Intraaxial

Intraaxial is a radiologic and neurosurgical descriptor for lesions that arise within the brain parenchyma, the functional tissue of the brain itself. It is used to distinguish these from extraaxial lesions, which occur outside the brain parenchyma, such as within the meninges, skull base, or cranial nerves.

The distinction between intraaxial and extraaxial lesions is important for diagnosis, prognosis, and management. On imaging, intraaxial lesions are located within brain tissue and are typically surrounded by parenchyma, often with edema and possible invasion into adjacent structures. Extraaxial lesions lie outside the brain parenchyma and may show a CSF cleft, broad-based dural contact, or a distinct separation from the surrounding brain.

Common intraaxial pathologies include primary brain tumors such as gliomas (including glioblastoma), intraparenchymal metastases, abscesses within brain tissue, intraparenchymal hemorrhages, and inflammatory or demyelinating lesions that affect brain tissue. The clinical presentation depends on the lesion’s location and size, frequently producing focal neurological deficits or seizures.

Management decisions are influenced by whether a lesion is intraaxial. Intraaxial lesions often require approaches that account for proximity to eloquent cortex and deep brain structures, with treatment options including surgical resection, biopsy, radiotherapy, and medical therapies tailored to the specific pathology.