# Case Report: Looks can deceive: acute postoperative progressive renal dysfunction and hyperkalemia without significant hydronephrosis

## TL;DR

A patient with kidney cancer developed severe kidney dysfunction and high potassium after surgery, but imaging failed to show obstruction for days, highlighting the limitations of relying on hydronephrosis for diagnosis.

## Contribution

This case highlights the rare occurrence of delayed hydronephrosis and obstruction without early radiographic signs, challenging standard diagnostic assumptions.

## Key findings

- A patient with metastatic RCC developed severe renal dysfunction and hyperkalemia post-nephrectomy without early hydronephrosis.
- Delayed hydronephrosis was confirmed 15 days later via nuclear medicine studies, showing obstructive physiology in the solitary kidney.
- Nephrostomy placement led to rapid renal function improvement, emphasizing the need for early suspicion of obstruction despite normal imaging.

## Abstract

Hydronephrosis is typically considered a hallmark radiographic finding of urinary tract obstruction, expected to develop within 7 days of onset. However, this timeline may not apply universally. We report a rare case of delayed-onset hydronephrosis in the context of borderline end-stage renal dysfunction following radical nephrectomy in a patient with metastatic renal cell carcinoma (RCC), emphasizing the limitations of imaging in the early diagnosis of obstruction.

A 59-year-old male patient with metastatic renal cell carcinoma underwent right cytoreductive nephrectomy for an 8.5-cm renal mass with significant retroperitoneal lymphadenopathy and pulmonary metastases. Preoperative imaging showed mild left-sided hydronephrosis, and baseline renal function was preserved [estimated glomerular filtration rate (eGFR) 68 mL/min/1.73 m2]. Postoperatively, the patient immediately began experiencing a rapidly progressive decline in renal function, with eGFR falling to 15 mL/min/1.73 m2 and serum potassium rising to 7.0 mmol/L. Repeat imaging performed 8 days following initial decline was unremarkable, with findings consistent with prior scans. Subsequent nuclear medicine studies confirmed delayed perfusion and obstructive physiology in the solitary kidney. A nephrostomy tube was placed 15 days following the decline, leading to rapid improvement in renal function (eGFR 44 mL/min/1.73 m2 by POD 41).

This case illustrates the potential for clinically significant obstruction to occur in the absence of early hydronephrotic changes on imaging. We hypothesize that hyperacute progressive obstruction may lead to rapid intrarenal pressure stabilization, limiting capsular stretch and delaying radiographic findings. The absence of pain and significant radiographic hydronephrosis contributed to diagnostic delay.

The absence of hydronephrosis on imaging cannot exclude obstruction, particularly in patients with a solitary functional kidney and high-risk features such as retroperitoneal malignancy. Early clinical deterioration should prompt a high index of suspicion and further diagnostic evaluation to prevent irreversible renal injury.