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??? 病例选自《Mayo Clinic Body MRI Case Review》  
History19-year-old pregnant woman with a 2-week history of right upper quadrant pain. 19岁孕妇，右上腹痛2周余。
Fig 3.12.1： 
Fig 3.12.2：
Imaging Findings
Coronal SSFSE (Figure 3.12.1) and axial T2-weighted FSE(Figure 3.12.2) images demonstrate massive dilatation of the CBD at the bifurcation, as well as the distal duct. Dilatation of perihilar intrahepatic ducts can be seen. Within the duct, there is a large filling defect or nodule, which is predominantly hypointense on the T2-weighted images and contains a central cystic region with a fluid-fluid level. 冠状位 SSFSE(Figure 3.12.1)、横断位T2WI FSE（Figure 3.12.1）示胆总管分叉处及远端明显扩张，肝门部肝内胆管扩张。扩张的胆管内可见巨大充盈缺损，T2WI以较低信号为主，其内部可见囊变及液液平。
Diagnosis
Choledochal cyst with intraductal hematoma 胆总管囊肿伴胆管内血肿
Comment
Choledochal cysts are rare entities, with an estimated incidence in the Western population of 1 in 100,000 to 150,000 live births. Rates are much higher in Asia, where the reported incidence is 1 in 1,000 live births. Choledochal cysts are more common in women, with a female to male ratio of 4:1. 胆总管囊肿是一种少见疾病，西方国家发病率约1/100000至1/150000，而在亚洲发病率明显更高，有文献报道活产儿中发病率约1/1000。胆总管囊肿女性发病多于男性，男女比例约1：4。
The etiology of choledochal cysts remains a controversial topic. The most popular theory is that they are the result of an abnormal pancreaticobiliary duct junction where the 2 ducts join outside the ampulla of Vater and form a long, common channel that then allows mixing of pancreatic and biliary contents. Activated pancreatic enzymes reflux into the biliary ducts and cause inflammation and deterioration of the biliary duct walls, leading to progressive dilatation.In support of this theory are several studies documenting increased levels of amylase in the bile of patients with choledochal cysts. Animal studies also have demonstrated that surgical creation of an abnormal pancreaticobiliary junction leads to cystic dilatation of the biliary ducts. Nevertheless, skeptics have been unable to show an abnormal pancreaticobiliary junction in as many as 20% to 50% of patients with choledochal cysts,which implies that this mechanism is probably not the only one involved. 胆总管囊肿的病因目前尚存在争议，大部分人认为与胰胆管发育异常有关：胰管和胆总管在Vater壶腹外融合，形成一个很长的共用管道，内含有胆汁和胰液，胰液里的活性酶返流至胆管，引起胆管壁的感染和退化，导致逐渐扩张。胆总管囊肿内的胰淀粉酶水平增高可以证实这一学说。动物实验也证实，手术吻合胰管和胆总管可以导致胆管扩张。 尽管如此，大约20%-50%的胆总管囊肿患者没有胰胆管融合畸形，这也说明该学说并非胆总管囊肿的唯一致病原因。
The classification scheme generally used for choledochal cysts is the Todani modification of the original system proposed by Alonso-Lej in 1959. Type I cysts involve the extrahepatic biliary tree and are the most common, representing 50% to 80% of all choledochal cysts, with type IA describing cystic dilatation of most or all of the extrahepatic biliarytree; type IB, focal segmental dilatation; and type IC, fusiform dilatation of the extrahepatic ducts. Type II cysts are discrete diverticula of the extrahepatic ducts connected to the common duct by a narrow stalk. Type III cysts represent choledochoceles—focal dilatationat the ampulla of Vater that projects into the duodenum. Type IVA cysts have multiple intra- and extrahepatic dilatations; in type IVB cysts, the multiple dilatations involve only the extrahepatic ducts. Type V represents Caroli disease, defined as multiple saccular or cystic dilatations of intrahepatic ducts. 1959年Alonso-Lej提出了胆管囊肿的分型方法，后来Todani做出了一些修改，这一分型方法得到了大家的一致认可和广泛应用。 I型为肝外胆管囊肿，也是最常见的亚型，约占全部胆总管囊肿的50%-80%，其中Ia为全部或大部分肝外胆管弥漫性扩张，Ib型为节段性扩张，Ic型为肝外胆管梭形扩张。 II型为肝外胆管憩室，并通过窄蒂连于共用胆管。
III型为胆总管末端囊肿--即Vater壶腹突入十二指肠处的局限性扩张。
IVa型为肝内外胆管的多发扩张，IVb型仅有肝外胆管多发扩张。 V型又称Caroli病，为肝内胆管的多发囊状扩张。
This classification system, although widely used, is not without controversy. If you have already read the discussion of Caroli disease, for example, you might remember that although Caroli disease is technically defined as intrahepatic biliary dilatation, a notable percentage of patients(in fact, probably a majority) also have involvement of the extrahepatic ducts,which makes the type IVA and type V classifications somewhat redundant. Some authors doubt whether Caroli disease belongs in this classification at all, since its frequent autosomal recessive inheritance and association with renal cystic disease and hepatic fibrosis are not shared by any other group of patients with choledochal cysts. Other authors have questioned whether type II cysts (diverticuli) and type III cysts (choledochoceles) are true choledochal cysts,since type II cysts generally have minimal inflammatory response and carcinogenic potential and there are alternative theories for the origin of choledochoceles. 虽然上述的分类方法得到了广泛的应用，但仍然存在争议。例如Caroli病定义为肝内胆管扩张，但相当一部分（甚至可能是大多数）也可以累及到肝外胆管，这就与IVa型重复了。 部分学者质疑Caroli病是否属于这一分类范畴内，因为Caroli病是一种常染色体阴性遗传病，常合并肾囊肿和肝纤维化，而这是其他亚型胆管囊肿所不具有的特征。 还有一部分学者对II型（胆管憩室）和III型（胆总管末端囊肿）是否为真性胆管囊肿存有疑问。II型胆管憩室一般会有轻微的炎性反应，有致癌的可能性；III型胆总管末端囊肿可能与其他类型存在不同的病因。
Choledochal cysts are considered a premalignant state, with cancers occurring more often in these patients and at an earlier age. The overall risk of cancer has been reported to be 10% to 15%, and the incidence rises with age (up to 75% for patients aged 70-80years).Adenocarcinoma(cholangiocarcinoma) is by far the most common histologic type. Development of carcinoma is thought to result from chronic inflammation that leads to cellular regeneration and dysplasia and, eventually, frank malignancy. 一般认为，胆总管囊肿是一种癌前病变，胆总管囊肿的患者患癌的几率增高、发病年龄降低。据文献报道，胆总管囊肿患者的癌症发病率约10%-15%，并且发病率随年龄增高而上升（70-80岁时甚至可高达75%）。腺癌（胆管细胞癌）是最常见的病理亚型。 胆管囊肿的癌变是由囊肿的慢性炎症引起，细胞再生和发育障碍，最终恶变形成恶性肿瘤。
This case might be classified as a type IVB choledochal cyst, with multiple (at least 2) regions of focal dilatation in the CBD. The large filling defect should probably raise some concern for neoplasm, and normally dynamic contrast-enhanced 3D SPGR images would answer that question. However, this patient was pregnant and so there was reluctance to give intravenous contrast. (Gadolinium-based contrast agents do cross the placenta, but there is little evidence to suggest that they are harmful to the fetus. Then again, there isn’t much evidence that they are completely safe either, and it is unlikely that anyone will ever perform the definitive experiment.) At surgery, this filling defect turned out to be a large hematoma. 本例为IVb型胆管囊肿，胆总管多发（至少2处）局限性扩张。囊肿内的大的充盈缺损要考虑肿瘤的可能性，一般动态增强扫描3D SPGR序列可以帮助诊断。但是本例患者为孕妇，不愿解释静脉注射造影剂。（钆剂可以通过胎盘组织，但是没有明确的证据证明钆剂对胎儿有害，不过也没有足够的证据证明钆剂对胎儿是安全的，没有人愿意去做这种实验。）最后，手术病理证实，这个充盈缺损是一个血肿。
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