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在MRI T2WI或磁敏感成像(magnetic susceptibility weighted imaging,SWI)序列上，脑实质内病灶周边岀现的低信号环，谓之铁环征，该低信号环随着时间的增加而逐渐增宽。
On the MRI T2WI or magnetic sensitive imaging (SWI) sequences, there is a susceptibility weighted ring around the lesions in the brain parentage, which is called the ferrogram sign. The low-signal ring widens gradually with the increase of time.铁环征是脑实质内海绵状血管瘤(cavevernous angloma,CA)的MRI表现，病灶周边低信号环为反复多次少量慢性出血病灶周围出现含铁血黄素沉积所致。Iron ring sign is the MRI manifestation of cavevernous angloma (CA) in the brain parenchyma. The low signal ring around the lesion is caused by hemosiderin deposition around the lesion with repeated and small amounts of chronic hemorrhage.CA非真性肿瘤，为先天性血管畸形之一。1966年，McCormik将颅内血管畸形分为：①毛细血管扩张症；②海绵状血管畸形或海绵状血管瘤；③动静脉畸形或动静脉血管瘤：④静脉性畸形或静脉性血管瘤；⑤血管曲张，包括大脑大静脉畸形等。CA non - true tumor, one of the congenital vascular malformations. In 1966, McCormik classified intracranial vascular malformations as: telangiectasia; Cavernous vascular malformation or cavernous hemangioma; Arteriovenous malformation or arteriovenous hemangioma: venous malformation or venous hemangioma; (5) Varicose vessels, including the great veins of the brain, etc.CA较少见，占颅内脑血管畸形的7%。典型的CA由丛状薄壁的血管窦样结构组成，肉眼呈紫红色或深红色血管性团块，显微镜下见病灶由密集而扩大的血管构成，管壁由菲薄的内皮细胞和成纤维细胞组成，缺乏弹力纤维和肌层且管腔内充满血液。管腔间有神经纤维分隔，无正常脑组织。由于CA的血管壁薄且缺乏弹性，因而易出血，病灶内有时可见数目不等的片状出血、钙化、胶质増生及坏死囊变灶，病灶周围可见含铁血黄素沉着或有机化的血块。CA is rare, accounting for 7% of intracranial cerebrovascular malformations. Typical CA consists of a plexiform thin-walled vascular sinus-like structure, with purple or dark red vascular masses to the naked eye. Microscopically, the lesion is composed of dense and enlarged blood vessels, and the tube wall is composed of thin endothelial cells and fibroblasts, lacking elastic fibers and muscular layers, and the lumen is filled with blood. There are nerve fibers separating lumen and no normal brain tissue. As the vascular wall of CA is thin and inelastic, it is prone to hemorrhage. Sometimes, different amounts of patchy hemorrhage, calcification, glial growth and necrotic cystic lesions can be seen in the lesions, and hemosiderin and organic blood clots can be seen around the lesions.CA是一种不完全外显性染色体显性遗传性疾病，具有家族遗传倾向，可发生在颅内任何部位。单发病灶明显多于多发，任何年龄均可被发现，与病灶的发生部位及病灶的变化有关。多无症状，常以颅内出血为首发症状，典型表现为癫痼发作、突发性头痛、进行性神经功能障碍等。CA is an incomplete exosomal dominant disease with familial predisposition. It can occur in any part of the brain. Single lesions are significantly more than multiple, can be found at any age, and is related to the location and changes of lesions. Most have no symptoms, usually intracranial hemorrhage has been the first symptom, typical manifestations of epilepsy, sudden headache, progressive neurological dysfunction, etc.CT及MR表现与其病理结构及演变过程密切相关。血流缓慢反复出血后的不同时期岀血成分沉积及血栓形成、钙化、胶质增生等继发病理变化是CA的主要影像学成像基础，而无占位效应或有轻微占位效应。CT and MR findings are closely related to their pathological structure and evolution. The accumulation of blood components and secondary pathological changes such as thrombosis, calcification and gliosis in different periods after slow and repeated bleeding are the main imaging basis of CA, but there is no mass effect or slight mass effect.CT表现多为界限清楚的圆形或卵圆形的等密度或稍高密度影其内可见颗粒征，即在略高密度背景内含有数量不一的颗粒状髙密度影和低密度影，前者为钙化，后者为血栓形成，颇具特征。有研究报道1组12例CT扫描16个病灶均呈稍高或高密度，7个病灶可见钙化除急性岀血或较大病灶，灶周一般无水肿带及占位征象。有学者认为瘤周水肿征在提示瘤内有无新鲜出血上具有一定诊断价值。CT增强扫描可表现不强化或周边轻度强化，少数等密度病灶表现为均匀强化，其强化程度主要取决于病灶内血栓形成和钙化的程度，血栓形成轻且钙化不明显者强化明显。CT features are mostly circular or ovoid with clear boundaries of equal density or slightly high density shadow, that is, there are different amounts of granular high-density shadow and low-density shadow in slightly high density background, the former is calcification, the latter is thrombosis, which is quite characteristic. Studies have reported that CT scan of 12 patients in a group showed slightly high or high density of 16 lesions, calcification was visible in 7 lesions except acute bleeds or large lesions, and there was generally no edema zone or space occupying signs around the foci. Some scholars believe that peritumor edema sign has certain diagnostic value in indicating whether there is fresh hemorrhage inside the tumor. CT enhanced scan can show no enhancement or mild peripheral enhancement, and a few lesions with equal density show uniform enhancement, the degree of enhancement mainly depends on the degree of thrombosis and calcification within the lesion, and the degree of enhancement is obvious for those with light thrombosis and insignificant calcification.MRI信号特征主要取决于瘤内出血的时间，反复少量出血是形成MR特征征象的主要因素。CA的MR表现，T1WI呈略低或低等混杂信号，出血可显示为高信号；T2WI呈高信号或混杂信号，病灶周围可见由岀血所致含铁血黄素沉着而形成的环状低信号，即铁环征，较为特征。CA出血MRI信号较复杂，T1WI和T2WI可均为高信号，也可T1WI呈高信号，T2WI呈低信号。随着病变的演变，当红细胞溶解、释放高铁血红蛋白，T2WI由低信号变为高信号；当巨噬细胞溶解，含铁血黄素在病变周围沉积，留下显著的环状低信号(铁环征),以T2WI更为明显；但有研究者选取在SE序列上表现阴性或不典型的CA病例，25例39个在SE T1WI上和26个(56.5%)MRI signal characteristics mainly depend on the time of intracranial hemorrhage, and repeated small amount of hemorrhage is the main factor for the formation of MR characteristic signs. The MR performance of CA showed slightly low or low mixed signals on T1WI, and the bleeding could show high signals. T2WI showed high signal or mixed signal, and circular low signal formed by hemosiderin induced by bleeds could be seen around the lesion, namely the iron ring sign, which is relatively characteristic. MRI signals of CA bleeding are complex, both T1WI and T2WI can have high signal, or high signal on T1WI and low signal on T2WI. With the evolution of the lesions, T2WI changes from low signal to high signal when red blood cells dissolve and release methemoglobin. When macrophages are lysed, hemosiderin is deposited around the lesion, leaving a significant circular hyposignal (iron sign), which is more obvious in T2WI. However, some researchers selected CA cases with negative or atypical SE sequences, 25 cases, 39 cases on SE T1WI and 26 cases (56.5%).在SE T2WI上呈等、低、高或混杂信号，未显示或未明显显示铁环征的病灶采用SWI序列检查，21个(45.7%)表现为完全低信号(3个在SE T2WI上亦为低信号),25个(54.3%)在低信号中伴有点状、条状或桑葚状髙信号，周围有较宽的低信号环，岀现明显的铁环征(7个在SE T1WI和SE T2WI上亦有显示)。MRI增强扫描可表现为强化与不强化，其机制同CT。典型CA的MRI表现为：①瘤体呈不同程度的混杂信号团；②铁环征，即瘤体外周圆形低信号环，在所有成像序列上均为黑色信号，以T2WI和SWI最明显；③反应性胶质增生呈长T1长T2信号；④瘤灶周围常无脑组织水肿及不明显占位效应；⑤病灶强化或不强化。In SE T2WI is high, low, or mixed signals, such as not to display or not clearly shows a hoop of lesions by SWI sequence examination, 21 (45.7%), characterized by low signal completely (three in SE is low signal on T2WI), 25 (54.3%) in the low signal with dot, strip or mulberries high signal, surrounded by wide rings of low signal file is now obvious hoop sign (7 in SE T1WI and T2WI 'SE has also shown). MRI contrast-enhanced scan can show enhancement and non-enhancement, and the mechanism is the same as CT. The MRI manifestations of typical CA were as follows: The tumor body presented mixed signal masses of different degrees; Hoop sign, namely the circular low signal ring around the tumor, was black signal on all imaging sequences, with T2WI and SWI being the most obvious; Reactive gliosis showed long T1 and long T2 signal; There is no cerebral edema and no obvious mass effect around tumor lesions; (5) Enhanced or not enhanced lesions.CA典型病例具有特征性的CT和MRI表现，诊断不难。诊断时应考虑与自发性脑岀血、血栓性AVM及岀血性原发、继发性脑肿瘤相鉴别。Typical CA cases have characteristic CT and MRI appearances, and the diagnosis is not difficult. It should be considered to differentiate from spontaneous brain bleeds, thrombotic AVM and primary and secondary brain tumors.
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