Brain and spinal cord abscesses: causes and pathogenesis

Causes of abscesses of the brain and spinal cord

It is not always possible to isolate the causative agent of the infection from the contents of the brain abscess. In about 25% of cases, the contents of the abscess are sterile. Among the isolated pathogens of hematogenous abscesses, streptococci (aerobic and anaerobic) predominate, often in association with bacteroides (Bacteroides spp.). With hematogenous abscesses, due to the lung abscess, Enterobacteriaceae (in particular, Proteus vulgaris) is often found. The same pathogens are characteristic for otogenic abscesses.

With penetrating craniocerebral trauma, the pathogenesis of brain abscesses is dominated by staphylococci (primarily St. Aureus). Also found causative agents of the genus Enterobacteriaceae.

In patients with various immunodeficiency states (reception of immunosuppressors after organ transplantation, HIV infection) among pathogens, Aspergillus fumigatus predominates.

[1], [2], [3], [4], [5], [6]

Pathogenesis of abscesses of the brain and spinal cord

The main ways of penetration of the infection into the cavity of the skull and the spinal canal are as follows:

• hematogenous;
• open penetrating craniocerebral trauma or spinal trauma;
• purulent-inflammatory processes in the paranasal sinuses;
• infection of the wound after neurosurgical interventions.

Conditions for the formation of an abscess in the case of infection are the nature of the pathogen (virulence of the pathogen) and a decrease in the immunity of the patient. In developed countries hematogenous abscesses are the most typical. In developing countries, brain abscesses are most often formed against the background of chronic inflammatory processes in adjacent tissues, which is associated with inadequate treatment of the latter. In approximately 25% of cases, it is not possible to establish a source that led to the formation of brain abscess.

With hematogenous abscesses, the source of bacterial emboli is most often inflammatory processes in the lungs (lung abscess, bronchiectatic disease, pleural empyema, chronic pneumonia). Bacterial embolus is a fragment of an infected thrombus from the vessel at the periphery of the inflammatory focus. The thrombus enters the large circle of blood circulation and is brought into the blood vessels of the brain, where it is fixed in vessels of small diameter (arteriol, precapillary or capillary). Less important in the pathogenesis of abscesses are acute bacterial endocarditis, chronic bacterial endocarditis, sepsis and gastrointestinal infections.

The cause of brain abscess in children often become "blue" heart defects, primarily the tetralogy of Fallot, as well as pulmonary arterio-venous shunts (50% of them are associated with Rundu-Osler syndrome - multiple hereditary telangiectasias). The risk of developing an abscess of the brain in these patients is about 6%.

With purulent inflammatory processes in the paranasal sinuses, the middle and inner ear, the spread of the infection can occur either retrograde through the sinuses of the dura mater and the cerebral veins, or with the direct penetration of the infection through the dura mater (at first a delimited focus of inflammation in the meninges and then - in the contiguous division of the brain). Less common are odontogenic abscesses.

With penetrating and open craniocerebral trauma, brain abscesses can develop as a result of direct infection into the cranial cavity. In peacetime, the proportion of such abscesses does not exceed 15%. In the conditions of combat operations, it significantly increases (gunshot and mine-explosive wounds).

Brain abscesses can also form against the background of intracranial infectious complications after neurosurgical interventions (meningitis, ventriculitis). As a rule, they arise in severe, weakened patients.

Pathomorphology

The formation of the abscess of the brain goes through several stages. Initially, a limited inflammation of the brain tissue - encephalitis ("early cerebrate", according to modern English-language terminology) develops. The duration of this stage is up to 3 days. At this stage, the inflammatory process is reversible and can be resolved either spontaneously or against antibiotic therapy. In case of insufficiency of protective mechanisms and in case of inadequate treatment the inflammatory process progresses, and by the 4-9th day in its center there is a cavity filled with pus that can increase. By the 10th-13th day around the purulent foci, a protective connective tissue capsule begins to form, preventing further spread of the purulent process. At the beginning of the 3rd week the capsule becomes denser, around it a gliosis zone is formed. The further course of cerebral abscess is due to the virulence of the flora, the reactivity of the organism and the adequacy of therapeutic and diagnostic measures. Sometimes an abscess undergoes reverse development, but more often, either an increase in its internal volume or the formation of new inflammatory foci along the periphery of the capsule.

Brain abscesses can be single and multiple.

Abscesses in subdural or epidural space are formed less often than intracerebral. Such abscesses are usually caused by the local spread of infection from adjacent purulent foci in the paranasal sinuses, and also occur with open craniocerebral trauma, osteomyelitis of the bones of the skull. As with intracerebral abscesses, a dense connective tissue capsule can form in the case of subdural and epidural abscesses. If this does not occur, a diffuse purulent inflammation develops in the corresponding space. Such a process, as in general surgery, is called subdural or epidural empyema.