It can be said that the main and first symptom of intracranial infection of any cause and at any site is headache. 1. Meningitis. Including pathogenic infections such as septic bacteria, viruses, Mycobacterium tuberculosis, spirochetes, and fungi, headache is often a very prominent clinical manifestation of the patient, regardless of the pathogen causing meningitis. Headache caused by meningitis is mainly due to inflammatory invasion of meninges, occurrence of meningeal and brain tissue edema, inflammatory exudation, and increased intracranial pressure, which causes involvement headache; in addition, inflammatory exudates, pathogenic toxins and harmful substances produced during infection can cause headache due to intracranial vasodilatation, and direct stimulation of meninges themselves, secondary to tonic contraction of cervical muscles, which produces headache. The headache of meningitis is usually preceded by fever or occurs simultaneously with fever. The headache is most intense in the acute phase and in severe cases, manifesting as diffuse pain, which may be distending, throbbing, knocking, or tearing pain. Common clinical meningitis include acute septic meningitis, tuberculous meningitis, viral meningitis, and fungal meningitis. These diseases are dangerous and should be diagnosed early and treated promptly. 2. Arachnoiditis. This is a non-specific chronic inflammation of the arachnoid membrane caused by different etiologies, which usually occurs after acute or chronic meningitis, with diffuse or limited thickening of the arachnoid membrane and adhesions to the dura mater, soft meninges, brain tissue, and cranial nerves, also known as adhesive arachnoiditis. Due to the adhesion of nerves, blood vessels and meninges, or obstruction of cerebrospinal fluid circulation, the formation of obstructive hydrocephalus produces cranial hypertension, which in turn causes headache, mostly persistent chronic headache, which is aggravated when the intracranial pressure increases significantly, and may also be accompanied by nausea, vomiting and optic papilledema. Common types include extensive cerebral arachnoiditis and limited adhesive cerebral arachnoiditis. 3. Encephalitis. This is a frequently mentioned disease, which refers to inflammation caused by pathogens invading the brain parenchyma, often causing headaches. On the one hand, patients with encephalitis tend to have high fever, and cerebral blood flow increases during fever, and toxins from various pathogens stimulate blood vessels, causing diffuse dilation of intracranial blood vessels and vascular headaches; on the other hand, due to inflammation of the brain parenchyma, extensive brain tissue necrosis, softening, hemorrhage, swelling, intracranial pressure In addition, inflammation of brain parenchyma may spread to the meninges and produce reflex muscle contraction headache. Common encephalitis include bacterial encephalitis, viral encephalitis, fungal encephalitis, and parasitic encephalitis. Those with clear etiology include epidemic B encephalitis, forest encephalitis, and herpes simplex virus encephalitis. 4.Brain abscess. This is also a common cause of headache. In general, the pathogenic bacteria are staphylococcus, streptococcus, and diplococcus pneumoniae. Patients are mostly seen in adolescents and children; have symptoms of systemic infection such as chills, fever, increased white blood cell count and neutrophil ratio in blood; have severe headache, nausea, vomiting, optic papilledema and other manifestations of high cranial pressure; have neuropsychiatric symptoms such as hemiplegia, isotropic hemianopia, diplopia or hypotonia, ataxia, nystagmus or indifference to expression, memory loss, personality change; have a history of septic infection in the ear or other parts of the body History of purulent infection in the ear or other parts of the body; cranial X-ray, head CT or MRI can help the diagnosis of the disease. 5.Cerebral cysticercus. It is caused by pig tapeworm parasites in the brain. The eggs become six-hook larvae and burrow into the intestinal wall at the duodenum, and then evolve into cysticercus larvae, which can live in subcutaneous tissue, muscle, brain, heart, liver, lung and peritoneum, etc. Parasitism in the brain is called cerebral cysticercosis. The meninges are irritated and the arachnoid membrane is adhered to, thus stimulating and pulling the relevant nerve roots such as trigeminal nerve roots and cervical nerve roots. Diagnosis of this disease should be made with the help of positive blood and cerebrospinal fluid cysticercosis immunoassay (indirect hemagglutination, complement binding and enzyme-linked immunosorbent assay, etc.), cranial CT scan showing multiple small circular hypodense areas or small annular hyperdense areas, and fecal examination1 to find nematode eggs or pregnancy nodules pieces, which can help to confirm the clinical diagnosis. 6. Cerebral syphilis. The incidence of syphilis has increased in recent years, when pale dense spirochetes invade the soft meninges and brain parenchyma and lead to persistent infection is called cerebral syphilis or neurosyphilis, which can be manifested as different degrees of meningitis or reactive skull base arachnoiditis, and can be clinically classified as syphilitic meningitis, meningeal vascular syphilis, paralytic dementia, etc. Headache is its common symptom, especially the two types of syphilitic meningitis and meningeal vascular syphilis, which have obvious headache with vomiting and meningeal irritation signs, their headache is more intense, fluctuating distension, and may be accompanied by hemiparesis, hemiplegia (such as numbness, hyperalgesia, etc.), isotropic hemianopia, aphasia, or limited epilepsy, hydrocephalus. The diagnosis of this disease depends mainly on cerebrospinal fluid examination and positive serum and cerebrospinal fluid dense spirochete antigens in addition to clinical manifestations. Treatmentl: Medical advice should be obeyed and penicillin or erythromycin should be used to treat the disease until the prescribed course of treatment.