The insula (of Reil) may be considered its own lobe in some anatomy texts. On axial images, this appears as a single strip of cortex tucked deep beneath the operculum. On sagittal images, it has a V-shape configuration, consisting of multiple gyri that converge inferiorly. The insula is encircled by the peri-insular sulci and also borders the Sylvian fissure. The limen insula, a potential conduit of disease spread between the frontal and temporal lobes lies near the apex of the insular triangle. The insula is functionally diverse (sensory, limbic, visceral, etc.) with various possible clinical manifestations with lesions, including one form of central pain syndrome. Further, it may be afflicted by a variety of pathologic processes such as limbic encephalitis, some toxic/metabolic conditions, and MCA infarcts. Due to challenges with neurosurgical access, lesions of the insular cortex such as malformations of cortical development may be good targets for less invasive techniques such as laser interstitial thermal therapy (LITT).

Additionally, the sub-insular white matter contains several important white matter tracts, including some important for the ventral language pathway.

Loss of gray-white differentiation, including the insula. This is emphasized with narrow W/L settings (middle image). A hyperdense left M1 segment is seen (righthand image).

Key Clinical Correlate Concepts of the Insula

1. The insular region has challenges as a target for open operations.

2. The insula is commonly involved with ischemic infarct. Subtle loss of gray-white differentiation of insular cortex may be an early CT sign.

3. The insula is also subject to various other toxic/metabolic insults and can be involved with limbic encephalitis.

4. The insula is a functionally heterogeneous area.