Definition: renal ectopia is defined as an atypically placed kidney, it may be abdominal, lumbar or pelvic and can be placed either ipsilaterally or controlaterally (crossed renal ectopia) [1].
Prevalence:
The incidence is 1:12.000 clinical, 1:900 postmortem cases and it varies by location [1]:
-One normal and one pelvic kidney : 1 in 3000-Crossed renal ectopia :1 in 7000-Ectopic thoracic kidney : 1 in 13000 -Solitary pelvic kidney - 1 in 22000.
During weeks 6 and 9 of human development, the kidney ascends from a pelvic position to the lumber region in a site just inferior to the adrenal glands. If the kidney does not ascend at all, it will remain in the pelvis and is referred to as a pelvic kidney. It remains unrotated and often preserves its fetal blood supply from the iliac vessels or the distal aorta [2].
The reasons of failure of the kidney to ascend have not been elucidated. Hypotheses include genetic variants, teratogenic effects, abnormalities of the urethral bud and metanephric blastema, and anomalous vasculature physically blocking ascent.
Sonographic findings
The antenatal sonographic diagnosis of ectopic kidney is difficult and it is due to several factors:
- The fetal adrenal glands are relatively large and may be diagnosed as fetal kidneys,
- Fetal Bowel sometimes may be found near the renal fossa and may be mistaken for a kidney
- It may be difficult sometimes to observe the fetal kidneys, due to lack of the normal echogenicity of the retroperitoneal fat surrounding the kidneys [3].
Clinical presentation
A simple ectopic kidney is usually asymptomatic. However, if malrotated there is a risk of calculus formation with consequent hydronephrosis wich may present as colicky pain, hematuria.
Other symptoms are:
-Urinary tract infection, lithiasis
-Renosigmoid fistulae
-Renovascular hypertension secondary to an anomalous blood supply (from the iliac arteries).
-Dystocia in the case of pelvic kidney.
Differential diagnosis:
Fused pelvic kidney
A pelvic kidney may be associated with other congenital anomalies; such as skeletal, genitourinary (agenesis of the opposite kidney) and cardiovascular malformations and anomalies of femal system reproductive system [4].
Management and prognosis
The antenatal diagnosis of ectopic kidney should not affect obstetric management.
Treatment options depend upon the presence of symptoms or complications. If an obstruction is present, surgery may be required for correction of the position of the kidney to allow better drainage of urine. In case of extensive renal damage, nephrectomy is indicated [5].
References
1. Meizner I, Yitzhak M, Levi A, et al. Fetal pelvic kidney: a challenge in prenatal diagnosis? Ultrasound Obstet Gynecol. 1995; 5:391–93.
2. Bauer SB. Anomalies of the upper urinary tract. In: Wein AJ, Kavoussi LR, Novick AC, Partin AW, Peters CA: Campbell Walsh Urology, ed 9. Philadelphia: Saunders Elsevier, 2007, 3278–3281.
3. Bavie, J.D.,Rosemberg,E.R. and Andreotti,M,D.(1983).The changing sonographic appearance of fetal kidneys during pregnancy. J. Ultrasound Med., 2,505.
4. Melek, R., Kelalis, P.P. and Burke, E.C.(1971). Ectopic kidney in children and frequency of association with other malformations. Mayo Clin. Pro., 46,461-7.
5. van den Bosch CM, van Wijk JA, Beckers GM, et al. Urological and nephrological findings of renal ectopia. J Urol. 2010;183:1574–78.