Chronic pain is classified as pain that lasts longer than three to six months. In medicine, the distinction between acute and chronic pain is sometimes determined by the amount of time since onset. Two commonly used markers are pain that continues at three months and six months since onset, but some theorists and researchers have placed the transition from acute to chronic pain at twelve months. Others apply the term acute to pain that lasts less than 30 days, chronic to pain of more than six months duration, and subacute to pain that lasts from one to six months. A popular alternative definition of chronic pain, involving no fixed duration, is "pain that extends beyond the expected period of healing".Chronic pain may originate in the body, or in the brain or spinal cord. It is often difficult to treat. Epidemiological studies have found that 8–11.2% of people in various countries have chronic widespread pain. Various non-opioid medicines are initially recommended to treat chronic pain, depending on whether the pain is due to tissue damage or is neuropathic. Psychological treatments including cognitive behavioral therapy and acceptance and commitment therapy may be effective for improving quality of life in those with chronic pain. Some people with chronic pain may benefit from opioid treatment while others can be harmed by it.
A supernumerary  kidney is an additional kidney to the number usually present in an organism. This often develops as the result of splitting of the nephrogenic blastema, or from separate metanephric blastemas into which partially or completely reduplicated ureteral stalks enter to form separate capsulated kidneys; in some cases the separation of the reduplicated organ is incomplete (fused supernumerary kidney). Less than a hundred cases are known of one or two supernumerary kidneys. See also
Supernumerary body part

References
Luciano A. Favorito; Ana Raquel M. Morais (May–June 2012). "Evaluation of supernumerary kidney with fusion using magnetic resonance image". IBJU. 38 (3): 428–429. doi:10.1590/s1677-55382012000300018. PMID 22765860.