Central Nervous System Infections of Herpesvirus Family
Section snippets
Mechanism of the herpesvirus infections
The skin, conjunctiva, and mucosa of the oropharynx or genitalia are the primary entry sites for HHV. Following replication in the inoculation site, they usually cause a hematogenous spread, called a viremia, to distant tissues [4]. All herpesviruses show some kind of neurotropism, either by hematogenous spread or neuronal transmission [1]. The neurovirulence of herpesviruses is mediated by the thymidine kinase gene and the termini of the L component [2]. The γ134.5 gene is required for the
Herpes simplex virus type 1
HSV is the most common cause of acute fatal sporadic encephalitis in human beings [15], [25], [26], [27]. It usually produces focal encephalitis rather than diffuse or nonfocal disease [15]. The actual vector of HSE is HSV-1 in most patients (>90%) and HSV-2 in the remainder [26], [28]. HSE was thought to account for 10% to 20% of all viral encephalitis, with an annual incidence of 1/250,000 to 500,000, before the introduction of West Nile virus encephalitis [25], [27]. Mainly, HSE is the
Herpes simplex virus type 2
HSV-2 mainly causes genital herpes and establishes latency in the sacral dorsal route ganglia. The virus can sexually infect the mouth and cause facial herpes [15]. Other manifestations of HSV-2 infection (eg, herpetic whitlow) are much less common. In the CNS, HSV-2 essentially causes neonatal encephalitis by infecting the neonate during its passage through the infected maternal birth canal, like other agents causing toxoplasmosis, other enteroviral infections, rubella, cytomegalic inclusion
Varicella zoster virus
The VZV actually causes acute febrile exanthematous illness (called varicella or chickenpox) in children. Following primary infection, VZV shows latency in the cranial nerve ganglia (usually trigeminal or geniculate), or the dorsal root ganglia (usually the thoracic level) throughout the lifetime of the host [16]. CNS complications of varicella infection, including cerebellar ataxia, meningoencephalitis, transverse myelitis, and aseptic meningitis, are rare, occurring in less than 1% of
Epstein-Barr virus
EBV frequently causes acute infectious mononucleosis and, rarely, chronic active EBV infection. Additionally, EBV is associated with nasopharyngeal carcinoma, Burkitt lymphoma, Hodgkin's disease, and lymphoproliferative disorders in immunocompromised patients [134]. Although CNS complications of EBV have been estimated to occur in 1% to 5% of patients who have infectious mononucleosis [135], the real burden of this entity is probably underestimated [136]. EBV involvement of the CNS causes a
Cytomegalovirus
Most of the immunocompetent population (60%–70%) in developed countries is infected with CMV by as early as 6 years of age and the rest become infected during their lifetime. Congenital CMV infections, presented as neonatal encephalitis or meningitis, are usually mortal and caused by transplacental seeding of the virus. Besides congenital CMV infection, the cellular and molecular mechanisms of CMV-related persistent infection, latency, and reactivation are not well understood. Although
Human herpesvirus type 6 and type 7
HHV-6 and HHV-7, together with CMV, belong to the Roseolovirus genus of the beta herpesvirus subfamily, and HHV-6 has two variants, namely HHV-6A and HHV-6B [159]. HHV-6, and occasionally HHV-7, cause roseola infantum (exanthema subitum) in children [21], [159]. Primary HHV-6 and HHV-7 infection occurs in early childhood, and serologic studies indicate that virtually all children have been infected with HHV-6 by 3 years of age, and 70% and 85% of immunocompetent children have been infected with
Human herpesvirus type 8
HHV-8, also known as Kaposi's sarcoma–associated herpesvirus, is a gamma herpesvirus associated with all forms of Kaposi's sarcoma in immunocompromised and immunocompetent patients, body cavity–based lymphoma, and multicentric Castleman disease [138]. HHV-8 is strongly neurotropic and, like HHV-6, some of its specific sequences have been detected in postmortem brain specimens from multiple sclerosis patients [168]. HHV-8 has been detected in the dorsal root ganglia of Kaposi's sarcoma patients,
B virus (Herpesvirus simiae)
The B virus (Herpesvirus simiae) is an alpha herpesvirus that is endemic among monkeys of the Macaca species and usually causes vesicles or ulcers similar to those associated with HSV-1 infection on the oral mucosal surfaces, skin, and conjunctiva of these primates [174]. The significance of the B virus is that it can cause fatal infections in human beings who work with these animals. Unlike HSE, the B virus can involve any region of the CNS and can cause fatal encephalitis, encephalomyelitis,
Summary
Although some MR imaging features of herpesvirus infections are diagnostic, as detailed above, the radiologic findings of herpetic infections usually do not allow the making of an exact differential diagnosis of clinical pictures caused by different subgroups of herpes family. Radiologic findings should be correlated with clinical and other laboratory findings, such as EEG and CSF findings, or herpesvirus DNA in CSF, augmented by a PCR test.
The characteristic imaging patterns of herpesvirus
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2021, Current Problems in Diagnostic RadiologyCitation Excerpt :Herpes simplex virus encephalitis has a high mortality rate (>70%) in untreated and poorly treated patients. HSV has a high affinity for the limbic system, which is often bilateral but asymmetric, extratemporal involvement can be seen in more than half of the patients.12 The involvement of the brainstem is not uncommon; it can get involved through the retrograde transmission of the virus through the cisternal segment of the trigeminal nerve or rarely via the facial nerve.
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