They are often associated with immune disorders such as HIV infection and diabetes 3).
Depending on the aggressiveness of the microorganism involved and on the patient's immunological condition, an infection may be extremely destructive and cause rapid clinical deterioration. The most common causative microorganisms identified are Streptococcus spp. and Staphylococcus spp 4).
Computed tomography scans show an irregular low-density lesion and, after contrast injection, observation of an enhanced-ring sign suggests the presence of a focal and/or cystic lesion, which is difficult to differentiate from other lesions. Magnetic resonance imaging is more sensitive and specific for the diagnosis. In the early phases of brain abscess development, an irregular, enhanced low signal suggests cerebritis. In the late stages, the vascularized capsule shows a ring-contrasted lesion. Using diffusion-weighted imaging, a restricted pattern can be observed. Spectroscopy can be useful for identifying a causative microorganism 5).
The best method of treatment is not yet defined. It can be managed by medical treatment alone, stereotactic aspiration of the pus and medical treatment, or microsurgical drainage surgical excision/drainage of the abscess.
Systemic antibiotic therapy is used for more than six weeks.
A microsurgical approach may be considered to be an important option for large abscesses that are multiloculated, close to the surface or contain thick fluid. Complete emptying of the purulent accumulation may diminish the required duration of antibiotic therapy 6).
Such lesions were invariably fatal before 1974, when the arrival of computed tomography and magnetic resonance imaging improved the prognosis.
Mortality was very high, and surgery would be prohibitive. The development of computed tomography and magnetic resonance imaging, improvements in surgical techniques and broad-spectrum antibiotics have improved the prognosis 7)
A 7-month-old baby girl presented with lethargy and poor oral feeding. She had the mild fever for 1 month. Brain computed tomography revealed the hypodense lesion in the pons. Brain magnetic resonance images (MRI) showed around 1.4-cm-sized rim-enhanced mass with perilesional edema and internal hemorrhage in the pons. The cerebral blood volume was increased in the rim-enhanced area. The provisional diagnosis was DIPG, but the mass did not show the expansile mass with encasement of the basilar artery on the ventral pons.
The biopsy was done via the floor of the fourth ventricle, and the pathologic findings showed the many inflammatory cells and CD68-immunopositive macrophage which were compatible with abscess. The antibiotics with ceftriaxone and metronidazole were administrated for 11 weeks, and the follow-up MRI showed the slightly small enhanced lesion without central necrotic area. Three years later, follow-up MRI revealed the encephalomalacic change and atrophy of the pons. She had the stable neurologic deficit of left facial palsy and right hemiparesis.
The biopsy could be necessary for pontine lesions without typical radiologic findings of DIPG 8).
A 59-year-old man with dental caries who presented with a 4-day history of progressive dizziness, double vision, gait ataxia, emesis, and left facial and body numbness. Fever, suboccipital headache, and difficulties in urinating and defecating were noted on admission. Acute brainstem infarction and suspected aspiration pneumonia were then diagnosed. Magnetic resonance spectroscopy and diffusion-weighted imaging demonstrated a solitary pontine abscess. The neurologic deficits continued improvement after he completed 8 weeks of intravenous antibiotics. The successful nonsurgical treatment of the brainstem abscess in this case was based on high clinical suspicion, early diagnosis, and early combination of corticosteroids and broad spectrum antibiotics 9).
A case of a 20-month-old child with a solitary medulla oblongata abscess. The abscess appeared to be in close proximity to the anterior medulla oblongata, but preoperative planning based on diffusion tensor imaging (DTI) tractography motivated us to try to remove this lesion through a midline suboccipital approach. The ventral medulla oblongata abscess was surgically removed via a telovelar approach. At the anterior wall of the 4th ventricle, a fenestration was made with pus release and evacuation of the cavity. The child was discharged 1 week later with an uneventful and full recovery.
Modern imaging modalities of the nervous system can be very helpful in preoperative planning. Functional visualization of the nervous system provided by modern imaging techniques, such as the DTI tractography, can alter the classic topographic concept of surgical approach. In the case presented, approaching an anterior medulla oblongata abscess based on DTI tractography data, through a suboccipital midline transventricular approach, proved to be an effective and safe technique 10).
A case of large brainstem abscess, treated successfully by surgical drainage after the failure of medical treatment. The patient had a large brainstem abscess extending from the midbrain down to the lower pons. She was in a poor neurological condition preoperatively, and was worsening despite intravenous antibiotics. The abscess was coming close to the surface in the lateral aspect of the mid-brain. The presumed source of infection was multiple dental abscesses. The brainstem abscess was approached by a subtemporal transzygomatic approach and drained completely after making an incision on the lateral surface of the midbrain. After the operation, the patient showed steady improvement. At six months after the surgery, the patient was fully conscious, talking fluently, and walking with the help of a walker. Her hemiparesis and co-ordination were improving. Surgical drainage of a brainstem abscess is indicated when medical therapy fails. Proper anatomical knowledge of the brain-stem and the selection of appropriate surgical approach is important for safe drainage of the abscess 11).
A case with a good result shows the usefulness of early diagnosis, careful clinical and radiological monitoring and combined medical and surgical management. A child 2 1/2 years of age was admitted to the department of neurosurgery for diagnosis and treatment of a brain stem lesion. The clinical context and discovery of an intrabronchial foreign body, as well as neuroradiological investigations, suggested a diagnosis of brain stem abscess. Initial treatment with broad spectrum antibiotics with good cerebral penetration was associated with an increase in the size of the abscess and clinical worsening. Stereotactic aspiration of lesion was performed by a transpeduncular approach under CT guidance and general anaesthesia. Secondary thoracotomy enabled removal of an intrabronchial needle. After evacuation, in spite of failure to identify the organism, neurological deficit resolved rapidly and the lesion no longer appeared on CT. Management of a brain abscess always includes antibiotics. They must cover the organisms most often encountered in brain abscesses and have good cerebral penetration. Medical treatment seems to suffice for small abscesses. A brain stem abscess with rapid clinical signs, together with current neuroradiogical diagnostic techniques, enables early discovery of such abscesses when they are still small. Treatment of brain stem abscesses includes primary antibiotic therapy, then stereotaxic drainage when there is any diagnostic doubt, poor clinical tolerability or antibiotic resistance 12).