Brain abscess is a limited accumulation of pus in the cranial cavity. There are three types of abscesses: intracerebral, subdural and epidural. The symptoms of a brain abscess depend on its location and size. They are not specific and can constitute a clinic of any volume education. A brain abscess is diagnosed according to CT or MRI of the brain. With small abscesses, they are subject to conservative treatment. Abscesses located near the ventricles of the brain, as well as causing a sharp rise in intracranial pressure, require surgical intervention, if it is impossible to perform it – stereotactic puncture of the abscess.
G06.0 Intracranial abscess and granuloma
A brain abscess is a limited accumulation of pus in the cranial cavity. There are three types of abscesses: intracerebral (accumulation of pus in the substance of the brain); subdural (located under the dura mater); epidural (localized above the dura mater). The main ways of infection penetration into the cranial cavity are: hematogenic; open penetrating traumatic brain injury; purulent-inflammatory processes in the paranasal sinuses, middle and inner ear; infection of the wound after neurosurgical interventions.
Among the isolated pathogens of hematogenic brain abscesses, streptococci predominate, often in association with bacteriotides (Bacteroides spp.). Enterobacteriaceae (including Proteus vulgaris) are characteristic of hematogenic and otogenic abscesses. In open penetrating traumatic brain injury, staphylococci (St. aureus) predominate in the pathogenesis of brain abscess, less often Enterobacteriaceae.
In various immunodeficiency conditions (immunosuppressive therapy after organ and tissue transplantation, HIV infection), Aspergillus fumigatus is isolated from the seeding of the contents of the brain abscess. However, it is often not possible to identify the causative agent of infection in the contents of the brain abscess, since in 25-30% of cases, the crops of the contents of the abscess turn out to be sterile. The disease is provoked by the following pathological conditions:
- Inflammatory processes in the lungs. Most often, the cause of the formation of hematogenous brain abscesses are bronchiectatic disease, pleural empyema, chronic pneumonia, lung abscess). A bacterial embolus becomes a fragment of an infected thrombus, which enters the large circulation and is carried by the blood flow into the vessels of the brain, where it is fixed in small vessels (precapillary, capillary or arteriole). Chronic (or acute) bacterial endocarditis, gastrointestinal infections and sepsis may play an insignificant role in the pathogenesis of abscesses.
- Traumatic brain injury. In the case of open penetrating TBI, a brain abscess develops due to direct infection into the cranial cavity. In peacetime, the proportion of such abscesses is 15-20%. In the conditions of hostilities, it increases significantly (mine-explosive wounds, gunshot wounds).
- ENT pathology. With purulent-inflammatory processes in the paranasal sinuses (sinusitis), middle and inner ear, two ways of spreading infection are possible: retrograde – through the sinuses of the dura mater and cerebral veins; and direct penetration of infection through the dura mater. In the second case, the delimited focus of inflammation is initially formed in the meninges, and then in the adjacent part of the brain.
- Postoperative complications. Brain abscesses formed against the background of intracranial infectious complications after neurosurgical interventions (ventriculitis, meningitis), occur, as a rule, in severe, weakened patients.
- Other diseases. Chronic (or acute) bacterial endocarditis, gastrointestinal infections and sepsis may play an insignificant role in the pathogenesis of hematogenic abscesses.
The formation of a brain abscess takes place in several stages.
- 1-3 days. A limited inflammation of the brain tissue develops – encephalitis (early cerebritis). At this stage, the inflammatory process is reversible. Its spontaneous resolution is possible, as well as under the influence of antibacterial therapy.
- 4-9 days. As a result of insufficient protective mechanisms or in the case of incorrect treatment, the inflammatory process progresses, in its center there is a cavity filled with pus, capable of increasing.
- 10-13 days. At this stage, a protective capsule of connective tissue is formed around the purulent focus, which prevents the spread of the purulent process.
- The third week. The capsule is finally compacted, a gliosis zone is formed around it. In the future, the development of the situation depends on the virulence of the flora, the reactivity of the body and the adequacy of therapeutic and diagnostic measures. It is possible to reverse the development of a brain abscess, but more often an increase in its internal volume or the formation of new foci of inflammation along the periphery of the capsule.
Symptoms of a brain abscess
To date, pathognomonic symptoms have not been identified. The clinical picture of brain abscesses is similar to the clinical picture of volumetric education, when clinical symptoms can range from headache to severe general cerebral symptoms associated with depression of consciousness and pronounced focal symptoms of brain damage.
In some cases, the first manifestation of the disease is an epileptiform seizure. Meningeal symptoms may be observed (with subdural processes, empyema). Epidural abscesses of the brain are often associated with osteomyelitis of the skull bones. There is a progressive increase in symptoms.
To diagnose a brain abscess, careful collection of anamnesis (the presence of foci of purulent infection, acute infectious onset) is of great importance. The presence of an inflammatory process associated with the appearance and aggravation of neurological symptoms is the basis for additional neuroimaging examination.
The accuracy of diagnosis by CT of the brain depends on the stage of abscess formation. In the early stages of the disease, diagnosis is difficult. At the stage of early encephalitis (1-3 days) CT detects a zone of reduced density of irregular shape. The injected contrast agent accumulates unevenly, mainly in the peripheral parts of the focus, less often in the center.
In the later stages of encephalitis, the contours of the focus acquire smooth rounded outlines. The contrast agent is distributed evenly throughout the periphery of the hearth; the density of the central zone of the hearth does not change. However, a repeated CT scan (after 30-40 minutes) determines the diffusion of contrast into the center of the capsule, as well as its presence in the peripheral zone, which is not typical for malignant neoplasms.
The encapsulated brain abscess on CT has the form of a rounded volumetric formation with clear, even contours of increased density (fibrous capsule). There is a zone of reduced density (pus) in the center of the capsule, an edema zone is visible along the periphery. The injected contrast agent accumulates in the form of a ring (along the contour of the fibrous capsule) with a small adjacent gliosis zone.
On a repeated CT scan (after 30-40 minutes), the contrast agent is not determined. When examining the results of computed tomography, it should be taken into account that anti-inflammatory drugs (glucocorticosteroids, salicylates) significantly affect the accumulation of contrast in the encephalitic focus.
MRI of the brain is a more accurate method of diagnosis. During MRI at the first stages of brain abscess formation (1-9 days), the encephalitic focus looks: hypointensive on T1-weighted images, hyperintensive on T2-weighted images. MRI at the late (encapsulated) stage of brain abscess: on T1-weighted images, the abscess looks like a zone of reduced signal in the center and on the periphery (in the edema zone), and along the contour of the capsule the signal is hyperintensive. In T2-weighted images, the abscess center is iso- or hypointensive, in the peripheral zone (edema zone) hyperintensive. The contour of the capsule is clearly outlined.
Differential diagnosis of brain abscess should be carried out with primary glial and metastatic tumors of the cerebral hemispheres. In case of doubts about the diagnosis, MH spectroscopy should be performed. In this case, differentiation will be based on the different content of amino acids and lactate in tumors and abscesses of the brain.
Other methods of diagnosis and differential diagnosis of brain abscess are uninformative. An increase in ESR, an increased content of C-reactive protein in the blood, leukocytosis, fever is a symptom complex of almost any inflammatory processes, including intracranial ones. Back-seeding of blood with brain abscesses is 80-90% sterile.
Treatment of brain abscess
At the encephalitic stage of the abscess (anamnesis – up to 2 weeks), as well as in the case of a small brain abscess (up to 3 cm in diameter), conservative treatment is recommended, which should be based on empirical antibacterial therapy. In some cases, stereotactic biopsy may be performed in order to finally verify the diagnosis and isolate the pathogen.
Abscesses that cause brain dislocation and increased intracranial pressure, as well as localized in the ventricular system area (pus entering the ventricular system often leads to fatal outcomes) are absolute indications for surgical intervention. Traumatic brain abscesses located in the area of a foreign body are also subject to surgical treatment, since this inflammatory process does not respond to conservative treatment. Despite the unfavorable prognosis, fungal abscesses are also an absolute indication for surgical intervention.
Contraindications to surgical treatment are brain abscesses located in vital and deep structures (visual tubercle, brain stem, subcortical nuclei). In such cases, it is possible to carry out a stereotactic method of treatment: puncture of the brain abscess and its emptying, followed by washing of the cavity and the introduction of antibacterial drugs. It is possible to wash the cavity both once and repeatedly (through a catheter installed for several days).
Severe somatic diseases are not an absolute contraindication to surgical treatment, since stereotactic surgery can also be performed under local anesthesia. An absolute contraindication to the operation can only be an extremely serious condition of the patient (terminal coma), since in such cases any surgical intervention is contraindicated.
The aim of empirical (in the absence of sowing or if it is impossible to isolate the pathogen) antibacterial therapy is to cover the maximum possible spectrum of pathogens. Recommended treatment programs:
- With a brain abscess without a TBI or a history of neurosurgery, the following treatment algorithm is shown: vancomycin; cephalosporins of the third generation (cefotaxime, ceftriaxone, cefixime); metronidazole. In the case of post-traumatic brain abscess, metronidazole is replaced with rifampicin.
- The causative agent of brain abscess in patients with immunodeficiency conditions (except HIV) is most often Cryptococcus neoformans, less often Candida spp or Aspergillius spp. Therefore, in these cases, amforeticin B or liposomal amforeticin B is prescribed. After the abscess disappears (according to neuroviualization studies), fluconazole is used for 10 weeks, subsequently the dose is halved and left as a maintenance.
- In patients with HIV, the causative agent of brain abscess is most often Toxoplasma gondii, therefore, empirical treatment of patients should include sulfadiazine with pyrimethamine.
After isolating the pathogen from the crop, the treatment must be changed, taking into account the antibioticogram. In the case of sterile seeding, empirical antibacterial therapy should be continued. The duration of intensive antibacterial therapy is at least 6 weeks, after that it is recommended to change antibiotics to oral and continue treatment for another 6 weeks.
The appointment of glucocorticoids is justified only in the case of adequate antibacterial therapy, since only with a positive prognosis, glucocorticoids can cause a decrease in the severity and reverse development of the capsule of a brain abscess. In other cases, their use may cause the spread of the inflammatory process beyond the primary focus.
The main methods of surgical treatment of intracerebral abscesses are simple or supply-flow drainage. Their essence lies in the installation of a catheter into the cavity of the abscess, through which the evacuation of pus is carried out, followed by the introduction of antibacterial drugs. It is possible to install a second catheter of a smaller diameter (for several days), through which an infusion of a solution for washing is carried out (most often, 0.9% sodium chloride solution). Drainage of the abscess must be accompanied by antibacterial therapy (first empirical, then taking into account the sensitivity to antibiotics of the isolated pathogen).
Stereotactic aspiration of abscess contents without drainage is an alternative method of surgical treatment of brain abscess. Its main advantages are lenient requirements for the qualification of medical staff (close attention and special knowledge are needed to control the functioning of the supply and exhaust system) and a lower risk of secondary infection. However, in 70% of the use of this method, there is a need for repeated aspiration.
In the case of multiple brain abscesses, it is necessary first of all to drain the focus, the most dangerous in terms of complications (breakthrough of pus into the ventricular system, dislocation of the brain), as well as the most significant in the clinical picture. In the case of empyema or subdural abscess of the brain, drainage is used without using the supply-flow system.
Prognosis for brain abscess
In predicting brain abscesses, the ability to isolate the pathogen from the crop and determine its sensitivity to antibiotics is of great importance, only in this case it is possible to conduct adequate pathogenetic therapy. In addition, the outcome of the disease depends on the number of abscesses, the reactivity of the body, the adequacy and timeliness of therapeutic measures. The percentage of deaths in brain abscesses is 10%, disability is 50%. In almost a third of the surviving patients, epileptic syndrome becomes a consequence of the disease.
With subdural empyema, the prognosis is less favorable due to the absence of the boundaries of the purulent focus, as this indicates a high virulence of the pathogen, or minimal resistance of the patient. The mortality rate in such cases is up to 50%. Fungal empyema in combination with immunodeficiency conditions in most cases (up to 95%) lead to death.
Epidural empyema and brain abscesses usually have a favorable prognosis. The penetration of infection through the intact dura mater is practically excluded. The rehabilitation of the osteomyelitic focus makes it possible to eliminate epidural empyema. Timely and adequate treatment of primary purulent processes, as well as full-fledged primary wound treatment during TBI, can significantly reduce the possibility of developing a brain abscess.