Yoo Aran, Jou Jonathan, Klopfenstein Jeffrey D, Kattah Jorge C
University of Illinois College of Medicine, Peoria, IL, United States.
Department of Neurosurgery, University of Illinois College of Medicine, Peoria, IL, United States.
Front Neurol. 2018 May 28;9:358. doi: 10.3389/fneur.2018.00358. eCollection 2018.
Infratentorial siderosis (iSS) is a progressive degenerative disorder targeting primarily the cerebellum and cranial nerve eighth; therefore, progressive ataxia and its neuro-otological findings are common. Toxicity from hemosiderin involves selectively vulnerable neurons and glia in these posterior fossa structures. Other neurologic findings may be present, though our focus relates to the cochlea-vestibular cerebellar involvement. Radiographic evidence of siderosis may be the result of recurrent, albeit covert bleeding in the subarachnoid space, or the consequence of an overt post-traumatic or aneurysmal subarachnoid hemorrhage (SAH). The radiographic iSS appearance is identical regardless of the SAH cause. A recent study provides compelling evidence to search and correct possible hemorrhage sources in the spinal canal. The removal of residual existing hemosiderin deposits that may potentially cause clinical symptoms remains as a major therapeutic challenge.
We reviewed large data sources and identified salient papers that describe the pathogenesis, clinical and neurotologic manifestations, and the radiographic features of iSS.
The epidemiology of iSS is unknown. In a recent series, clinically evident iSS was associated with recurrent SAH; by contrast, in a follow-up period ranging from weeks up to 11 years after a monophasic episode of SAH, radiographic siderosis was clinically silent. However, the post-aneurysmal or post-trauma SAH sample size in this single study was small and their observation period relatively short; moreover, the burden of intraneuronal hemosiderin is likely greater with recurrent SAH. There are a few reports of late iSS, several decades after traumatic SAH. A recent report found subjective hearing loss in aneurysmal SAH individuals with radiographic siderosis. Only in recent years, it is safe to perform magnetic resonance imaging (MRI) in post-aneurysmal SAH, because of the introduction of titanium, MRI-compatible aneurysm clips.
iSS can be associated with significant neurotologic and cerebellar morbidity; the recurrent SAH variant is frequently clinically symptomatic, has a shorter latency and greater neurotologic disability. In these cases, a thorough search and management of a covert source of bleeding may stop clinical progression. The frequency and clinical course of radiographic iSS after traumatic and post-aneurysmal SAH is largely unknown. Detection of radiographic iSS after trauma or aneurysm bleeding suggests that the slower clinical course could benefit from an effective intervention if it became available. The use of cochlear implants is a valid alternative with advanced hearing impairment.
幕下铁沉积症（iSS）是一种进行性退行性疾病，主要累及小脑和第八对脑神经；因此，进行性共济失调及其神经耳科表现较为常见。含铁血黄素的毒性选择性地累及这些后颅窝结构中易受损的神经元和神经胶质细胞。可能会出现其他神经系统表现，不过我们关注的是耳蜗 - 前庭小脑受累情况。铁沉积症的影像学证据可能是蛛网膜下腔反复（尽管隐匿）出血的结果，或者是明显的创伤后或动脉瘤性蛛网膜下腔出血（SAH）的后果。无论SAH的病因如何，iSS的影像学表现都是相同的。最近一项研究提供了令人信服的证据，表明需要查找并纠正椎管内可能的出血源。清除可能导致临床症状的残留含铁血黄素沉积物仍然是一项重大的治疗挑战。
我们查阅了大量数据源，并确定了描述iSS的发病机制、临床和神经耳科表现以及影像学特征的重要文献。
iSS的流行病学情况尚不清楚。在最近一系列病例中，临床明显的iSS与反复SAH有关；相比之下，在单次SAH发作后数周至11年的随访期内，影像学铁沉积症在临床上并无症状。然而，在这项单一研究中，动脉瘤后或创伤后SAH的样本量较小，观察期相对较短；此外，反复SAH时神经元内含铁血黄素的负担可能更大。有几篇关于创伤性SAH数十年后出现迟发性iSS的报道。最近一项报告发现，有影像学铁沉积症的动脉瘤性SAH患者存在主观听力丧失。仅在近年来，由于引入了与MRI兼容的钛制动脉瘤夹，在动脉瘤后SAH患者中进行磁共振成像（MRI）才变得安全。
iSS可伴有明显的神经耳科和小脑病变；反复SAH型通常具有临床症状，潜伏期较短且神经耳科残疾程度更高。在这些病例中，彻底查找并处理隐匿的出血源可能会阻止临床进展。创伤性和动脉瘤后SAH后影像学iSS的发生率和临床过程在很大程度上尚不清楚。创伤或动脉瘤出血后检测到影像学iSS表明，如果有有效的干预措施，临床病程较慢的情况可能会从中受益。对于重度听力障碍，使用人工耳蜗是一种有效的替代方法。
