Fetal pyelectasis (FP) refers to a prominence / dilatation or the renal pelvis in utero. It is the mild end of the fetal hydronephrosis spectrum.
Fetal pyelectasis can be a relatively common finding in an antenetal ultrasound scan, often detected at the routine 2nd trimester morphology scan. There is a recognised male predilection. The estimated prevalence is at ~ 2% of routine second trimeter scans 13.
Pyelectasis can result from a number of factors. In the majority of cases, it is physiological and resolves spontateously. However, it may also herald the presence or evolution of renal tract pathology, such as :
- fetal PUJ obstruction
- fetal VUJ obstruction
- urethral obstruction - e.g. posterior urethral valves
- vesicoureteric reflux
- duplex kidney
- trisomy 21: presence and strength of this association is currently under debate and at best considered very mild.
Fetal pyelectasis is assessed on axial plane ultrasound through the fetal renal pelvices. It is considered present if measurements are above the levels stated below
- > 4 - 4.5 mm at 18 - 20 weeks (i.e. the routine 2nd trimester)
- > 5 mm at ~ 20 - 29 weeks
- > 6 mm at 32 weeks
- persistent fetal pyelectasis : > 7 mm in the 3rd trimester 8
* Different publications state the values differently for gestational ages. If you an expert on this we would love your help :)
Fetal pyelectasis can also be affected by maternal hydration - physiological fetal pyelectasis 5.
The vast majority of cases (~ 96%) with mild pyelectasis in the second trimester resolve, either during pregnancy or in the early postpartal period. The risk of post-natal renal pathology is increased with :
- increasing degree of pelvic dilatation
- in-utero progression
- bilateral involvement
The presence of fetal pyelectasis is sometimes considered a soft sign for chromosomal abnormalties : see associations above
Antenatally detected renal pelvic dilatation, especially in isolation, is considered a weak predictor of vesicoureteric reflux 7 although postnatal sonographic evaluation is often recommended.
Some advocate a repeat prenatal scan at 30 - 40 weeks gestation for all fetuses with 6 mm or more of renal pelvic dilatation is detected prior to 28 weeks as well as postnatal follow-up for persistent pyelectasis 10.
Post natally, most cases with pyelectasis resolve spontaneously in the first year of life and invasive procedures are not required. More content required
- 1. Thornburg LL, Pressman EK, Chelamkuri S et-al. Third trimester ultrasound of fetal pyelectasis: predictor for postnatal surgery. J Pediatr Urol. 2008;4 (1): 51-4. doi:10.1016/j.jpurol.2007.04.005 - Pubmed citation
- 2. Allen KS, Arger PH, Mennuti M et-al. Effects of maternal hydration on fetal renal pyelectasis. Radiology. 1987;163 (3): 807-9. Radiology (abstract) - Pubmed citation
- 3. Yamamura Y, Swartout JP, Anderson EA et-al. Management of mild fetal pyelectasis: a comparative analysis. J Ultrasound Med. 2007;26 (11): 1539-43. J Ultrasound Med (full text) - Pubmed citation
- 4. Nyberg DA, Souter VL. Sonographic markers of fetal trisomies: second trimester. J Ultrasound Med. 2001;20 (6): 655-74. J Ultrasound Med (abstract) - Pubmed citation
- 5. Babcook CJ, Silvera M, Drake C et-al. Effect of maternal hydration on mild fetal pyelectasis. J Ultrasound Med. 1998;17 (9): 539-44. J Ultrasound Med (abstract) - Pubmed citation
- 6.Anderson N, Clautice-engle T, Allan R et-al. Detection of obstructive uropathy in the fetus: predictive value of sonographic measurements of renal pelvic diameter at various gestational ages. AJR Am J Roentgenol. 1995;164 (3): 719-23. AJR Am J Roentgenol (abstract) - Pubmed citation
- 7. Walsh G, Dubbins PA. Antenatal renal pelvis dilatation: a predictor of vesicoureteral reflux? AJR Am J Roentgenol. 1996;167 (4): 897-900. AJR Am J Roentgenol (abstract) - Pubmed citation
- 8. Ahmad G, Green P. Outcome of fetal pyelectasis diagnosed antenatally. J Obstet Gynaecol. 2005;25 (2): 119-22. doi:10.1080/01443610500041446 - Pubmed citation
- 9. Chudleigh T. Mild pyelectasis. Prenat. Diagn. 2001;21 (11): 936-41. Prenat. Diagn. (link) - Pubmed citation
- 10. Wilson RD, Lynch S, Lessoway VA. Fetal pyelectasis: comparison of postnatal renal pathology with unilateral and bilateral pyelectasis. Prenat. Diagn. 1997;17 (5): 451-5. Prenat. Diagn. (link) - Pubmed citation
- 11. Corteville JE, Dicke JM, Crane JP. Fetal pyelectasis and Down syndrome: is genetic amniocentesis warranted? Obstet Gynecol. 1992;79 (5 ( Pt 1)): 770-2. - Pubmed citation
- 12. Wickstrom EA, Thangavelu M, Parilla BV et-al. A prospective study of the association between isolated fetal pyelectasis and chromosomal abnormality. Obstet Gynecol. 1996;88 (3): 379-82. doi:10.1016/0029-7844(96)00211-6 - Pubmed citation
- 13. Entezami M, Albig M, Knoll U et-al. Ultrasound Diagnosis of Fetal Anomalies. Thieme. (2003) ISBN:1588902129. Read it at Google Books - Find it at Amazon
Synonyms & Alternative Spellings
|Synonyms or Alternative Spelling||Include in Listings?|
|Fetal renal pelvic dilatation||✗|
|Fetal renal pelvic dilatation (RPD)||✗|
|Mild fetal pyelectasis||✗|
|Fetal pyelectasis (FP)||✗|