Overview
Renal colic refers to the severe pain caused by kidney stones (nephrolithiasis), which are crystallized deposits formed from solutes in urine. These stones can obstruct urinary flow and lead to intense discomfort, commonly in the kidneys, ureters, or bladder.

Pathophysiology

1. Kidney Function:

   • Kidneys filter waste, regulate electrolytes, and produce urine.

   • Nephrons in the kidneys filter blood through a process of glomerular filtration, tubular reabsorption, secretion, and excretion.

   • Urine is concentrated in the collecting ducts and drains into the ureters, then the bladder.

2. Kidney Stone Formation:

   • Supersaturation of urine leads to solutes crystallizing, forming kidney stones.

   • Crystals act as a nidus (point of growth), leading to the development of larger stones (calculi).

   • Stones often lodge in areas where the ureter naturally narrows, such as:

     • Ureteropelvic junction (near the kidney)

     • Pelvic brim (where the ureter turns)

     • Ureterovesical junction (near the bladder)

3. Pain Mechanism:

   • Pain from renal colic arises from ureteral spasms, inflammation, and dilation of the kidney due to obstructed urine flow.

   • Size of the stone is not directly related to pain intensity; smaller stones can cause excruciating pain if lodged in a narrow passage.

Risk Factors

1. Demographics:

   • Common in adults aged 20–60.

   • Higher incidence in men (3:1 ratio).

   • Less common in children and the elderly.

2. Diet:

   • High intake of animal proteins, sodium, and oxalates increases risk.

   • Dehydration leads to concentrated urine, promoting stone formation.

3. Medical History:

   • Conditions like hyperparathyroidism, Crohn's disease, and gout increase risk.

   • Family history of stones significantly raises the likelihood of development.

   • Previous episodes of kidney stones increase the risk of recurrence.

4. Medications and Lifestyle:

   • Use of certain medications (e.g., carbonic anhydrase inhibitors) and obesity are linked to higher risks.

Clinical Presentation and Examination

1. Pain Characteristics:

   • Sudden onset of severe, colicky pain in the flank or groin.

   • Pain may radiate to the testicles or labia and occur in waves.

   • Nausea, vomiting, dysuria, and urinary frequency often accompany the pain.

2. Physical Examination:

   • Patients may be restless and unable to find a comfortable position.

   • Fever and diaphoresis suggest coexisting infection.

   • Urine dip tests may reveal haematuria (blood in urine).

Differential Diagnoses

1. Aortic Aneurysm (especially in patients over 50)

2. Appendicitis

3. Diverticulitis

4. Pyelonephritis

5. Gynecological causes (e.g., ectopic pregnancy, ovarian torsion)

6. Testicular conditions (e.g., torsion)

Complications

• Hydronephrosis: Backflow of urine can damage the kidneys.

• Infections: Obstructive pyelonephritis or pyonephrosis can develop, leading to sepsis.

Management

1. Pain Relief:

   • NSAIDs like diclofenac are the first-line treatment for pain control.

   • Opioids (e.g., codeine, morphine) may be used if necessary.

   • Antiemetics (e.g., ondansetron) help manage vomiting associated with renal colic.

2. Imaging and Further Care:

   • CT KUB (Kidneys, Ureters, and Bladder) is the preferred diagnostic tool.

   • Ultrasound is recommended for pregnant women and children.

   • Admission is necessary for patients with systemic infection, uncontrolled pain, or those at risk (e.g., single kidney, pregnancy, CKD).

3. Discharge and Follow-up:

   • Patients should be given advice on preventing recurrence through hydration and dietary adjustments.

   • Follow-up imaging may be required to confirm stone passage.

References

1. Acute Renal Colic - StatPearls - NCBI Bookshelf

2. Renal Colic | Ureteric Stones | Geeky Medics

3. Kidney Stone Management in Primary Care - British Journal of General Practice

Additional resources:

• Video on renal physiology