CHAPTER 23: INFECTIOUS DISEASES OF THE NERVOUS SYSTEM
Brain Abscess
Abscesses in the brain are usually caused by bacterial or fungal infection. Streptococcus equi is commonly found to be the etiology of brain abscesses. organism into the brain tissue. Generally, the source of the pathogen is a center of infection somewhere else in the body. This can be a local infection, such as a sinus infection, a guttural pouch infection or a tooth abscess, or it can be a distant infection such as heart or kidney infection. Septicemia may result in brain abscess if the blood-brain barrier is insufficient to keep the pathogen from entering the blood supply to the brain. Another rout of entry for pathogens is through a penetrating wound that connects the external environment with the cranial cavity. Brain abscesses can form as a result of the introduction of a Once the pyogenic agent has entered the brain it causes an reaction where the site of infection is surrounded by a connective tissue capsule. The pathogen interacts with immune cells to produce a collection of pus that begins to put pressure on the surrounding brain tissue as the pus accumulates. This increase in intracranial pressure causes dysfunction of the neurons of the brain surrounding the abscess and may cause ischemic necrosis of parts of the brain through the occlusion of the blood vessels supplying the brain. Brain abscesses are seen most commonly in mature individuals, especially those who have recently suffered from open head trauma or those individuals who are immunocompromised or on long-term corticosteroid therapy. Transmission is through blood. The clinical signs and symptoms seen with brain abscesses are dependent on the area(s) of the brain affected by the abscess mass. The most common part of the brain to be affected by abscess is the . In the case of cerebral abscess, the clinical signs and symptoms would be dementia, head pressing, circling, blindness, seizure and coma. In the case of cerebellar abscess there would be ataxia, dysmetria and head tilt or head tremor. Brain stem abscess may be seen as impairment of cranial nerve function, drowsiness, stupor or coma. Brain abscess may be accompanied by muscular stiffness of the neck, shoulders and back as well as by systemic signs of infection such as fever, anorexia and depression. In the horse brain abscess is diagnosed through clinical signs and symptoms as well as scan or MRI of the brain. It may be helpful to analyze a blood sample as well as a CSF sample to look for indications of infection, though the presence of pathogen or antibodies in either of these fluids is not a definite indicator of a brain abscess. To determine the etiological agent it is necessary to aspirate the abscess and perform a culture. In the case of bacterial brain infection treatment with IV antibiotics DMSO and NSAID’s is necessary. Drainage of the abscess site and the removal of foreign material form the brain may also be needed in some cases. Fungal brain infections are much harder to treat as most antifungal medications are neurotoxic.
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