Reconstruction of the Ascending Reticular Activating System with Diffusion Tensor Tractography in Patients with a Disorder of Consciousness after Traumatic Brain Injury

Abstract

This work describes the reconstruction of the ascending reticular activating system (ARAS) with diffusion tensor tractography in three patients with altered consciousness after traumatic brain injury. A diffusion tensor tractography was performed in three patients with impaired consciousness after a severe traumatic brain injury. A 1.5 T scanner was used to obtain the tensor sequences; axial tensors were acquired. Post-processing was performed, and the mean fractional anisotropy (FA) values were recorded. The FA maps were used to do a manual tracing of the following regions of interest (ROIs): the ventromedial midbrain, the anterior thalamus, and the hypothalamus. Case 1 presented destruction of the right dorsal and ventral tegmental tracts as well as destruction of the right middle forebrain bundle, case 2 had destruction of the right dorsal tegmental tract, and case 3 had destruction of the bilateral ventral and dorsal tegmental tracts, as well as destruction of the right middle forebrain bundle. The affected fibers of the ascending reticular activating system with diffuse axonal injury and the FA values abnormalities in the ascending reticular activating system in three patients with a disorder of consciousness (DOC) after traumatic brain injury are described.

Keywords: arousal; ascending reticular activating system; consciousness; diffusion tensor imaging; neurosurgery; tractography; traumatic brain injury.

Figure 1. Schematic illustration of the reconstruction of the ascending reticular activating system (ARAS) fiber tracts with tractography in a normal subject.

(A) The three regions of interest (ROIs) are represented with numbers: 1) midbrain, 2) thalamus, 3) hypothalamus. (B) The different tracts of the ARAS can be observed resembling a “y”. MFB = Middle Forebrain Bundle, DR = Dorsal Raphè, ARAS = Ascending Reticular Activating System, ROI = Region of Interest.

Figure 2. Case 1. Non-enhanced brain magnetic resonance imaging (MRI) after an emergent decompressive craniectomy.

(A) Multiple ischemic changes in the right temporal lobe and in the right basal ganglia  areobserved (arrow). (B, C) Susceptibility-Weighted Magnetic Resonance Imaging show hypo-intense images in the mesencephalon and in the right anterior thalamus (arrows), demonstrating grade III diffuse axonal injury.

Figure 3. Case 1. Regions of interest (ROIs) traced for multi-seeding in color and T2 fractional anisotropy maps for the ascending reticular activating system (ARAS) fiber tracking.

ROIs in the (A) ventromedial mesencephalon, (B) the hypothalamus bilaterally, and (C) the anterior thalamus bilaterally are demonstrated (arrows).

Figure 4. Case 1. Average diffusion coefficient and fractional anisotropy fiber tracking of the ascending reticular activating system (ARAS).

Reconstruction of deterministic tractography is observed. (A) A lateral view of the tractography demonstrates the left ARAS fiber tracts. A considerable decrease in the number of the fibers of the DR tract is noted. A partial disconnection between the intra-thalamic complex and the DR tract is also noted. (B) A destruction of the right fibers of the ARAS is observed, including a destruction of the ventral tegmental tract, the dorsal tegmental tract and of the MFB tract. MFB = Middle Forebrain Bundle, DR = Dorsal Raphè, ARAS = ascending reticular activating system.

Figure 5. Case 2. Cervical spine computed tomography (CT) and magnetic resonance imaging (MRI) scans.

(A, B) A C2-C3 complex fracture (Anderson 3) with traumatic spondylolisthesis (Hangman 2) is observed (arrows). (C, D) A traumatic spondylolisthesis C2-C3 with a C2 contusion with marked myelopathy is demonstrated (arrowheads).

Figure 6. Case 2. Axial computed tomography (CT) of the head.

(A) Right thalamic contusions (arrow) with (B) traumatic subarachnoid hemorrhage (arrowheads) are demonstrated.

Figure 7. Case 2. Average diffusion coefficient tractography tracing of the ascending reticular activating system (ARAS).

(A) A left posterolateral view of the ARAS tractography is presented, demonstrating the ARAS fiber tracts. (B, C) Superior views of a fusion of the tractography and the volumetric axial T1 shows a destruction of the right dorsal tegmental tract in direct relationship with the presence of a right thalamic contusion (arrow). ARAS = Ascending Reticular Activating System, MFB = Middle Forebrain Bundle, DR = Dorsal Raphè.

Figure 8. Case 3. Non-contrast magnetic resonance imaging (MRI) of the head.

(A, B) Axial T2 weighted imaging (T2WI) and (C) susceptibility-weighted magnetic resonance imaging (SWI) axial slices showing multiple hemorrhagic contusions (arrows) in both frontal lobes as well as in the genu and anterior body of the corpus callosum with corresponding perilesional edema, as well as multiple cortico-subcortical hemorrhagic contusions (arrowheads).

Figure 9. Case 3. Average diffusion coefficient tractography of the ascending reticular activating system (ARAS).

(A, B) An anterior and inferior view of the ARAS tractography is presented, demonstrating the ARAS fiber tracts. A destruction of the right dorsal tegmental and right MFB tracts is denoted, as well as a destruction of the left dorsal and ventral tegmental tracts. (C) A destruction of bi-frontal commissural, association, and projection fibers is demonstrated. ARAS = Ascending Reticular Activating System, MFB = Middle Forebrain Bundle, DR = Dorsal Raphè.