Inflammatory and Infectious Lesions of the Brainstem

Non-neoplastic brainstem (BS) lesions span a wide range of pathologies, including abscesses, encephalitis, demyelinating disorders, paraneoplastic and connective tissue diseases (CTDs), and vasculitis. In many cases, the underlying etiology is readily apparent, and a specific treatment can be initiated at the time of presentation. This concerns, for example, patients with known multiple sclerosis who develop symptoms or signs of BS dysfunction. When this is not the case, the initial diagnostic approach is dependent on the clinical setting and paraclinical findings. When dealing with space-occupying lesions, the initial focus is to differentiate BS tumors from abscesses or pseudo-tumoral inflammatory lesions. Early distinction between neoplastic and non-neoplastic lesions will help avoid unnecessary surgery and its potential complications. With encephalitic lesions, the focus shifts towards excluding a life-threatening condition such as infectious BS encephalitis. Establishing an early preliminary diagnosis in this setting is essential in order to choose the most appropriate empiric treatment. Whatever the scenario is, in depth knowledge of non-neoplastic disorders of the brainstem and their epidemiological, clinical, biological and imaging features is essential to guide the diagnostic approach. This chapter will address the various infectious and inflammatory disorders of the brainstem, with a particular emphasis on their clinical presentation, key radiological and laboratory findings, and general principles of management.