Brain abscess: an abscess caused by a purulent bacterial infection located in the brain tissue. A small number of brain abscesses can also be caused by fungi and protozoa. Brain abscesses can develop at any age, with young adults being the most common. With the development of diagnostic and therapeutic techniques, the morbidity and mortality rate of the disease has decreased significantly. Etiology and pathology: Brain abscesses are generally secondary to purulent infections in the body and can be classified into the following five categories according to the source of bacteria: otogenic, nasogenic, hematogenic, traumatic, and cryptogenic brain abscesses. Otogenic can be secondary to chronic purulent otitis media and mastoiditis, mostly in the temporal lobe; nasogenic brain abscess is caused by the invasion of purulent infection in the adjacent paranasal sinuses into the skull; hematogenic brain abscess is mostly caused by purulent infection in other parts of the body, and the bacterial emboli are disseminated to the brain via arterial blood flow and form multiple brain abscesses; traumatic brain abscess is mostly secondary to open brain injury, especially in view of penetrating brain injury or incomplete debridement surgery. In traumatic brain abscesses, the pathogenic bacteria invade directly through the wound or foreign bodies or broken bone fragments enter the skull and form brain abscesses; cryptogenic is the gradual development of brain abscesses from hidden bacteria in the brain parenchyma when the primary foci of infection are not obvious or hidden and the body’s resistance is weak. The pathogens of brain abscess are mainly various septic bacteria, including streptococcus, staphylococcus, pneumococcus, Escherichia coli, Proteus mirabilis and Pseudomonas aeruginosa. Brain abscesses caused by fungi, mainly mycobacteria, are rare and are mainly seen in immunocompromised patients. Abscesses are mostly solitary and can also be multiple. Brain abscess formation can be divided into 4 stages: early encephalitis stage, late encephalitis stage, early envelope formation stage and late envelope formation stage. The process of abscess formation is related to the type and virulence of the pathogenic bacteria, the resistance of the body and the response to drug therapy. Abscesses generally form initially in 1-2 weeks and completely in more than 4-8 weeks. Clinical manifestations: Brain abscesses can be broadly categorized into five clinical types according to their clinical manifestations: acute fulminant, meningitis, latent, cerebral tumor, and mixed. Clinically, patients can present three major symptoms such as acute systemic infection symptoms, increased intracranial pressure and focal localization symptoms of the nervous system, and in severe cases, brain herniation formation and abscess rupture can occur. In the early stage, acute systemic infection symptoms, fever, headache, vomiting, neck resistance and meningeal irritation may occur, and in severe cases, acute intracranial hypertension, brain herniation and death may occur. Symptoms of intracranial hypertension can be manifested as headache, the location of which is related to the intracranial lesion, and jet vomiting with varying degrees of mental and consciousness disturbance. Focal signs may include central paralysis, aphasia, epilepsy, and ataxia. Brain herniation formation and abscess rupture are possible crises of abscess, which can worsen the condition and lead to high fever, coma, and even death. Lumbar puncture cerebrospinal fluid examination can be helpful for diagnosis: cerebrospinal fluid leukocytes can be mildly to moderately elevated, usually below 50-100×106/L, mainly neutrophils, and in a few cases of combined septic meningitis the cerebrospinal fluid leukocyte count can be more than several thousand, protein is also correspondingly increased, and sugar is reduced. Cranial X-ray can reveal inflammatory lesions of mastoid process, paranasal sinus and temporal bone rock. Brain CT is an important method to diagnose brain abscess. The typical CT presentation of brain abscess is a well-defined or indistinct hypodense foci with uniform ring enhancement around the abscess after intravenous contrast injection, and there may be hypodense edematous bands in the brain tissue near the abscess, and the ventricular system may be compressed and pushed. Magnetic resonance imaging (MRI) can show early lesions earlier than CT, is more sensitive than CT in showing early brain necrosis and edema, can distinguish between pus and edema strong, determine envelope formation, and enhanced MRI shows circumferential enhancement of the abscess wall. Diagnosis: The diagnosis of this disease is based on clinical features, epidemiological data, MRI and cerebrospinal fluid examination. The presence of primary septic infection, history of open craniocerebral injury, localizing symptoms of focal neurological damage with headache, vomiting, optic papillary edema or signs of meningeal irritation should be considered for the presence of brain abscess, and CT and MRI can accurately demonstrate multiple and multifocal brain abscesses and peri-abscess tissue. Differential diagnosis: Brain abscess needs to be differentiated from septic meningitis, brain tumor, epidural or subdural abscess and venous sinus thrombosis. 1.Purulent meningitis: especially otogenic meningitis. Rapid onset, severe headache, fever, obvious signs of meningeal irritation, but no focal neurological signs, significant elevation of cerebrospinal fluid leukocytes and protein, further imaging may also be performed to identify. 2. Metastatic tumor: Patients usually have no symptoms of primary infection foci, progress slowly, and the cerebrospinal fluid cell count is mostly normal. Head CT and MRI examination can show the characteristics of the lesion to help differentiate. 3.Epidural or subdural abscess: it exists in combination with brain abscess or can occur independently. Generally, simple epidural lacks the manifestations of increased intracranial pressure and focal neurological damage. Subdural abscesses are rapidly progressive, with marked impairment of consciousness and signs of meningeal irritation. Angiography may show the brain surface as an avascular area, and CT reveals low-density images of abscesses on the brain surface. Treatment: Before the abscess is completely confined, aggressive anti-inflammatory and cerebral edema control treatment should be administered. After abscess formation, surgery is the only effective treatment. Depending on the urgency of the disease, the clinicopathological stage, the site and scope of the abscess, and the response of the body, comprehensive treatment should be provided, including: general treatment, strengthening nutrition, paying attention to water-electrolyte balance and acid-base imbalance; reasonable application of antibacterial drugs that can cross the blood-brain barrier; patients with high intracranial pressure may be given dehydration and hormones to reduce inflammation; abscess formation may be treated with surgical puncture and pus aspiration, catheter drainage, and abscess removal if necessary. For patients with neurological deficits, rehabilitation treatment can be provided.