Causes of Flank Pain

Overview

Flank pain is a relatively common condition seen in a variety of settings, from general practice to any number of specialties. Many possible etiologies for flank pain exist and a number are commonly seen in urology.

One simple way to conceptualize flank pain is to divide it into major categories, according to its relationship to the kidney, as follows:

• Non-renal causes of flank pain, such as musculoskeletal problems
• Parenchymal problems, which involve the actual kidney tissue (eg, infection, inflammation)
• Non-parenchymal problems, which often relate to impaired kidney drainage

A broad differential should be utilized when approaching the patient with flank pain. Often, the history and physical examination will greatly narrow the potential diagnoses, and well-selected laboratory and imaging tests will confirm the actual cause. Overall, approaching flank pain with a basic conceptual framework aids the proper and efficient diagnosis of its underlying etiology. 

Non-Renal Etiologies

Non-renal etiologies of flank pain are usually local processes that result in inflammation or nerve irritation. Common causes include the following:

• Musculoskeletal strain
• Musculoskeletal contusion
• Dermatologic conditions
• Neurologic conditions
• Compression from local growth of a mass
• Referred pain from thoracic pathologies

Muscle pain

A strain, contusion, or other injury of the back or flank can lead to a dull aching discomfort or soreness in the thoracolumbar area. The discomfort is often exacerbated by activity and can be reproduced by palpation. The patient may have a history of heavy lifting or repetitive bending at work or during physical activity. An empiric trial of local heat application with analgesics and/or anti-inflammatory medications may help with both diagnosis and treatment. 

Rib pain

A fractured or injured 11th or 12th rib can cause flank pain with anterior and inferior radiation similar to the pain distribution of renal colic. While this is usually from trauma, sometimes prolonged violent coughing can cause the injury. Displacement of the fractured rib is rare. Renal injury from the fracture is uncommon but possible in the setting of significant trauma. 

Direct palpation of the involved rib usually produces intense pain. Deep respiration is also painful.

The diagnosis is usually made clinically, but can be confirmed by radiographic findings. Costochondritis or inflammation of the rib without a fracture can also duplicate the pain distribution of renal colic and is differentiated by the absence of a visualized fracture.

Vitamin D deficiency was the reported cause of flank pain in 187 patients with distinct tenderness over the tips of the lowermost ribs that could not be explained by history and radiology. Very low serum levels of 25 (OH) vitamin D was detected in all of the cases. Relief of flank pain was reported within 2 months in 55.1% of patients treated for vitamin D deficiency.[1]

Neuropathic Pain 

Neuropathic flank pain secondary to radiculitis can occur when the upper lumbar or lower thoracic nerve roots are injured. An injury to the costovertebral junction or vertebral transverse process can also produce  similar pain secondary to local effects. The typical source of the pain is inflammation, compression, or trapping of the involved nerves.

When the pathology involves the 10th, 11th, or 12th ribs, the discomfort mimics renal colic in its distribution and is usually described as sharp or stabbing. The pain is often acute and can radiate anteriorly and inferiorly. Movement exacerbates the pain. Similarly, the presence of an abdominal aortic aneurysm can also produce pain by stretching renal parenchymal innervation that travels along the renal artery. The diagnosis and treatment of radicular pain can be challenging, often requiring a multi-disciplinary approach.

Another cause of neuropathic flank pain is herpes zoster (shingles). Classically accompanied by a dermatomal skin eruption, this infection of nerve cell bodies produces burning pain that generally is limited to a discrete band that corresponds to a dermatome. The pain usually appears before the characteristic skin changes and can persist for extended periods after cutaneous resolution (post-herpetic neuralgia).

Diagnosis is usually straightforward when the dermatologic signs are present and is supported by abrupt exacerbation of the pain with light skin contact. If diagnosed early, treatment may help accelerate resolution of the episode and reduce the likelihood of prolonged discomfort. See Herpes Zoster for more information on this topic.

Pleural pain  

Pleuritis, or inflammation of the pleura, can cause sharp stabbing pain in the thoracolumbar region, which may mimic renal colic. The cause of the pleuritis may be infectious (eg, tuberculosis, pneumonia) or noninfectious (eg, lupus erythematosus, pulmonary embolism). If such a process is suspected, an appropriate workup should be pursued promptly, to confirm the diagnosis and treat the underlying issue.

Local infection 

Infection in the retroperitoneal space, such as a retroperitoneal abscess, can lead to flank pain as a result of local inflammation.Such abscesses may result from a urinary tract infection, but also can develop from pathologies of the enteric system. Diagnosis is achieved through imaging and, as with any abscess, drainage is the key to treatment. 

Renal Parenchymal Etiologies

Renal parenchymal etiologies consist of pathologic processes involving the renal parenchyma. Often, these conditions produce pain as a result of tissue inflammation or infarction, but stretching of the renal capsule from edema or hematoma also produce pain. A variety of conditions related to the renal parenchyma can produce flank pain, as reviewed below. 

Pyelonephritis

Pyelonephritis is a common cause of flank pain, but discomfort from it is usually described as a relatively mild dull ache rather than typical renal colic. Patients with diabetes are at an increased risk for pyelonephritis and its complications.

Fever, chills, nausea, and vomiting are the most common signs and symptoms. Patients with pyelonephritis often attempt to avoid movement, while those with renal colic often move persistently in an attempt to find a comfortable position. 

Flank and costovertebral angle tenderness are present and can be confirmed with percussion. Other signs of urinary tract infection, such as suprapubic pain, dysuria, frequency, and urgency, are often present. Fever, leukocytosis, and pyuria are typical findings.

Obtaining a urine culture is necessary to direct appropriate treatment following intiial empiric therapy. In the setting of suspected pyelonephritis or flank pain with presumed infection, obtaining renal imaging is warranted to rule out obstruction and infection of the upper urinary tract, which requires prompt urologic consultation and intervention. See Acute Pyelonephritis for more information.

Renal abscess

Renal abscesses present simiarly to pyelonephritis, but often may be more severely symptomatic. The formation of renal abscesses is thought to result from insufficiently treated pyelonephritis or hematogenous dissemination of infection. Patients with diabetes are at increased risk of renal abscess development. Pain from a renal abscess is thought to result not only from local tissue inflammation, but also parenchymal edema that causes the renal capsult to stretch.

Examination and laboratory findings are similar to those in pyelonephritis. Renal abscesses may be difficult to distinguish from certain renal lesions on ultrasonography. CT shows specific findings in cases of renal abscess and it remains the best choice for diagnosis[2] and should prompt expedient urologic consultation for drainage. 

Renal infarction

Renal infarction is assumed to be rare, which may lead it its misdiagnosis at initial presentation as acute renal colic, pyelonephritis, or an acute abdomen. Pain results from tissue infarction, producing classic flank discomfort from a renal origin. Case series have shown renal infarction to be more common in older individuals and those with conditions that may promote thrombus development, particularly atrial fibrillation.[3, 4] However, any interruption of blood supply, such as arterial compression by an extrinsic mass or impaired flow secondary to an abdominal aortic aneurysm, can produce a renal infarction.

The most common presenting signs and symptoms are flank pain and hematuria. Other common manifestations include fever, nausea, and vomiting. Leukocytosis may be present. Definitive diagnosis is generally made by performing an imaging study, with or without angiography. In the acute setting, prompt treatment is essential to minimize loss of renal function. 

Venous obstruction

Renal vein thrombosis is a relatively rare condition that can produce flank pain. By impairing renal outflow, a renal vein thrombus leads to the backup of blood within the renal parenchyma, which stretches the renal capsule and causes pain. Additionally, the impaired blood flow can lead to renal ischemia, which also creates discomfort. Obstruction of the renal vein can also result from more central pathologies of the venous system, as well as extrinisic compression of the venous system by a mass or anatomical variant such as nutcracker syndrome.

Treatment of renal vein thrombus involves anticoagulation and hydration. A thorough diagnostic workup should also be pursued to identify the etiology of the thrombus, which often involves a malignancy.[5]  

Renal tumor

A renal tumor may cause flank pain due to rapid expansion and stretching of the renal capsule. Alternatively, it may impair renal blood flow via tumor thrombus within the renal vein. A urothelial tumor in the renal pelvis may cause pain secondary to ureteral obstruction.

Presentation of a renal tumor with pain as the intial symptom is a poor prognostic sign, as it suggests advanced disease. Examination may reveal signs and symptoms of cancer, including weight loss, malaise, and fatigue. Hematuria is also another poor prognostic indicator, as it too suggests advanced disease.

Imaging should utilize a contrast-enhanced cross-sectional modality to evaluate the full extent of the neoplasm. Urology consultation is warranted for further workup and treatment. See Renal Cell Carcinoma for more information. 

Non-Parenchymal Renal Etiologies

Most non-parenchymal etiologies of renal pain involve obstruction of the urinary tract. Such obstruction, whether intrarenal, in the proximal ureter, or as distal as the bladder or urethra, can produce classic renal colic due to dilation of the intrarenal collecting system. Additionally, the upper urinary tract itself is well innervated and irritation by a foreign body (eg, kidney stone, ureteral stent) can trigger flank pain even if no hydronephrosis is present.

Nephrolithiasis 

Flank pain is the classic presenting symptom of urinary calculi and is the predominant cause of flank pain in the absence of fever. Nephrolithiasis is becoming increasingly common in the industrialized world and the amount of healthcare utilized to treat these patients is growing accordingly. Flank pain from nephrolithiasis can result from marked dilation of the proximal urinary tract as well as local inflammation and possible ischemia. In some settings, renal colic pain rarely, if ever, occurs without obstruction.

Classic renal colic is described as crampy flank pain radiating downward to the groin and is often accompanied by nausea and vomiting. On examination, flank palpation and percussion often confirm the pain. Hematuria and pyuria are often present and may result from scraping and irritation of the urinary tract by the stone, although a urine culture in this setting is needed to rule out infection.

If an upper tract stone is suspected, imaging is necessary to confirm the diagnosis. Studies of various modalities (eg, ultrasound, computed tomography, x-ray) have shown varying leves of diagnostic efficacy, with patient-specific factors often playing a part.[6]  In the setting of uncontrollable pain, inability to tolerate oral intake, or concomitant urinary tract infection, urologic consultation to pursue surgical management should be considered.  See Nephrolithiasis for more information. 

Stricture disease 

Broadly defined, a stricture is a concentric narrowing within the wall of a tubular structure. Within the urinary tract, this  can occur at any level from the intrarenal collecting system, through the ureter, to the urethra. If a stricture is severe enough, urinary drainage can be impaired and the urinary system proximal to this level can become dilated. Stricture may result from congenital problems (eg, infundibular stenosis, ureteropelvic junction obstruction, posterior urethral valves) or be iatrogenically induced (eg, repeated endoscopic procedures, laser damage, inadvertent electrocautery ).

Patients with obstruction in this setting will present with renal colic that may worsen after fluid intake. The pain can be confirmed on examination by flank palpation or percussion. Diagnosis involves imaging with modalities similar to those used for nephrolithiasis. Specialized studies to assess renal function and drainage are also often employed.  A urologist should be consulted for treatment, which involves drainage of the obstructed proximal urinary tract and often provides immediate relief. See Ureteral Stricture for more information.

Extrinsic compression

Similar to stricture disease, wihch is an intrinsic obstruction of the urinary tract, almost all portions of the urinary tract are also at risk for extrinsic obstruction. Large pelvic or retroperitoneal masses may directly compress the ureter, impairing renal drainage and leading to proximal dilation of the urinary tract, which causes pain. Retroperitoneal fibrosis is another  common cause of ureteral distortion and obstruction. Endometriosis has also been noted to result in ureteral compression. Finally, iatrogenic compression of the ureter can occur as a result of surgical clips, sutures, or staples placed along the course of the ureter; this highlights the relevance of obtaining an accurate surgical hstory.

Symptoms are similar to those of other obstructive processes and workup is pursued similarly, as well. Consultation with a urologist is warranted for drainage of the obstructed proximal urinary tract. Definitive treatment of the extrinsic process can be pursued to resolve the obstruction. See Retroperitoneal Fibrosis for more information.

 Bladder outlet obstruction

Any impairment of bladder emptying can result in the backup of urine into the ureters, and subsequently the kidneys. Like other obstructive etiologies, such backup and dilation can result in flank pain.

A patient with bladder outlet obstruction will generally present with suprapubic fullness and urinary urgency. If this is acute, uncomfortable bladder distention can be a symptom. However, if the obstruction is chronic and developed gradually over a long time period, no such symptoms may be present. Abdominal examiation may reveal a palpably full bladder and enlarged prostatate on digital rectal examination.

Treatment involves urethral catheter placement to drain the bladder. If that is not possible, then consultation with a urologist is indicated to pursue other drainage options. See Benign Prostatic Hypertrophy for more information. 

Intraluminal obstruction 

With hematuria of renal origin, the development of blood clots within the renal pelvis can lead to subsequent ureteral obstruction and flank pain as the clots pass. These blood clots may result from iatrogenic causes, such as percutaneous renal biopsies or stone procedures, or from underlying medical problems, such as blood dyscrasias, renal tumors, hemophilia, sickle cell disease, or glomerulonephritis.

Examination and workup are similar to those with other obstructive processes. Treatment involves urologic consultation for hematuria workup and relief of the obstruction. See Hematuria for more information. 

Papillary necrosis can cause ureteral obstruction as sloughed papilla pass down the ureter. Analgesic abuse, liver cirrhosis, and diabetes are the most common risk factors for this condition; other known causes are sickle cell disesase, vasculitis, and tuberculosis. The actual sloughing of the renal papilla is caused by vascular ischemia, which leads to coagulative necrosis of the renal medullary pyramids. Diagnosis is aided by cross-sectional imaging. See Papillary Necrosis for more information.