Secondary Neurodegeneration: A General Approach to Axonal and Transaxonal Degeneration

CNS WM tracts are mainly composed of axons, and when these structures undergo apoptosis or lose their integrity, neurodegeneration may occur. Secondary neuronal degeneration can be classified as axonal degeneration and involves only the first neuron in a pathway (Wallerian degeneration of the corticospinal tract being its prototype) or be classified as transaxonal degeneration and involve more than a single neuron in a common pathway, usually a closed neuronal circuit, in specific tracts, such as the dentate-rubro-olivary tract, tracts of the limbic system, corticopontocerebellar tract, cranial nerve tracts, and nigrostriatal pathway. This study aimed to review the anatomy of the main CNS tracts susceptible to secondary neuronal degeneration and to illustrate, through different imaging modalities, the findings associated with this poorly explored and understood process involved in the pathophysiologic substrate of numerous neurologic diseases.

Learning Objective: Recognize the anatomy of the main CNS tracts susceptible to secondary neuronal degeneration and identify its main imaging findings in different imaging modalities.