Flank Pain: Symptoms, Causes and Treatment

Flank pain—a discomfort or ache in the side area of the body, between the ribs and the hip—affects millions each year and can range from mild twinges to severe, disabling agony. Because it can originate from many organ systems, identifying the source of flank pain is crucial for effective treatment. This article unpacks the key symptoms, diverse causes, and modern approaches to treating flank pain, drawing from recent clinical and research insights.

Symptoms of Flank Pain

Flank pain isn’t just a single feeling—it’s a spectrum of sensations, sometimes accompanied by additional symptoms that help narrow down its cause. Recognizing the patterns of pain and associated features is the first step toward diagnosis.

Location	Sensation	Associated Signs	Source(s)
Side/Back	Sharp, dull, or aching	Tenderness, radiating pain	1,2,6
Lower Ribs	Localized tenderness	Skin sensitivity, swelling	1,7
Unilateral/Bilateral	Constant or intermittent	Hematuria, fever, urinary symptoms	6,9,4
Flank/Abdomen	Neuropathic pain	Altered skin sensation	7

Table 1: Key Symptoms of Flank Pain

Pain Location and Character

Flank pain typically manifests on one or both sides of the body, between the lower rib cage and the hip. The quality of pain varies—it may be sharp and sudden, dull and aching, or even burning in certain neuropathic syndromes 7. In some cases, pain is felt more in the back or abdomen and may radiate toward the groin.

Associated Signs and Symptoms

• Tenderness: Pressing over the affected area often exacerbates the pain, especially in musculoskeletal or nerve-related causes 1,7.
• Urinary Symptoms: Blood in the urine (hematuria), frequent urination, or painful urination suggest a urinary tract origin 4,6.
• Systemic Symptoms: Fever, nausea, or vomiting can indicate infection or inflammation.
• Skin Changes: Some causes, like nerve entrapment (LACNES), may cause altered skin sensation or hypersensitivity at the site 7.
• Other Features: In rare cases, flank pain may be accompanied by symptoms such as varicocele (enlarged veins in the scrotum), gynecological complaints, or even orthostatic hypotension, providing clues to less common diagnoses 6.

Acute vs. Chronic Presentation

• Acute Flank Pain: Sudden onset, often severe, commonly points toward conditions like kidney stones or acute infections 2,3.
• Chronic Flank Pain: Lasts weeks to months, may be linked to musculoskeletal issues, nerve entrapment, or rare syndromes such as Loin Pain Hematuria Syndrome (LPHS) 9,7.

Causes of Flank Pain

Because the flank region houses several organs and structures, its pain can result from a wide variety of causes—some benign, others requiring urgent attention.

Major Cause	Common Examples	Clinical Clues	Source(s)
Renal/Urologic	Kidney stones, infections	Hematuria, urinary changes, colic pain	2,3,4,5
Musculoskeletal	Rib osteomalacia, strain	Local tenderness, no urinary findings	1,7
Vascular	Nutcracker syndrome	Left-sided pain, hematuria, varicocele	6
Neuropathic	LACNES, LPHS	Neuropathic pain, altered sensation	7,9
Gastrointestinal	Appendicitis, diverticulitis	GI symptoms, localized fever	5
Rare/Other	Eosinophilic ureteritis	Unexplained obstruction, atopy history	8

Table 2: Common Causes of Flank Pain

Genitourinary Causes

Kidney Stones (Urolithiasis)

• The most frequent cause of acute flank pain, presenting with severe, colicky pain often radiating to the groin. Hematuria is common 2,3,4.
• Diagnosis relies on imaging, with unenhanced helical CT (UHCT) now considered the gold standard due to its high sensitivity and specificity 2,3,5.

Urinary Tract Infections

• Can cause dull, aching pain with fever and urinary symptoms. Pyelonephritis (kidney infection) is a classic example 5.

Other Urologic Disorders

• Conditions like renal tumors, cysts, or rare ureteral diseases (e.g., eosinophilic ureteritis) may also present with flank pain 5,8.

Musculoskeletal and Metabolic Causes

Rib Osteomalacia from Vitamin D Deficiency

• Not all flank pain is urologic—rib osteomalacia, often due to vitamin D deficiency, can cause localized tenderness over the lower ribs 1.
• This pain is typically not associated with urinary abnormalities, and responds well to vitamin D supplementation.

Muscular Strain or Injury

• Overuse, trauma, or poor posture can lead to localized muscle or ligament pain in the flank region.

Vascular Causes

Nutcracker Syndrome

• A rare but important cause, involving compression of the left renal vein, leading to left-sided flank pain, hematuria, and sometimes pelvic congestion symptoms 6.
• Diagnosis requires imaging and clinical correlation.

Neuropathic and Nerve Entrapment Syndromes

Lateral Cutaneous Nerve Entrapment Syndrome (LACNES)

• Chronic, localized neuropathic flank pain due to nerve entrapment. Presents with a point of maximal pain and sometimes altered skin sensation 7.
• Diagnosis is clinical, often confirmed by pain relief after local anesthetic injection.

Loin Pain Hematuria Syndrome (LPHS)

• Uncommon syndrome with chronic, severe flank pain and hematuria, often without clear cause 9.
• Management is challenging and may require neuromodulation therapies for refractory cases.

Gastrointestinal and Other Causes

• Diseases like appendicitis, diverticulitis, or hepatic and biliary conditions may mimic renal colic and cause flank pain 5.
• Gynecologic disorders (e.g., adnexal masses) can also present as acute flank pain, particularly in women 5.

When No Cause Is Found

• In up to 43% of cases undergoing advanced imaging, no clear cause for flank pain is identified, especially in the absence of urinary infection 4.
• A structured approach and follow-up are crucial in these cases to avoid missed diagnoses.

Treatment of Flank Pain

Effective treatment of flank pain hinges on identifying its underlying cause. Management ranges from simple analgesia to advanced interventions, depending on severity and diagnosis.

Approach	Indications	Key Interventions	Source(s)
Symptomatic Care	Mild, self-limited pain	Analgesics, rest	10
Medical Therapy	Infection, vitamin D deficiency	Antibiotics, vitamin D, hydration	1,10
Minimally Invasive	Stones, nerve entrapment	Stone removal, nerve blocks	2,7,9
Surgical/Advanced	Rare/complex cases (NCS, LPHS)	Stenting, denervation, neuromodulation	6,9

Table 3: Treatment Approaches for Flank Pain

Initial Symptomatic Management

• Analgesia: Most acute flank pains are initially managed with pain relievers such as NSAIDs or acetaminophen 10.
• Hydration: Encouraged, especially in suspected stone disease, to aid passage of stones 2.

Condition-Specific Treatments

Kidney Stones

• Small Stones: May pass spontaneously; pain managed with analgesics, hydration 2,3.
• Large/Obstructive Stones: May require minimally invasive procedures (e.g., lithotripsy, ureteroscopic removal) 2.
• Refractory Cases: Surgical intervention is rare but may be required for complex stones.

Urinary Tract Infections

• Antibiotics: For bacterial infections, along with supportive care 10.
• Hospitalization: Required in severe or complicated cases.

Vitamin D Deficiency/Rib Osteomalacia

• Supplementation: Oral or injectable vitamin D leads to resolution of pain in most cases within two months 1.
• Monitoring: Repeat assessment to ensure deficiency correction.

Nerve Entrapment Syndromes (LACNES)

• Local Anesthetic Injection: Provides immediate and often long-term relief for many patients 7.
• Other Interventions: Surgery, manual therapy, or pulsed radiofrequency for refractory cases.

Nutcracker Syndrome

• Conservative Management: Observation in mild cases.
• Endovascular/Surgical: Stenting or embolization for severe, symptomatic cases 6.

Loin Pain Hematuria Syndrome (LPHS)

• Multimodal Pain Management: Includes physiotherapy, psychological support, neuropathic analgesics 9.
• Interventional Procedures: Nerve blocks, denervation, or more advanced neuromodulation (e.g., dorsal root ganglion stimulation) in refractory cases 9.
• Surgical Options: Autotransplantation or nephrectomy in rare, severe cases.

Rare Causes (e.g., Eosinophilic Ureteritis)

• Surgical Resection: Of stenosed ureteral segments; corticosteroids in select cases 8.

The Role of Imaging in Management

• Ultrasound: Useful for initial assessment, especially to detect hydronephrosis or larger stones 2.
• Unenhanced Helical CT (UHCT): Gold standard for stone detection and for identifying alternative diagnoses 2,3,5.
• Other Modalities: IVU, MRI, or specialized tests as indicated by clinical suspicion 2.

Structured Diagnostic Approach

A careful history, physical examination, and judicious use of laboratory and imaging studies are essential. Rushing to surgical intervention without a comprehensive evaluation can miss non-urologic causes or rare conditions 10.

Conclusion

Flank pain is a frequent yet complex complaint with a diverse range of causes. A careful, systematic approach is essential for accurate diagnosis and effective management.

Key Takeaways:

• Flank pain may be sharp, dull, or neuropathic, and often presents with clues like tenderness, hematuria, or altered skin sensation.
• Causes range from common (kidney stones, infections) to rare (nerve entrapment, vascular syndromes, vitamin D deficiency).
• Imaging, especially unenhanced helical CT, plays a central role in both diagnosis and identifying alternative causes.
• Treatments vary from simple analgesia and correction of deficiencies, to advanced interventions such as nerve blocks, stenting, or neuromodulation—tailored to the underlying cause.
• In many cases, a structured diagnostic and therapeutic approach ensures the best outcomes and minimizes unnecessary interventions.

By understanding the spectrum of symptoms, recognizing red flags, and using modern diagnostics wisely, clinicians and patients can work together to find relief and prevent complications from this common, sometimes enigmatic pain.