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REVIEW ARTICLE
Year : 2015  |  Volume : 63  |  Issue : 3  |  Page : 329-337

Brain abscess: Heuristics, principles, pathobiology, practice


1 Department of Anatomy, King Edward Memorial Hospital and Seth Gordhandas Sunderdas Medical College, Parel, Mumbai, Maharashtra, India
2 Department of Neurosurgery, King Edward Memorial Hospital and Seth Gordhandas Sunderdas Medical College, Parel, Mumbai, Maharashtra, India

Date of Web Publication5-Jun-2015

Correspondence Address:
Atul Goel
Department of Neurosurgery, King Edward VII Memorial Hospital, Parel, Mumbai - 400 012, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0028-3886.158192

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 » Abstract 

Brain abscess is an uncommon but a compelling reality in neurosurgical practice. Its focal, local, and systemic manifestations conceal its infective and obsessive nature. There are many a lesson that a brain abscess, as a bio-phenomenon, offers to the medical fraternity in general and the neurosurgeons, in particular. From Skt. puyati = to stink, comes the word "pus," meaning something foul, putrid, or rotten. From ab = away, and cedre = to go, comes the term "abscess" which is but nature's ingenious way of creating a fluid-filled cavity that will eventually rupture to an exterior to get rid of the non-self contents and proceed to healing. A brain abscess is special in the sense that it is, in general, more solid than fluid for reasons the human body and brain know best.


Keywords: Brain abscess; immunity; pathophysiology


How to cite this article:
Kothari M, Goel A, Muzumdar D. Brain abscess: Heuristics, principles, pathobiology, practice. Neurol India 2015;63:329-37

How to cite this URL:
Kothari M, Goel A, Muzumdar D. Brain abscess: Heuristics, principles, pathobiology, practice. Neurol India [serial online] 2015 [cited 2022 Dec 8];63:329-37. Available from: https://www.neurologyindia.com/text.asp?2015/63/3/329/158192



 » Heuristics Top


The appellation 'heuristic' (from Gk. Heureka/eureka, meaning 'I have found, serving to find out') implies a state conducive to understanding, explanation, or discovery. [1] Heuristics (in line with statistics, genetics and mechanics) is scientific temper that urges you to draw lessons from a natural phenomenon. The outstanding heuristic aspect, inter alia, of brain abscess is its ability to be "a cogent clarifier of the confused concept of immunity." [2] Brain abscess allows Brain to be read as 'Balanced Reactivity and Immunity Noticeable,' for its acknowledged rarity in the brain illustrates "immunity," and the clinical and pathological features of the fait accompli brain abscess reveal body's reactivity at its wisest. [2]

The very etymology [3] of the term immunity comes to our rescue. Im = not and munis = service, connotes freedom from work/duty/service, a state of aristocratic passivity towards a potentially conflictual situation. An average adult human generally lives at peace - symbiotically - with its microbial load of over 2 kg, the microbes outnumbering the human cell population tenfold. [4] It pays to bear in mind an aphorism enunciated by a text on internal medicine. Friendship between microbes and man is the rule and enmity an exception. This microbial blanket of life covering our skin and mucosae is the human body's 'surfinsic/surferior' milieu, [5] endowed soon after birth, and symbiotically coexisting with each one of us unto the grave. This is immunity being innately wise nonreactivity. [6] As and when the tissues have to deal with a microbial pathogen, the body exhibits the reactivity, in the form of inflammation, pus, abscess, and so on. The very finely tuned balance of immunity-nonreactivity is an animal body's license to survive, being a part of vis medicatrix naturae "(the healing power of nature)," [7] that using immunity-nonreactivity assures the integrity of the body, through health and disease, including trauma. The body's reactive repertoire [6] deals with the "nonself" in a prototypic way-recognize, react, reject, repair, and restore to status quo ante as best as possible.

The vector-assembly to achieve this constitutes' cellulohumoral reactivity insuring selfsame totality' or CHRIST for short. [2] Little wonder that processes as diverse as microbial infection, wound-healing, graft rejection or the so-called autoimmune phenomena are mediated by what we call, for want of any kinder term, inflammation. Inflammation, a gift from CHRIST, is animal body's greatest invention and your only license to survive the rough and tumble of life, manage severe infections, heal massive traumatic/operative wounds, and peremptorily throw away well-intended but nonself grafts.

Let us now picturize how abscess-n-pus, the two powerful arms of vis medicatrix naturae work. [7] CHRIST detects a splinter, a modicum of microbes, a bit of dead tissue, and sets into motion, cellulo-humoro-vascular reaction to occasion the classical Celsusian signs of inflammation namely calor, rubor, tumor, dolor, and the galenical functio laesa. If the inflammatory cellulitis cannot dispose off the non-self focus, CHRIST sets about throwing a fibrous barricade-the wall of the upcoming abscess. CHRIST knows that the only way to discharge the non-self focus to the exterior is to spawn a fluid-filled cavity, under tension, by, if need be, lyzing the person's own tissues. To make the saga complete, it pays to study the typical composition of pus: [7] "A liquid inflammation product made up of cells (leucocytes) and a thin fluid called liquor puris." [7] The brain, in its innate wisdom, largely denies itself the hydrodynamic option of a fluid-filled tense cavity, making the abscess-focus more solid than fluid for the brain knows that any such venture could direct the abscess to burst into a ventricle (intraventricular rupture of brain abscess [IVROBA]) with disastrous consequences.

Immunity makes brain's inflammation and abscessing uncommon. [8],[9] Reactivity assures a sequence of events that creates pathology that makes the patient ill, alerts the clinician, and rewards the operator.


 » Principles Top


There is little that can be called original since a sharp flint opened an abscess, and some horse hair threaded through the first thorn needle sewed up a wound. Yet it all goes on, bit by bit, and the wheel of progress turns just a little in any man's lifetime.

-Sir Harold Gillies and Ralph Millard

  • A brain abscess is an ordinary pathology in an extraordinary location. A brain abscess like abscesses anywhere else begs obeyance to an aphorism of John Hilton: Whenever/wherever there is pus, let it out
  • The ordinariness of abscessing and its demand for drainage turn extraordinary because of the abscess's location - in the brain, superficial or deep, in areas eloquent or noneloquent, and so on. The path to the site can be treacherous and hence the need for skill and experience of a high order, backed fully by state-of-the-art diagnostic and operative technology
  • It is not too uncommon experience that a brain abscess resolves itself in-situ without operative intervention but under assistance from drug therapy. This is where brain's immunity and reactivity overrule Hilton's aphorism, by not insisting on an outlet to the exterior, and yet offering complete healing
  • The systemic features - fever, leukocytosis, tachycardia - may be beguilingly absent. The chief reason is that the abscessogenic pathology sees to it that the process does not spill over into neuraqua (cerebrospinal fluid [CSF]), and hence not into general circulation. [10] This trick of nature explains why neuraqual (CSF) examination is more often unrewarding in the diagnosis of brain abscess
  • The above disadvantage inherent in the absence of systemic features of toxicity is more than offset by the rapidity with which a brain abscess grows - in hours/days/weeks - to occasion symptoms and signs of a rapidly growing intracranial mass. The patient's brain literally urges the clinician to take note. Time is of essence. If you as a clinician were to sleep over the issue, the patient may never wake up. Yoshikawa and Goodman [11] sum up this drama by picturizing brain abscess whose seeming benignancy belies "the ominous and precarious nature of intracranial mass dynamics"
  • Subdural empyema, comprising 13-23% of localized intracranial infections traceable to paranasal sinusitis and otogenic foci, presents a glaring systemic contrast: Apart from signs of expanding intracranial mass, the patient is manifestly ill, toxic, with high fever and leukocytosis. Speedy location, timely drainage, if need be through a skull flap, is rewarding
  • Guided by the wisdom of innate immunity, the reactivity of tissues that spawn a brain abscess is not very keen to liquefy the contents of the abscess. Towards this end, the blood vessels surrounding the abscess wall [12] activate their fibroblasts to spawn collagen (collagenization) that permeates the abscess [13] to give it the characteristic of a brain tumor, both density-wise and image-wise. Thus, a brain abscess is a pyoma rather than a pyocoele [2]
  • While a brain pyoma radiologically (and clinically) mimics a cytoma (tumor primary/secondary), the two differ in the former being avascular, [13],[14] a fact that explains the absence of systemic features such as pyrexia and leucocytosis, and the local unhelpful features of neuraqua (CSF)
  • The sharp contrast between the commonality of metastatic brain tumors - "by far the most common intracranial tumors" [15] - and the uncommonality, bordering on rarity, [2],[16] of brain abscesses in the midst of pyemias and septicemias unfolds the fact that the blood-brain-barrier, better called NEAT/NEST (Neuraqua Endothelial Audited/Selective Transport), [2],[10] is easily pervious to circulating tumor cells but stoically impervious to circulating microbes. The commonness of tuberculosis (TB)-spine and the uncommonness of the TB of the spinal cord is verifiable pathologic testimony to the immunity that spinal neuraxis exhibits against the next-door mycobacterial pathogen. In case the microbes jump the barrier, the neuraxial blood vessels so rigidly isolate them that they stay away from neuraqua. Further, the vessels collagenize the microbes to bury them, nay, even calcify them as in tuberculomas
  • Whereas the abscess itself gets "fibrosed" [17] by an input of collagen, the abscess wall gets no tether on the neuraxial tissue offering thus a clear plane [18] of cleavage that allows the abscess to be excised en masse. Nowhere else in the human body is such an operative privilege available vis-a-vis an abscess.


The readily available plane of cleavage raises the issue - is excision of an abscess preferable to its aspiration? If the aspiration is resorted to, the neuraxial tissue has the burden of dissolving the abscess wall before status quo ante is restored. The abscess wall, however inflamed-n-purulent, comprises all self and is, therefore, capable of being gradually resolved to almost total attrition by CHRIST. Several reports have advocated excision of the abscess as the procedure of choice as it is followed by lower incidence of recurrence, shorter hospital stay, and less "fibrosis" and seizures.

  • All brain abscesses-single/multiple, bacterial/mycobacterial/fungal - pathogenetically behave in a prototypic manner, and yield rewardingly to drainage and/or ablation. Brain abscess is one area where the niceties and nuances of microbial isolation and antibiotic-sensitivity (or resistance) can be set aside, without much harm to the patient. [2]
  • Although brain abscess is as old as mankind, its recorded clinical history dates back to 1752 when Morand, [19] a French surgeon, successfully drained an ethmoidotemporal brain abscess. In 1891, a Turkish surgeon [20] successfully excised a brain abscess. In 1876, in England, Macewen diagnosed a case of brain abscess that proved to be so at postmortem for the family refused surgery. [21] By 1893, [22] Macewen had reported a highly successful operative series. It would seem that brain abscess obliged everyone who dared to tackle it scientifically, and thus paving the way for bolder neurosurgery to blossom into a full-fledged surgical discipline. King [23] introduced marsupialization of brain abscess in 1924, and Dandy [24] introduced aspiration in 1926. Sargent [25] suggested enucleation of an encapsulated brain abscess in 1928. In 1936, Vincent [26] popularized complete excision and proved its value. In 1971, Heineman et al. [27] were the first to report the successful medical management of a brain abscess
  • After the foregoing, much water has flown down the river, but as of 2008, there is not much change [2] in the abscess's behavior and therapeutic outcome, the results being essentially the same be it the preantibiotic era, [22] the antibiotic era, [28] and now, the era of declining efficiency of the antimicrobials.


One can generalize that morbidity/mortality, and safety/survival in the case of a brain abscess are not so much related to the offending microbe, or to the sophistication of management, as much as to the avoidance of delay in diagnosis and decompression - by aspiration and/or ablation.

Before we go on to pathology, a certain amplification of and clarity on terms will be helpful. While an abscess generally means a pyocele, Marcus Aurelius Severinus, [3] in 1632, used abscess or abscessus to connote a solid tumor or growth. Hence, when it comes to the brain abscess, the Severnian truth of the abscess being more a pyoma than a pyocele prevails. It needs to be realized that the oft-used term pyogenic abscess (to really mean abscess of nonfungal/nonmycobacterial origin) is a tautology that must be avoided.

The use of the term pyoma for a brain abscess evokes its inflammatory (and pyogenic) sense, as also its solid tumor nature, that when excised tantamounts to a pyomectomy. Further, its rapid clinical course allows it to be called a tachypyoma, a lesion whose expeditious drainage and/or excision allows tachyrecovery as well.

The hitherto confused issue of the very term "immunity" can be resolved by replacing it with the all-embracing term "integrity", the inspiration for the term and concept having come from Burnet's mini-classic integrity of the body. [29] Integrity is a field force that strives to retain-n-restore the wholeness or oneness of the animal body. It has two arms: (a) Immunity or non-reactivity that knowledgeably remains passive so as to excite no inflammation, etc., thus retaining body's integrity. (b) Munity or reactivity that reacts against anything that is nonself (infection, graft, wound) to give rise to inflammation, abscess, pus, and so on, till the non-self-focus is eliminated, and integrity restored.

The widely used term, "immunocompromised" merits elaboration. [5] If the intraneuraxial abscess, like infections elsewhere in the body, is more common in the so-called immunocompromised subjects, each such abscess cries from the rooftop that it is a seat of active, dynamic inflammation, and hence a focus, if at all, of hyperimmunity, better called hyperreactivity. Where exactly is the "compromise," and what is its nature?

What really happens is that the so-called immunosuppressants given to a human are in general anticytotics that compromise the integrity of the tissues, especially the epithelia and the mucosae. [5] This forces the innocent microbial commensals to be pushed deeper into the body where there is no escape but to occasion an abscess to eliminate these willy-nilly guests. So the right terms would be, (a) SICKness-Structural Integrity Compromised Kemically, and (b) nonopportunistic but opportunized [2] organisms. Summing up, one can say that the so-called immunocompromise is an iatrogenic SICKness that opportunizes hitherto friendly microbes into setting up reactive abscessive foci in the body.

Microbial menagerie

It is humbling and interesting to realize that from the Macewenean time until this moment, the exact identification of the microbes and the appropriate antibiotics have not been as life-saving as the promptness with which Hilton is obeyed - let the pus be out. Hence, the following listing is of more academic than practical interest, covered as the human body is by a blanket of microbes of the most diverse types. The ubiquity of microbes renders age-differences insignificant.

  • Bacteroides, peptostretococci, and streptococci are commonly isolated from brain abscesses of contiguous origin
  • Staphylococci, streptococci, Clostridia, and Enterobactericea are mostly identified in abscesses in patients with head-trauma, gunshot wounds, open depressed fractures, foreign body in the head wound, basal skull fractures with neuraqual (CSF) fistula, and prior neurosurgical procedures, including shunts
  • Peptostreptococci and streptococci (especially viridans and microaerophillics) are common in brain abscesses secondary to cyanotic heart diseases
  • Streptococci, staphylococcus (aureus), Pseudomonas and Bacteroides are culturable from brain abscesses secondary to pulmonary abscess, bronchiectasis, or empyema, and are located mostly in the middle cerebral artery distribution
  • Fungal infections, toxoplasma, streptococci, staphylococci, and Pseudomonas are the opportunized microbes that get converted by the so-called immunocompromise that encourages the formation of brain abscesses, so often multiple
  • It pays to bear in mind that anaerobes [30] dominate brain abscesses, that mixed infections are common, and that antibiosis must include, from the very start, adequate, and sustained dosage of metronidazole
  • Tuberculosis (TB) is endemic to developing countries, and so is tubercular brain abscess and tuberculomas. In our series of 715 cases, tubercular abscess outnumbered bacterial and fungal absesses, combined. The presence of prior or accompanying extracerebral TB is not obligatory. Tubercular abscess and tuberculoma can, however, be a squeal to TB meningitis.



 » Pathobiology Top


Pathology is the accomplished tragedy; physiology the basis on which our treatment rests.

-Edward Martin

Brain, "like nothing so much as a lump of porridge" is innately strong. [9] Direct injection of virulent bacteria into the brain of an animal seldom results in an abscess formation. In fact, this condition has been produced consistently only by injecting the culture medium along with the bacteria or by causing necrosis of tissue at the time the bacteria are inoculated. A leading reason for the above nonreactivity is that the whole neuraxis, during embryonic ontogenesis, 'escapes' tolerance in the thymus [31],[32] thus acquiring "immune privilege" connoting the faculty to ignore reactive (antigenic) stimulus. Immune privilege is clearly designed to dampen down inflammatory responses in certain vital organs. The same suppressive mechanism would apply equally to inflammation caused by an infectious or self-antigen. Neurons, like muscle cells, belong to the category of perennial/immortal/postmitotic cell populations wherein cell multiplication ceases soon after birth. The cells tend to be very large. Both nondivisibility and large size endow nonreactivity.
"In most instances of bacteremia or septicemia, the nervous system seems not to be infected… With respect to the formation of brain abscess, the resistance of cerebral tissue to infection is notable… The arachnoid membrane (in fulminant meningitis) tends to serve as an effective barrier to the spread of infection into the brain substance… Only rarely does acute bacterial meningitis result in a brain abscess." [9] The brain can wear an intimate garb loaded with virulent microbes and yet stay clear of them.

However, when a non-self-focus comprising a colony of microbes lodges within the neural tissue, threatening its integrity, the body's immunological reactive forces go into action to set up firstly inflammation, rightly eulogized by the Nobelist Florey [33] as "the backbone of pathology." If timely bodily or therapeutic assistance arrives, this stage of cerebritis gets resolved. However, the next step in the continuing dialogue between the microbial non-self-focus and the immune forces is the creation of a barricade all around to form the abscess wall that limits its spread on the one hand, and the lyzing of body cells into the abscess cavity to spawn a fluid-filled cavity on the other. Just as the solid fetus is delivered after its bag of water dilates the maternal passage, so does the fluid-filled abscess strives to find a path to the exterior, throw away the non-self-material, and then heal the gap left behind. This in the brain, or elsewhere, is a design to deliver to the "exterior" the non-self-focus. In the brain, this exterior is the fragile ventricle on one side, and the delicate cortex overlaid by the skull on the other. No wonder, immunity of the brain guides its immune forces to forge a pyoma rather than a pyocele.

The wall of the abscess, the so-called pyogenic membrane, is a throbbing and alive vital tissue, lined on the exterior by vessels and on the interior with the so-called pus cells, all comprising self. In the brain, or elsewhere, once the pus is drained out (carrying with it the 'non-self' focus), the walls of the membrane, being nothing but self-tissue, juxtapose themselves, weld with each other, heal the whole abscess wound, and so often, leave behind no telltale evidence. That is why success with the aspiration of brain abscess may match that obtained through its excision. Let it be realized that inflammation, pus and abscess are nature's greatest inventions designed to restore the integrity of the animal body. [6]

Brain abscess exhibits, when single/multiple, unilocular/multilocular, four stages, [34] and five zones. [30] Such an "idealized" [8] picture is not always available but does allow a working description of its evolution.

The four stages are early cerebritis (or cerebellitis), late cerebritis, early capsule, and late capsule, each discernible through imaging modalities. The five zones [18] are:

  • A well-formed necrotic center
  • A peripheral zone of inflammatory cells, macrophages, and fibroblasts
  • A dense collagenous capsule
  • A layer of neovascularity associated with continuing cerebritis; and
  • Reactive astrocytes, gliosis, and cerebral edema external to the capsule.


The denseness of the capsule is purposive. The final or capsule stage occurs from the day 10 onwards and is associated with a well-vascularized abscess wall, in effect sequestrating the lesion to protect the surrounding normal parenchyma from additional damage. [18] The plane of cleavage between zones four and five forms the bedrock of excisional ease and success. The evident peri-abscess cerebral edema plays a significant role in enhancing the plane of cleavage between the abscess wall and the surrounding neural tissue. Rich in reactivated astrocytes, the edematous fluid, limits the spread of infection. Periabscess edema can be friendly to the neuraxis and does not warrant the routine use of anti-edema measures.

A vascular explanation has been generally advanced that the capsule tends to be thicker on the side of the gray matter and relatively thin on the side of the white matter, because of the greater vascularity of the gray area. While this may well be true, sight should not be lost of the fact that an abscess guides itself in such a way that it chooses not to invade, or rupture into the neuronal layers of the cortex. The price that it exacts is that its thinness predisposes the abscess to advance towards and rupture into the ventricle.

When it comes to the brain, fungi [5] do not behave less decently. The tenacity of the wisdom of the fungally abscessing brain comes from a report on the "Improved survival in central nervous system aspergillosis: A series of immunocompromized children with leukemia undergoing stereotactic resection of aspergillomas." [35] The elaborate title tells a long story whose cardinal feature is that in each child and every abscess, successful image-guided resection of the lesion was possible. "Complete resection of the abscess yielded gross findings of a viscous fluid contained by a firm rubbery wall surrounded by soft capsule." [35]

The acknowledged low incidence of brain abscess, the world over, in the face of so much of head-trauma in the developed and developing world, and so much of septicemia and pyemia in both, allows one to declare brain abscesses as being very uncommon, if not rare. Its rarity can delude the clinician into missing it. Clinician, beware!
"The incidence of brain abscess has remained stable in the antibiotic era; nevertheless, it is generally regarded as a rare disease, with large autopsy series reporting an occurrence rate of 0.18-1.3%… a brain abscess remains a significant problem in the developing world, particularly in children living in poverty… with the male: female ratio being 2:1. In some series, brain abscess secondary to otitis media displays a bipolar age distribution, with two peaks, one in children and the other after 40 years. In contrast, a brain abscess secondary to paranasal sinus infection usually occur between 10 and 30 years of age." [8]

Congenital heart disease remains the most commonly identified cause of brain abscess in children. Due to the increase in the incidence of immune suppression in the pediatric population undergoing chemotherapy for cancer, or immunosupression for bone marrow transplantation, these children frequently have fungal infections in addition to severe systemic infections.

Differential diagnosis

Radiological features alone are inadequate to differentiate a brain abscess from inflammatory granuloma (tuberculoma), neurocysticercosis, toxoplasmosis, metastasis, glioma, resolving hematoma, infarct, hydatid cyst, lymphoma, and radionecrosis. However, fever, meningism, raised erythrocyte sedimentation rate (ESR), multilocularity, leptomeningeal or ependymal enhancement, reduction of ring enhancement in a delayed scan and finding of gas within the lesion may help in the diagnosis of an abscess. It is preferable to misdiagnose a brain abscess than to miss it.


 » Routes: Continuity, Contiguity, Circuitry, Crypticality Top


Direct, clear continuity between pathogen/s and parenchyma produces a poor ground for abscess formation. No wonder, despite their enormous numbers, head injuries and procedural/operative trauma remain immune to abscessing. Contiguity accounts for the largest number of brain abscesses as the brain is usually infected by paranasal sinuses and the commonly infected middle ear. The brain's infected neighbor decides which part it wants to form an abscess in. Otogenic brain abscesses are most commonly located in the temporal lobe or the cerebellum; conversely, 85-95% of cerebellar abscesses are associated with ear or mastoid infections. Usually, these lesions are solitary.

In an order of decreasing frequency, brain abscesses are otogenic, hemogenic, cyanogenic, and sinogenic. Cyanotic heart diseases presumably devitalize the neuroangiothelium rendering brain susceptible to abscessing.

The brain's circulatory oneness with the rest of the body renders it susceptible to abscess formation in pyemia, septicemia, fungemia, lung abscess, pelvic infections, and so on. The immunity-nonreactivity that the neuroangiothelium exhibits against widely circulating microbes accounts for the freedom that the neuraxis enjoys. In 15-20% of cases, the brain abscess is cryptic [36] - you can't guess the source. Presumably, the route is vascular, often from undetected periodontal sepsis.

Metastatic abscesses result from hematogenous dissemination of microorganisms from a remote site of infection. The three common causes are pulmonary, cardiac, and cryptogenic. These abscesses occur deep at the corticomedullary junction in the distribution of middle cerebral artery and have a left sided predilection.


 » Clinical Features - Cold Abscess and Hot Tumor Top


The clinical course of a patient with a brain abscess may range from indolent to fulminant; however, the duration of symptoms is 2 weeks or less in about 75% of patients. In most cases, the prominent clinical manifestations of brain abscess reflecting the expanding intracerebral manifestations are often nonspecific and depend on several variables (e.g., the virulence of the infecting organisms, the patient's immune status, the location of the abscess or abscesses, and the presence or absence of associated meningitis or ventricular rupture). Only a minority of patients displays the classic triad of fever, headache, and focal neurologic deficits.

A brain abscess exhibits focally a fast growing-pyoma (that starts showing off from the stage of cerebritis), a locale that is poor in reactivity (hence often sterile, uninformative neuraqua-CSF), and an unexplainable absence of systemic reactivity in terms of fever, leukocytosis, ESR, and C-reactive protein. Such a contrast may be present in as high as 50% of cases. However, all the symptoms-n-signs of a space occupying lesion abound.

Compared to a cytoma (brain tumor) that is tardy in its growth, a brain pyoma/mycoma marks the rapidity of its expansion in terms of days. Any delay may mean a disastrous coning or an IVROBA (intraventricular rupture of brain abscess).

One can thus sum up brain abscess's clinical picture as one of cold abscess or a hot (volcanic) tumor. It is like a fire in an oil well, and all that you can do, you must do at the earliest.

Multiple abscesses account for 5-50% of all brain abscesses, and are found more often in immunocompromised patients as compared to a solitary abscess. The frequency of intraventricular rupture is also more in these cases.

Certain important points need to be borne in mind whenever a pediatric brain abscess is encountered. The triad of fever, headache, and neurological deficit occurs in less than one-half of patients. The fever is frequently low grade, and the child often does not appear toxemic. In the neonate, a brain abscess is a potential cause of irritability, a bulging fontanelle, and a rapid increase in head circumference. Focal neurological signs are not always present. However, if symptomatic, neurological signs will vary with the abscess location.

We would do well to quote verbatim, the neurologist, Simon, [21] who succinctly summed up the clinical features of a brain abscess: 'Signs of infection may be minimal or absent. Almost half of the affected patients maintain a normal body temperature and fewer than one-third show a peripheral white cell count >11,000/cumm. Neck stiffness is rare in the absence of increased intracranial pressure.
"Otherwise, the presenting features resemble those of any expanding intracranial mass. A headache of recent onset is the most common symptom, representing distortion or irritation of pain-sensitive structures within the cranial vault, especially those of the great venous sinuses and the dura mater about the base of the brain. If the process continues untreated, isolated headache increases in severity and becomes accompanied by focal signs such as hemiparesis or aphasia, followed by obtundation and coma. The period of evolution may be as brief as hours or as long as many days to weeks with more indolent organisms. Seizures may occur with abscesses that involve the cortical gray matter."

The reader would do well to peruse the [Table 1],[Table 2],[Table 3],[Table 4] and [Table 5] that summarize our experience with brain abscesses numbering 715, over the period of 8 years (from 1998 to 2006).
Table 1: The inordinately high incidence of TB abscess reflects the Indian susceptibility. Despite rampant bacterial sepsis of the sinuses, ear and teeth, the incidence is assuringly low. The poor fungal rate reflects poor iatrogeny

Click here to view
Table 2: Of the 280 bacterial abscesses, 189 have been otogenic. The ear leads

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Table 3: The predominant involvement of the temporal lobe in bacterial abscess declares its otogenic origin

Click here to view
Table 4: The therapeutic outcome does not get sullied by the multiplicity of brain abscess

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Table 5: Both aspiration and ablation are helpful

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 » Investigations Top


It is possible and pertinent to divide investigations into two phases. The first phase is of-oma or a rapidly expanding intra-neuraxial mass, where time and the best imaging modality is of compelling essence. That done, the abscess gets aspirated and/or ablated, and phase two of investigations begins. This is (a) pus-oriented, entailing culture, and sensitivity studies, and (b) follow-up-oriented, needing serial images to see that the abscess ends up getting totally resolved. Routine counts and hemoglobin may help to assess the general health status of the patient.

Diffusion-weighted magnetic resonance imaging (MRI) is highly useful. Magnetic resonance spectroscopy can help to differentiate a brain abscess (pyoma) from a tumor (cytoma) by demonstrating amino acids within the contents of the abscess, a finding that is essentially diagnostic of the presence of activated polymorphonucleocytes, and thus of bacterial or less likely parasitic infection.


 » Treatment Top


Here's good advice for practice: Go into partnership with nature; she does more than half the work and asks none of the fee.

-Martin Fischer

Technicized High Element of Suspicion-Speedily Locate Adroitly Manage -AAAA-success-assuring triad

A global survey of the surgery of brain abscess, 1752-2008, would drive home the relevance of the above acronymic triad. THEOS (meaning religion) stands for Technicized High Element of Suspicion - the moment you suspect, go technically all hog-scans and co. till you hit a SLAM (meaning winning all tricks in the game) connoting Speedily Locate Adroitly Manage. The simple-looking neuraqual (CSF) examination fails to help for two reasons: It chooses to get unaffected, and a thoughtless tap could precipitate herniation. The Quartet of adroit management is antimicrobialize, aspirate, and/or ablate and over an extended time, antiepilepticize. It is advisable to administer anticonvulsant therapy for 2 years to all patients with cerebral abscess. Discontinuation of antiepileptic drugs can be considered when the patient is seizure free after surgery and EEG shows no epileptic activity. Needless to say, THEOS-SLAM-AAAA comprises "the basic principles of abscess management." [2],[36]

The First A, for want of any sensitivity-guidance has to be a strong cocktail led by penicillin, and fortified by others, including metranidazole. The Second A may entail repeated aspiration under image control. The Third A is capable of teaching a neurosurgeon that the oma-like abscess tends to be isolated from brain tissue and lends itself to ready enucleation. The Fourth A is a protracted must. The first three A's must be in hurried succession. The antimicrobial cocktail gets replaced by a specific one on identifying the visitor.
"Untreated brain abscesses can be fatal. Surgical excision provides the initial therapy as well as diagnosis of brain abscess." [37] The surgical success is underscored neurosurgically by the generalization that "the method of surgical treatment (aspiration and/or excision) is of less importance than adherence to the basic principles of surgical management" whereby brain abscess single/multiple, unilocular/multilocular offers an equal therapeutic reward.

Until recently, imaging innovations have served to facilitate the surety and the speed of diagnosis. Instrumental ingenuity, however, is now a ready and trustable hand-maiden to the surgeon in the operative room. Stereotaxy, navigation tools, intraoperative computed tomography scan/MRI, ultrasonography and so on have revolutionized the management of brain abscess, assuring both precision and promptness to whichever procedure is used.

Needless to say, the primary source of infection - local or systemic - must be attended to vigorously. Steroids and anti-inflammatory medication fall into the category of personal preferences of the attending neurosurgeon. They are not a must; they are sufficiently innocuous and so enjoy a place in the drug armamentarium.

After a historical and a global perusal on brain abscess, one arrives at a sense of humility and reverence. One recalls the Bard of Stratford-on-Avon, who poetized:

In nature's infinite book of secrecy/A little I can read.

-Antony and Cleopatra, 1, ii, line 11

 
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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]

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