**Question:** A 52-year-old woman undergoes a sigmoid resection with primary anastomosis for recurrent diverticulitis. She returns to the emergency room 10 days later with left flank pain and decreased urine output; laboratory examination is significant for a white blood cell (WBC) count of 20,000/mm3. She undergoes a CT scan that demonstrates new left hydronephrosis, but no evidence of an intra-abdominal abscess. Which of the following is the most appropriate next step in management?

A. Apply antibiotics
B. Perform a nephrostomy
C. Re-explore the abdomen for abscess drainage
D. Continue with the current treatment plan

**Correct Answer:** B. Perform a nephrostomy

**Core Concept:**
The scenario involves a patient who has undergone sigmoid resection for diverticulitis and presents with left flank pain, decreased urine output, and elevated WBC count. The CT scan demonstrates left hydronephrosis without evidence of an intra-abdominal abscess. This suggests a potential renal obstruction caused by hydronephrosis leading to renal failure, pyonephrosis, or a renal abscess.

**Why the Correct Answer is Right:**
Given the patient's clinical presentation, the most appropriate management step is to perform a nephrostomy. The primary reason for choosing nephrostomy is the presence of left hydronephrosis, which indicates obstruction of the urinary tract, leading to potential renal compromise.

**Why Other Options are Incorrect:**
A. Applying antibiotics: Although antibiotics are essential in treating the underlying diverticulitis, they do not address the renal issue caused by hydronephrosis.

C. Re-exploring the abdomen for abscess drainage: The patient does not have an intra-abdominal abscess, as confirmed by the CT scan, so this management approach is not relevant.

D. Continue with the current treatment plan: Given the deterioration of renal function and symptoms, continuing the current treatment does not address the renal issue caused by hydronephrosis.

**Clinical Pearl:**
Performing a nephrostomy relieves the obstruction and allows proper drainage of the obstructed kidney, preventing further renal compromise and potentially reversing acute kidney injury. This intervention aligns with the patient's clinical presentation, while the other options do not address the primary concern of renal obstruction and subsequent renal compromise.