Sung Jo Jang, Jan Do Lee

Department of Physical Medicine and Rehabilitation, College of Medicine, Yeungnam University, Namku, Daegu, Republic of Korea

How to cite this article: Jang SH, Lee HD (2017) Diffusion tensor tractography studies on mechanisms of recovery of injured fornix. Neural Regen Res 12(10):1742-1744.

Funding: is work was supported by the National Research Foundation (NRF) of Korea Grant funded by the Korean Government (MSIP)(2015R1A2A2A01004073).

Diffusion tensor tractography studies on mechanisms of recovery of injured fornix

Sung Jo Jang, Jan Do Lee＊

Department of Physical Medicine and Rehabilitation, College of Medicine, Yeungnam University, Namku, Daegu, Republic of Korea

How to cite this article: Jang SH, Lee HD (2017) Diffusion tensor tractography studies on mechanisms of recovery of injured fornix. Neural Regen Res 12(10):1742-1744.

nerve regeneration; fornix; diffusion tensor tractography; recovery mechanism; memory assessment scale; Papez; neural regeneration

Introduction

Clarification of mechanisms of recovery following brain injury is clinically important because such information provides a scientific basis for neurorehabilitation and prediction of prognosis. The mechanisms of recovery of an injured brain are based on the following concepts: 1) Reserve axons and synapse to be revealed for particular functions following injury of the ordinarily dominant system and 2) collateral sprouting from an intact neuron to a denervated region)(Bach y Rita, 1981a, b; Jang and Kwon, 2014a). Therefore,the mechanisms for recovery of an injured fornix might be based in part on the involvement of the neural connectivity of the fornix and recent studies have suggested that the neural connectivity of the fornix is much wider and more complex than the classical concept of the fornix anatomy: in detail, the anterior fornical body has high connectivity with the anterior commissure, corpus callosum, medial temporal lobe, and brain areas relevant to cholinergic nuclei (the basal forebrain region and brainstem), while the posterior fornical body has connectivity with the cerebral cortex, corpus callosum, and brainstem (Jang and Kwon, 2013, 2014a, b).

In this article, DTT studies on the mechanisms of recovery of an injured fornix in patients with brain injury were reviewed. Relevant studies were identified using the following electronic databases (PubMed and MEDLINE) from 1966 to 2016. The following key words were used: DTI, DTT,fornix, fornical crus, memory, traumatic brain injury, brain tumor, and brain injury.is review was limited to studies of humans with brain injury. Finally, five studies were selected and reviewed (Yeo and Jang, 2013; Lee and Jang, 2014; Jang et al., 2016; Jang and Lee, 2016; Jang and Seo, 2016).

Recovery Mechanisms of Injured Fornical Crus Revealed by DTT

Table 1 Previous diffusion tensor imaging studies on mechanisms of recovery of injured forni

Figure 1 Mechanisms of recovery of injured fornical crus determined by diffusion tensor tractography.

In 2003, Yeo and Jang estimated the fornix in a patient who complained of memory impairment for 3 years after direct head trauma due to an in-car accident (loss of consciousness:30 minutes).e patient showed memory impairment on the Memory Assessment Scale (MAS, global memory: 70 [2%ile]),although total intelligence on the Wechsler Intelligence Scale(WAIS) was within the normal range (total IQ: 109) (Wechsler,1981; Williams, 1991). On 3-year DTT, discontinuation of both fornical crus in the proximal portion was observed and a nerve tract originating from the right fornical body extended to the right temporal lobe through the splenium of the corpus callosum (mechanism 2). Another nerve tract originating from the lefornical column passed the lemedial temporal lobe(mechanism 4). As a result, the authors concluded that these nerve tracts of the fornix observed in this patient were the result of nerve reorganization following bilateral injury of the fornix crus (Yeo and Jang, 2013).

Subsequently, in 2014, Lee and Jang followed up the changes of an injured fornix for 8.5 months from 2 weeks to 9 months aer onset in a patient with mild traumatic brain injury (TBI)due to a pedestrian car accident. On 9-month DTT, two nerve tracts originating from each fornical column extended to each medial temporal lobe, respectively (mechanism 4) and a neural tract originating from the right fornical body and crus extended to the right medial temporal lobe (mechanism 2).e patient showed a total score of 86 for mild memory impairment on the Memo Assessment Scale at 2 weeks aer onset, however,her memory had recovered to be within normal range, with a score of 105 at 9 months aer onset (Williams, 1991).erefore, the authors concluded that three neural tracts from both fornical columns and the right forncal body and crus were the apparent mechanisms of recovery of the injured fornix (Lee and Jang, 2014).

In 2016, Jang and Lee reported on the recovery process for an injured fornical crus following mild TBI due to an in-car traffic accident. The patient complained of memory impairment since the onset of head trauma and showed mild memory impairment with global memory (77[6%ile]) on the MAS at 2 months aer onset (Williams, 1991).e patient underwent rehabilitation, including cognitive therapy and cholinergic drugs until 12 months after onset. She showed significant improvement of memory impairment with global memory: 90(25%ile) on the MAS at 12 months aer onset.A discontinuation of the lefornical crus was observed on 2-month DTT. However, on 12-month DTT, the lediscontinued fornical crus was shortened, instead, a nerve tract from the right fornical body extending to the left medial temporal lobe via the splenium of the corpus callosum and the lefornical column was elongated to the lemedial temporal lobe (mechanism 3).e authors assumed that the recovery of memory impairment in this patient was attributed to the above nerve tract (mechanism 3) (Jang and Lee, 2016).

Recently, Jang et al. (2016) reported on a patient with moderate TBI resulting from a car accident, which occurred while riding a bicycle, who showed nerve tracts from the bilateral fornical columns to each medial temporal lobe following bilateral injury of the fornical crura. He showed memory impairment at 4 months aer onset as the global memory: 79 (8%ile) on the MAS and his memory impairment was improved to normal range, as the global memory: 99 (47%ile) on the MAS at 16 months aer onset (Williams, 1991). Discontinuations of the proximal portion of bilateral fornical crura were observed on both 4-month and 16-month DTTs. On 16-month DTT, both fornical columns were connected to each medial temporal lobe through the new nerve tracts (mechanism 4) and a new nerve tract originating from the lefornical column was connected to the right medial temporal lobe via the lemedial temporal lobe and the splenium of the corpus callosum (mechanism 5).

During the same year, Jang and Yeo investigated the recovery process of injured fornical crura following a neurosurgical operation for a brain tumor (Jang and Seo, 2016).e patient showed severe memory impairment aer craniotomy and navigator assisted removal of craniopharyngioma at the suprasellar space. Discontinuation of both fornical crura was observed on 2-month DTT. However, on 6-month DTT, fornical crura emerged from the end of the fornical body on both sides and were elongated to the medial temporal lobe on both sides on 20-month DTT.e authors suggested that the injured fornical crus recovered via the normal pathway of the fornical crus in this patient (mechanism 1) (Jang and Seo, 2016).

To conclude, in this article, five DTT studies (four studies: traumatic brain injury, and one study: brain tumor) on mechanisms of recovery of injured fornical crus in patients with brain injury were reviewed. The frequency of mechanisms of recovery of an injured fornix was in the following order: mechanism 4 three times, mechanism 2 twice, mechanism 1 three times, and mechanism 5 once.ese DTT studies on mechanisms of recovery of injured fornical crus appeared to provide useful information for clinicians caring for patients with brain injury, however studies on this topic are still in the beginning stages.erefore, we could not describe the factors which could affect the acting recovery mechanism among five mechanisms after injury of fornical crus. These factors might include brain pathology, severity and location of injury of fornical crus, and patient’s gender or age.

In-depth DTT studies on this topic, particularly those involving large numbers of subjects and other brain pathologies,should be encouraged. In addition, the limitation of DTT should be considered: regions of fiber complexity and crossing fibers hinder full reflection of the underlying fiber architecture,resulting in possible underestimation of the nerve tracts (Parker and Alexander, 2005; Wedeen et al., 2008; Yamada et al., 2009).

Author contributions: SHJ was responsible for research design and data acquisition. HDL was in charge of conception and design of this study,acquisition and analysis of data, and manuscript authorization. Both of these two authors approved the final version of this paper.

Conflicts of interest:None declared.

Data sharing statement: Datasets analyzed during the current study are available from the corresponding author on reasonable request.

Plagiarism check:Checked twice by ienticate.

Peer review:Externally peer reviewed.

Open access statement:is is an open access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under identical terms.

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＊Correspondence to:Han Do Lee,

lhd890221@hanmail.net.

orcid:

0000-0002-1668-2187

(Han Do Lee)

10.4103/1673-5374.217355

Accepted: 2017-05-10

Copyedited by Li CH, Song LP, Zhao M