13.6: Kidney Stones

Kidney stones form when crystals build up, and while many remain silent in the kidney, they often become painful and symptomatic when they move into and obstruct the ureters.

Master this section and you'll be able to:

• Describe what kidney stones are, how they form, and list common risk factors for developing them.
• Explain why stones cause pain when they move into the ureters and identify common symptoms of a urinary tract stone.
• Recognize how kidney stones are diagnosed and treated.

Nephrolithiasis

Nephrolithiasis (pronunciation) is the medical condition marked by the presence of renal calculi (pronunciation), commonly known as kidney stones. It refers to solid pieces of material that form in the kidneys when certain substances in the urine, such as calcium or uric acid, crystallize. Renal calculi — plural for one renal calculus — may be as small as a grain of sand or as large as a pearl.  

Most kidney stones pass out of the body on their own, but some become lodged in the ureters. The most common locations are where the renal pelvis narrows to become the ureter, and where the ureter enters the urinary bladder. When this happens, the stone can block the flow of urine and cause intense pain. The pain is usually felt in the flank (the side of the body — posterolateral region — between the ribs and the hip.) Additional symptoms may include hematuria (blood in the urine), fever and chills, vomiting, foul-smelling urine that may appear cloudy, or dysuria (painful urination). 
Note: Blood in urine supports the diagnosis but absence of blood does not rule it out.

Common Types of Kidney Stones

Kidney stones come in several types, each named for the crystals that form them.

• Calcium stones (most common): calcium-oxalate or calcium-phosphate stones. They develop when a person is not drinking enough fluids or consumes too many high-oxalate foods.
   
• Uric acid stones appear more often in people who eat large amounts of animal protein.
   
• Struvite stones often form in response to urinary tract infections (UTIs) and can grow into very large “staghorn” stones.
   
• Cystine stones are a rare type of kidney stone caused by a genetic disorder called cystinuria. In people with cystinuria, the kidneys do not properly reabsorb cystine, an amino acid that normally stays dissolved in the blood. As a result, too much cystine enters the urine. Cystine does not dissolve well in urine. When its concentration becomes too high, it crystallizes and forms stones.

Many factors increase the risk of developing kidney stones. These include dehydration, a high intake of meat, sodium, or sugars, certain medications, and a family history of stones. Previous stomach or intestinal surgery or specific medical conditions such as cystic fibrosis, diabetes, gout, obesity, inflammatory bowel disease, osteoporosis, parathyroid disorders, and conditions that elevate calcium or oxalate levels in the urine can also increase the risk.

Kidney stones may lead to several complications if they obstruct urine flow or irritate the urinary tract. A blockage can cause hydronephrosis, where the kidney swells with trapped urine, and stones can also lead to kidney infections, repeated UTIs, or acute kidney injury. Over time, recurrent stones may contribute to chronic kidney disease, highlighting the importance of early diagnosis and prevention.

Most stones form in the kidneys, but they often do not cause symptoms until they leave the kidney and enter the ureter. Inside the kidney, stones may sit quietly for months or years without being noticed. Once a stone drops into the ureter, the narrow muscular tube, the body reacts strongly. The ureter tries to push the stone toward the bladder with waves of peristalsis, which is why people feel sudden, severe flank pain.

So, in terms of location:

• More stones exist in the kidneys, because that is where they actually form.

• More symptomatic or “detected” stones are found in the ureters, because that is where they get stuck and cause pain, obstruction, or hematuria.

Clinically, stones in the kidney may be found incidentally on imaging, but stones in the ureter are far more likely to bring a patient to the ER.

The single best diagnostic evidence for kidney stones is a non-contrast CT scan of the abdomen and pelvis. The reason why CT-scans are the gold standard in the diagnosis of nephrolithiasis is that they detect >95% of kidney and ureteral stones. CT scans (unlike regular X-rays) can also visualize the size and exact location of all stone types (calcium, uric acid, cystine, and struvite), and finally, this method can identify complications such as complete obstruction or hydronephrosis. 

Figure \(\PageIndex{1}\): CT Scan of the Abdomen with Multiple Renal Calculi. Note in the axial cross-section image on the left that axial CT images are displayed as if you are standing at the patient’s feet and looking up toward their head. Because you are facing the patient, the patient’s right side appears on the left side of the image, and the patient’s left side appears on the right side of the image. 
The bright structures are bone, since osseous tissue is very dense. Surrounding fat appears dark, which helps outline abdominal organs. This image shows multiple renal calculi. (https://commons.wikimedia.org/wiki/F...al_calculi.jpg)

 

Case Study: Sudden Flank Pain in the Emergency Department

Patient Presentation

A 54-year-old woman arrives at the emergency department complaining of severe pain in her left flank. She describes the pain as intense and cramp-like, coming in waves rather than remaining constant. At times, the pain becomes so strong that she almost doubles over and cannot find a comfortable position.

She also reports that earlier in the day she noticed what looked like blood in her urine, and as the day progressed, the pain began to radiate from her lower back around to the left groin.

Questions

1. Where is the flank located anatomically? Use some of the anatomical terminology that you learned in Module 1.

2. Why might pain that radiates from the flank to the groin suggest involvement of the ureter rather than the kidney alone?

3. Why do you think this pain comes in waves instead of being constant?

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Medical History

The patient has a history of uterine fibroids, also called leiomyomas. These are noncancerous growths of smooth muscle that develop in the wall of the uterus and are very common in women.

Although fibroids can cause pelvic pain or abnormal bleeding, they usually do not cause flank pain or blood in the urine.

Questions

4. Which body system is primarily affected by uterine fibroids?

5. Why is it important to consider a patient’s medical history even when it may not directly explain the current symptoms?

6. Based on the symptoms so far, do uterine fibroids seem like the most likely cause of this patient’s pain? Why or why not?

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Physical Examination and Laboratory Findings

On physical examination, the health care provider notes left costovertebral angle tenderness. This means that pressing on the area overlying the kidney causes pain.

A urine sample shows visible blood.

Urinalysis confirmed hematuria.

Question

7. List two possible causes of hematuria and how could a solid object inside the ureter lead to blood appearing in the urine?

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Differential Diagnoses

Before imaging, several conditions are considered:

• Urinary tract calculus
• Urinary tract infection
• Renal mass
• Ovarian torsion

Questions

8. Which of these conditions is most consistent with sudden, severe pain that comes in waves?

9. Which condition on the list is most likely to be associated with fever?

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Imaging 

The noncontrast CT scan of the abdomen and pelvis came back as follows:

Figure \(\PageIndex{2}\): CT Imaging of the Patient's Abdomen. Visible in this coronal (frontal) CT image, which displays the kidneys, ureters, and surrounding abdominal structures is the fact that the left kidney is mildly hydronephrotic (swollen) and there is mild inflammation of the surrounding fat. A dense, small (5mm), calcification is seen in the left ureter.  Interpretation: Left ureteric calculus

Questions

10. Why is CT imaging preferred over plain X-ray for detecting kidney stones?

11. Why is correct image orientation especially important in cases involving paired organs like the kidneys?

12. What does hydronephrosis indicate about urine flow and why does the ureter appear dilated above the stone?

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Diagnosis: Left Ureteric Calculus

The question now is: will the stone pass on its own? As it turns out:

• Stones 5 mm or smaller often pass spontaneously
• Larger stones are more likely to require intervention (see below).

 

Treatment

Extracorporeal Shock Wave Lithotripsy (ESWL)

ESWL is a noninvasive procedure used to treat some of the kidney and ureter stones without surgery. A machine outside the body sends focused, high-energy shock waves through the skin and soft tissues until they reach the stone. The repeated shock waves create tiny fractures that break the stone apart, eventually reducing it to pieces as small as grains of sand. These small fragments can then move through the ureter more easily and pass out of the body in the urine. ESWL works best for stones that are not extremely large and are located where the shock waves can be accurately targeted.

Percutaneous Nephrolithotomy

This technique is used for large, irregularly shaped, or difficult-to-reach kidney stones, especially when ESWL has not worked or when the patient is not a good candidate for other minimally invasive procedures. In this technique, the surgeon makes a small incision in the back directly over the kidney and inserts a nephroscope, which is a slender instrument equipped with a fiberoptic camera. Through this tract, the surgeon can visualize the stone and use specialized tools to break it apart and remove it. This method is more invasive than ESWL but very effective for stones that would otherwise be impossible to pass.