8th August 2024

Infectious and inflammatory causes

When considering an infectious or inflammatory cause of a space-occupying lesion, it is essential to ascertain any risks for immunosuppression, recent travel history, and the patient’s social context. Presentation is classically with headache and fever, potentially in combination with cranial nerve signs, meningeal irritation, seizures, or change in mental state or conscious level.

Inflammatory causes may present insidiously without a pre-existing diagnosis, for example in neurological manifestations of systemic lupus erythematosus. They may result in a range of symptoms, ranging from subtle focal neurology to seizures and coma.

Important things to establish when considering a patient with a potential infectious or inflammatory brain lesion:

• Is there underlying immune suppression? HIV, diabetes, and end-stage renal disease receiving haemodialysis are all risk factors for brain abscess formation, and it is important to consider opportunistic pathogens such as Toxoplasma gondii, the risk of which is increased by a low CD4 count (<100). Some medications, especially immunomodulatory agents, have been associated with PML.
• Has there been recent operative management of the brain or head and neck, including dental procedures?
• Is there a recent history of sinusitis, otitis or dental infection? The majority of brain abscesses form by direct spread, and there are characteristic organisms for different sites of origin:

• Has the patient recently travelled to an area where certain parasites are endemic? Taenia solium, for example, is known to be endemic in many regions of Central and South America and is the causative agent for neurocysticercosis.
• Are there risk factors for TB?
• Is there a history suggestive of an underlying systemic disorder? A careful systems review and examination is essential, especially if considering vasculitis or granulomatous disease, or MS-related lesions.

Initial investigation is via CT brain imaging with contrast, although once again MRI with gadolinium contrast provides best resolution; these may demonstrate ring-enhancing lesions. Lumbar puncture is frequently contraindicated, and it may be that direct biopsy is most diagnostic. It is also essential to perform blood cultures, and HIV serology may be helpful.

If there is suspicion of a brain abscess, broad-spectrum antibiotic therapy with good aerobic and anaerobic cover should be instituted urgently – this may include vancomycin, ceftriaxone, or metronidazole. Once a causative organism or underlying condition is identified, targeted therapy should be initiated, though neurosurgical intervention may be required. Steroids should be given if there is vasogenic oedema and mass effect, and prophylactic anticonvulsant therapy may be indicated.