Ectopy, renal

Renal ectopy is the term for a kidney lying outside the renal fossa. As stated in Chapter 2 (Sect. 2.1.1), the kidney migrates cephalad early in gestation to arrive at its normal position. Abnormality of the ureteral bud or metanephric blastema, genetic abnormalities, teratogenic causes, or anomalous vasculature, acting as a barrier to ascent, are reasons for failure of the kidney to complete its ascent (Malek et al. 1971). The incidence of renal ectopy in postmortem studies varies from 1 in 500 (Campbell 1930) to 1 in 1,290 (Thompson and Pace 1937). There is a slight predilection for the left side, and 10% of cases are bilateral (Fig. 4.1). 

Simple renal ectopy refers to a kidney that remains in the ipsilateral retroperitoneal space. The most common position is in the pelvis - pelvic or sacral kidney - opposite the sacrum and below the aortic bifurcation. The lumbar or iliac ectopic kidney is one that is fixed above the crest of the ilium, but below the level of L2 and L3. Malrotation frequently accompanies renal ectopy (Fig. 4.1) (Kissane 1983 Daneman and Alton 1991 Ritchey 1992 CuRRARiNO et al. 1993). 

The differentiation between renal ptosis and renal ectopy can be difficult. In renal ptosis the renal artery arises from the aorta to the normal level and the ureter is of normal length. In renal ectopy the ureter is short, corresponding to the location of the kidney. Renal ptosis results from hypermobility of the kidney in the retroperitoneal space, usually in obese people who have rapidly lost weight. The ptotic kidney can usually be manipulated into its normal position. 

The contralateral kidney may be abnormal in up to 50% of patients (Malek et al. 1971). There is a 10% incidence of contralateral renal agenesis. In up to 70% of children with pelvic kidney there is associated VUR (Kramer and Kelalis 1984). In most cases of renal ectopy the adrenal gland is in normal position. Genital anomalies were found ranging from 15% of males to 75% of females (Thompson and Pace 1937 Downs et al. 1973). Skeletal anomalies occur in up to 50% of children, cardiovascular lesions were found in 9 out of 21 children (Malek et al. 1971) and gastrointestinal abnormalities in one-third of patients (Ritchey 1992). 

Excessive cranial migration of the kidney results in a thoracic kidney or in a superior ectopic kidney (N Guessen et al. 1984), lying below a thin membranous portion of the diaphragm. An intrathoracic kidney occurs in fewer than 5% of the cases of renal ectopy, with an incidence of 1 in 13,000 autopsies (Campbell 1930). The left side is more commonly... 

Generally it is difficult to distinguish between crossed renal ectopy with fusion and crossed renal ectopy without fusion by US (Fig. 4.6a) or by excretory urography. In contrast, CT and MRI are able to establish the correct diagnosis. MRI in particular can also provide information about the vascular supply, which is quite variable. Multiple anomalous branches to both kidneys are possible, arising from... 

The most common associated abnormality is that of VUR (Fig. 4.6b) (Kramer and Kelalis 1984). Therefore, VCU should be performed in all of these patients. Skeletal anomalies, imperforate anus, and cardiovascular anomalies have an increased incidence (Abeshouse and Bhisitkul 1959). Patients with solitary crossed ectopy have a higher incidence of genital abnormalities, probably related to the renal agenesis (Kakei et al. 1976). 

Abeshouse BS, Bhisitkul I (1959) Crossed renal ectopia with and without fusion. Urol Int 9 63-91 Boatman DL, Kolln CP, Flocks RH (1972) Congenital anomalies associated with horseshoe kidney. J Urol 107 205-207 Buntley D (1976) Malignancy associated with horseshoe kidney. Urology 8 146-148 Campbell MF (1930) Renal ectopy. J Urol 24 187-198 Campbell MF (1970) Anomalies of the kidney. In Campbell MF, Harrison JH (eds) Urology, vol 2,3rd edn. Saunders, Philadelphia, pp 1416-1486... 

Kramer SASA, Kelalis PP (1984) Ureteropelvic junction obstruction in children with renal ectopy. J Urol 5 331-336... 

---