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1、Greater and Lesser Omenta: Normal Anatomy and Pathologic Processes,大网膜和小网膜的正常解剖及异常影像表现,Eunhye Yoo, MD, Joo Hee Kim, MD, Myeong-Jin Kim, MD,大网膜和小网膜是个非常复杂的解剖区域。正因为如此，网膜病变从积液到弥漫性网膜浸润，CT表现表现多种多样，同时又无特征性。网膜不仅是限制病变扩散的屏障，同时又是病变传播的途径。 累及网膜的病变：感染、炎症、 肿瘤、 外伤 和坏死。高分辨率螺旋CT扫描同时行MPR 能很好显示网膜的解剖结构和病变状况。充分认识网膜的影像解剖和
2、病变的各种CT表现及一些特征性征象，对诊断和治疗具有非常必需的。,CT 扫描参数和重建技术 采用 16-section CT scanner，平扫和 增强: 0.5-second rotation time, 0.75-mm collimation, 3-mm section thickness, 35-cm field of view, 3-mm reconstruction thickness, 12-mm feed per rotation, 120 kV, and 140 mA。常规采用3-mm section thickness 断面图像 。后处理工作站进行 sagittal、 co
3、ronal, or oblique 多平面重建。,正常解剖 大网膜主要由脂肪组织和一些细小扭曲的胃网膜血管 gastroepiploic vessels构成。 CT表现为位于前腹壁下，胃、横结肠和小肠前之间的一组不同宽度的 脂肪组织, 。在大网膜和邻近的软组织结构间的腹水衬托下，大网膜显示为一单纯的脂肪层., 一旦网膜出现异常的软组织病变，则显示 为模糊状、条索状、结节状影和肿块. 小网膜由肝胃韧带和肝十二指肠韧带组成，它将胃小弯、远侧十二指肠和肝脏 连接起来，覆盖小网膜的前方。肝胃韧带内含 胃左血管和胃左组淋巴结。肝十二指肠韧带，为小网膜侧方厚层，内含门静脉、肝动脉、肝外胆管和,肝门组淋巴结
4、。 正常情况下小网膜囊是闭合的, 只有它的边如胃后壁、胰腺体部才可以在CT上显示。,Greater and Lesser Omenta: Normal Anatomy and Pathologic Processes1,Drawing of the anatomy of the greater and lesser omenta ： The greater omentum (GO) is composed of a double layer of peritoneum that extends from the greater curvature of the stomach (S) infe
5、riorly. Its descending and ascending portions usually fuse to form a four-layer vascular fatty apron; the resulting space is contiguous with the lesser sac (LS). The lesser omentum (LO) connects the lesser curvature of the stomach and proximal duodenum with the liver (L) and contains blood vessels,
6、nerves, and lymph nodes. The lesser sac is empty and collapsed so that only parts of its boundaries, such as the posterior gastric wall and pancreatic body, are observed on axial CT scans. Ao = aorta, C = colon, K = kidney, P = pancreas, Sp = spleen, 1 = falciform ligament, 2 = gastrohepatic ligamen
7、t, 3 = gastrosplenic ligament.,Greater and Lesser Omenta: Normal Anatomy and Pathologic Processes1,Ao = aorta, C = colon, K = kidney, P = pancreas, Sp = spleen, 1 = falciform ligament, 2 = gastrohepatic ligament, 3 = gastrosplenic ligament.,Axial,Greater and Lesser Omenta: Normal Anatomy and Patholo
8、gic Processes1,coronal,Ao = aorta, C = colon, K = kidney, P = pancreas, Sp = spleen, 1 = falciform ligament, 2 = gastrohepatic ligament, 3 = gastrosplenic ligament.,Greater and Lesser Omenta: Normal Anatomy and Pathologic Processes1,Ao = aorta, C = colon, K = kidney, P = pancreas, Sp = spleen, 1 = f
9、alciform ligament, 2 = gastrohepatic ligament, 3 = gastrosplenic ligament.,大网膜病变 。大网膜病变的CT征象：(a)多灶性，边界不清的浸润性病灶： 癌性腹膜炎、结核性腹膜炎、恶性间皮瘤、腹膜假性粘液瘤、 淋巴瘤和肝硬化源性门脉高压。(b) 囊实性肿块： 原发性和继发性肿瘤和感染病变; (c) 其它各类病变： 网膜梗塞坏死、 异物肉芽肿、血肿和 疝。,A、多灶性，边界不清，浸润性病灶Multifocal, Ill-defined, Infiltrating Lesions a. 肝硬化源性网膜水肿b. 播散性腹膜肿瘤c.
10、 感染性腹膜炎癌性腹膜炎、恶性间皮瘤和淋巴瘤等播散性腹膜肿瘤和结核性腹膜炎的鉴别是十分困难的，因为它们临床症状不典型，影像征象重叠（ overlapping imaging features）。网膜异常的CT征象如fatty stranding 、 结节状浸润（ nodular infiltration） 、肿块和网膜饼（ omental caking）在各种病变中均可显示，并没有明显差异。,Greater and Lesser Omenta: Normal Anatomy and Pathologic Processes,肝硬化源性网膜水肿（infiltrative edema from l
11、iver cirrhosis）合并门脉高压的肝硬化是弥漫性网膜性病变最常见的原因之一，肝硬化患者在CT上常常可以显示网膜、肠系膜和后腹膜水肿。网膜水肿的CT 表现多种多样： 从轻度的薄雾状到边界清楚的肿块范围内的一系列改变，和其它网膜病变的表现并无异样。,b. 弥漫性腹膜肿瘤（diffuse peritoneal tumor）肿瘤腹膜种植转移 原发灶大多来自胃、胰腺、结肠、子宫和膀胱，血运性转移多来自恶性黑色素瘤（ malignant melanoma）、乳腺癌和肺癌。 癌性腹膜炎的征象 ： 腹水、腹膜增厚、种植性结节和网膜浸润 （omental infiltration）但是这些征象并非癌性
12、腹膜炎所特有，也可以存在于其它种类的病变累犯种植于腹膜：间皮瘤 mesothelioma、结核 和 淋巴瘤病。 因此，我们在临床工作中首先应该 努力寻找消化道和泌尿道的原发肿瘤。大家知道，网膜饼是癌性腹膜炎的一个常见征象，但不是其特征性征象。网膜增厚轮廓呈不规则状改变才是癌性腹膜炎较为有用的征象。,.,Peritoneal carcinomatosis from the stomach in a 22-year-old man with epigastric pain。CT scans show large amounts of ascites, diffuse nodular omental
13、 infiltration (omental cake) (arrows), and abnormal gastric wall thickening 。,Peritoneal carcinomatosis in a 30-year-old woman with malignant melanoma. CT scan shows hematogenous dissemination of malignant nodules in the peritoneal space including the omentum (arrows), retroperitoneal spaces, and th
14、e subcutaneous fat layer of the abdomen.,c. 感染性腹膜炎 infectious peritonitis 结核性腹膜炎起因肺结核的血性播散和肠系膜淋巴结结核的破溃，支持结核性腹膜炎 CT 表现: 1、腹膜稍增厚，边缘光滑。smooth peritoneum with minimal thickening 2、肠系膜显著强化，合并直径5mm的多发大结节。pronounced enhancement, mesenteric involvement with macronodules (5 mm in diameter)3、细薄的网膜线。a thin ome
15、ntal line (fibrous wall covering the infiltrated omentum)4、肿大淋巴结，中心为低密度(caseous necrosis), 5、多发钙化。 纤维粘连型结核性腹膜炎虽然比较少见，其特征为包裹腹腔积液呈多房状改变。巨大网膜肿块和肠袢分离和固定。,Tuberculous peritonitis in a 38-year-old woman with abdominal distention for 1 week. CT scan shows a large amount of ascites with even peritoneal thic
16、kening (arrowhead) and diffuse omental infiltration (arrow) without associated lymphadenopathy. The initial impression was carcinomatosis. When the primary malignancy is unclear, the differential diagnosis should include tuberculous peritonitis, particularly in endemic areas. The final diagnosis was
17、 tuberculous peritonitis.,D、恶性腹膜间皮瘤Malignant peritoneal mesothelioma 腹膜恶性间皮瘤很少见，占人体所有间质瘤的 12%33%。恶性腹膜间皮瘤CT表现多种多样。常见：腹水、不规则或结节状腹膜增厚、肠系膜星芒状改变（ a “stellate” pattern of the mesentery）、 肠壁增厚和网膜受累，其包括：脂肪间隙细条状、污斑状、散在分布网膜结节和网膜饼（ finely infiltrated fat with a “smudged” appearance to discrete omental nodules or omental caking）。 有时也表现为上腹部一个较大的但大小尚可测量的肿块，同时合并少量腹水和腹膜上一些散在分布结节。s a large quantifiable mass in the upper abdomen with minimal ascites and discrete nodules scattered over the peritoneum.,
