**3. Subdural empyema, cerebral abscess and septic cerebral emboli**

Subdural empyema is the accumulation of pus in the subdural space which is usually a complication of cranial surgery and untreated postoperative meningitis. Purulent meningitis is another cause of subdural empyema, since primary purulent meningitis infection's rate has decreased drastically due to vaccinations and early diagnosis as well as antibiotic treatments, we will be focusing on postoperative meningitis and subsequently subdural empyema. Other pathologies such as chronic sinusitis, otitis media and mastoiditis, if left untreated contribute to formation of subdural empyema and mostly cerebral abscess formation. Odontogenic sources are also important to be mentioned, as often poor dental hygiene or invasive dental procedures are the origin of subdural empyema or cerebral abscess formation. Immunocompromised patients have a higher susceptibility for postoperative and primary infections, therefore they must be treated with care and normalization of their immune system prior to surgeries is required to prevent postoperative complications, for instance in cases where patients are on prolonged immunosuppressant drugs such as steroids due to chronic diseases, or other immunosuppressive drugs for treating autoimmune diseases, reduction of dose and even a complete halt of treatment for a temporary time should be considered if doing so does not interfere with the course of surgery or patient's primary treatment, reducing the dose of immunosuppressant drugs can be very effective in decreasing the PNM and in general postoperative infections.

#### *Infections and Sepsis Development*

Accumulation of pus in the subdural spaces irritates the meninges as well as the arachnoid membrane causing arachnoiditis, this in return can cause irritation of the cerebrum and cause cerebritis. If this process is not disrupted properly and intime, then cerebral abscess formation is occurring. With time as the abscess is maturing, it's wall thickens, and it gets bigger and bigger. The symptom presentation of patients can be very different and vary in a vast range, patients can have mild to severe meningitis signs or severe epileptic seizures and signs of increase intracranial pressure. In cases where an ongoing meningitis is not healed completely and it becomes chronic, the patient's signs and symptoms improve temporarily, but meantime the ongoing chronic cerebritis is leading to abscess formation. Depending on the site of abscess formation severe symptoms such as seizures, hemiparesis, agitation, aggressiveness and even loss of consciousness can occur (in accordance with lesion localization neurological deficits are present). **Figure 2** demonstrates a right sided temporal lesion with rim enhancement, perifocal edema and central diffusion restriction. The patient developed a sudden left sided hemiparesis due to the perifocal edema, and acute drainage and abscess excision was done to minimize neurological damage and complications.

Treatment of subdural empyema and cerebral abscess can be surgical or conservative, depending on their size and symptoms of the patient. Smaller abscesses or subdural empyemas can be treated with systematic antibiotics if they are not causing severe neurological deficits which are acute emergencies, such as hemiparesis, loss of consciousness, decreased arousal state and uncontrollable seizures.

#### **Figure 2.**

*Rim enhancement on T1 imaging (upper left) and perifocal edema on T2 (upper right) scans in this case are indicative for brain abscess. DWI sequences (lower images) show diffusion restriction in the areas as well as in the right lateral ventricle. It is to be noticed that the occipital horns of the lateral ventricles are also filled with pus and diffusion restriction can be seen there as well (lower right image).*

#### *Infections in Neurosurgery and Their Management DOI: http://dx.doi.org/10.5772/intechopen.99115*

If the above-mentioned symptoms are present, regardless of the size, surgical drainage and systemic antibiotic therapy should be started as soon as possible. In other scenarios where the mentioned symptoms are absent and the size of the abscess is not causing mass effect and midline shift, then proper antibiotic treatment can be the first line treatment, and if it fails or patient deterioration occurs, then surgical removal and drainage should be considered.

**Figure 3** demonstrates a severe case of odontogenic subdural empyema which required immediate surgical drainage due to mass effect of the empyema and the neurological status of the patient. Multiple surgeries had to be carried out to achieve an acceptable level of drainage. In **Figure 4** post-operative scans show a significant reduction in contrast enhancement and no diffusion restriction can be seen on the DWI sequence. Surgical treatment was followed by intensive intravenous antibiotic treatment (intravenous Vancomycin, Ceftriaxone and Metronidazole).

#### **Figure 3.**

*Contrast enhanced T1 MRI scan (left side) shows contrast enhancement on the arachnoid membrane and dura diffusely on the right hemisphere. Next to the falx cerebri similar alteration are seen and cavitation between falx and dura is noticeable. On the right sided image, we can see diffusion restriction in the hypointense areas seen on T1 sequences. These alterations show accumulation of pus in the subdural space.*

#### **Figure 4.**

*Post-operative contrast enhanced T1 scan (left image) showing a significant decrease in contrast enhancement; Craniectomy site on the right fronto-temporal region and a burr hole on the left frontal region can be seen. DWI scans show no diffusion restriction.*

Septic cerebral emboli are not common findings, and their diagnosis is quite challenging as they often resemble tumor like masses. Septic emboli usually originate from a distant organ via hematogenous spread and after seeding in the CNS they cause abscess formation. Cardiac vegetations are the most common cause of septic cerebral embolization and patients who have gone under valve replacements are at a greater risk of developing cardiac vegetations and consequently septic cerebral embolization. Differential diagnosis is the key point of a proper treatment here and the course of disease development plays a crucial role in differentiating septic cerebral emboli from other pathologies such as tumor masses or granulomas. A sudden onset of signs and symptoms with intracranial lesions should alert the physician for possibility of septic cerebral embolization and if ongoing inflammatory or infectious diseases or comorbidities such as DM, autoimmune disorders, existing mechanical heart valves are present then the probability of septic embolization significantly increases.
