Neuronal injury and axonal degeneration: Pathologic mechanisms and findings beyond Wallerian changes.

Secondary neuronal degeneration refers to progressive structural changes occurring in neuronal pathways following a primary insult. This article reviews characteristic imaging patterns of anterograde, retrograde, and trans-synaptic degeneration in the central nervous system. Radiologic features are described in the context of common clinical scenarios, including stroke, trauma, tumor, demyelination, and neurodegenerative disease. Imaging findings are presented alongside relevant pathophysiologic mechanisms, focusing on tract involvement such as the corticospinal, pontocerebellar, cerebelloolivary, transcallosal, and cranial nerves. Recognizing these patterns may help radiologists interpret chronic or post-treatment imaging changes with greater confidence and clinical relevance.