Presumptive Congenital Unilateral Renal Agenesis With Contralateral Dysplasia/Hypoplasia in a Golden Retriever

BACKGROUND: Congenital renal agenesis with contralateral dysplasia/hypoplasia represents an exceptionally rare morphological presentation in dogs, with only one previous case documented worldwide. CASE DESCRIPTION: A 4-year-old Golden Retriever (Canis lupus familiaris) presented with polyuria, polydipsia, inappetence and urinary incontinence. Laboratory findings revealed severe azotaemia, hyperphosphataemia and non-regenerative anaemia. RESULTS: Multimodal diagnostic imaging demonstrated complete presumptive left renal agenesis with a small dysplastic remnant and severe presumptive right renal dysplasia/hypoplasia with loss of normal renal architecture. The dog showed initial improvement with supportive care but experienced progressive deterioration, with euthanasia elected 18 days after presentation. CONCLUSIONS: This case documents an extremely rare morphological pattern of presumptive congenital renal abnormalities in a dog with an atypically late clinical presentation. The findings emphasise the diagnostic value of imaging in differentiating congenital renal disease from acute kidney disease and expand the current understanding of its potential clinical course in adult dogs.