A brain abscess is a collection of bacterial infection within the brain. An abscess is usually walled off and separated from the surrounding tissues. It begins by a small amount of bacteria and grows into a larger collection. It can be caused by an infection that began somewhere else in the body, such as the nose, ears, or sinuses, and spread to the brain. It can spread by way of the blood or through the bone. Brain abscesses can also be caused by a penetrating trauma that leaves a source of infection, or can be a complication after surgery.
There are about 1500-2500 cases in the U.S. annually. It occurs in males more frequently than in females. Risk factors that may predispose an individual to a brain abscess are any pulmonary abnormalities, bacterial endocarditis, head trauma with penetration, chronic sinus infections, chronic middle ear infections, and AIDS. A brain abscess can also be a complication of any untreated bacterial infections in the head, such as strep throat, sinus infections, and ear infections as mentioned above. They cannot be caused by a cold or a virus. The most common bacteria found in brain abscesses is a bacteria called streptococcus. Under the microscope it appears as chains of round bacterial cells.
Symptoms are usually related to increased pressure within the brain due to a rapidly growing mass. The patient can experience headaches, nausea or vomiting, drowsiness, inattention, or confusion. They can even exhibit seizures or weakness/paralysis of the arms or legs. The abscess can be found on a CT or MRI. Blood work and further studies may be done to search for a source of infection.
It is treated with intravenous antibiotics given through a “PICC” line, which is a line going into the vein usually in the arm. Intravenous (meaning through the vein) antibiotics are typically given for 6-8 weeks and then switched to medicines by mouth. Head scans are done every two weeks to see if the infection is growing or shrinking. Steroids may also be given to decrease the swelling of the surrounding brain tissue.
If the abscess if larger than 3cm, if the location is particularly concerning, or if the patient is not doing well, then surgical drainage of the abscess is needed in addition to the medication. Drainage can also help identify the bacteria causing the abscess. If the abscess continues to be resistant to the medicines or it is found to be fungal, then a surgical excision is done. This involves actually removing the abscess from the brain.
The outcome depends on location in the brain and severity of infection. After a course of medicines or surgery the patient improves. If the brain abscess was severe the patient may have neurologic deficits that continue. But for uncomplicated brain abscesses that are treated, the outcome is usually good.
Lindsey Parker PA-C and Justin F. Fraser M.D.
McPhee, S.; Papadakis, M.; Tierny, L. (2008). Current Medical Diagnosis and Treatment. 47th edition. McGraw Hill-Medical.