Brain abscess

General information

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 brain substance), subdural (located under the dura mater), and epidural (localized above the dura mater). The main routes of infection into the cranial cavity are hematogenous, open penetrating craniocerebral trauma, purulent-inflammatory processes in the sinuses, middle, and inner ear, and wound infection after neurosurgical interventions.

Reasons

Streptococci predominate among the isolated causative agents of hematogenous brain abscesses. Hematogenic and otogenic abscesses are characterized by Enterobacteriaceae (including Proteus vulgaris). In open penetrating craniocerebral trauma in the pathogenesis of brain abscess prevails Staphylococcus aureus, less often Enterobacteriaceae.

In various immunodeficiency states (immunosuppressive therapy after organ and tissue transplantation, HIV infection), Aspergillus fumigatus is isolated from a culture of brain abscess contents. However, it is often impossible to identify the infectious agent in the contents of a brain abscess, as in 25-30% of cases, cultures of abscess contents are sterile. The disease is provoked by the following pathologic conditions:

• Inflammatory processes in the lungs. The most common causes of hematogenous brain abscesses are bronchiectasis, pleural empyema, chronic pneumonia, and lung abscesses. A bacterial embolus becomes a fragment of an infected thrombus, which enters the large circulation circle and is carried by the blood flow to the brain vessels, fixed in small vessels (precapillary, capillary, or arteriole). Chronic (or acute) bacterial endocarditis, GI infections, and sepsis may play a minor role in the pathogenesis of abscesses.
• Craniocerebral trauma. In the case of open penetrating traumatic brain injury, a brain abscess develops due to direct penetration of infection into the cranial cavity. In peacetime, the proportion of such abscesses is 15-20%. In combat conditions, it increases many times (mine blast wounds, gunshot wounds).
• ENT pathology. In purulent-inflammatory processes in the sinuses (sinusitis), middle and inner ear, there are two possible ways of infection spread: retrograde – through the sinuses of the dura mater and cerebral veins; and direct penetration of infection through the dura mater. In the second case, a delimited focus of inflammation is initially formed in the dura mater and then in the adjacent brain.
• Postoperative complications. Brain abscesses formed against the background of intracranial infectious complications after neurosurgical interventions (ventriculitis, meningitis) usually occur in severe, weakened patients.
• Other diseases. A minor role in the pathogenesis of hematogenous abscesses can play a chronic (or acute) bacterial endocarditis, GI infections, and sepsis.

Symptoms of a brain abscess.

No pathognomonic symptoms have been identified to date. The clinical picture of brain abscesses is similar to that of a brain neoplasm, with symptoms ranging from headache to severe generalized cerebral symptoms associated with depression of consciousness and marked 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 gradual increase in symptoms.

Diagnosis

A careful collection of anamnesis (presence of foci of purulent infection, acute infectious onset) is essential in diagnosing a brain abscess. An inflammatory process associated with the appearance and aggravation of neurological symptoms is a reason for additional neuroimaging examination.

The accuracy of diagnosis by CT scan 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 determines 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 focus’s contours become smooth and rounded. The contrast agent is distributed evenly around the entire periphery of the focus; the density of the central zone does not change. However, on repeat CT (after 30-40 minutes), contrast diffusion into the center of the capsule and its presence in the peripheral zone is determined, which is not typical for malignant neoplasms.

On a CT scan, an encapsulated brain abscess looks like a rounded volumetric mass with clear, even contours of increased density (fibrous capsule). In the center of the capsule, there is a zone of low density (pus), and a zone of edema is visible around the periphery. The injected contrast agent accumulates in the form of a ring (along the contour of the fibrous capsule) with a small adjacent zone of gliosis.

A contrast agent is not detected on repeat CT scans (after 30-40 minutes). When examining the CT scan results, anti-inflammatory drugs (corticosteroids, salicylates) significantly affect contrast accumulation in the encephalitic focus.

MRI of the brain is a more accurate method of diagnosis. When MRI is performed at the first stages of brain abscess formation (1-9 days), the encephalitic focus looks like hypointense on T1-weighted images and hyperintense on T2-weighted images. MRI at the late (capsulated) stage of brain abscess: on T1-weighted images, the abscess appears as a zone of reduced signal in the center and periphery (in the edema zone), and along the contour of the capsule, the signal is hyperintense. On T2-weighted images, the center of the abscess is iso- or hypointense, while in the peripheral zone (edema zone), it is hyperintense. The contour of the capsule is clearly outlined.

Treatment for a brain abscess

Abscesses causing brain dislocation and increased intracranial pressure, as well as those localized in the area of the ventricular system (pus entering the ventricular system is often fatal), are absolute indications for surgical intervention. Traumatic brain abscesses located in the area of the foreign body are also subject to surgical treatment, as this inflammatory process does not lend itself to conservative treatment. Despite the unfavorable prognosis, fungal abscesses are also an absolute indication for surgical intervention.

Brain abscesses in vital and deep structures (optic tubercle, brain stem, subcortical nuclei) are contraindications to surgical treatment. In such cases, a stereotactic method of treatment is possible: puncture of the brain abscess and its emptying, followed by washing of the cavity and administration of antibacterial drugs. It is possible to lavage the cavity both single and multiple times (through a catheter installed for several days).

Medical treatment

The aim of empirical (in the absence of culture or if the pathogen cannot be isolated) antibiotic therapy is to cover the broadest possible spectrum of pathogens. Recommended treatment programs:

• In brain abscesses without a traumatic brain injury or a history of neurosurgery, the following treatment algorithm is indicated: vancomycin, III generation cephalosporins, metronidazole. In case of posttraumatic brain abscess, metronidazole is replaced by rifampicin.
• In patients with HIV, the causative agent of brain abscess is most often Toxoplasma gondii, so empiric treatment of patients should include sulfadiazine with pyrimethamine.

After the pathogen is isolated from the culture, the treatment should be changed, considering the antibiogram. In the case of a sterile culture, empirical antibiotic therapy should be continued. The duration of intensive antibiotic therapy is at least six weeks, after which it is recommended to change to oral antibiotics and continue treatment for another six weeks.

Surgical treatment

The main surgical treatment methods for intracerebral abscesses are simple or inflow-outflow drainage. Their essence is the installation of a catheter into the abscess cavity, through which the evacuation of pus is carried out, followed by the introduction of antibacterial drugs. It is possible to install a second catheter with a smaller diameter (for several days), through which the infusion of a solution for lavage (most often, 0.9% sodium chloride solution) is carried out. Drainage of the abscess should be accompanied by antibiotic therapy (first empirical, then – taking into account the sensitivity to antibiotics of the isolated pathogen).

In the case of multiple brain abscesses, it is necessary first to drain the nidus, which is the most dangerous in terms of complications (breakthrough of pus into the ventricular system, brain dislocation) and the most significant in the clinical picture. In the case of empyema or subdural brain abscess, drainage is applied without using the inflow and outflow system.

All these treatment options are available in more than 90 hospitals worldwide (https://doctor.global/results/diseases/brain-abscess). For example, Brain abscess surgical treatment can be done in 12 clinics across India for an approximate price of 2.1 K (https://doctor.global/results/asia/india/all-cities/all-specializations/procedures/brain-abscess-surgical-treatment). 

Prognosis in brain abscess

In predicting brain abscesses, the ability to isolate the causative agent from the culture and determine its sensitivity to antibiotics is of great importance; only in this case is it possible to carry out adequate pathogenetic therapy. In addition, the outcome of the disease depends on the number of abscesses, the reactivity of the organism, and the adequacy and timeliness of treatment measures. The percentage of lethal outcomes in brain abscesses is 10%, disability – 50%. Almost one-third of surviving patients have epileptic syndrome as a consequence of the disease.

In subdural empyemas, the prognosis is less favorable due to the lack of borders of the purulent focus, which indicates a high virulence of the pathogen or the patient’s minimal resistance. Lethality in such cases is up to 50%. Fungal empyemas, in combination with immunodeficiency states in most cases (up to 95%), lead to a lethal outcome.

Epidural empyema and brain abscesses usually have favorable prognoses. Infection penetration through the intact dura mater is virtually impossible. Sanitation of the osteomyelitis focus eliminates epidural empyema. Timely and adequate treatment of primary purulent processes, as well as complete primary wound care in traumatic brain injury, can significantly reduce the possibility of brain abscess development.