Brain Abscess: When the Scalpel Is the Best Antibiotic

“Ubi pus, ibi evacua,” Latin aphorism meaning “where [there is] pus, evacuate it.

Hippocrates, father of Western Medicine, 460 BCE

“Nonoperative strategy was associated with twice the risks of mortality and rupture, and one-third of patients required subsequent neurosurgery. These results support recommendations for neurosurgical drainage of brain abscess.” 

Emilie Marie Eriksen, et al., “Nonoperative Versus Neurosurgical Treatment of Brain Abscess…,” Clinical Infectious Diseases, February 15, 2026

About five decades ago, one of my mentors introduced me to what he called “The Five Rules of Internal Medicine.” Rule 4 was: “Keep your patients out of the hands of surgeons at all costs.”

Such playful disdain of surgeons by an internist reflected the sometimes competitive relationship between the two specialties. That sometimes competitive relationship has now evaporated due, in large part, to in the unequivocal evidence showing that using the scalpel is sometimes the only successful way to treat certain conditions, including some infections.

Recently, a Danish study demonstrated the critical role neurosurgical intervention (incision and drainage) plays in the treatment of a brain abscess, a life-threatening infection. That study prompted me to write this week’s post.

What is a brain abscess? Brain (cerebral) abscesses are pus-filled swellings in the brain. They usually occur when bacteria or fungi enter the brain tissue after an infection or severe brain injury. They are caused by inflammation and collection of infected material from local sources (ear, dental, paranasal sinuses, mastoid air cells), or from remote infections in the lung, heart (endocarditis), kidney, etc. They may also be introduced into the brain through a skull fracture or surgical procedure. In young children, congenital heart disease can be a risk factor. Although brain abscesses can occur at any age, they are most common in the third decade of life.

Brain abscesses are not common; in the U.S., an estimated 1,500 to 2,000 cases happen each year. They are, however, regarded as a medical emergency.

Brain swelling caused by the abscess can disrupt the blood and oxygen supply to the brain. There is also the risk of the abscess rupturing. If left untreated, a brain abscess can cause permanent brain damage or death.

Pathogens: The microbiology is usually bacterial, including a variety of gram-negative and gram-positive bacteria, such as, Staphylococcus aureus, and anaerobes, like Streptococcus intermedius, Bacteroides, Prevotella, and Fusobacterium. Less common etiologies are fungi and parasites.

Brain abscesses can originate locally or spread from other parts of the body. It is therefore important to look for and determine the primary lesion as failure to treat the primary source will result in relapsing infection.

Symptoms: Symptoms of a brain abscess are present in about two-thirds of patients for 2 weeks or less and largely depend on the size and location of the space-occupying lesions. (Hall, W., Mefin, F., 2024, Brain Abscess, StatPearls Publishing). They include:

• Headache

• Change in mental status (confusion, irritability)

• Fever

• Seizures

• Changes in vision

• Problems with nerve function, such as muscle weakness or paralysis

• Slurred speech

Diagnosis: The diagnosis of brain abscess is strongly considered by findings on a CT or MRI scan of the head. If an abscess is found, a procedure known as a CT-guided aspiration may be used to remove a sample of pus for testing (staining for microorganisms and culture).

Treatment: Treatment usually includes antimicrobials (antibiotics or antifungals) and surgery. Treatment with antimicrobials usually begins before a diagnosis is confirmed. (Cultures of blood and of abscess material with antibiotic susceptibility testing are key in establishing an etiology and guiding therapy.)

Surgery involves either draining the pus through a hole in the skull (simple aspiration) or opening the skull and removing the abscess entirely (craniotomy). With modern treatment, including rapid diagnosis, appropriate antimicrobials, and surgical incision and drainage, the mortality from a brain abscess can be as low as 5-10%.

Key role of surgical intervention: For years there has been debate about whether brain abscesses can be treated with antimicrobial agents alone, without surgical drainage. That debate appears to have now come to end.

Recently, Danish researchers published the results of a study that strongly supports neurosurgical drainage of brain abscess. (Eriksen, E., et al., “Nonoperative Versus Neurosurgical Treatment of Brain Abscess: An Emulated Trial Nested Within a Nationwide, Population-Based Cohort,” Clinical Infectious Diseases, February 15, 2026). The study was comprised of 558 Danish adults diagnosed with brain abscesses. Analyses of treatment strategy showed that a nonoperative approach was associated with a statistically significant higher mortality and other unfavorable outcomes compared with those who underwent surgery. The researchers concluded, “These results support recommendation for neurosurgical drainage of brain abscess.”

Why are abscesses so difficult to cure with antimicrobials alone? Brain abscesses aren’t unique in their need for surgical intervention for a cure. Virtually all organs in the human body (skin, lungs, liver, kidneys, abdomen, uterus, etc.) are susceptible to abscess formation if microbes gain access to the tissue. And abscesses, in general, are difficult to cure with antibiotics alone for several biological and physical features of the abscess environment, such as, poor drug penetration, altered microbial physiology and poor penetration of immune cells into the core of abscesses.

Abscesses form a walled-off cavity containing pus (dead neutrophils, tissue debris, and proteins). The surrounding tissue develops a fibrous capsule, and because antibiotics reach tissues through the bloodstream, very little antibiotic actually reaches the center of an abscess. Also, the internal environment of pus can inactivate or reduce the activity of certain antibiotics. The abscess capsule isolates the infection from further immune clearance by neutrophils and antibodies. Hence, Hippocrates and classic surgical teaching had it right: Ubi pus, ibi evacua.

Postscript: times change, rules change.  I often used “The Five Rules of Internal Medicine” when I taught medical students. I even added five more of my own. (Peterson, P., 2013, Get Inside Your Doctor’s Head: 10 Commonsense Rules for Better Decisions about Medical Care, Johns Hopkins University Press). But internal medicine has changed dramatically during the course of my career. Some internists now practice in subspecialties in which they perform invasive procedures, such as biopsies and the insertion of various devices. Therefore, my mentor’s Rule 4 needed to be modified. It now reads: “Don’t agree to an invasive procedure without understanding why it’s needed—and without getting a second opinion.” And, as the title of my book suggests, always use common sense.