Flank pain describes discomfort located in the side of the body, specifically the area between the lower ribs and the top of the hip bone, extending across the back. This region is home to several important organs, most notably the kidneys, which makes pain here a frequent cause for medical concern. Flank pain is a symptom, not a specific disease, and can manifest as anything from a minor, temporary ache to a sign of a severe underlying condition. Understanding the characteristics of this pain is the first step toward determining its origin, which could involve the urinary tract, muscles, spine, or even the digestive system.
Understanding the Qualities of Flank Pain
The nature of flank pain is highly variable and provides valuable clues for diagnosis. The sensation may be described as sharp, stabbing, or cramp-like, often suggesting an acute process like an obstruction. Alternatively, the pain might present as a persistent, dull ache, which is more commonly associated with inflammation or infection.
Pain originating in the flank frequently spreads downward toward the abdomen, groin, or even the testicle or labia, which strongly implicates the ureter. Other symptoms accompanying the pain are also important, such as nausea, vomiting, or changes in urinary habits like increased frequency or a burning sensation during urination. These accompanying signs help distinguish between a simple muscle issue and a complex internal problem.
Primary Causes in the Urinary System
The most serious and common causes of flank pain involve the urinary system, specifically the kidneys and ureters. Pain from this system occurs when there is rapid distention or stretching of the renal capsule or spasm of the ureteral smooth muscle.
Kidney Stones (Nephrolithiasis)
Kidney stones, or nephrolithiasis, are a frequent culprit, causing a type of pain known as renal colic. This pain is typically excruciating, sudden in onset, and comes in distinct waves. The pain characteristically begins in the flank and radiates toward the groin as the stone travels down the ureter, often accompanied by vomiting due to the shared nerve pathways.
Kidney Infection (Pyelonephritis)
A kidney infection, or pyelonephritis, presents with a different type of flank discomfort. This condition results from bacteria, most commonly Escherichia coli, ascending the urinary tract to the kidney tissue. The pain is usually a dull, constant ache in the flank region, often accompanied by systemic symptoms like high fever, chills, and painful urination. The distinguishing feature is often tenderness when lightly tapping the area over the kidney, known as costovertebral angle tenderness.
Non-Urinary Sources of Flank Pain
Musculoskeletal issues are a frequent non-urinary source, including muscle strain or a herniated disc in the lumbar spine. Pain from a strained muscle is typically a dull ache that worsens predictably with specific movements like bending, twisting, or lifting, and often improves with rest.
Spinal problems, such as a compressed nerve from a herniated disc, can also cause pain that radiates into the flank. This nerve-related pain often travels down the leg or is accompanied by numbness or tingling, which is rarely seen with kidney pain. Another non-urinary cause is the neurological pain from a shingles outbreak (herpes zoster). This pain is often described as deep, burning, or electric-shock-like, occurring along the path of a single nerve root and frequently preceding the appearance of the characteristic unilateral, blistering rash.
Gastrointestinal conditions can also refer pain to the flank area. For instance, appendicitis often begins as vague, central abdominal pain before localizing to the lower right abdomen, but can occasionally present with referred flank pain. Diverticulitis, which involves inflammation of pouches in the colon, typically causes pain in the lower left abdomen but may also present as left-sided flank pain. The location of the pain, along with associated digestive symptoms like diarrhea, constipation, or bloating, helps distinguish these causes from urinary issues.
Critical Signs Requiring Emergency Care
Any severe, sudden-onset flank pain accompanied by systemic signs of infection should prompt an emergency room visit. These signs include a high fever, shaking chills, or signs of shock such as dizziness, fainting, or a rapid, weak pulse.
The inability to urinate, especially if combined with sudden, severe pain, suggests a complete blockage of the urinary tract by a stone or clot. Flank pain following any kind of trauma or injury to the back or side is also an urgent concern, as it may indicate internal organ damage or bleeding. Acute flank pain can also be a symptom of a ruptured abdominal aortic aneurysm (AAA), a life-threatening vascular event that presents with severe, acute pain in the abdomen, back, or flank, and sometimes hypotension. In males, sudden, severe flank pain that radiates to the groin may be a referred symptom of testicular torsion, a condition requiring immediate surgical intervention to save the testicle.