Statistics from Altmetric.com
Supernumerary kidney is one of the least common forms of congenital renal abnormality and is usually discovered when it presents complications.1,2 The diagnosis of supernumerary kidney is confined to a mass of renal tissue that has no parenchymatous connection with the definitive kidney.3 The published literature on supernumerary kidney is scarce. Here, we report a case that presented as indirect inguinal hernia.
A 36 year old man suffering from chronic asthma presented with a painful swelling in the left inguinal region, which he first noticed one month previously. The swelling measured 5.0 × 4.0 cm, was situated on the medial aspect of the inguinal ligament, and was reducible with positive cough impulse. The scrotum on the left side was empty. An abdominal scan showed normal organs, including two normal kidneys. A diagnosis of indirect inguinal hernia with undescended left testis was made and the patient underwent surgery. The hernial sac included an atrophic testis (2.0 × 1.5 × 1.0 cm) and another small bean shaped mass (3.0 × 2.0 × 2.0 cm), which was studied histopathologically.
The testis showed a positive string sign on the cut surface. The other mass had a grey white cut surface, with an intact capsule. Sections of the testis showed seminiferous tubules with thickened basement membranes containing inactive germ cells and some having only Sertoli cells. These features were consistent with cryptorchid testis. Sections from the bean shaped mass showed a kidney-type structure, with cortex and medulla. The glomeruli and tubules were seen in their developmental stages, with immature mesenchymal tissue interspersed in between (fig 1). These features were consistent with a diagnosis of supernumerary kidney because the patient had two normal kidneys in the abdomen.
A supernumerary kidney is a rare congenital anomaly. About 70 such cases have been reported in the international literature.4 However, to the best of our knowledge, this is the first reported case of a supernumerary kidney in a hernial sac. A supernumerary kidney usually lies within the renal fascia, caudal to the normal organ. Because the kidney was located below the second lumbar vertebra in this case, we prefer to classify it as an ectopic supernumerary kidney.2
In humans, the metanephros or permanent kidney begins to develop early in the 5th week of intrauterine life. It arises from two different sources. The collecting tubules, renal pelvis, and ureter develop from the lower end of the Wolffian duct, whereas the glomeruli and tubules differentiate from the caudal end of the nephrogenic cord (metanephric mesoderm).3 The lesion is thought to be caused by the formation of two ureteric buds arising from different positions in the Wolffian duct, which reach the metanephric blastema at such divergent positions that aberrant divisions result in two kidneys on one side. The supernumerary kidney is smaller, can be hypoplastic, and is usually not well organised histologically.5 This case has been reported for its rarity and also because of its unusual presentation with cryptorchid testis as inguinal hernia.