Nonlesional

Nonlesional refers to a medical condition or finding in which no physical abnormality, or lesion, is identified on imaging or during clinical examination. The term is frequently used in neurology, neurosurgery, and radiology to describe patients who exhibit symptoms or neurological deficits but for whom magnetic resonance imaging (MRI), computed tomography (CT), or other investigative modalities do not reveal any structural brain abnormality, tumour, infarct, demyelinating plaque, or cystic lesion.

In epilepsy practice, a nonlesional epilepsy is one in which no epileptogenic focus is visualized on high‑resolution MRI or video‑EEG monitoring. These patients are often classified as having focal cortical dysplasia that may be microscopic or as generalized epilepsy syndromes that lack a focal structural correlate. Surgical options for nonlesional epilepsy are limited to invasive EEG monitoring or stereotactic radiofrequency ablation and rely on electroclinical mapping rather than a visible lesion.

In neurosurgical head trauma, a nonlesional traumatic brain injury describes patients who present with cognitive, motor, or psychiatric sequelae after diffuse axonal injury that is not detectable on routine CT scans. Diffusion tensor imaging and advanced MRI sequences can sometimes reveal subtler axonal damage, but the absence of visible contusions or haemorrhage characterizes the nonlesional label.

The distinction between lesional and nonlesional is critical for prognosis, treatment planning, and genetic counseling. Nonlesional conditions may still involve subtle microstructural or metabolic abnormalities, and research continues to improve imaging sensitivity to capture these changes.