brain abscess


Brain Abscess

 

Definition

Brain abscess is a bacterial infection within the brain.

Description

The brain is usually well insulated from infection by bacteria, protected by the skull, the meninges (tissue layers surrounding the brain), the immune system, and the highly regulated barrier between the bloodstream and the brain. Under certain circumstances, however, bacteria can invade the brain and cause a localized infection called an abscess. Brain abscess is relatively rare, accounting for 1 in 10,000 hospital admissions. Single abscess occurs in 75% of cases, and the remainder of cases involve multiple abscesses. If not treated, brain abscess is almost always fatal.

Causes and symptoms

One-half of all brain abscesses are caused by the spread of bacteria from a nearby infection. Sources of bacteria include:
  • middle ear infections (otitis media) orinfectionsin the bony spaces in front of the middle ear (mastoiditis)
  • sinus infections
  • an abscessed tooth.
Other sources of bacteria include lung infections, abdominal infection, infection of the heart's lining (endocarditis) penetrating heart wounds, and neurosurgery.Acquired Immune Deficiency Syndrome (AIDS) or the presence of another immune deficiency greatly increases the risk of brain abscess. Approximately 25% of cases have no detectable cause of infection.Brain abscess can be caused by a variety of organisms, many of them related to ear and sinus infections. Many times brain abscess cases are caused by two or more bacteria. In 30-60% of cases, the bacteria combination includes streptococci, microorganisms that can live without oxygen (anaerobes), and enterobacteria. A small number of cases are caused by yeast, fungi, and single-cell organisms (protozoa).The symptoms of brain abscess often develop slowly, usually within a period of about two weeks. The most common symptoms are:
  • headache
  • neurologic symptoms related to the specific part of the brain that is infected
  • altered mental status
  • seizures

Diagnosis

Diagnosis of brain abscess is performed by using a computed tomography scan (CT) or a magnetic resonance imaging (MRI) scan to determine the site of infection. Tissue removal (biopsy) is usually performed as well. A biopsy is performed to determine the type of bacterium involved. Biopsies can also be used to rule out tumor or other noninfectious localized lesions, which may look the same on the scans.Other tests are performed to determine the source of the infection. These tests include blood cultures, x rays of the chest, and a physical exam of the ears, sinuses, and teeth. A test for human immunodeficiency virus (HIV) is usually also performed.

Treatment

Treatment for brain abscess begins with intravenous antibiotics, chosen to match the infecting bacterium if known, or to cover a wide spectrum of possibilities if not. Treatment usually continues for six to eight weeks.Aspiration surgery is almost always done to drain the abscess. In this procedure, a needle is guided to the infected site by CT scan, and fluid is removed (aspirated) from the abscess. Aspiration may be repeated several times until the bacteria are completely killed or removed. Surgical removal of infected or dead tissue may be needed in some cases. For patients with many sites of infection, aspiration or surgical removal is not done because of the increased difficulty and risk of the procedure. For these patients, antibiotic therapy alone is used. Steroid treatment is controversial, but may be indicated in some cases.

Prognosis

Even with prompt treatment, brain abscess is fatal in about 20% of cases. About half of those who survive have some residual neurological problems, including seizures in many patients.There are several reasons why patients with brain abscess can have a poor prognosis. The illness may not be diagnosed correctly or an accurate diagnosis may take additional time. The patient may receive an antibiotic that does not match the infecting organism. Sometimes the infection may not be limited to a definite area in the brain, making diagnosis and treatment difficult. The small number of cases caused by fungal infection may take additional time to diagnose. A patient may also have a poor prognosis because there is more than one abscess, the location of the abscess may be deep within the brain, or the infection may have moved into many locations within the brain. Severe complications can result from brain abscess, including comma and brain rupture. In 80-100% of cases involving brain rupture, the patient dies.

Prevention

Brain abscess may be preventable by prompt and aggressive treatment of the infections which give rise to it, especially sinus and ear infections.

Resources

Books

Fauci, Anthony S., et al., editors. Harrison's Principles of Internal Medicine. New York: McGraw-Hill, 1997.

Key terms

Aspiration — Removal of fluid from a closed space through a needle.Biopsy — The removal of a tissue sample for examination.

abscess

 [ab´ses] a localized collection of pus in a cavity formed by the disintegration of tissue. Abscesses are usually caused by specific microorganisms that invade the tissues, often by way of small wounds or breaks in the skin. An abscess is a natural defense mechanism in which the body attempts to localize an infection and wall off the microorganisms so that they cannot spread throughout the body. As the microorganisms destroy the tissue, an increased supply of blood is rushed to the area. The cells, bacteria, and dead tissue accumulate to form a clump of cream-colored liquid, which is the pus. The accumulating pus and the adjacent swollen, inflamed tissues press against the nerves, causing pain. The concentration of blood in the area causes redness. The abscess sometimes “comes to a head” by itself and breaks through the skin or other tissues, allowing the pus to drain. Local applications of heat may be used to facilitate localization and drainage. Abscess, cross section. alveolar abscess a localized suppurative inflammation of tissues about the apex of the root of a tooth.amebic abscess an abscess cavity of the liver resulting from liquefaction necrosis due to entrance of Entamoeba histolytica into the portal circulation in amebiasis; amebic abscesses may also affect the lungs, brain, and spleen.Bartholin abscess acute infection of a Bartholin gland with symptoms including pain, swelling, cellulitis of the vulva, and dyspareunia. Treatment is incision and drainage of the abscess. Cultures should be obtained to rule out infections by Neisseria gonorrhoeae or Chlamydia.Bezold's abscess one deep in the neck resulting from a complication of acute mastoiditis.brain abscess see brain abscess.Brodie's abscess a circumscribed abscess in bone, caused by hematogenous infection, that becomes a chronic nidus of infection.cold abscess one of slow development and with little inflammation, usually tuberculous.diffuse abscess an uncircumscribed abscess whose pus is diffused in the surrounding tissues.gas abscess one containing gas, caused by gas-forming bacteria such as Clostridium perfringens. Called also Welch's abscess.miliary abscess one composed of numerous small collections of pus.pancreatic abscess one that occurs as a complication of acute pancreatitis or postoperative pancreatitis caused by secondary bacterial contamination.perianal abscess one beneath the skin of the anus and the anal canal.periapical abscess inflammation with pus in the tissues surrounding the apex of a tooth.periodontal abscess a localized collection of pus in the periodontal tissue.peritonsillar abscess a localized accumulation of pus in the peritonsillar tissue subsequent to suppurative inflammation of the tonsil; called also quinsy.phlegmonous abscess one associated with acute inflammation of the subcutaneous connective tissue.stitch abscess one developed about a stitch or suture.thecal abscess one in the sheath of a tendon.wandering abscess one that burrows into tissues and finally points at a distance from the site of origin.Welch's abscess gas abscess.

brain

 [brān] that part of the central nervous system contained within the cranium, comprising the forebrain (prosencephalon), midbrain (mesencephalon), and hindbrain (rhombencephalon); it develops from the embryonic neural tube. The brain is a mass of soft, spongy, pinkish gray nerve tissue that weighs about 1.2 kg in a human being. It is connected at its base with the spinal cord, which is also part of the central nervous system. Called also encephalon. (See also color plates.)
The brain is made up of billions of nerve cells, intricately connected with each other. It contains centers" >nerve centers (groups of neurons and their connections) which control many involuntary functions, such as circulation, temperature regulation, and respiration, and interpret sensory impressions received from the eyes, ears, and other sense organs. Consciousness, emotion, thought, and reasoning are functions of the brain. It also contains centers or areas for associative memory which allow for recording, recalling, and making use of past experiences.Cerebrum. The largest and main portion of the brain, the cerebrum is made up of an outer coating, or cortex" >cerebral cortex, consisting of matter" >gray matter, several cell layers deep, covering the hemispheres" >cerebral hemispheres. The cortex is the thinking and reasoning brain, the intellect, as well as the part of the brain that receives information from the senses and directs the conscious movements of the body.
In appearance the cortex is rather like a relief map, with one very deep valley (longitudinal fissure) dividing it lengthwise into symmetrical halves, and each of the halves again divided by two major valleys and many shallower folds. The longitudinal fissure runs from the brow to the back of the head, and deep within it is a bed of matted white fibers, the corpus callosum, which connects the left and right hemispheres" >cerebral hemispheres.
The major folds of the cortex divide each hemisphere into four sections or lobes: the lobe" >occipital lobe at the back of the skull, the lobe" >parietal lobe at the side, the lobe" >frontal lobe at the forehead, and the lobe" >temporal lobe at the temple. The Senses. The major senses of vision" >vision and hearing" >hearing have been well mapped in the cortex; the center for vision is at the back, in the occipital lobe, and the center for hearing is at the side, in the temporal lobe. Two other areas have been carefully explored, the sensory and motor areas for the body, which parallel each other along the fissure of Rolando. In the sensory strip are the brain cells that register all sensations, and in the motor strip are the nerves that control the voluntary muscles. In both, the parts of the body are represented in an orderly way.
It is in the sensory areas of the brain that all perception takes place. Here sweet and sour, hot and cold, and the form of an object held in the hand are recognized. Here are sorted out the sizes, colors, depth, and space relationships of what the eye sees, and the timbre, pitch, intensity, and harmony of what the ear hears. The significance of these perceptions is interpreted in the cortex and other parts of the brain. A face is not merely seen; it is recognized as familiar or interesting or attractive. Remembering takes place at the same time as perception, so that other faces seen in the past, or experiences linked to that face are called up. Emotions may also be stirred. For this type of association the cortex draws on other parts of the brain by way of the communicating network of nerves. Memory. In the temporal lobe, near the auditory area, is a center for memory" >memory. This center appears to be a storehouse where memories are filed. When this area alone is stimulated, a particular event, a piece of music, or an experience long forgotten or deeply buried is brought to the individual's mind, complete in every detail. This is a very mechanical type of memory; when the stimulation is removed the memory ends. When it is applied again, the memory begins again, not where it left off, but from the beginning. Brainstem. This is the stemlike portion of the brain connecting the cerebral hemispheres with the spinal cord, and comprising midbrain, pons, and medulla oblongata. Some consider it to include the diencephalon. Thalamus. This organ lies beneath the cortex, deep within the cerebral hemispheres. It is a relay station for body sensations, and integrates these sensations on their way to the cortex. The thalamus is an organ of crude consciousness and of sensations of rough contact and extreme temperatures, either hot or cold. It is principally here that pain is felt. In the thalamus, responses are of the all-or-nothing sort; even mild stimuli would be felt as acutely painful if they were not graded and modified by the cortex.Hypothalamus. This organ lies below the thalamus, at the base of the cerebrum. It is small (no larger than a lump of sugar), but takes part in such vital activities as the ebb and flow of the body's fluids and the regulation of metabolism, blood sugar levels, and body temperature. It directs the body's many rhythms, including those of activity and rest, appetite and digestion, sexual desire, and menstrual and reproductive cycles. The hypothalamus is also the body's emotional brain. It is the integrating center of the autonomic nervous system, with its sympathetic and parasympathetic branches, and is located close to the pituitary gland. Midbrain. Just below the thalamus is the short narrow pillar of the midbrain. This contains a center for visual reflexes, such as moving the head and eyes, as well as a sound-activated center, obsolete in humans, for pricking up the ears. Medulla Oblongata. Below the midbrain is the medulla oblongata, the continuation upward of the spinal cord. In the medulla, the great trunk nerves, both motor and sensory, cross over, left to right and right to left, producing the puzzling phenomenon by which the left cerebral hemisphere controls the right half of the body, while the right hemisphere controls the left half of the body. This portion of the brain also contains the centers that activate the heart, blood vessels, and respiratory system. Cerebellum. The cerebellum (Latin for “little brain”) is attached to the back of the brainstem, under the curve of the cerebrum. It is connected, by way of the midbrain, with the motor area of the cortex and with the spinal cord, as well as with the semicircular canals, the organs of balance. The function of the cerebellum is apparently to blend and coordinate motion of the various muscles involved in voluntary movements. It does not direct these movements; that is the function of the cortex. The cortex, however, operates in terms of movements, not of muscles. As a conscious function the cortex may, for example, direct the arm to pick up a glass of water; the cerebellum, which operates entirely below the level of consciousness, then translates this instruction into detailed actions by the 32 different muscles in the hand, plus several more in the arm and shoulder. When the cerebellum is injured, the patient's movements are jerky and uncoordinated.Cranial Nerves. These are twelve nerves that arise within the skull. All but the olfactory nerve emerge from the brainstem. Most, with the important exception of the vagus nerve, serve the head and neck. See also cranial nerves.Protection of the Brain. The brain is protected by the bony skull and by three layers of membranes, the meninges. Between the middle and inner layer is a space filled with cerebrospinal fluid, which serves as a shock absorber. The same system of membranes and fluid protects the spinal cord. The brain is protected from harmful substances in the bloodstream by a barrier called the blood-brain barrier, which keeps some of the substances out of the brain entirely and delays the entry of others for hours or even days after they have penetrated the rest of the body. Projection areas of the brain.brain abscess a localized suppurative lesion within the intracranial cavity; most cases are secondary to middle ear infections. Other causes include compound fracture of the skull with contamination of brain tissue, sinusitis, and infections of the face, lung or heart. Symptoms include fever, malaise, irritability, severe headache, convulsions, vomiting, and other signs of intracranial hypertension. Treatment consists of surgical removal of the infected area and administration of antibiotics.brain death the irreversible cessation of all brain activity for an appropriate observation period, at least 24 hours, so that cardiopulmonary functions must be artificially maintained. A presidential commission in the USA accepted criteria for such a diagnosis, including cessation of all brain functions, including cerebral functions and brainstem (reflex) functions; irreversibility of the cessation; establishment of the cause of coma, sufficient to explain the loss of brain function; exclusion of possibility of recovery of brain function; and persistence of the cessation for an appropriate period of observation or trial of therapy. Complicating conditions must also be excluded. Called also irreversible coma.brain scanning a nuclear medicine procedure for the detection of brain tumors, areas of stroke syndrome, abscesses, hematomas, and other intracranial lesions. A radiopharmaceutical, such as 99mTc-pertechnetate, is injected intravenously and is carried to the brain, where it localizes around any lesion that alters the blood-brain barrier. A scintillation camera makes an image of the distribution of radioactivity in which a lesion appears as a region of increased activity. tomography" >Computed tomography brain scanning is an alternative procedure, which is more effective than radionuclide scans for the detection of some lesions.brain tumor a neoplasm of the intracranial portion of the central nervous system. Any abnormal growth within the skull creates a special problem because it is in a confined space and will press on normal brain tissue and interfere with the functions of the body controlled by the affected parts. This is true whether the tumor itself is benign or malignant. Fortunately, the functions of certain areas of the brain are well known, and a disturbance of some specific function guides the clinician to the affected area. If diagnosed early, a benign tumor often can be removed surgically with a good chance of recovery. Malignant tumors are more difficult to remove. The causes of brain tumors are not known. They are not common, but they can occur at any age and in any part of the brain. Some originate in the brain itself, while others metastasize from a tumor in another part of the body.
The symptoms of brain tumor vary and depend on the location and size of the tumor. Headache together with nausea is sometimes the first sign. The headache can be generalized or localized in one part of the head, and the pain is usually intense. Vomiting can be significant if it is sudden and without nausea. Disturbances of vision, loss of coordination in movement, weakness, and stiffness on one side of the body are also possible symptoms. Loss of sight, hearing, taste, or smell may result from brain tumor. A tumor can also cause a distortion of any of these senses, such as seeing flashes at the sides of the field of vision, or smelling odors or hearing sounds that do not exist. It can affect the ability to speak clearly or to understand the speech of others. Varying degrees of weakness or paralysis in the arms or legs may appear. A tumor may cause convulsions. Changes in personality or mental ability are rare in cases of brain tumor. When such changes occur they may take the form of lapses of memory or absentmindedness, mental sluggishness, or loss of initiative.wet brain brain edema.

brain abscess

A focal collection of pus within the cerebral or cerebellar parenchyma, arising from direct spread of an adjacent infection (e.g., meningitis, sinusitis, mastoiditis) or from haematogenous spread from elsewhere.
Frequency
1–2% of all intracranial space occupying lesions in developed countries and 8% in developing countries. Solitary abscesses are typically temporal or cerebellar, and caused by direct spread from adjacent foci (paranasal sinus); multiple abscesses typically develop at the junction of the white and grey matter of regions supplied by the middle cerebral artery.
 
Clinical findings
Classically develops in three phases
(1) Invasion—headache, nausea;
(2) Latent—transient paroxysmal headaches, malaise;
(3) Apparent—localising signs, CSF pressure effects.
Diagnosis
History, CT scan; high index of suspicion in patients with unexpected symptoms and signs if they have received antibiotics.
Mortality
High.

brain abscess

Neurology A localized intracranial infection filled with pus due to a bacterial infection

brain abscess

The serious consequence of access of pus-forming organisms to the inner parts of the brain, by spread through the bone following middle ear infection (OTITIS MEDIA and MASTOIDITIS) or severe sinusitis, by spread by the blood, or as a result of a penetrating injury of the brain by an infected object or missile.