Penumbra (medicine)
Encyclopedia
In pathology
and anatomy
the penumbra is the area surrounding an ischemic event such as an ischemic, thrombotic or embolic stroke
. Immediately following the event, blood flow and therefore oxygen
transport is reduced locally, leading to hypoxia
of the cells
near the location of the original insult. This can lead to cell death and amplify the original damage from the infarction
; however, the penumbra area may remain viable for several hours after an ischemic event due to the collateral arteries that supply the penumbral zone. As time elapses after the onset of stroke, the extent of the penumbra tends to decrease; therefore, in the emergency department
a major concern is to protect the penumbra by increasing oxygen transport and delivery to cells in the danger zone, thereby limiting cell death. The existence of a penumbra implies that salvage of the cells is possible. There is a high correlation between the extent of spontaneous neurological recovery and the volume of penumbra that escapes infarction; therefore, saving the penumbra should improve the clinical outcome.
One widely accepted definition for penumbra describes the area as "ischemic tissue potentially destined for infarction but not yet irreversibly injured and the target of acute therapies." The original definition of the penumbra referred to areas of the brain that were damaged but not yet dead, and offered promise to rescue the brain tissue with the appropriate therapies.
PET is the gold standard for imaging, but because PET is neither widely available nor rapidly accessible current research focuses on improved MRI techniques. The penumbral area can also be detected based upon an integration of three factors. These factors include: the site of vessel occlusion, the extent of oligaemia (hypoperfused
area surrounding the penumbra, but not at risk of infarction ) at that moment, and the mismatch between this perfusion
defect and the area of the brain already infarcted
, mapping the cerebral blood flow, and quantifying oxygen and glucose consumption to define these areas. The second decade revealed the mechanism of the neuronal cell death. As the Biochemical pathways were dissected penumbral science became a rapidly evolving area of molecular biology. The third decade of penumbral research found a transitional leap as using Positron Emission Tomography
(PET) scanning can identify brain tissue with decreased blood flow and Magnetic Resonance Imaging
(MRI) has the ability to detect portions of the ischemic tissue that has not yet died. These images have allowed vision into the brain to see the areas of tissue that may be salvaged, the penumbra. Research has now entered into the fourth decade, which leaves researchers wondering why the penumbra has failed as there has not been a neuroprotectant found. A deeper dissection of the penumbra may be needed to make the huge leap to viable clinical therapies as research still tries to understand the complex response of stoke
and the transitional zones between injury and repair.
The penumbral areas have significant functional implications in terms of patients' regaining their motor ability. In order to save these penumbral areas as best as possible, health care professionals will often administer a blood thinner to dissolve the blockages in the affected area that are causing the lack of blood flow. Best efforts should be made to saving penumbral areas, as research has demonstrated that the amount of penumbral tissue saved and spontaneous neurologic recovery are highly related.
Pathology
Pathology is the precise study and diagnosis of disease. The word pathology is from Ancient Greek , pathos, "feeling, suffering"; and , -logia, "the study of". Pathologization, to pathologize, refers to the process of defining a condition or behavior as pathological, e.g. pathological gambling....
and anatomy
Anatomy
Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...
the penumbra is the area surrounding an ischemic event such as an ischemic, thrombotic or embolic stroke
Stroke
A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
. Immediately following the event, blood flow and therefore oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
transport is reduced locally, leading to hypoxia
Hypoxia (medical)
Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...
of the cells
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
near the location of the original insult. This can lead to cell death and amplify the original damage from the infarction
Infarction
In medicine, infarction refers to tissue death that is caused by a local lack of oxygen due to obstruction of the tissue's blood supply. The resulting lesion is referred to as an infarct.-Causes:...
; however, the penumbra area may remain viable for several hours after an ischemic event due to the collateral arteries that supply the penumbral zone. As time elapses after the onset of stroke, the extent of the penumbra tends to decrease; therefore, in the emergency department
Emergency department
An emergency department , also known as accident & emergency , emergency room , emergency ward , or casualty department is a medical treatment facility specialising in acute care of patients who present without prior appointment, either by their own means or by ambulance...
a major concern is to protect the penumbra by increasing oxygen transport and delivery to cells in the danger zone, thereby limiting cell death. The existence of a penumbra implies that salvage of the cells is possible. There is a high correlation between the extent of spontaneous neurological recovery and the volume of penumbra that escapes infarction; therefore, saving the penumbra should improve the clinical outcome.
One widely accepted definition for penumbra describes the area as "ischemic tissue potentially destined for infarction but not yet irreversibly injured and the target of acute therapies." The original definition of the penumbra referred to areas of the brain that were damaged but not yet dead, and offered promise to rescue the brain tissue with the appropriate therapies.
PET is the gold standard for imaging, but because PET is neither widely available nor rapidly accessible current research focuses on improved MRI techniques. The penumbral area can also be detected based upon an integration of three factors. These factors include: the site of vessel occlusion, the extent of oligaemia (hypoperfused
Ischemia
In medicine, ischemia is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue. It may also be spelled ischaemia or ischæmia...
area surrounding the penumbra, but not at risk of infarction ) at that moment, and the mismatch between this perfusion
Perfusion
In physiology, perfusion is the process of nutritive delivery of arterial blood to a capillary bed in the biological tissue. The word is derived from the French verb "perfuser" meaning to "pour over or through."...
defect and the area of the brain already infarcted
Research
The first decade of research focused on physiologic profile of the penumbra tissue after strokeStroke
A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
, mapping the cerebral blood flow, and quantifying oxygen and glucose consumption to define these areas. The second decade revealed the mechanism of the neuronal cell death. As the Biochemical pathways were dissected penumbral science became a rapidly evolving area of molecular biology. The third decade of penumbral research found a transitional leap as using Positron Emission Tomography
Positron emission tomography
Positron emission tomography is nuclear medicine imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide , which is introduced into the body on a...
(PET) scanning can identify brain tissue with decreased blood flow and Magnetic Resonance Imaging
Magnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
(MRI) has the ability to detect portions of the ischemic tissue that has not yet died. These images have allowed vision into the brain to see the areas of tissue that may be salvaged, the penumbra. Research has now entered into the fourth decade, which leaves researchers wondering why the penumbra has failed as there has not been a neuroprotectant found. A deeper dissection of the penumbra may be needed to make the huge leap to viable clinical therapies as research still tries to understand the complex response of stoke
Stoke
-United Kingdom:*Stoke is one of the most common place names in the United Kingdom and in historical documents.Originally from the Old English 'stoc' meaning 'place', it came to be used in two special senses, i) a religious place and ii) a secondary settlement It can refer to any of the following...
and the transitional zones between injury and repair.
The penumbral areas have significant functional implications in terms of patients' regaining their motor ability. In order to save these penumbral areas as best as possible, health care professionals will often administer a blood thinner to dissolve the blockages in the affected area that are causing the lack of blood flow. Best efforts should be made to saving penumbral areas, as research has demonstrated that the amount of penumbral tissue saved and spontaneous neurologic recovery are highly related.