Bacteria can spread to the brain within the circulation and settle within blood vessels, resulting in weakening of the wall, the formation of aneurysms, and rupture. This is particularly associated with bacterial endocarditis, and osteomyelitis.
This usually affects the extracranial vessels but may involve the arteries of the CNS. The infiltrate consists of lymphocytes and plasma cells and the intima and adventitia become thickened. The form of vasculitis within the meninges is referred to as Heubner's arteritis (Figure 16).
| Figure 16.|
Huebner's arteritis. This is a form of chronic vasculitis that occurs in Syphilis. The infiltrate is composed mainly of lymphocytes and plasma cells and results in thickening of the wall of the vessel.
This is the cause of Lyme disease and the organism is able to penetrate the blood-brain barrier at an early stage of the disease. The organism is carried by Deer Ticks.
A variety of viruses are associated with vasculitis, including human immunodeficiency virus (HIV), although the mechanism of action is uncertain and appears to be multifactorial. Polyarteritis nodosa is known to be associated with antibodies to hepatitis C and viral nucleic acids, but the role of these in the aetiology is uncertain.
A variety of fungi occasionally involve blood vessels, particularly in immunocompromised patients, although they show weak pathogenicity. The most common forms in the UK are Aspergillus and Candida. They may be the cause of haemorrhage.