Bilateral Renal Cysts with Possible Duplication Anomalies: The presence of small cysts in both kidneys along with the suggestion of duplicated collecting systems or prominent columns of Bertin makes this a likely diagnosis. The size and location of the cysts, along with the renal dimensions, are consistent with benign cysts often found in the general population, especially in the context of worsening chronic kidney disease (CKD).

Chronic Kidney Disease (CKD) with Incidental Findings: The worsening CKD could be the primary concern, with the cysts and possible duplication anomalies being incidental findings. CKD can lead to various changes in kidney morphology, including cyst formation.
Simple Renal Cysts: The small cysts identified could be simple renal cysts, which are common and usually benign. Their presence does not necessarily indicate a more complex condition.
Renal Duplication Anomalies: The possibility of duplicated collecting systems, as suggested by the ultrasound, could be a congenital anomaly. This condition can sometimes be asymptomatic and discovered incidentally.

Polycystic Kidney Disease (PKD): Although less likely given the small number and size of the cysts, PKD is a condition that must be considered due to its potential for significant morbidity and impact on kidney function. It's crucial to rule out PKD, especially if there's a family history.
Renal Cell Carcinoma: While the cysts are described as small, any cystic lesion in the kidney raises the possibility of renal cell carcinoma, especially if there are solid components or if the cysts exhibit suspicious features on imaging.
Ureteropelvic Junction Obstruction (UPJO): If the duplication anomalies are associated with obstruction, this could lead to significant kidney damage over time. UPJO can sometimes present with worsening kidney function and must be considered.

Multicystic Dysplastic Kidney (MCDK): This condition is typically identified in childhood but could be considered if the "duplicated collecting system" description is suggestive of a more complex dysplastic condition.
Autosomal Recessive Polycystic Kidney Disease (ARPKD): Although rare and typically presenting in childhood, ARPKD could be a consideration if there are other systemic signs or a family history suggestive of this condition.
Tuberous Sclerosis Complex (TSC): This genetic disorder can lead to the development of renal cysts and angiomyolipomas. It's a rare condition but should be considered if there are other clinical findings suggestive of TSC.