Single congenital renal cyst -- Dysplastic kidney

Clinical History

Premature neonate with antenatal diagnosis of cystic flank mass was born to a diabetic English mother in poor respiratory condition. After initial treatment patient was referred to our hospital for further management. Per-cutaneous drainage of cyst was contemplated with persistent leakage of urine from drain over protracted period of about two months.

Imaging Findings

Antenatal Ultrasound revealed a large cyst of about 6 cm in left adrenal fossa. Left kidney was not commented. Neonatal ultrasound confirmed the presence of cyst with some solid debris inside. Left renal tissue was seen to be stretched around this mass supero-medially. Right kidney was normal.
Plain radiograph demonstrated fullness of left flank.
Per-operative nephrostogram showed no communication with pelvicalyceal system. Single renal cyst without demonstrable communication with pelvicalyceal system and continuous urine excretion through nephrostomy led to the suspicion of dysplastic kidney.
MRI images showed the cystic nature of mass i.e., Low signal on T1W & Intermediate to High signal on T2W images.
Dimercaptosuccinic acid (DMSA) scanning was performed to delineate renal tissue and its relationship with this mass. Standard images showed small-sized hypo-functioning left kidney with 18% contribution. On the basis of entire findings left nephrectomy was done. Intra-operatively, kidney was found to be dysplastic with atretic ureter.

Discussion

Abdominal masses are common in newborns with prevalence of 1 in 1000 live births [1]. Amongst these, about 55% are of renal origin [2]. Multicystic dysplastic kidney (MCDK) is the 2nd commonest renal mass after hydronephrosis, followed by PUJ obstruction. Autosomal recessive polycystic disease with bilateral involvement is another significant renal pathology in this age group. Non renal masses include neuroblastoma & adrenal haemorrhage.
Multicystic dysplastic kidney results from an insult before 8th-10th week of gestation during metanephric differentiation [3] under the influence of various gene expressions [1]. Sporadic obstruction / atresia of ureter not only arrests the growth of ureteric bud & inhibit induction and maturation of nephrons but also culminates in cyst formation from collecting tubules. Time of insult can predict the degree of involvement of urogenital sinus. Pre-maturity & maternal diabetes are two independent risk factors. It is reported to be 1 in 4300 live births and is slightly more prevalent in males. Unilateral MCDK is more compatible with life, having left sided preponderance of 2:1. Minor urogenital anomalies are frequent observations such as contralateral PUJ obstruction [2] - was not present in our case.
Dysplastic kidney could be an incidental finding on routine antenatal or postnatal ultrasound. It might remain asymptomatic for a considerable period where fully functional contralateral kidney compensates for the diseased kidney. In few instances, patient can present with abdominal mass, hypertension or dull ache.
Depending upon disease expression ultrasound features may be varied, including multiple cysts of different sizes, intervening parenchyma & non-visualisation of renal pelvis. In partially affected kidneys number of visualised cysts could be restricted up to 5 cysts. In very few cases, only giant single cyst represents renal dysplasia. DMSA scanning is preferred over excretory urography as contrast concentration ability is poor in neonatal kidneys [3]. It depicts negligible relative function of the affected kidney as renal artery is absent or rudimentary. Voiding urography is needed to delineate the concomitant reflux or contralateral PUJ obstruction [4]. Rarely cross-sectional imaging might be required in challenging cases.
Surgical removal is considered in symptomatic cases [5]. Pyeloroplasty could be offered in concurrent contralateral PUJ obstruction. If asymptomatic, dysplastic kidney can be left untreated with expectant regression over time. Fear of malignant transformation although negligible, mandates continuous follow up.
Single giant congenital renal cyst with partial dysplasia is an unusual case and should be considered while making differential diagnosis.

Differential Diagnosis List

Final Diagnosis

Single congenital renal cyst -- Dysplastic kidney

URL:	https://www.eurorad.org/case/9928
DOI:	10.1594/EURORAD/CASE.9928
ISSN:	1563-4086