The claustrum and its projection system in the human brain: a microsurgical and tractographic anatomical study

The goal in this study was to examine the microsurgical and tractographic anatomy of the claustrum and its projection fibers, and to analyze the functional and surgical implications of the findings.

Fifteen formalin-fixed human brain hemispheres were dissected using the Klingler fiber dissection technique, with the aid of an operating microscope at x 6-40 magnification. Magnetic resonance imaging studies of 5 normal brains were analyzed using diffusion tensor (DT) imaging-based tractography software.

Both the claustrum and external capsule have 2 parts: dorsal and ventral. The dorsal part of the external capsule is mainly composed of the claustrocortical fibers that converge into the gray matter of the dorsal claustrum. Results of the tractography studies coincided with the fiber dissection findings and showed that the claustrocortical fibers connect the claustrum with the superior frontal, precentral, postcentral, and posterior parietal cortices, and are topographically organized. The ventral part of the external capsule is formed by the uncinate and inferior occipitofrontal fascicles, which traverse the ventral part of the claustrum, connecting the orbitofrontal and prefrontal cortex with the amygdaloid, temporal, and occipital cortices. The relationship between the insular surface and the underlying fiber tracts, and between the medial lower surface of the claustrum and the lateral lenticulostriate arteries is described.

The combination of the fiber dissection technique and DT imaging-based tractography supports the presence of the claustrocortical system as an integrative network in humans and offers the potential to aid in understanding the diffusion of gliomas in the insula and other areas of the brain.