**6. Atypical infections**

Atypical infections are quite rare and therefore very misleading, their diagnosis is very challenging and if not diagnosed correctly, the course of treatment can be very different and ineffective. The term atypical applies when the infection is caused by an organism which is not known to cause CNS infection or has not been

reported yet, or infections which happen without any background or any obvious reason. Recently a case of septic cerebral embolus caused by Corynebacterium mucifaciens was described in a diabetic patient, C. mucifaciens is a normal flora of the skin and it can also be found in sterile body fluids [13]. Immunocompetent patients usually have a lower risk for atypical infections, but patients with defective immune system tend to have superinfections and even infections caused by organisms which normally do not cause any pathology. Course of disease development plays a crucial role in diagnosing these atypical infections, for example patients on prolonged antibiotic treatment, steroid treatment or immunosuppressants and in general immunocompromised patients should be considered for atypical strains of bacterial infection. If atypical strains are cultured or isolated in the abovementioned patient categories, they should not be precepted as contamination or false positive results but rather considered as atypical pathogens and they should be further investigated in order to confirm diagnosis.

The other scenario would be when a healthy immunocompetent individual suffers an atypical bacterial infection, this too should not be considered as false positive results or contamination, but rather it should be alarming as most immunocompromised patients are unaware of their condition are considered immunocompetent until such infections come along. This in turn does not mean that if a healthy individual is infected by atypical strains, then a defective immune system is the cause; this simply has to be investigated further to rule out any defects of the immune system and find the origin and primary cause of atypical infection. Healthy immunocompetent individuals can also be infected by atypical bacterial strains without any background or comorbidities playing along.

#### **Figure 6.**

*T1 contrast enhanced images (upper images) show a cystic like lesion with perifocal edema and rim enhancement in the right temporal lobe, at the level of the internal capsule. T2 scans (middle images) reveal the extent of perifocal edema and the fluid content of the lesion. Diffusion restriction can be seen on DWI sequences (lower images) which is a typical finding for cerebral abscess.*

#### **Figure 7.**

*Complete resolution of the lesion is seen after proper antibiotic treatment. The post gadolinium MRI scan was done for control purposes after 1 year.*

Atypical bacterial infections should be reported so that, medical society all over the world can recognize the possibility of infection by these strains in immunocompetent or immunosuppressed individuals. Treatment of atypical strains remains the same as typical strains, except for if standard antibiotic treatment fails to control the infection, a more aggressive antibiotic treatment profile should be chosen.

**Figure 6** shows the first ever reported case of cerebral embolus caused by C. mucifaciens by Tahaei et al. The radiographic findings are very typical for cerebral abscess or metastatic tumor lesions, and simply because the relevance of metastatic tumors and brain abscesses are much higher than septic emboli, the possibility of a cerebral septic embolus is often ignored, and they can be misdiagnosed and mistaken for tumors initially. A biopsy confirmed the diagnosis of septic cerebral embolus and proper antibiotic treatment based on antibiogram results were started after empiric treatment. In **Figure 7** the complete resolution of the septic embolus is seen after proper antibiotic treatment.

### **7. Spinal infections**

They represent about 4% of all cases of osteomyelitis and 2–7% of all musculoskeletal infections. The incidence is between 1:20000 and 1:100000 and it has been increasing in the last decades [14–17].

Spinal infections can be extremely destructive and can cause instability and progressive neurological symptoms. Diagnosis of spinal infection is very challenging due to the fact that they mimic other noninfectious degenerative disorders [17].

#### **7.1 Pathogenesis**

Spinal infection can develop in three different ways:

• hematogenous spread


The sources of hematogenous infections are usually the skin, respiratory tract, genitourinary tract, gastrointestinal tract or the oral cavity through bacteremia. The extensive prevertebral venous plexus in the vertebral column provides a sophisticated anatomical background for spreading of bacterial infection. In adults, discitis mostly originates from one of the neighboring endplates, which are necrotized by a septic embolus, while the disc is infected secondarily. Spread from contiguous tissue is rare and mainly occurs in adjacent infections, including retropharyngeal abscess, esophageal ruptures, and infected implants [17, 18].
