Kidney Stone (Nephrolithiasis)

Understanding Kidney Stones

A kidney stone is a hard mineral deposit that forms in the kidney and can travel down the urinary tract, causing severe pain. Before we examine how this condition appears on imaging, let's understand why prompt evaluation is important.

Here's how accurate non-contrast CT is at detecting kidney stones:

Think of a kidney stone like a pebble in a garden hose—when it blocks the flow, pressure builds up upstream (hydronephrosis) causing pain. The stone's size determines if it will pass on its own or needs intervention.

What Is a Kidney Stone?

Kidney stones (nephrolithiasis) are hard deposits made of minerals and salts that form inside the kidneys. They can affect any part of the urinary tract from kidneys to bladder.

Common stone types:

| Type | Frequency | Composition | Risk Factors | |------|-----------|-------------|--------------| | Calcium oxalate | 70-80% | Calcium + oxalate | Dehydration, high oxalate diet | | Calcium phosphate | 10-15% | Calcium + phosphate | Renal tubular acidosis | | Uric acid | 5-10% | Uric acid | Gout, high protein diet | | Struvite | 5-10% | Magnesium ammonium phosphate | Chronic UTI | | Cystine | ＜1% | Cystine | Genetic disorder |

Why CT is gold standard:

• Highest sensitivity for detecting stones (even small ones)
• Shows exact size and location
• Identifies obstruction and complications
• Detects alternative diagnoses (appendicitis, aneurysm)
• No contrast needed (avoids allergic reactions)

How Kidney Stones Appear on CT

Non-contrast CT of the abdomen and pelvis (stone protocol) is the first-line imaging test for suspected kidney stones.

Key Findings Pattern

When evaluating for kidney stones on CT, radiologists assess specific critical features:

When Your Doctor Orders This Test

Here's a typical scenario where CT is ordered for suspected kidney stone:

Common presenting symptoms:

• Severe flank pain (renal colic) radiating to groin
• Nausea and vomiting
• Hematuria (blood in urine)
• Urinary urgency and frequency
• Inability to find comfortable position

Red flags requiring urgent evaluation:

• Fever or chills (infected stone - emergency)
• Single kidney with obstruction
• Anuria (unable to urinate)
• Uncontrollable pain despite medications
• Sepsis signs

Differential Diagnosis

Several conditions can mimic kidney stone pain:

How Accurate Is CT for Kidney Stones?

Non-contrast CT is the gold standard for kidney stone detection:

What Happens Next?

Management depends on stone size, location, and symptoms:

Frequently Asked Questions

Will my kidney stone pass?

Spontaneous passage depends on size: ＜5 mm (80-90% pass), 5-10 mm (50-60% pass), ＞10 mm (＜10% pass without intervention). Location also matters - distal ureteral stones pass more easily than proximal ones.

How long does it take to pass?

Most stones that pass do so within 1-2 weeks. Average time is 1-3 weeks depending on size and location. Medical expulsive therapy (tamsulosin) can facilitate passage. If no passage after 4 weeks, intervention is typically recommended.

Will I need surgery?

Not necessarily. Most stones ＜10 mm can be managed with medical expulsive therapy (watchful waiting with medications). Surgery is typically needed for: stones ＞10 mm, stones failing to pass after 4 weeks, severe obstruction, or infected stones.

What causes kidney stones?

Common causes include: dehydration (low urine volume), diet (high sodium, oxalate, animal protein), obesity, family history, certain medications, and medical conditions (hyperparathyroidism, renal tubular acidosis, gout). Stone analysis and metabolic testing can identify specific causes.

How can I prevent recurrence?

Prevention strategies include: drink 2-3 liters of water daily, reduce sodium intake, normal calcium intake (don't restrict), limit animal protein, limit oxalate-rich foods (spinach, nuts), maintain healthy weight, and follow specific recommendations based on stone type.

References

Medical Disclaimer: This information is for educational purposes. Kidney stones require management by a urologist or emergency physician. Always seek immediate medical care for fever with suspected kidney stone.