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Brain abscess (brain abscess)

Brain abscess - in short

If pathogens get into the brain, they can infect it. This can lead to local inflammation. If this causes pus to collect in a kind of capsule and form a new cavity in the tissue in question, doctors speak of a brain abscess. The pathogens are mostly bacteria. In many cases, the germs migrate into the brain from another source of infection (ear, nose, tooth root). Sometimes the bacteria enter the brain through the blood. Open head injuries or operations on the brain are very rarely the cause. Initially, the symptoms are mostly unspecific and can manifest themselves in poor performance and concentration, as well as fever and stiff neck. Paralysis and epileptic seizures as well as increasing headaches can also occur. The diagnosis is confirmed by imaging procedures (cCT, cMRT) and the detection of pathogens in the blood and the focus of infection. The therapy is usually a combination of surgery and antibiotics.

What is a brain abscess?

An abscess in the brain is a localized (local) inflammatory reaction in the brain. The penetration of pathogens into the brain initially leads to inflammation in the tissue (focal encephalitis). As the inflammation progresses, it can lead to a collection of pus in a capsule formed by connective tissue. These newly created, pus-filled cavities are known as abscesses.

A brain abscess is rare, but it can be life-threatening. The number of new diseases occurring annually (incidence) is given as 0.3 to 1.3 cases per 100,000 people.

Brain Abscess - Where in the Brain Can Abscesses Occur?

In principle, an abscess (encapsulated collection of pus) can occur in any region of the brain. A distinction is made between an epidural, subdural and intracranial abscess, similar to bleeding, depending on where it occurs.

The epidural and subdural abscesses are rare; the pus-filled, encapsulated foci are usually found directly in the brain tissue (intracranial).

Epidural / subdural location

If the abscess lies over the hard meninges (dura mater), the doctor speaks of an epidural location (epi-Greek: on, over) - it is located between the hard meninges and the cranial bone.

If the abscess lies under the hard meninges, this is called the subdural position (sub-Latin: under, below) - it is located between the hard meninges and the soft meninges surrounding the brain (pia mater).

Intracranial position

The abscess is located in the matter of the brain

Causes and Risk Factors: What Causes Brain Abscesses?

A brain abscess occurs when pathogens enter the brain. This usually happens via the bloodstream or from nearby sources of infection (neighborhood processes). This means that there is inflammation elsewhere in the body, the pathogens are distributed further with the bloodstream and then penetrate the brain via the blood-brain barrier. The body's own defense cells and messenger substances now migrate to this site of infection and trigger inflammation. This can result in the formation of pus, which consists of, among other things, killed pathogens, immune cells and destroyed tissue cells. If the pus is enclosed in a kind of capsule in the relevant brain tissue, creating a new cavity, it is a brain abscess. In principle, it can form in any brain region.
Usually bacteria are the cause. Streptococci, Bacteroides and Pseudomonas species are among the most common pathogens. Streptococci are usually more likely to cause infections that affect the ear or upper respiratory tract. For example, sinusitis or otitis media. The other germs can also attack the respiratory tract. A bacterial inflammation in the area of ​​the tooth roots is also a possible place of origin.

Sometimes, however, fungi also trigger a brain abscess. Bacteria enter the brain even more rarely through a head injury (open head trauma) or as part of an operation.
Those who have a restricted immune system are at a higher risk of developing a brain abscess. The body's defenses are impaired, for example, if someone has to take medication that suppresses the immune system (immunosuppressants) or in people with AIDS.

Symptoms: what symptoms do brain abscesses cause?

The symptoms that indicate an abscess in the brain are rather unspecific: depending on which areas of the brain are affected, seizures (epileptic seizures) or sensory disorders can occur. Patients also report memory problems and poor concentration. Further neurological complaints such as paralysis on one side can occur in the course of the disease. Doctors speak of so-called "neurological focus symptoms".
Only later, when the abscess is larger and takes up more space, does it often lead to headaches, which last longer and increase. In addition, nausea and vomiting often occur. These complaints are known as "intracranial pressure signs".

Signs that are more likely to have inflammation include a fever or a stiff neck. Fever occurs in around 50 percent of those affected.

Important: A brain abscess is often triggered by a focus of inflammation outside the brain. If, for example, the above symptoms occur as a result of a sinus infection, otitis media or an inflamed tooth root, those affected should definitely seek clarification from a doctor. This is all the more true for people with a weakened immune system.
A pus focus in the brain can be life-threatening. Especially if the inflammation spreads or the abscess capsule presses on other brain regions.

Diagnosis: how are brain abscesses diagnosed?

The most important method for detecting a brain abscess is magnetic resonance tomography (MRT) of the skull. Abscesses can also be detected by computed tomography of the skull (cCT). If the findings are unclear, the administration of contrast medium into a vein can be useful for both imaging methods in order to enable a more precise differentiation of the findings. With this diagnostic method (cMRI) with contrast medium, the doctor can even draw conclusions about the stage of the abscess. However, in rare cases, an abscess is difficult to differentiate from a brain tumor, especially glioblastoma.

Blood tests are also carried out. Inflammation parameters, such as the so-called C-reactive protein (CRP), can be determined here. In 60 to 90 percent of the cases there is an increase in this value. In principle, the pathogen can also be detected. The pathogen is identified through a blood culture or a direct removal of abscess contents. However, both detection methods do not provide a 100% reliable result - neither if they are "positive" or "negative".

A thorough physical exam is also important. Here, attention is also paid to possible sources of infection, which means that additional examinations of the teeth, the throat and pharynx and the auditory canals are carried out. If no inflammatory process was found in the neighborhood, the diagnosis must also clarify sources of origin that are further away, such as the lungs, heart, skin or bones. The focus search (source of origin) should be carried out before a neurosurgical procedure so that the abscesses and, if necessary, the cause of the infection can be eliminated in one go. Risk factors for immunodeficiency, such as HIV (human immunodeficiency virus) or diabetes mellitus, must also be clarified.

Therapy: how are brain abscesses treated?

If it is clear that the abscess is a brain, the patient is usually given antibiotics over a period of several weeks (usually four to eight weeks) to kill the causative pathogen. Treatment is always initially carried out in the hospital (inpatient admission).
In addition, a neurosurgical intervention is usually carried out, most often the so-called abscess aspiration. The surgeon sucks off the pus through an opening in the skullcap. This procedure is also of particular importance if the attending physician has not been able to definitively clarify beforehand whether it is an abscess or a tumor.

Depending on where the inflammation is and how big the abscess is, sometimes a bigger procedure may be necessary.

In addition - depending on the need - drugs are used that help against seizures (anticonvulsants) or reduce excessive swelling in the brain (cerebral edema) (cortisone preparations).

Consulting expert:

Dr. med. Frank Huber is a specialist in neurology as well as a doctor in neurology and has the additional title of chiropractic. He is the chief physician of the Clinic for Neurology at the St. Marien Clinic in Amberg and also sits on the hospital's ethics committee. Huber is a member of the German Society for Neurology and regularly gives lectures in public, including on the subject of strokes.