Recovery of an injured fornix in a stroke patient

Bilateral fornix infarction presented with acute amnesia: case report

Acute episodes of amnestic syndrome can be a challenging diagnostic problem. Except for nonvascular etiology, thalamic strokes or infarction involving several temporal lobe structures has been reported in earlier cases. The authors report a patient who suddenly developed memory loss without any other focal neurologic deficits. Brain magnetic resonance imaging (MRI) with diffusion-weighted imaging (DWI) performed 1 day after onset revealed acute infarction involving the bilateral fornix column and the genu of corpus callosum. Because simple fornix infarcts often have no obvious positive neurological signs, most of the related manifestations were provided by family members, are easy to be diagnosed falsely, and missed in clinical areas, we suggest that bilateral fornix infarction should be considered in the diagnosis of an acute onset amnestic syndrome.

Injury of the Precommissural Fornix in a Patient with Subarachnoid Hemorrhage: A Case Report

OBJECTIVES

We investigated injury of the pre- or postcommissural fornix in a patient with subarachnoid hemorrhage (SAH) using diffusion tensor imaging.

CASE DESCRIPTION

A 48-year-old male patient was diagnosed as SAH due to rupture of the right middle cerebral artery bifurcation aneurysm. After 9 weeks from onset, he was transferred to the rehabilitation department and he showed memory impairment. The whole fornix was reconstructed using single-tract fornix model based on a fiber assignment by continuous tracking, and separated fornices (pre- and postcommissural fornices) were reconstructed using 2-tract fornix model based on a probabilistic tractography method. The fractional anisotropy (FA), mean diffusivity, and fiber volume were measured in the patient and 6 normal control subjects. The integrities of both reconstructed whole fornices that were reconstructed using probabilistic tractography method were preserved. By contrast, in the results of 2-tract fornix model, the precommissural fornices showed discontinuations in both fornical cruses. In addition, the FA and fiber volume of both precommissural fornices in the patient were decreased by more than 2 standard deviations of those of normal control subjects.

CONCLUSIONS

Separate evaluations of the pre- and postcommissural fornices using 2-tract fornix model would be useful for diagnosis in patients with memory impairment following SAH.

The differences of the precommissural and postcommissural fornix in the hippocampal location: a diffusion tensor tractography study

PURPOSE

The precommissural fornix and postcommissural fornix have different connections to the basal forebrain and septal region, and mammillary body, respectively. However, little is known about the differences of the precommissural fornix and postcommissural fornix in the hippocampal location. In this study, using diffusion tensor tractography, we investigated the differences of the precommissural fornix and postcommissural fornix in the hippocampal location.

METHODS

We recruited 25 healthy volunteers for this study. For reconstruction of the precommissural fornix and postcommissural fornix, we placed the seed region of interest on the septal nucleus, and the mammillary body, respectively. The target regions of interest (ROI) was given on the crus of the fornix on the coronal image. Evaluations of the anatomical location of the precommissural fornix and postcommissural fornix were performed using the highest probabilistic location in the hippocampal formation.

RESULTS

The precommissural fornix and postcommissural fornix were located at an average of 83.9 and 87.5% between the lateral margin of the red nucleus and collateral sulcus on the axial plane, and 77.2 and 81.4% between the lateral margin of the midbrain and the inferior longitudinal fasciculus on the coronal plane. Significant differences of location in the medio-lateral direction were observed in the axial and coronal plane (p < 0.05). However, no significant differences of location in the antero-posterior direction were observed between precommissrual and postcommissural fornix (p > 0.05).

CONCLUSIONS

The reconstructed precommissural fornix and postcommissural fornix were connected to the cornu ammonis 1(CA1) of the hippocampus, and the precommissural fornix was located more laterally to the postcommissural fornix in the CA1.

Compensatory Neural Tract from Contralesional Fornical Body to Ipsilesional Medial Temporal Lobe in a Patient with Mild Traumatic Brain Injury: A Case Report

The authors attempted to demonstrate the compensatory process for an injured fornical crus after mild traumatic brain injury, using follow-up diffusion tensor tractography. A 50-yr-old female patient had a mild traumatic brain injury resulting from a collision that occurred while driving a sedan that was hit from the side. The patient complained of memory impairment since the onset of head trauma and underwent neuropsychologic evaluation at 2 mos after onset with global memory: 77 (6%ile) on the Memory Assessment Scale. She underwent rehabilitation, including cognitive therapy and cholinergic drugs until 12 mos after onset. At that time, she showed improvement of memory impairment with global memory: 90 (25%ile) on the Memory Assessment Scale. On 2-mo diffusion tensor tractography, a discontinuation was observed in the left fornical crus. By contrast, on 12-mo diffusion tensor tractography, the left discontinued fornical crus was shortened; instead, a neural tract from the right fornical body extended to the left medial temporal lobe via the splenium of the corpus callosum and the left fornical column was elongated to the left medial temporal lobe. The authors report on a patient who showed a compensatory neural tract from the contralesional fornical body to the ipsilesional medial temporal lobe via the corpus callosum after mild traumatic brain injury.

Perspectives on the neural connectivity of the fornix in the human brain

The fornix is involved in the transfer of information on episodic memory as a part of the Papez circuit. Diffusion tensor imaging enables to estimate the neural connectivity of the fornix. The anterior fornical body has high connectivity with the anterior commissure, and brain areas relevant to cholinergic nuclei (septal forebrain region and brainstem) and memory function (medial temporal lobe). In the normal subjects, by contrast, the posterior fornical body has connectivity with the cerebral cortex and brainstem through the splenium of the corpus callosum. We believe that knowledge of the neural connectivity of the fornix would be helpful in investigation of the neural network associated with memory and recovery mechanisms following injury of the fornix.

Neural connectivity of the lateral geniculate body in the human brain: diffusion tensor imaging study

A few studies have reported on the neural connectivity of some neural structures of the visual system in the human brain. However, little is known about the neural connectivity of the lateral geniculate body (LGB). In the current study, using diffusion tensor tractography (DTT), we attempted to investigate the neural connectivity of the LGB in normal subjects. A total of 52 healthy subjects were recruited for this study. A seed region of interest was placed on the LGB using the FMRIB Software Library which is a probabilistic tractography method based on a multi-fiber model. Connectivity was defined as the incidence of connection between the LGB and target brain areas at the threshold of 5, 25, and 50 streamlines. In addition, connectivity represented the percentage of connection in all hemispheres of 52 subjects. We found the following characteristics of connectivity of the LGB at the threshold of 5 streamline: (1) high connectivity to the corpus callosum (91.3%) and the contralateral temporal cortex (56.7%) via the corpus callosum, (2) high connectivity to the ipsilateral cerebral cortex: the temporal lobe (100%), primary visual cortex (95.2%), and visual association cortex (77.9%). The LGB appeared to have high connectivity to the corpus callosum and both temporal cortexes as well as the ipsilateral occipital cortex. We believe that the results of this study would be helpful in investigation of the neural network associated with the visual system and brain plasticity of the visual system after brain injury.

Neural connectivity of the anterior body of the fornix in the human brain: diffusion tensor imaging study

A few studies have reported on the neural connectivity of the fornix in the human brain, however, little is known about the neural connectivity of the anterior body of the fornix. In this study, we used diffusion tensor imaging in investigation of the neural connectivity of the anterior body of the fornix in normal subjects. Forty healthy subjects were recruited for this study. A seed region of interest was placed on the anterior body of the fornix using the FMRIB Software Library. Connectivity was defined as the incidence of connection between the anterior body of the fornix and any neural structure of the brain at the threshold of 5, 25, and 50 streamlines. In all subjects, the anterior body of the fornix showed 100% connectivity to the anterior commissure and hypothalamus at thresholds of 5, 25, and 50. On the other hand, regarding the thresholds of 5, 25, and 50, the anterior body of the fornix showed connectivity to the septal forebrain region (53.8, 23.8, and 15.0%), frontal lobe via anterior commissure (41.3,12.5, and 10.0%), medial temporal lobe (85.0,66.3, and 62.5%), lateral temporal lobe (75.0, 56.3, and 35.0%), occipital lobe (21.3, 5.0, and 1.3%), frontal lobe via septum pellucidum (28.8, 13.8, and 8.8%), tegmentum of midbrain (7.5, 5.0, and 0%), tectum of midbrain (2.5,0, and 0%), and tegmentum of pons (5.0,0, and 0%). The anterior body of the fornix showed high connectivity with the anterior commissure and hypothalamus, and brain areas relevant to cholinergic nuclei (the septal forebrain region and brainstem) and memory function (the medial temporal lobe).