Horseshoe kidney

Risk factors are male gender, smoking, coffee drinking, anatomic abnormalities like obstructions or horseshoe kidney, and exposition to chemical carcinogens like aniline, aromatic amine, and benzidine, as the metabolites of these substances are excreted into the urinary tract. 

During the ascent of the kidneys they cross the umbilical arteries. Malposition of the umbilical arteries may cause the developing nephrogenic blastemas to come together. Fusion of the nephrogenic masses in the midline would result in a horseshoe kidney. This occurs early in embryogenesis, before rotation is complete, and therefore malrota-tion is present in all cases (Fig. 4.2c,d) (Ritchey 1992). 

Fig.4.2a-d. Typical appearance of horseshoe kidney in a 19-month-old girl a on a plain radiograph b on US c on intravenous urography d on VCU by reflux... 

Horseshoe kidney is the most common type of renal fusion and one of the most frequent renal anomalies. It is usually characterized hy fusion of the lower poles across the midline hy an isthmus lying anterior, seldom posterior, to the aorta and inferior vena cava (Dajani 1966). Occasionally the lower poles are connected only hy fibrous hands. The horseshoe kidney is usually positioned low in the abdomen with the isthmus lying just below the junction of the inferior mesenteric artery and aorta. The incidence varies from 1 in 400 (Glenn 1959) to 1 in 1,800 (Campbell 1970). The abnormality is more common in males. 

The incidence of associated anomalies is much higher if the horseshoe kidney is discovered in the newborn period. In postmortem examinations of 99 infants with horseshoe kidneys, 78% had malformations of other organ systems such as the central nervous system, the gastrointestinal tract, and the skeletal and cardiovascular system (Zondek and Zondek 1964). One-third of patients with horseshoe kidney had at least one other abnormality (Boatman et al. 1972). Several well-known syndromes are associated with fused kidney. Trisomy 18 has an incidence of 21% (Warkany et al. 1966 Boatman et al. 1972). In US studies, Lippe et al. (1988) noted horseshoe kidneys in 7% of patients with Turner s syndrome. In patients with neural tube defects, there is also an increased incidence of horseshoe kidneys (Whitaker and Hunt 1987). Nearly one-third of patients with a horseshoe kidney remain undiagnosed throughout life (Glenn 1959 Pitts and Muecke 1975). 

Ureteropelvic junction obstruction by a high ureteral insertion or an anomalous renal vessel is the most common cause of hydronephrosis, which occurs in 30% of patients diagnosed during life. Urolithiasis develops in 20% of patients with a horseshoe kidney. Stasis secondary to hydronephrosis, but with metabolic factors are also the reasons (Evans and Resnick 1981). 

In all children with a horseshoe kidney, VUR should be excluded. The upper urinary tract dilatation may be secondary to VUR (Fig. 4.2d). More than 100 renal malignancies have been reported in patients with horseshoe kidney (Buntley 1976). The risk of developing a Wilms tumor increases sevenfold in patients with a horseshoe kidney (Mesrobi an etal. 1985). 

Horseshoe kidney is the most common type of renal fusion. Hydronephrosis, urolithiasis, and VUR are associated anomalies and effects. The risk of Wilms tumor is increased sevenfold. 

Crossed renal ectopia is the second most common fusion anomaly after horseshoe kidney, with an incidence of 1 in 7,000 autopsies (Abeshouse and Bhisitkul 1959). The crossed ectopic kidney lies on the opposite side from the ureteral insertion of the bladder. There are four varieties of renal crossed ectopia (Fig. 4.4) (McDonald and McClellan 1957 Abeshouse and Bhisitkul 1959). Crossed renal ectopia with fusion occurs in 85%,... 

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... 

Currarino G, Wood B, Majd M (1993) The genitourinary tract and retroperitoneum. Congenital renal anomalies. In Silverman FN, Kuhn JP (eds) Caffey s pediatric X-ray diagnosis an integrated imaging approach, vol 2, 9th edn. Mosby, St Louis, pp 1223-1243 Dajani AM (1966) Horseshoe kidney a review of 29 cases. Br J Urol 38 388-402... 

Daneman A, Alton DJ (1991) Radiographic manifestations of renal anomalies. Radiol Clin North Am 29 351-363 Downs RA, Lane JW, Burns E (1973) Solitary pelvic kidney its clinical implications. Urology 1 51-56 Evans WP, Resnick MI (1981) Horseshoe kidney and urolithiasis. J Urol 125 620-621... 

Glenn JF (1959) Analysis of 51 patients with horseshoe kidney. N Engl J Med 261 684-687 Kakei H, Kondo A, Ogisu BI, Mitsuya H (1976) Crossed ectopia of solitary kidney a report of two cases and a review of the literature. Urol Int 31 470-475 Kissane JM (1983) Congenital malformations. In Heptinstall RH (ed) Pathology of the kidney, vol 1, 3rd edn. Little, Brown, Boston, pp 83-140... 

Mesrobian HJ, Kelalis PP, Hrabovsky E, Othersen HB, DeLo-rimier A, Nesmith B (1985) Wilms tumor in horseshoe kidneys a report from the National Wilms Tumor Study. JUrol 133 1002-1003... 

Zondek LH, Zondek T (1964) Horseshoe kidney in associated congenital malformations. Urol Int 18 347-356... 

Horseshoe kidney may present UPJ obstruction due to the crossing between the vessels and the ureters. This usually involves one of the collecting systems (Fig. 5.19). 

Fig. 5.19. UPJ obstruction and horseshoe kidney. Left side UPJ obstruction on the IVU...

Fig. 5.31. VUR into an ectopic ureter inserting into the posterior urethra (patient with pelvic horseshoe kidney)...

Contralateral VUR may be present in about 10%-20% of patients with multicystic dysplastic kidney (Fig. 11.29). VUR is also present in a significant number of other uropathies, i.e., horseshoe kidney, crossed fused kidney, UPJ, and UVJ obstruction. Therefore, in any anomaly of this type, a VCU should be advised for a complete workup (Atiyeh et al. 1992 Ring et al. 1993 Song et al. 1995 Avni et al. 1997 Cascio et al. 1999). 

When only one kidney is found, the second one must be searched in all the other potential locations, especially in the pelvis. Other ectopic locations such as crossed fused or horseshoe kidney (Fig. 13.5) can be detected, and the diagnosis is confirmed by the presence of the typical corticomedullary differentiation (Jeanty et al. 1990 Meizner and Bernhard 1995). 

Fig. 13.5. Horseshoe kidney. Transverse scan ofthe low fetal abdomen. The horseshoe kidney (arrowheads) is identified thanks to the corticomedullary differentiation. B, bladder Sp, spine...

In utero drug exposure and infections Horseshoe kidney (B)... 

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