Brain Abscess

GENERAL PRINCIPLES

• Brain abscess in the immunocompetent host is usually bacterial in origin and the result of spread from a contiguous focus (mastoiditis, sinusitis, dental infection), septic emboli from endocarditis, bacteremia, trauma, or surgery.

• Infection is often polymicrobial, with viridans streptococci, S. aureus, and anaerobes being the most common pathogens; staphylococci and gram-negative bacilli predominate after surgery. Streptococcus anginosus is especially associated with abscess formation. In immunocompromised hosts, etiologies include invasive fungal infection, Nocardia, and TB; in HIV-infected patients, toxoplasmosis is a leading consideration.⁸

DIAGNOSIS

• Diagnosis is radiographic, with ring-enhancing lesions seen on MRI or CT scan.

• A microbiologic etiology should be determined by aspiration, biopsy, or surgery.

TREATMENT

• Empiric therapy should cover the most likely pathogens based on the primary infection site. A third- generation cephalosporin (ceftriaxone) combined with metronidazole and vancomycin is started in immunocompetent hosts and narrowed when culture data are available. Use cefepime or ceftazidime instead of ceftriaxone after neurosurgical procedures or head trauma.

• Neurosurgical consultation is imperative for drainage; cultures must be sent to enable pathogen-

directed therapy, as a prolonged course of antibiotic therapy is often needed.

• Follow-up imaging to assess improvement determines length of therapy.

Neurocysticercosis

• Neurocysticercosis should be suspected in patients from Mexico and Central and South America who present with seizures.

• Ingested eggs of Taenia solium differentiate into larvae, which disseminate to brain and other tissues and form cysts.

• Brain imaging reveals characteristic multiple unilocular cysts that eventually calcify.

• Treatment consists of anticonvulsants, albendazole or praziquantel, with concomitant glucocorticoids to decrease the inflammatory response, and/or surgery.⁹