**1. Introduction**

#### **1.1 General aspects**

Central nervous system (CNS) infections are challenging in terms of correct and on time diagnosis, therefore treating them are quite complicated and require correct understanding of its origin, type of infection and severity of it. Here in this chapter, we will be discussing the most common CNS infections within the field of neurosurgery as well as their best treatment and patient management.

As a known fact, CNS infections can cause very mild to severe signs and symptoms as well as neurological deficits if left untreated or not treated properly. Identification of the primary source of infections are very important, as quite often seen, the source can be infected foreign bodies, or an infection originating somewhere else in the body. In surgical units, wound contamination and deficiencies in correct post-operative patient care are other common sources of infection.

In this chapter we will be discussing infectious diseases which are commonly seen in neurosurgical wards or infections which require neurosurgical interventions, therefore a vast majority of CNS infections which do not require surgical management and-or not occurring in neurosurgical wards are not discussed here.

Various risk factors contribute to the occurrence of infections, general risk factors such as existing co-morbidities (Diabetes mellitus (DM), Anemia, AIDS etc.), the use of immunosuppressant drugs, chronic existing infectious diseases and abnormalities of the immune system are among most common risk factors. Factors such as specific patient skin bacterial composition and local bacterial resistance patterns play an important role in post-operative surgical site infections. Indeed, the extend of aseptic practice and use of proper prophylactic antibiotics before/ during surgery is another factor contributing to the occurrence/prevention of post-operative surgical site infection. However, there are studies where indicate that prophylactic use of antibiotics before surgery increase the rate of post-operative infections.

To minimize the risk for post-operative infections, it is recommended that a strict patient screening to be done in order to minimize risk factors which contribute to infections. Patients with higher blood glucose levels are monitored and their glucose profile and therapy are modified if needed, to achieve an acceptable blood glucose level. Patients on immunosuppressant drugs need greater attention pre-operatively and immunosuppressant drugs should be discontinued temporarily (if no contraindications) to minimize the risk of post-operative infections. Anemia should be corrected if present at the time of admission and screening for multi resistant bacteria should be done for every patient which is planned to undergo an elective surgery. All patients, regardless of their immune system and microbiological status should be given a proper Betadine bath the morning before the surgery, and proper prophylactic antibiotics should be administered intravenously, about 20 minutes before the skin incision is made. For longer procedures it is recommended to administer the prophylactic antibiotic once more while the surgery is going on. Proper wound closure, maintaining a good blood flow to the surgical site and proper fixation of existing wound drains with respect to the aseptic technique drastically can decrease the post-operative surgical site infection rate.

#### **1.2 Pathogenesis**

Understanding the pathomechanism of CNS infections and infection routes are necessary for proper diagnosis and proper treatment therefore in this section the basics to understand these infections are discussed. Since viral infections are not common in neurosurgical wards, and post-operative infections are mainly bacterial infections, we will be discussing the bacterial pathogenesis of the most common CNS infections here.

In general, bacterial infections reach the CNS by means of the hematogenous spread, but usually the organisms which are colonizing on the surface of the mucosal membranes of the nasopharyngeal cavities are responsible for most of the bacterial pre-operative infections of the CNS. These organisms can find their way to the nasal sinuses and then via the sinuses to the meninges and intracranial cavity. The blood brain barrier (BBB) is a very effective to repel and reduce the penetration of unwanted substances and organisms to the intracranial cavity, but sustained bacteremia and inflammatory and cytotoxic mediators of these organisms cause damage to the BBB and this in turn causes increase permeability of the BBB which is in fact the reason why these pathogenic organisms progress further and end up in the subdural and subarachnoid spaces. In most of cases the intracranial infections are originating from the adjacent ongoing inflammatory processes such as mastoiditis, otitis media, sinusitis and rhinitis [1].

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

The mucosal membranes in the oral and nasal cavities are lined with different types of bacteria in high quantities which are the normal flora of these mucus membranes, these organisms usually do not cause any CNS infections unless immunodeficiencies are present or these organisms find their way into the intracerebral space and start colonizing there. Skull base fractures are usually causing cerebrospinal fluid (CSF) leakage and this in return is facilitating the migration of bacteria from these adjacent places into the intracranial space causing various problems such as meningitis, cerebritis, intracerebral abscess, fistulas and subdural empyema formation. It is of great importance to mention that infection and inflammation of distant or adjacent organs can also be causing septic cerebral embolization which can be very challenging and hard to identify and differentiate from other lesions such as metastatic lesions or tuberculomas. Endocarditis and cardiac vegetations are among the common cause of septic cerebral embolization, but in general any distant or adjacent infection which spreads through the hematogenous pathway and causes septicemia can be causative of septic cerebral embolization.

The mechanism behind spinal infections is somewhat the same and the blood spine barrier which is the equivalent of BBB is having the same role in protection and isolation of the spinal cord. Spinal epidural abscess or empyema formations are mainly caused by hematogenous spread of bacteria, but besides this paravertebral injections, acupuncture and epidural catheters can be direct causes of bacterial colonization and formation of spinal epidural abscess and empyema. If the inflammation reaches the bony structures of the spinal column, then the term spondylitis is used to describe the latter. There are different forms of spondylitis, the most common type being spondylodiscitis which involves the inflammation of the vertebral body and the adjacent disco-ligamental system. Spondylodiscitis are usually complications of spine surgery but spontaneous forms of it in diabetic patients or patients who are on steroid or immunosuppressant therapy drugs can be found. The pathogenesis of these infections is also via the hematogenous spread and even simple infections such as urinary tract infections if left untreated can be a cause for septicemia and advancement of the infection to the spinal column.

## **1.3 Diagnosis**

Diagnosing CNS infections require multiple tests and imaging, performing the right type of modality at the right time plays a crucial role in early and correct diagnosis. At early stages, infections of CNS can lack absolute neurological signs and only general inflammatory signs and symptoms are present, with progression of the infection, milder complains such as headaches and malaise appear and as the infection progresses further neurological signs and symptoms begin to appear as well. Most of the patients complain of headaches which are partly responsive to NSIADs, fatigue, nausea and vomiting, photosensitivity and with progression of the infection epileptic seizures and paresis can occur. In patients with spinal epidural abscess or severe spondylodiscitis, paraparesis with back pain which radiates to lower extremities can be the very first signs and symptoms of patients.

Depending on the patient's history, physical examination, signs and symptoms and laboratory findings, if a CNS infection is suspected then immediate action to confirm diagnosis should be done by performing supplementary tests such as imaging and lumbar puncture if necessary. CSF cell count as well as CSF biomarkers (such as IFN-γ, TNF-α, IL-2, IL-6, CD8, MIF, NfH-SM135, GFAP-SM126, S100B) analysis are necessary to confirm the presence of inflammatory process in CNS [2], but since these CSF findings in most of the inflammatory states are similar, a differential diagnosis becomes challenging based on the CSF cell analysis therefore further steps such as image acquisition is needed to be able to proceed further. The

physical findings such as meningeal irritation signs (Brudzinski's and Kernig's sign) and photosensitivity are not enough for the establishment of any type of CNS infection; even in cases where beside the above mentioned signs and symptoms, pyrexia and increased inflammatory markers are present, a definite diagnosis of CNS infection cannot be made, because conditions like subarachnoid hemorrhage (SAH) can have the very same clinical findings, and the origin of pyrexia or elevated inflammatory factors can be something rather than the CNS. For establishing a diagnosis of CNS infection imaging techniques are necessary since without it other specific conditions such as SAH cannot be surely ruled out (despite positive CSF cell count for red blood cells (RBCs) as lumbar puncture (LP) can be traumatic) and abnormalities such as subdural empyema, cerebral abscess or fistulas cannot be detected.

MRI scans are the gold standard when it come to the imaging of the CNS, since the resolution and clarity of the MRI scans for soft tissue detection are much better and higher than CT scans, their use are more prominent in detection of CNS infections. CT scans are also capable of detecting abnormalities such as subdural empyema or cerebral abscess, but since the radiologic features of these conditions on CT scans are not very specific and very similar with other pathologies, once the suspicion of subdural empyema or cerebral abscess is raised, a contrast enhanced MRI should be done to confirm or rule out the diagnosis. In case of the spinal column infections and epidural abscess or empyema in the spine, MRI is the preferred choice due to its capability of detecting diffusion restriction both in bony structures and soft tissues as well as having a higher sensitivity and specificity for detecting lesions in the spinal canal.
