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.^[1] This can be determined by spectrophotometry (measuring the absorption of particular wavelengths of light) or visual examination. It is unclear which method is superior.^[2]

A common test for SAH 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.^[1] 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.^[3]

The yellow appearance is caused by red blood cells entering the CSF 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 CSF 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.^[4] Recent guidelines, however, suggest that spectrophotometry should be performed. This relies on the fact that bilirubin absorbs light of wavelengths between 450–460 nm.^[5] 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.^[1]

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.^[6] Xanthochromia, specifically, relates to the color of chemically altered CSF 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.^[7]

Spectrophotometry

Xanthochromia is in itself a unique condition that alters the visual appearance of CSF fluid. There are other sorts of pigment colors that can be found in the CSF which also alter its visual appearance as well can denote a specific illness or condition. The distinct color of xanthochromia (translucent yellow) is a by-product of blood entering the cerebrospinal column and infiltrating the contained CSF, known as bilirubin (the degradation of heme). The formation of bilirubin is significant as it declares the presence of subarachnoid hemorrhage via centrifuge exhibiting the yellowish xanthochromic color. Although a CT scan has been proven to be about 98% effective and lumbar puncture more conclusive, for the two percent unaccounted by CT scans there are cases however when a computed tomography scan and or a lumbar puncture with visual inspection fail to show conclusive results regarding SAH.

Spectrophotometry, which is a quantified measurement of spectral transmission and of reflection properties as a function of wavelength, has proven to be more effective as a ‘fail safe’ in determining whether or not a patient is showing signs of SAH.^[8] Spectrophotometry functions on the idea that every color and material, or substance has its own distinct spectral transmittance. Every material has its own defining characteristics of which spectrophotometry can take into account via gloss, texture, color, and spatial attributes.^[8] Spectrophotometry has proven effective in determining whether a patient may have xanthochromia, and subsequently SAH, as visual inspection via lumbar puncture may not always be conclusive. In most cases critical CSF samples are either contaminated by oxyhemoglobin or contain low levels of bilirubin. In regards to these conditions the detection of xanthochromia becomes unreliable concerning visual inspection, predominantly when viewed under incandescent lighting or a tungsten desk lamp (corresponding to CIE standard illuminant A).^[7] Spectrophotometry allows for a calibrated uniform detection among samples that can determine the presence of xanthochromia production in the CSF at even the smallest percentages of color saturation (about .62%).^[7]

Controversy over whether or not to identify xanthochromia through spectrophotometry or via visual inspection persists.^[9]

See also

• Xanthochromism

References