Several conditions can cause pain in the left flank. According to the University of Maryland Medical Center, flank pain may indicate problems with the kidneys, although other tissues or structures---some within the abdomen, some outside the abdomen---can also cause flank pain, or pain in the side of the torso. Flank pain can be mild, moderate or severe. In some cases, flank pain can limit a person's activities of daily living and decrease her quality of life.
Intercostal Neuralgia
Intercostal neuralgia is a rare condition that can cause left-sided flank pain. According to the Columbia University Medical Center, the characteristic pain pattern of intercostal neuralgia is a band-like distribution that wraps around the side of the torso. Intercostal neuralgia causes pain in the intercostal spaces of the chest wall. The intercostal spaces are the spaces between a person's ribs. Intercostal neuralgia involves acute, spasmodic pain that manifests along the course of the intercostal nerves in the lateral, or outside, aspect of the chest wall. Compression of the intercostal nerves is the primary cause of this condition. Certain factors may increase the likelihood of intercostal nerve compression and rib cage neuralgia, or nerve pain, including an enlarged abdomen, an abdominal muscle tissue rupture or tear, scar tissue around the affected nerve, excessive abdominal muscle straining, and certain musculoskeletal conditions.
Pyelonephritis
Pyelonephritis, also known as a kidney infection, is a relatively common cause of left-sided flank pain. Pyelonephritis is a urinary tract infection that usually begins in the urethra or bladder and migrates up the urinary tract to the kidneys. Numerous risk factors can increase a person's likelihood of developing pyelonephritis, including being female, obstruction of the urinary tract, a compromised immune system, damage to the nerves supplying the bladder, prolonged use of a urinary catheter and any medical condition that causes urine to flow in the opposite direction. Common signs and symptoms associated with pyelonephritis include back, flank or groin pain; abdominal pain; fever; frequent urination; the persistent urge to urinate; a burning feeling during urination; and pus or blood in the urine. Pyelonephritis can cause serious health complications if left untreated, such as permanent kidney damage and septicemia, or blood poisoning, according to MayoClinic.com.
Kidney Stones
Kidney stones, also known as renal calculi, can cause left flank pain. Kidney stones are solid masses made up of tiny crystals. Multiple kidney stones can be present in the kidney or ureter at the same time. One of the most common causes of kidney stones is dehydration, according to MedlinePlus. When a person is dehydrated, certain substances within the urine can combine to create small crystals that eventually become kidney stones. In most cases, kidney stones do not cause symptoms until they travel down the ureters toward the bladder. If the stone or stones block the flow of urine through the ureters, the affected-side kidney can swell, causing severe pain. Along with severe pain in the back, flank, abdomen and groin, common signs and symptoms associated with kidney stones include blood in the urine, chills, fever, nausea and vomiting.
