The Complex Structure of the Anterior White Commissure of the Human Brain: Fiber Dissection and Tractography Study.

OBJECTIVE: Commissural fibers are necessary for bilateral integration, body coordination, and complex cognitive information flow between the hemispheres. The anterior commissure (AC) has a complex architecture interconnecting areas of the frontal, temporal and occipital lobes. The present study aims to demonstrate the connections and the course of the anterior (ACa) and posterior (ACp) limb of the AC using fiber dissection and diffusion tensor imaging (DTI) of the human brain. METHODS: Fiber dissection was performed in a stepwise manner from lateral to medial on 6 left hemispheres. The gray matter was decorticated and the ACa-ACp was exposed. The ACa and ACp tracts were demonstrated using a high-spatial-resolution DTI with a 3T magnetic resonance unit in 13 cases. RESULTS: Using both techniques showed that the AC has complex interconnections with large areas of the frontal (olfactory tubercles, anterior olfactory nucleus, olfactory bulb, and the orbital gyri), temporal (amygdaloidal nuclei, temporal and perirhinal cortex), and occipital (visual cortex) lobes. The ACp makes up the major component of the AC and is composed of temporal and occipital fibers. We observed that these fibers do not make a distinct bundle; the temporal fibers joined the uncinate fasciculus and the occipital fibers joined the sagittal striatum to reach their targets. CONCLUSIONS: Being aware of the course of the AC is important during transcallosal and interforniceal approaches to the third ventricle tumors and temporal lobe epilepsy surgery. The intermingling fibers of the AC can provide a better understanding of the unexplained deficit that may occur during regional surgery.

Challenging Anterior Inferior Cerebellar Artery in Retrosigmoid Vestibular Schwannoma Removal.

OBJECTIVE: Referring to the anterior inferior cerebellar artery (AICA) traversing a cerebellopontine angle tumor during retrosigmoid vestibular schwannoma (VS) removal as a challenging AICA (c-AICA), we describe incidence, anatomic characteristics, mechanism of development of c-AICA, and surgical techniques used to remove VS while preserving the AICA. METHODS: Review of surgical records and videos of 150 patients who underwent retrosigmoid VS removal revealed 10 patients (7%) with c-AICAs. Retrospective analysis of these 10 patients was performed. RESULTS: Surgical findings classified c-AICAs as c-AICAs with subarcuate artery (SAA) and c-AICAs without SAA. In c-AICAs with SAA (7/10), the SAA had an anchoring effect in the development of the c-AICA. The most challenging c-AICAs (i.e., c-AICAs reaching the porus acusticus, entering the internal auditory canal, and adhering to the dura) were associated with short cisternal SAAs (4/7). We preserved the most challenging c-AICA with the surrounding dura by drilling the posterior wall to preserve the posterior wall dura. AICAs adhering to the porus acusticus dura were not associated with long cisternal SAAs. Sacrificing the SAA caused no neurologic deficits. c-AICAs were preserved in all patients, and tumors were removed with no complications related to AICAs. CONCLUSIONS: c-AICAs occur more often than expected. The anatomy of the SAA is related to the development and characteristics of c-AICAs. Although preserving a c-AICA is challenging and necessitates a complex dissecting technique, understanding of anatomic characteristics and appropriate surgical management of c-AICAs enable VS removal while preserving the AICA.