Horseshoe kidney with multicystic dysplastic left moiety.

Sir

A most common renal fusion anomaly seen in children is horseshoe kidney (HSK). Association with other congenital anomalies in HSK are well documented in literature; however, only a few cases of HSK with multicystic dysplastic kidney (MCDK) are reported till date.

Our case was a three-month-old male child referred to our institute with an antenatally diagnosed case of HSK. The perinatal period was uneventful. Parents complained of lower abdominal fullness after birth with no urinary symptoms. Computed tomography (CT) scan of the abdomen performed in the institute, from where the patient was referred at two months of age, suggested HSK with left moiety MCDK [Figure 1]. Ultrasonography (USG) of the abdomen performed in our institute also had similar findings with normal contralateral kidney, bladder, and ureter. As the patient had normal blood pressure and no features of urinary tract infection, no further investigation was done during follow-up. During the last follow-up at six months of age, the patient was asymptomatic.

Figure 1

Horseshoe kidney with multicystic dysplastic left moiety. (a) Non-contrast — enhanced CT showing left renal moiety replaced by multiple cysts (arrows) with normal isthmus (asterix) and almost complete absence of overlying cortex. (b) Contrast-enhanced CT image showing multiple non-enhancing cysts (arrows) with normal enhancing isthmus (asterix) and right moiety

The reported incidence of HSK is 1 in 400 live births and is more common in males.[1] There is frequent association of other anomalies in children with HSK, especially when discovered in the neonatal period. Boatman et al reported that one-third of patients with HSK had at least one or the other abnormality.[2] Multicystic dysplasia is the most common type of renal cystic disease and one of the most common causes of an abdominal mass in infants. Most cases are asymptomatic and discovered on prenatal sonography. Although USG can diagnose the presence of MCDK in one half of HSK, the investigation is operator dependant and subtle clues such as malrotation of the contralateral segment may be missed.[3] A dimercaptosuccinic acid (DMSA) scan reveals absence of function in the affected segment, but it may or may not indicate the presence of an HSK.

The possibility of MCDK in an HSK may be suggested by the presence of a palpable mass close to the midline, a USG report suggesting abnormal rotation and fusion along the lower renal poles, or a DMSA scan indicating polar fusion. The condition can be confirmed using a cross-sectional imaging study such as CT or magnetic resonance imaging (MRI), which also provides information on the degree of involvement of the isthmus and contralateral kidney.[3] The most commonly associated anomaly with MCDK are contralateral ureteropelvic junction obstruction and contralateral vesicoureteric reflux. HSK is infrequently associated with MCDK. In a 1994 review, only 18 such cases had been recorded.[4]

Inadvertent damage to the contralateral normal pelvis and renal vasculature resulting from the inability to achieve a wider view of the unexpected operative findings has been reported in HSK with MCDK.[3] Due to proximity of the vessels of the normal segment and possibility of damage to the great vessels, small MCDKs in HSK may be left alone and managed conservatively.[5] As more information on this rare combination becomes available, expectant management, as in case of unilateral MCDK, should become the norm; moreover, surgery is indicated in the presence of recurrent infections, pain, or a palpable mass.