The common diseases affecting the central nervous system are meningitis, septic thrombophlebitis, subdural empyema (subdural abscess), extradural abscess and cranial osteomyelitis. A brain abscess forms when fungi, viruses, or bacteria reach your brain through a wound in your head or an infection somewhere else in your body. Heart and lung infections are among the most common causes of brain abscesses. However, brain abscesses can also begin from an ear or sinus infection, or even an abscessed tooth.
Brain abscess causes
- Extension of infection from chronic suppuration of the middle ear and mastoid (Otogenic).
- Extension of infection from paranasal sinuses (rhinogenic).
- Metastatic abscesses from lung abscess, empyema, and infective endocarditis (hematogenous). And Congenital cyanotic heart disease.
- Introduction of infection from outside, e.g., head injury.
In the tropics, the vast majority of cases developing into these diseases are secondary to ear or sinus diseases.
In the early stage, there is hyperemia and focal and generalized edema of the Brain. In the next stage foci of necrosis and suppuration form, which coalesce to form Abscess. The wall is made up of fibroblasts, microglia, and astrocytes. Due to an extension of infection, multiple abscesses may develop.
The common sites for otogenic abscesses are the ipsilateral temporal lobe or cerebellum; rarely they may be in the opposite occipital lobe. Rhinogenic abscesses are mainly frontal in location. Metastatic abscesses are mostly seen in the frontal lobe, and they are multiple. Hematogenous abscess from cardiac lesions is located mainly in the territory of the middle cerebral artery.
In more than 3/4th of the cases, the causative organisms are single, but in fourth multiple pathogens are seen. In otogenic and rhinogenic abscesses-streptococci, staphylococci, pneumococci, E.Coli, B.Proteus, and B pyocyaneus are common. In metastatic abscesses, staphylococci and Streptococcus viridans are the most common organisms, but anaerobes also may be seen. In congenital cyanotic heart disease, the microorganisms include Gram-negative bacilli, anaerobic streptococci, and H.influenzae.
Clinical presentation: The patient presents with generalized signs of infection, features of raised intracranial tension and focal neurological signs depending upon the location of the abscess.
Proper therapy of mastoiditis and sinusitis prevents the development of brain abscess. In subjects with cyanotic congenital heart disease, any neurological disorder should raise the suspicion of brain abscess, and early investigation and treatment should be instituted.