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xanthochromia
Xanthochromia (from the Greek ''xanthos (ξανθός)''=yellow and ''chroma (χρώμα)''=colour), is the yellowish appearance of cerebrospinal fluid (which envelops the brain) in particular medical conditions, especially subarachnoid hemorrhage. This can be determined by spectrophotometry (measuring the absorption of particular wavelengths of light) or visual examination. It is unclear which method is superior.
A common test for subarachnoid hemorrhage is computed tomography (CT, a type of brain scan), but this identifies only 98% of cases in the first 12 hours after the symptoms and becomes less useful afterwards. Therefore, obtaining cerebrospinal fluid (after a CT scan) by lumbar puncture is recommended if someone has characteristic symptoms (e.g. a thunderclap headache) but no blood visible on the CT.〔 According to one article it is not necessary if the images were taken with a third generation CT scan in the first six hours after the onset of the symptoms and no blood is present on the scan. However, this is not standard of care.
The yellow appearance is caused by red blood cells entering the cerebrospinal fluid during the bleeding. The cells are eventually destroyed by the body, releasing their oxygen-carrying molecule heme, which is degraded by enzymes into the yellow-green pigment bilirubin. Heme from red blood cells that enter the cerebrospinal fluid for a different reason, e.g., because a small blood vessel was damaged during the lumbar puncture (traumatic tap), has no time to be digested in this fashion, and bilirubin is therefore absent. Many laboratories rely on the color of the fluid alone when reporting the presence or absence of xanthochromia. Recent guidelines, however, suggest that spectrophotometry should be performed. This relies on the fact that bilirubin absorbs light of wavelengths between 450–460 nm. Two related substances that are also released when heme is metabolized are oxyhemoglobin and methemoglobin (the absorption ranges are 410-418 nm and 403-410 nm respectively) may also be detected during this process.〔
==Origin==
Xanthochromia is derived from the Greek word xanthos meaning yellow in chroma. Medically, it is used to denote patients that may suffer from subarachnoid Hemorrhage. Subarachnoid Hemorrhage occurs when abnormal blood vessels burst causing blood to fill the cavity between the brain and the skull eliciting severe pressure capable of inducing intense headaches, dizziness, vomiting, confusion and even death. Xanthochromia, specifically, relates to the color of chemically altered cerebrospinal fluid often present in people suspected of having cerebral trauma. Typically cerebrospinal fluid associated with Xanthochromia is yellow in appearance displaying absorption levels between 450 and 460 nm.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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