What term describes an infection of the brain parenchyma with a predominance of mononuclear leukocytes?

The term that describes an infection of the brain parenchyma characterized by a predominance of mononuclear leukocytes is indeed encephalitis. This condition specifically refers to inflammation of the brain tissue itself and often involves viral infections, such as those caused by herpes simplex virus or other pathogens. The presence of mononuclear leukocytes, particularly lymphocytes, indicates a viral infection rather than a bacterial one, which typically produces a neutrophilic response.

In contrast, meningitis primarily affects the meninges, the protective membranes covering the brain and spinal cord, and is often associated with an increase in neutrophils if bacterial in nature. An abscess refers to a localized collection of pus within the brain caused by a bacterial infection, leading to an inflammatory response that favors neutrophils. Myelitis refers to inflammation of the spinal cord and is not descriptive of brain parenchyma infection. Therefore, encephalitis is the correct term for this scenario, as it directly addresses the infection occurring within the brain's neural tissue and aligns with the given immunological response.