Abuhamad AZ. Effect of maternal hydration on fetal renal pyelectasis.Obstet Gynecol. 1998 Jul;92(1):137-41
  17. Anderson NG, Allan RB, Abbott GD. Fluctuating fetal or neonatal renal pelvis: marker of high-grade vesicoureteral reflux. Pediatr Nephrol. 2004 Jul;19(7):749-53. Epub 2004 May 6.
  18. Persutte WH, Hussey M, Chyu J, Hobbins JC. Striking findings concerning the variability in the measurement of the fetal renal collecting system.
    Ultrasound Obstet Gynecol. 2000 Mar;15(3):186-90.
  19. Graif M, Kessler A, Hart S, Daitzchman M, Mashiach S, Boichis H, Itzchak Y. Renal pyelectasis in pregnancy: correlative evaluation of fetal and maternal collectingsystems. Am J Obstet Gynecol. 1992 Nov;167(5):1304-6.
  20. Devaussuzenet V, Dacher JN, Eurin D, Monroc M, Le Dosseur P. Postnatal echography and cystography after prenatal diagnosis of minor dilatation of the kidney pelvis. Prospective study of 89 cases]J Radiol. 1997 Jan;78(1):27-31
  21. Walsh G, Dubbins PA. Antenatal renal pelvis dilatation: a predictor of vesicoureteral reflux?AJR Am J Roentgenol. 1996 Oct;167(4):897-900.
  22. Capello SA, Kogan BA, Giorgi LJ Jr, Kaufman RP Jr. Prenatal ultrasound has led to earlier detection and repair of ureteropelvic junction obstruction. J Urol. 2005 Oct;174(4 Pt 1):1425-8.
  23. Lim DJ, Park JY, Kim JH, Paick SH, Oh SJ, Choi H. Clinical characteristics and outcome of hydronephrosis detected by prenatal ultrasonography.J Korean Med Sci. 2003 Dec;18(6):859-62
  24. Strauss A, Fuchshuber S, Burges A, Heer I, Hasbargen U, Hepp H. Fetal obstructive uropathy--diagnosis and possible treatments]Z Geburtshilfe Neonatol. 2001 May-Jun;205(3):117-21.

 


 

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