Injury of the Papez circuit in a patient with traumatic spinal cord injury and concomitant mild traumatic brain injury

Little is known about brain injury in concomitant mild traumatic brain injury (TBI) following traumatic spinal cord injury (TSCI). In this study, we reported on a male patient with memory impairment who showed injury of the Papez circuit following TSCI and concomitant mild TBI. A 59-year-old male underwent posterolateral fusion on T11–L2 due to an L1 burst fracture after falling from a height of 10 meters. The patient had a T10 incomplete lesion (American Spinal Injury Association impairment scale C) and he complained of memory impairment, which was detected after transfer to the rehabilitation department. The patient met the criteria of mild TBI and showed memory impairment at 4 weeks after onset as follows: Wechsler Adult Intelligence Scale: 101 and the Memory Assessment Scale (global memory: 61 [1%ile >]). On 4-week diffusion tensor tractography, the entire Papez circuit including thalamocortical tract, fornix, mammillothalamic tract, and cingulum was reconstructed in both hemispheres except for the left thalamocortical tract between the anterior thalamic nuclei and cingulated gyrus, and the right mammillothalamic tract between the mammillary body and anterior thalamic nuclei, which were thinner compared with the opposite side. In this patient, injury of the Papez circuit was related to memory impairment. Traumatic brain injury (TBI) is frequently concomitant with TSCI (Richards et al., 1988; Wei et al., 2008). However, the precise incidence of comorbidity of TBI with TSCI has not been clearly determined: the estimated prevalence of concomitant TBI in patients with TSCI is 40– 60% (Davidoff et al., 1988; Richards et al., 1988; Wei et al., 2008). Because of the high incidence of comorbidity of TBI with TSCI, diagnosis of concomitant TBI has been an important topic in rehabilitation of patients with TSCI (Wei et al., 2008). Diffusion tensor tractography (DTT), which is derived from diffusion tensor imaging (DTI), has enabled diagnosis of brain injuries not detected on conventional brain MRI and has been used in diagnosis of brain injuries which were concomitant with TSCI (Wei et al., 2008). However, little is known about brain injury in concomitant mild TBI, which accounts for 70–90% of all cases of TBI, following TSCI (De Kruijk et al., 2001). Memory impairment is a major clinical feature following mild TBI (Kurca et al., 2006). The Papez circuit, consisting of the hippocampus, fornix, mammillary body, anterior thalamic nucleus, cingulate gyrus, cingulum, and parahippocampal gyrus, is an important neural structure for memory, particularly episodic memory (Papez, 1995; Markowitsch, 1997). DTT has enabled three-dimensional reconstruction and evaluation of the entire neural tracts in the Papez circuit and many studies have reported on injury of neural structures in the Papez circuit in patients with mild TBI (Niogi et al., 2008; Lee and Jang, 2014; Yang et al., 2016). However, no study on injury of the Papez circuit in patients with concomitant mild TBI following TSCI has been reported so far. In this study, we reported on a patient with memory impairment who showed injury of the Papez circuit was detected on DTT following TSCI and concomitant mild TBI. A 59-year-old male who suffered an L1 burst fracture after falling from a height of 10 meters while driving a car underwent posterolateral fusion on T11–L2 with regional autograft bone and allograft bone at the neurosurgery department of a university hospital. After 2 weeks from onset, he was transferred to the rehabilitation department of the same hospital to undergo rehabilitation. The patient had a T10 incomplete lesion (American Spinal Injury Association impairment scale C) and he complained of memory impairment, which was detected after transfer to the rehabilitation department. The patient met the criteria of mild TBI: loss of consciousness 2 minutes, post-traumatic amnesia approximately 4 minutes, Glasgow Coma Scale score 15, and no specific lesion on conventional brain MRI performed at 4 weeks after onset (Figure 1A) (Alexander, 1995). The patient showed memory impairment at 4 weeks after onset: Wechsler Adult Intelligence Scale: 101 and the Memory Assessment Scale (global memory: 61 (1%ile >), short term memory: 71 (3% ile), verbal memory: 73 (4% ile), and visual memory: 66 (1% ile) (Wechsler, 1981; Williams, 1991). The study protocol was approved by the institutional review board of Yeungnam University Hospital (approval No. YUMC 2015-07-064). DTI data were acquired at 4 weeks after onset using a 6-channel head coil on a 1.5 T Philips Gyroscan Intera (Philips, Ltd., Best, The Netherlands) with single-shot echo-planar imaging. For each of the 32 non-collinear diffusion sensitizing gradients, 70 contiguous slices were acquired parallel to the anterior commissure-posterior commissure line. Imaging parameters were as follows: acquisition matrix = 96 × 96; reconstructed to matrix= 192 × 192; field of view = 240 × 240 mm; repetition time = 10,398 ms; echo time = 72 ms; parallel imaging reduction factor = 2; b = 1,000 s/mm; and a slice thickness of 2.5 mm. The Oxford Centre for Functional Magnetic Resonance Imaging of the Brain (FMRIB) Software Library was used to analyze DTI data with routine options (0.5 mm step lengths, 5,000 streamline samples, curvature thresholds = 0.2). Prior to the fiber tracking, eddy current correction was applied to correct the head motion effect and image distortion using FMRIB Software Library.