Renal Pain
Definition, Causes, Clinical Features, Differential Diagnosis and Evaluation
Definition
Renal pain is pain arising from the kidney, renal pelvis, or upper urinary tract. It is typically felt in the flank or loin, near the costovertebral angle. This area lies posteriorly between the 12th rib and the vertebral column. Pain may radiate to the abdomen, groin, genital organs or inner thigh depending on whether the kidney, renal pelvis or ureter is involved.
Renal pain occurs mainly by two mechanisms:
-
Distension of the renal capsule
The renal capsule is sensitive to stretching. Enlargement or inflammation of the kidney produces a dull, constant, aching pain.
-
Distension and spasm of the renal pelvis or ureter
Sudden ureteric obstruction raises intraluminal pressure and causes severe pain, traditionally called renal colic. More accurately, it is often called ureteric colic, because the obstructed ureter is usually the source of the severe pain.
Smith and Tanagho’s General Urology, pp. 281-282, describes renal colic as pain related to stretching of the collecting system or ureter, while non-colicky renal pain is related to distension of the renal capsule.
Types of Renal Pain
1. Non-colicky renal pain
This is a dull, constant, aching or dragging pain felt in the loin. It is caused by stretching of the renal capsule due to renal enlargement, inflammation, oedema, haemorrhage or hydronephrosis.
Characteristics
- Dull and continuous
- Located in the flank or renal angle
- Usually does not radiate markedly to the groin
- May worsen with movement, pressure or percussion over the renal angle
- Associated symptoms depend on the cause, such as fever, dysuria, haematuria or reduced urine output
Examples
- Acute pyelonephritis
- Hydronephrosis
- Polycystic kidney disease
- Renal tumour
- Renal infarction
- Perinephric abscess
- Renal haemorrhage
2. Renal or ureteric colic
Ureteric colic is a sudden, severe pain due to acute obstruction of urine flow, most commonly by a ureteric calculus. Obstruction results in increased pressure above the blockage, distension of the renal pelvis and ureter, smooth-muscle spasm and increased ureteric peristalsis.
Characteristics
- Sudden onset of severe unilateral flank pain
- Pain may fluctuate in intensity but often does not completely disappear
- Patient is restless, anxious, sweaty and unable to lie still
- Nausea and vomiting are common
- Haematuria may be present
- Pain may radiate from the loin to the abdomen, groin, scrotum, testis, vulva or labium
- Urgency, frequency and dysuria may occur with a distal ureteric stone
A stone may be small but cause severe pain if it acutely obstructs the ureter. Conversely, a large staghorn calculus may produce only a dull ache. Harrison’s Principles of Internal Medicine, 22nd ed., pp. 2551-2557.
Causes of Renal Pain
A. Obstructive Causes
1. Renal or ureteric calculus
This is the commonest cause of acute renal or ureteric colic. A stone may obstruct the renal pelvis, ureteropelvic junction, ureter, or ureterovesical junction.
Associated features
- Severe colicky flank pain
- Haematuria
- Nausea and vomiting
- Restlessness
- Radiation of pain to groin or genitalia
- Dysuria, urgency and frequency in lower ureteric obstruction
2. Hydronephrosis
Hydronephrosis means dilatation of the renal pelvis and calyces due to obstruction to urine flow. It may result from stone, stricture, tumour, prostatic enlargement, pregnancy, or congenital pelviureteric junction obstruction. It generally causes a dull aching flank pain, although acute obstruction can cause colic.
3. Ureteric stricture
A ureteric stricture may develop after surgery, radiation, tuberculosis, stone disease, trauma or previous instrumentation. It causes gradual obstruction and may produce persistent loin pain, recurrent urinary infection or declining renal function.
4. Blood clot obstructing the ureter
Blood clots can obstruct the ureter after trauma, tumour, renal haemorrhage, anticoagulant use or surgery. This may mimic ureteric stone colic.
5. Sloughed renal papilla
Papillary necrosis can lead to passage of a sloughed papilla into the ureter and obstruction. It may occur in diabetes mellitus, analgesic abuse, sickle-cell disease, severe pyelonephritis and urinary obstruction.
6. Extrinsic compression of the ureter
The ureter may be compressed by:
- Retroperitoneal fibrosis
- Pelvic tumour
- Enlarged lymph nodes
- Cervical or ovarian malignancy
- Pregnancy
- Retroperitoneal mass
The onset is generally gradual, so severe acute colic is less typical.
B. Infective and Inflammatory Causes
1. Acute pyelonephritis
Acute pyelonephritis is infection and inflammation of the kidney and renal pelvis. Inflammation causes oedema and stretching of the renal capsule.
Features
- Constant loin pain
- Fever and chills
- Dysuria, urgency and frequency
- Nausea and vomiting
- Costovertebral angle tenderness
- Pyuria and bacteriuria on urine examination
2. Pyonephrosis
Pyonephrosis refers to pus in an obstructed renal collecting system. It is a serious urological condition. The patient may have fever, flank pain, sepsis, renal dysfunction and features of urinary obstruction. Urgent hospital assessment and drainage are required.
3. Renal or perinephric abscess
A renal abscess or perinephric abscess can produce fever, persistent flank pain, malaise, weight loss and marked tenderness over the kidney region.
4. Renal tuberculosis
Renal tuberculosis can cause chronic flank discomfort, dysuria, frequency, haematuria and sterile pyuria. It should be considered in chronic or recurrent urinary symptoms, especially with systemic symptoms or a history of tuberculosis exposure.
C. Vascular Causes
1. Renal infarction
Renal infarction occurs when arterial blood supply to part or all of the kidney is blocked, usually from embolism or thrombosis. It produces sudden persistent flank pain and may be associated with fever, nausea, vomiting, haematuria, raised lactate dehydrogenase and acute kidney injury.
2. Renal artery thrombosis or embolism
Acute renal artery occlusion may cause severe constant flank or abdominal pain, nausea, vomiting, haematuria, oliguria and renal impairment. It requires urgent evaluation.
3. Renal vein thrombosis
This may occur in nephrotic syndrome, malignancy, dehydration and hypercoagulable states. It can cause flank pain, haematuria, proteinuria and impaired renal function.
4. Renal haemorrhage
Renal bleeding may follow trauma, anticoagulant therapy, tumour rupture, vascular abnormality or angiomyolipoma. Pain occurs due to renal enlargement or perinephric bleeding.
D. Renal Enlargement and Cystic Diseases
1. Polycystic kidney disease
Patients with autosomal dominant polycystic kidney disease may have flank or abdominal pain due to:
- Expansion of renal cysts
- Bleeding into a cyst
- Infection of a cyst
- Renal stone formation
- Enlargement and distortion of the kidney
When assessing chronic flank pain in polycystic kidney disease, infection, stones and tumour should first be excluded. Comprehensive Clinical Nephrology, 7th ed., p. 1960.
2. Renal tumour
Renal cell carcinoma may cause a dull aching flank pain, haematuria and palpable renal mass. However, this classic triad is uncommon and usually suggests advanced disease. Pain may occur due to haemorrhage, obstruction, tumour enlargement or invasion of adjacent structures.
3. Renal cyst
A simple renal cyst is usually asymptomatic but may cause pain if it becomes very large, haemorrhages, becomes infected or causes obstruction.
E. Traumatic Causes
Renal trauma may be blunt or penetrating. Blunt trauma commonly follows road traffic accidents, falls, sports injuries or assault. The patient may have flank pain, bruising, abdominal tenderness, haematuria, shock or a palpable mass.
Trauma with hypotension, gross haematuria, severe flank tenderness or a suspected renal injury requires urgent imaging and specialist assessment.
Radiation of Renal and Ureteric Pain
The pattern of radiation helps identify the likely level of ureteric obstruction:
| Site of lesion | Pain pattern |
|---|
| Kidney or renal pelvis | Flank and costovertebral angle pain |
| Upper ureter | Flank pain radiating anteriorly to upper abdomen |
| Mid-ureter | Pain to lower abdomen or iliac fossa |
| Lower ureter | Pain radiating to groin, testis, scrotum, vulva or labium |
| Ureterovesical junction | Suprapubic pain, urgency, frequency and dysuria |
A lower ureteric stone can cause bladder irritation and be mistaken for cystitis. In stone disease, urine may show red and white blood cells, but culture may be negative. Harrison’s Principles of Internal Medicine, 22nd ed., p. 2557.
Differential Diagnosis of Renal Pain
Flank pain should not automatically be diagnosed as kidney pain. A wide range of disorders can mimic renal or ureteric colic.
1. Musculoskeletal Conditions
- Lumbar muscle strain
- Lumbar spondylosis
- Prolapsed intervertebral disc
- Vertebral fracture
- Osteoarthritis of the spine
- Sacroiliac joint disease
- Rib fracture
- Myofascial pain
Musculoskeletal pain is often related to movement, posture or local tenderness. It is usually not associated with urinary symptoms, fever, haematuria or costovertebral angle tenderness.
2. Gastrointestinal Conditions
Acute appendicitis
Right lower ureteric pain can resemble appendicitis, especially when the stone is near the right pelvic brim.
Acute cholecystitis
A stone near the right ureteropelvic junction can occasionally mimic acute cholecystitis.
Diverticulitis
Left lower ureteric pain can be confused with left-sided acute diverticulitis.
Peptic or duodenal ulcer
May cause upper abdominal pain that radiates to the back.
Acute pancreatitis
Usually produces severe upper abdominal pain radiating to the back, with vomiting and abdominal tenderness.
Intestinal obstruction
Colicky abdominal pain with vomiting, abdominal distension, constipation and failure to pass flatus may mimic colic but is usually more central or bilateral.
3. Vascular Conditions
Abdominal aortic aneurysm
A leaking or ruptured abdominal aortic aneurysm can mimic renal colic, particularly left-sided flank pain. It is a life-threatening emergency, especially in an older patient with hypotension, collapse, abdominal or back pain, or a pulsatile abdominal mass.
Aortic dissection
May cause severe chest, back, abdominal or flank pain with pulse deficits or hypotension.
Mesenteric ischaemia
Severe abdominal pain with vascular risk factors should raise suspicion of mesenteric ischaemia.
4. Gynaecological Conditions
In women, the following should be considered:
- Ectopic pregnancy
- Ovarian torsion
- Ruptured ovarian cyst
- Pelvic inflammatory disease
- Endometriosis
- Dysmenorrhoea
A pregnancy test is necessary in women of reproductive age who present with acute abdominal, pelvic or flank pain.
5. Neurological and Dermatological Conditions
Herpes zoster
Pain, burning or hypersensitivity in a dermatomal distribution may occur before the appearance of characteristic vesicular rash.
Radiculopathy
Nerve-root compression from spinal disease can cause unilateral back or flank pain with radiation, numbness or weakness.
6. Genital Conditions
- Testicular torsion
- Epididymo-orchitis
- Inguinal hernia
These can cause lower abdominal, groin or scrotal pain and may be confused with a distal ureteric stone.
Clinical Evaluation of Renal Pain
History
Important points include:
- Site, onset, duration and severity of pain
- Character: dull, aching, colicky, burning or stabbing
- Radiation of pain
- Previous stones, urinary infection or renal disease
- Fever, chills, nausea and vomiting
- Dysuria, frequency, urgency or nocturia
- Haematuria, gravel or stone passage
- Oliguria, anuria or reduced urine output
- Trauma
- Drug history, especially anticoagulants and analgesic overuse
- Pregnancy possibility
- Past history of diabetes, gout, tuberculosis, malignancy or polycystic kidney disease
Examination
Examine the patient’s general condition and vital signs. Look for fever, tachycardia, dehydration, hypotension and signs of shock.
Abdominal examination should assess:
- Flank tenderness
- Costovertebral angle tenderness
- Palpable kidney or abdominal mass
- Suprapubic fullness suggesting retention
- Guarding, rigidity or rebound tenderness
- Pulsatile abdominal mass suggesting abdominal aortic aneurysm
Costovertebral angle tenderness can be present in pyelonephritis or urinary obstruction.
Merck’s renal assessment guidance notes that it may indicate pyelonephritis or obstruction caused by calculi.
Investigations
Appropriate investigations include:
-
Urinalysis
Tests for blood, protein, pus cells, nitrites and glucose.
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Urine microscopy, culture and sensitivity
Required when infection is suspected.
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Blood tests
- Complete blood count
- Serum creatinine and urea
- Electrolytes
- Blood glucose
- C-reactive protein
- Liver function tests if another abdominal cause is possible
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Pregnancy test
Essential in women of reproductive age with acute abdominal or pelvic pain.
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Ultrasonography
Detects hydronephrosis, renal mass, enlarged kidney and some renal or ureteric stones. It is preferred in pregnancy and often used first in children.
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Non-contrast CT of kidneys, ureters and bladder
This is highly sensitive for stones and can also identify alternative diagnoses. For adults with suspected renal colic,
NICE recommends urgent low-dose non-contrast CT within 24 hours, except in pregnancy, where ultrasound is preferred.
Red-Flag Features
Urgent referral or emergency assessment is needed for renal pain with:
- Fever or suspected sepsis
- Obstruction with urinary infection
- Anuria or severe oliguria
- Solitary kidney with obstruction
- Acute kidney injury
- Persistent vomiting or dehydration
- Uncontrolled severe pain
- Pregnancy with severe pain or suspected obstruction
- Gross haematuria with instability
- Hypotension, collapse or suspected abdominal aortic aneurysm
- Severe trauma
- Altered mental status
An obstructed infected kidney is a urological emergency and needs urgent hospital treatment, antibiotics and relief of obstruction.
Conclusion
Renal pain is usually felt in the loin or flank and may be dull and constant due to capsular distension, or severe and colicky due to ureteric obstruction. Ureteric stones are the most frequent cause of acute renal colic, but infection, hydronephrosis, cystic disease, tumour, trauma, vascular disease and obstruction from other causes must also be considered. Careful history, clinical examination, urinalysis, blood tests and imaging are necessary to establish the cause and exclude dangerous non-renal conditions such as appendicitis, ectopic pregnancy, pancreatitis and abdominal aortic aneurysm.