History and MR images
History: A 61-year-old man presented to the emergency department following a short episode of transient memory loss. According to his wife, he went to work as usual that morning; however, on returning home in the afternoon, he was forgetting a number of recent events and was repeatedly asking a number of questions.
病史：
61岁男性，因短暂性记忆丧失急诊入院。据他妻子描述，那天早上患者像往常一样去上班；然而，当下午回到家时，患者忘记了很多最近发生的事情，并且反复地询问了许多问题。
There were no features of retrograde amnesia, with the patient still being able to recall his identity, recognize his family members, and carry out usual functions. This lasted for about 30 minutes, after which his memory slowly returned; however, he could not remember what had happened during this episode. He denied any associated headache, weakness, speech problems, or sensory disturbance. There was no witnessed loss of consciousness or seizure activity. The patient also denied any recent stressful event or head injury, and this was the first such episode of memory impairment. His medical history was notable for hypertension, diabetes, and a 20-pack-year history of smoking. There was no past history of transient ischemic attacks, strokes, or migraine.没有逆行性遗忘的表现，患者仍能回忆起自己的身份，认识自己的家庭成员，执行功能正常。该症状持续了约30分钟，之后记忆慢慢恢复；然而，他不记得在该期间发生了什么。他否认有任何相关的头痛、虚弱、语言问题或感觉障碍，也没有意识丧失或癫痫发作。患者还否认了近期有压力性事件或头部外伤，这是第一次出现记忆障碍。既往有高血压、糖尿病病史，吸烟史20年，没有短暂性脑缺血发作、中风或偏头痛的病史。
On examination, he was fully alert, oriented, and cognitively intact. Parameters, including blood pressure, were normal, and a full neurological examination was unremarkable. Blood investigations were within normal limits, and brain CT showed no abnormalities. In view of his risk factors, the working diagnosis was that of an ischemic stroke, and he was admitted for further investigation and started on antiplatelet therapy. Echocardiogram and carotid Doppler ultrasound showed no abnormalities.体格检查中，患者意识清醒，定向及认知功能完整。血压等处于正常范围，全面的神经系统检查无明显异常。血液检查结果正常，颅脑CT未见异常。考虑到患者存在危险因素，临床诊断为缺血性卒中，收住院进一步检查并开始抗血小板治疗。超声心动图及颈动脉多普勒超声均未见异常。
An MRI exam of the brain was performed approximately 26 hours from the onset of symptoms. Select axial diffusion-weighted (DWI; b = 1000, 4-mm slice thickness) images (top) and corresponding apparent diffusion coefficient (ADC) maps (bottom) are shown below. Click to enlarge.在症状发作后约26小时进行了颅脑MRI扫描。横断位DWI（b = 1000，4 mm层厚）（上）和ADC（下）如下所示。
图一
Axial T1-weighted (image A), T2-weighted (image B), and fluid-attenuated inversion-recovery (FLAIR; image C) images at the level of the hippocampi are shown below. Click to enlarge.
横断位海马层面T1WI（图A）、T2WI（图B）和FLAIR（图C）如下图。
图二
Findings
Image 1: Select axial images and corresponding ADC maps demonstrate bilateral punctate hyperintensities in the CA1 region of the hippocampi (red arrows) with corresponding signal loss on ADC (blue arrows).
Image 2: No abnormalities are demonstrated.
影像表现
图1：横断位DWI、ADC图显示双侧海马CA1区点状高信号（红箭头），相应ADC呈低信号（蓝色箭头）。
图2：未见异常。
Differential diagnosis
Diagnosis: Transient global amnesia
鉴别诊断
1、短暂性全面遗忘症
2、后循环缺血性梗死
3、边缘性脑炎
4、长期癫痫发作
诊断: 短暂性全面遗忘症
Treatment
The case was discussed at the neurology multidisciplinary team meeting where it was agreed that the clinical and MRI findings supported the diagnosis of transient global amnesia. The patient remained well and was discharged with no driving restrictions or need for imaging follow-up.治疗
该病例进行了神经多学科的讨论，一致认为临床和MRI表现支持短暂性全面遗忘症的诊断。患者状态良好，出院时没有限制驾驶，也不需要影像的随访。
Discussion
Transient global amnesia
Transient global amnesia is a clinical disorder characterized by sudden-onset anterograde amnesia with temporal disorientation and iterative questioning due to the inability to form new memories. Long-term memory, language, visual-spatial orientation, and executive functions are typically preserved, with no other associated focal neurological deficit. Episodes characteristically resolve completely within 24 hours, with a return to baseline cognition. Retrograde amnesia is variably present.短暂性全面遗忘症（TAG）
短暂性全面遗忘症是一种临床症状，其特征表现是突然发作的顺行性遗忘，伴有时间定向障碍，并且由于无法形成新的记忆而反复提问。长期记忆、语言、视觉空间定位和执行功能通常是保留的，没有其他相关的局灶性神经障碍。症状多在24小时内完全缓解，并恢复至平素认知状态。伴逆行性遗忘者表现多种多样。
This syndrome usually occurs between the fifth and seventh decades of life, and there is no significant gender predilection. The reported incidence is of five to 10 per 100,000 population. Cited precipitating factors include emotional stress, physical exertion, pain, and the Valsalva maneuver.该病症好发于50-70岁，没有明显的性别差异。据报道，发病率为每10万人中5-10例。公认的诱发因素包括情绪紧张、体力消耗、疼痛和Valsalva手法。
While this is a well-described disorder, the exact etiology of this condition remains obscure. Various theories have been postulated, including venous congestion (secondary to retrograde cerebral venous blood flow), focal ischemia, migraine, and epilepsy. None of these, however, clearly explains all the clinical features.虽然这是一种良性的病症，但其确切病因仍不清楚。已经提出了各种假说，包括静脉淤血（继发于脑静脉血的逆流）、局灶性缺血、偏头痛和癫痫。然而，这些都不能确切解释所有的临床特征。
The diagnosis of transient global amnesia is based on its clinical features. Criteria such as those established by Hodges and Warlow serve as guidance. MRI is, nonetheless, recommended to exclude stroke or structural pathology, where there is diagnostic uncertainty. While imaging in such cases is usually normal, it is now well-known that transient global amnesia may be accompanied by characteristic MRI changes involving the hippocampus. Structurally, the cornu ammonis or hippocampus proper is divided into four distinct zones, based upon their sensitivity to hypoxia and histological differences. CA1 (Sommer’s sector) is known as the vulnerable zone, CA2 and CA3 as the resistant sectors, and CA4 as medium vulnerability sector. Classic diffusion-weighted imaging (DWI) findings in transient global amnesia consist of unilateral or bilateral small punctuate hyperintense lesions in the CA1 region of the hippocampal cornu ammonis. These changes were first described in 1998 by Strupp et al. Since that time, various studies have been carried out and shown that certain factors may improve the visibility of these findings on MRI. These include high-resolution DWI, higher B values, thin slice thickness (2-3 mm), and a delay of 48 to 72 hours between symptom onset and scanning. In fact, in cases in which the initial MRI performed within 24 hours is normal but clinical suspicion for transient global amnesia remains high, repeat imaging is recommended.短暂性全面遗忘症的诊断基于其临床特征。Hodges和Warlow制定的标准可以作为指导。尽管如此，MRI仍作为建议性检查以排除中风或实质性病变。虽然这些病例的影像往往是正常的，但众所周知，短暂性全面遗忘症可能伴发特征性的海马异常MRI表现。根据对缺氧的敏感性及组织学差异性，Ammon角或海马分为四个区：CA1 (Sommer’s扇区)为易损区，CA2和CA3为耐受区，CA4为中等易损区。短暂性全面遗忘症的典型DWI表现是单侧或双侧海马CA1区点状高信号。这一表现在1998年被Strupp等人首次描述。从那时起，各种研究陆续开展，并发现某些因素可能提高其在MRI上的可见性，包括高分辨率DWI、较高B值、薄层扫描（2-3mm）以及症状发生48-72小时内进行扫描。事实上，如果24小时内的首次MRI检查是正常的，但临床怀疑是短暂性全面遗忘症，推荐复查。The localization of this pathological process to the CA1 area on imaging may give an indication of its causation. It is understood that neurons in this region of the hippocampus are particularly susceptible to metabolic stress, suggesting that transient global amnesia may result from a physiological temporary inhibition of memory formation. Interestingly, the fact that DWI changes in transient global amnesia do not appear in the hyperacute phase, unlike the restricted diffusion seen in ischemia, further supports the theory that these imaging findings are due to an entirely different pathological process. These lesions have been noted to resolve on follow-up MRI performed after six to 12 months.该病症影像定位于CA1区可能提示其发病原因。众所周知，该区域的神经元特别容易受到代谢应激的影响，提示短暂性全面遗忘症可能是由于记忆形成的生理性暂时抑制造成的。有趣的是，与缺血时的弥散受限不同，短暂性全面遗忘症的DWI异常并不在超急性期出现，其进一步支持了以下理论，即这些影像反映了完全不同的病理过程。该影像表现在6到12个月的MRI随访中消失。
Differential diagnoses for abnormal signal intensity in the hippocampi include posterior circulation ischemia, limbic encephalitis, and protracted seizures. These conditions, besides being readily distinguishable clinically, can also be distinguished radiologically to a certain degree. While in transient global amnesia the signal hyperintensities seen on DWI are punctate and located laterally within the hippocampi, in posterior circulation infarcts the hippocampal lesions are larger in size with associated additional areas of restricted diffusion seen in the posterior cerebral artery territory, such as the occipital lobe, thalamus, and corpus callosum. In protracted seizures, besides hippocampal signal abnormalities, additional changes may occur in the pulvinar and cortex. Furthermore, limbic encephalitis involves other limbic structures besides the hippocampus, such as the parahippocampal gyrus, cingulate gyrus, and insula.海马异常信号的鉴别诊断包括后循环缺血、边缘性脑炎和长期癫痫发作。这些症状除了在临床上容易区分外，影像表现上也有一定的不同。DWI上，短暂性全面遗忘症的病灶是点状的，且位于海马外侧；后循环梗死的海马病变范围较大，且伴有后循环供血区的其他区域的弥散受限，如枕叶、丘脑和胼胝体。在长期癫痫发作中，除了海马信号异常外，枕叶及皮质也会出现异常。此外，边缘性脑炎还涉及海马之外的其他边缘结构，如海马旁回、扣带回和岛叶。
No treatment or driving restriction is required, and the condition does not usually recur in the majority of cases. Outpatient follow-up with additional imaging if clinically indicated is the mainstay of management. Several studies have shown that there is no difference in prognosis or cognitive function in patients with and without DWI changes. This also applies to the comparison of patients with transient global amnesia with age-matched controls. Of note, some studies have raised the possibility of an association between recurrent transient global amnesia and primary progressive aphasia, a rare neurological disorder characterized by progressive language impairment.无需治疗、也无驾驶限制，大多数无复发倾向。如果有临床指征，则门诊进行影像随访。多项研究表明，伴或不伴DWI异常的患者在预后和认知功能方面无差异性。同样地，在与年龄相匹配的正常人群比较中，也无差异性。值得注意的是，一些研究提出了复发性短暂全面遗忘症和原发性进行性失语症（一种罕见的以进行性语言障碍为特征的神经系统疾病）之间存在关联的可能性。
In conclusion, the recognition of imaging findings in transient global amnesia is essential for radiologists in order to avoid such patients being misdiagnosed with ischemia or other pathology, especially in cases in which the clinical picture is atypical.综上所述，对于影像科医生来说，认识短暂性全面遗忘症的影像表现是至关重要的，可以避免此类患者误诊为缺血或其他病变，尤其当临床表现不典型时。
Learning points
While the diagnosis of transient global amnesia is based on its clinical features, neuroimaging is important to exclude other sinister causes of global amnesia.
Classic DWI findings in transient global amnesia consist of unilateral or bilateral small punctate hyperintense lesions in the CA1 region of the hippocampal cornu ammonis.
Recognition of this sign is of the utmost importance for radiologists in order to allow for an accurate diagnosis and differentiation from ischaemic pathology.
学习要点
1、虽然短暂性全面遗忘症的诊断是基于临床特征，但神经影像学对于排除其他凶险原因造成的全面遗忘是重要的。
2、短暂性全面遗忘症的典型DWI表现为单侧或双侧海马CA1区点状高信号。
3、对于影像科医生，认识这一征象是至关重要的，有助于准确诊断及与其他缺血性病变的鉴别。
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