I. Otogenic and nasogenic brain abscess: Otogenic brain abscess is the most common, accounting for about 2/3 of brain abscesses. it is secondary to chronic suppurative otitis media and mastoiditis. Infection occurs by two routes: (1) inflammation erodes the tympanic ventricle cover and wall and spreads to the brain through the dural vessels and conduction vessels, often in the temporal lobe and rarely in the parietal or occipital lobe; (2) inflammation invades the cerebellum via the top of the mastoid tubercle, the posterior lateral wall of the rock bone, through the dura or lateral sinus vessels. Nasogenic brain abscesses are caused by the invasion of purulent infection from the adjacent paranasal sinuses into the skull. For example, in frontal sinusitis, septal sinusitis, maxillary sinusitis or pterygoid sinusitis, the infection spreads intracranially through the conduction vessels at the base of the skull, and the abscesses mostly occur in the anterior part of the frontal lobe or at the base.
The formation of brain abscess is a continuous process and can be divided into three phases.
(i) Acute meningitis and encephalitis phase: After the septic bacteria invade the brain parenchyma, the patient shows obvious systemic infection reaction and pathological changes of acute restricted meningitis and encephalitis. The central part of the encephalitis gradually softened and necrotic, with many small liquefied areas and edema of the surrounding brain tissue. There may be a meningeal inflammatory reaction when the lesion site is superficial.
(b) Suppurative phase: softening foci of encephalitis are necrotic, liquefied, fused to form abscesses, and gradually increase in size. If the fused small abscess cavities are spaced, they become multi-room brain abscesses with surrounding brain tissue edema. The patient’s systemic signs of infection improve and stabilize.
(iii) Envelope formation period: Generally, after 1 to 2 weeks, the granulation tissue at the periphery of the abscess is initially formed by the proliferation of fibrous tissue and glial cells, and the abscess envelope is completely formed in 3 to 4 weeks or longer. The speed of formation of the envelope is related to the type and virulence of the causative organism and the resistance of the body and its response to antimicrobial therapy.
When the resistance of the organism is weak, the cryptogenic bacteria in the brain parenchyma gradually develop into brain abscess. Cryptogenic brain abscess is essentially an occult type of hematogenic brain abscess.
The principles of management of brain abscess are: before the abscess is completely confined, active anti-inflammatory and cerebral edema control treatment should be carried out. After abscess formation, surgery is the only effective treatment method.
(i) Anti-infection: the corresponding bacterial-sensitive antimicrobial agents should be selected for the causative organisms of different kinds of brain abscesses. For those whose primary foci are not yet detected by bacterial culture or negative culture, antimicrobial agents with broader antibacterial spectrum and easy to pass the blood-brain barrier should be selected according to the condition. Penicillin, chloramphenicol and gentamicin are commonly used.
(B) Lowering cranial pressure treatment: for the increase of intracranial pressure caused by cerebral edema, mannitol and other hypertonic solutions are often used for rapid, intravenous drip. Hormones should be used with caution to avoid weakening the body’s immune system.
(iii) Surgery
1.Puncture and pus aspiration: this method is simple and easy to perform, with little damage to brain tissue. It is suitable for those who have large abscess, thin abscess wall, abscess deep in or located in the important functional area of brain, infants, old people or physically weak people who can hardly tolerate surgery, as well as those whose condition is critical and whose abscess is punctured and extracted as an emergency treatment measure.
2.Continuous drainage by catheter: In order to avoid repeated puncture or spread of inflammation, a soft rubber tube with an inner diameter of 3~4mm is left in the abscess cavity when the abscess is punctured for the first time, and the abscess is pumped, flushed and injected with antimicrobial agent or contrast agent at regular intervals to understand the reduction of the abscess cavity, and the tube is usually left for 7~10 days. At present, CT stereotactic puncture and pus extraction or catheter drainage technology has its superiority.
3.Excision and drainage: for traumatic brain abscess, wound infection, difficulty in abscess removal or retention of foreign body in the skull, foreign body is often removed at the same time as drainage of abscess.
4.Abscess excision: the most effective surgical method. It is suitable for surgical resection of abscesses with intact envelope formation and located in non-important functional areas; multiroom or multiple brain abscesses; traumatic brain abscesses containing foreign bodies or broken bone fragments. The operation method of brain abscess resection is similar to that of general brain tumor resection, and it is necessary to avoid abscess rupture and reduce pus contamination as much as possible during the operation.
The formation of brain abscess is a continuous process and can be divided into three stages.
(i) Acute meningitis and encephalitis stage: After the septic bacteria invade the brain parenchyma, the patient shows obvious systemic infection reaction and pathological changes of acute restricted meningitis and encephalitis. The central part of the encephalitis gradually softened and necrotic, with many small liquefied areas and edema of the surrounding brain tissue. There may be a meningeal inflammatory reaction when the lesion site is superficial.
(b) Suppurative phase: The softening foci of encephalitis are necrotic, liquefied, fused to form abscesses, and gradually increase in size. If the fused small abscess cavities are spaced, they become multi-room brain abscesses with surrounding brain tissue edema. The patient’s systemic signs of infection improve and stabilize.
(iii) Envelope formation period: Generally, after 1 to 2 weeks, the granulation tissue at the periphery of the abscess is initially formed by the proliferation of fibrous tissue and glial cells, and the abscess envelope is completely formed in 3 to 4 weeks or longer. The speed of formation of the envelope is related to the type and virulence of the causative organism and the resistance of the body and its response to antimicrobial therapy.
When the resistance of the organism is weak, the cryptogenic bacteria in the brain parenchyma gradually develop into brain abscess. Cryptogenic brain abscess is essentially an occult type of hematogenic brain abscess.