What are the differential diagnoses for left renal enlargement associated with a 7.1 mm left renal calculus?

Differential Diagnoses for Left Renal Swelling with 7.1 mm Left Renal Stone

The most critical differential diagnosis for left renal swelling (nephromegaly) in the presence of a 7.1 mm renal stone is obstructive hydronephrosis with acute pyelonephritis, which requires urgent evaluation to prevent irreversible renal damage and sepsis. 1

Primary Differential Diagnoses

Obstructive Causes (Most Urgent)

• Acute obstructive hydronephrosis: A 7.1 mm stone has significant potential to cause ureteral obstruction, leading to proximal collecting system dilation and renal swelling 1
• Acute pyelonephritis with obstruction: Infected obstructed kidney represents a urologic emergency requiring urgent decompression 1
• Pyonephrosis: Purulent material in an obstructed collecting system, manifesting as renal enlargement with stone disease 1

Inflammatory/Infectious Causes

• Acute pyelonephritis without obstruction: Renal parenchymal infection can cause nephromegaly independent of obstruction, with increased renal cortical echogenicity 1
• Acute glomerulonephritis: Kidneys may be enlarged in the setting of acute glomerular inflammation, though typically bilateral 1
• Renal abscess: Focal or diffuse parenchymal infection causing localized or generalized renal swelling 1

Vascular Causes

• Renal vein thrombosis (RVT): Can present with flank pain and hematuria mimicking renal calculus, with renal enlargement; calcified RVT may be mistaken for stone on imaging 2
• Acute arterial infarction: Causes acute renal swelling with pain and hematuria 2

Neoplastic Causes (Less Likely but Critical)

• Renal cell carcinoma: Up to 8% of RCCs are hyperechoic and can coexist with stones; nephromegaly may indicate advanced disease 3, 4
• Transitional cell carcinoma: Can cause obstruction and renal swelling 1
• Wilms tumor (pediatric population): Rarely presents with hematuria, but should be considered in children 1

Other Parenchymal Causes

• Acute tubular necrosis: From prolonged obstruction or contrast exposure, causing renal swelling 5
• Infiltrative disorders: Lymphoma, leukemia, or amyloidosis causing nephromegaly 5
• Compensatory hypertrophy: If contralateral kidney is atrophic or absent 6

Essential Diagnostic Workup

Immediate Clinical Assessment

• Vital signs and sepsis evaluation: Fever, tachycardia, hypotension indicate infected obstructed kidney requiring emergency intervention 1
• Urinalysis with microscopy: Assess for pyuria, bacteriuria, hematuria (glomerular vs non-glomerular), and crystalluria 1, 4
• Serum creatinine and BUN: Evaluate for acute kidney injury from obstruction 3, 4
• Complete blood count: Leukocytosis suggests infection; anemia may indicate chronic process 1
• Blood cultures if febrile: Before initiating antibiotics 1

Imaging Evaluation

• Renal ultrasound with Doppler: Assess for hydronephrosis severity, resistive indices (elevated in obstruction), renal vein patency, and parenchymal thickness 1, 5, 2
• Non-contrast CT abdomen/pelvis: Gold standard for stone characterization, definitive assessment of obstruction, and evaluation for complications (perinephric stranding, abscess) 3, 4
• Contrast-enhanced CT (if renal function permits): Essential if RVT, renal mass, or vascular abnormality suspected 2

Critical Clinical Pitfalls to Avoid

• Do not assume all renal swelling with stones is simple obstruction: RVT can mimic renal calculus with similar presentation and may appear calcified on imaging 2
• Never delay intervention in febrile obstructed patients: Infected obstructed kidney requires urgent decompression (nephrostomy or stent) within hours to prevent sepsis and renal loss 1
• Do not overlook coexisting malignancy: Renal masses can coexist with stones; evaluate for solid components or unusual stone morphology 3, 4, 7
• Recognize that ultrasound has limitations: May miss stones <3mm and cannot reliably exclude obstruction in early phases; CT is definitive 4
• Consider bilateral imaging: Even with unilateral symptoms, assess contralateral kidney for baseline function and anatomic variants 5

Management Algorithm Based on Clinical Presentation

Septic/Febrile Patient with Obstruction

• Immediate broad-spectrum antibiotics after blood cultures 1
• Urgent urologic consultation for decompression (percutaneous nephrostomy or retrograde stent) 1
• ICU admission if hemodynamically unstable 1

Non-Septic Obstructed Patient

• Hydration and analgesia 4
• Urology referral for stone management (ESWL, ureteroscopy, or PCNL depending on stone location and size) 8
• Medical expulsive therapy may be considered for distal stones, though 7.1 mm has lower spontaneous passage rate 3

Renal Swelling Without Clear Obstruction

• Nephrology consultation for possible glomerulonephritis, interstitial nephritis, or infiltrative disease 1, 5
• Consider renal biopsy if diagnosis unclear and renal function deteriorating 1
• Hematology evaluation if systemic symptoms suggest lymphoproliferative disorder 6

Suspected Vascular Etiology

• CT angiography to evaluate renal vessels 2
• Anticoagulation if RVT confirmed 2
• Vascular surgery consultation if arterial pathology identified 2

The 7.1 mm stone size is significant because stones >5-6 mm have substantially lower spontaneous passage rates and higher likelihood of requiring intervention, making early urologic involvement essential. 3, 8