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1、正常胸腺及胸腺病变CT表现 The Normal and Abnormal Thymus CT imaging finding,南方医院影像中心 2009级博士研究生 吕晓飞,Content,胸腺是一种复杂的淋巴上皮器官,具有调节细胞免疫的功能,在人类正常免疫中是不可缺少的。,CT及MR在胸腺异常的诊断中有重要作用,有利于评价是否正常及胸腺病变的范围。,正常CT表现(形态、大小、密度),胚胎发育,正常胸腺解剖位置及异位胸腺,胎儿第6周,胸腺起源于第三及第四咽囊; 第7周,胸腺始基延长并呈圆柱状形态,形成胸腺咽管,逐渐移行至前纵隔; 第8周,胸腺始基于下极融合; 第10周,肝脏组织及骨髓内的小淋
2、巴样细胞移行至胸腺始基; 第1416周,胸腺进一步分化形成皮质及髓质成分。,胚胎发育,正常胸腺解剖位置,位于前上纵隔,上达胸廓入口(甚至突入颈部接近甲状腺下缘),下至心包前面上部,两侧临近纵隔胸膜,后面贴附心包及左头臂静脉及主动脉弓。 胸腺的位置上界不超过胸骨柄上缘,下缘不超过左心室上缘或主动脉根部层面,外缘不超过上腔静脉、主动弥弓外缘其前缘位置正常可随周围结构改变而向左或向右移位。,正常胸腺解剖,异位胸腺,Ectopic and accessory thymic tissue may occur anywhere along the path of descent (thymopharyng
3、eal duct) as the result of failure of descent, sequestration, or failure to involute. Ectopic or accessory thymic tissue may be found in the vicinity of the superior vena cava, brachiocephalic vessels, and aorta. Rarely, it may be found in the posterior mediastinum or even in the dermis .,异位胸腺,Figur
4、e 1. Normal thymus with a cervical component in a 12-year-old boy. (a) Sagittal ultrasonographic (US) image shows the mediastinal and cervical components of the thymus (black arrows) attached to the lower pole of the thyroid (white arrow) via the thyrothymic ligament (arrowhead). Note the “starry sk
5、y” appearance of the thymus; this is created by hyperechoic fat against the background of the remaining hypoechoic lymphoid tissue. (b) Corresponding anatomic drawing shows the mediastinal (arrowheads) and cervical (arrows) components of the thymus.,异位胸腺,Figure 2. Cervical component of the thymus in
6、 a 3-year-old boy with a strong maternal family history of papillary thyroid carcinoma. The cervical component was misinterpreted as an “exophytic tumor of the thyroid gland.” Contrast-enhanced CT scans show a normal mediastinal thymus (arrows in A) and its cervical component (arrows in B). Follow-u
7、p studies 2 years later showed no change, and the patient remained asymptomatic.,异位胸腺,Figure 3. Ectopic parapharyngeal thymus in a 7-week-old boy with a “mass” in the right mandib-ular angle. Coronal contrast materialenhanced T1-weighted magnetic resonance (MR) image shows an enhancing parapharyngea
8、l mass (arrow), which is isointense relative to the mediastinal thymus (arrowhead). At needle biopsy, the mass was proved to be ectopic thymic tissue.,正常CT表现(形态),9岁以下多呈方形或梯形,10岁以后随年龄变化较大。,正常CT表现(大小),胸腺的形态随年龄而异,年轻人(特别是25岁以下者)的正常胸腺的大小和 重量有较大的差异。,国内研究学者认为胸腺的厚度随年龄变化,变化最大是在20-49岁之间,总体来说是从大到小再到大,大于60岁有增大趋
9、势;60岁,可超过30mm。宽度则随年龄增大而增大。,正常CT表现(密度),在6-19岁人群中胸腺的CT密度与肌肉相同或稍高,CT值 约为30Hu。 由于随年龄增加腺体遂渐消失而代之以脂肪,故从青 春期至25岁期间,以前外凸的外缘变得扁平或内陷,CT 值比肌肉低。 25岁后胸腺进一步萎缩,不再能见到明确的软组织密度 的胸腺结构,但可见在较丰富的脂肪背景上软组织密度 岛,萎缩的速度和程度因人而异。在83%的小于50岁的 人群中还可见正常胸腺。 此后前纵隔完全脂肪化,但大部分人还可见到密度稍高于 脂肪的残存的纤维性胸腺框架。,NORMAL or ABNORMAL?,On the basis of
10、this review, we have drawn the following conclusions regarding the appearance of the thymus gland and the detection of thymic abnormalities: The thymus gland is largest at puberty, and its overall size does not change significantly with age. It occupies essentially all of the mediastinal compartment
11、 anterior to the aortic arch, superior vena cava, and great vessels throughout life. 2. After puberty, parenchymal atrophy within the gland occurs, with the greatest percentage of parenchymal replacement by fat occurring between the ages of 31 and 40. 3. After age 40, the presence of a spherical or
12、oval focal soft-tissue mass within the thymus gland usually represent a neoplasm. 4. Before age 40, differentiation of a small thymoma from normal residual thymic parenchymal tissue may be impossible on the basis of size alone. 5. At all ages, a thymoma usually produces a focal bulge in the normally
13、 smooth adjacent visceral-pleural surface.,Moore, A.V., et al. , Age-related changes in the thymus gland: CT-pathologic correlation. AJR Am J Roentgenol, 1983. 141(2): p. 241-6.,(二)肿瘤病变,(一)非肿瘤病变,1.胸腺增生 2.胸腺淋巴样(滤泡性)增生 3.胸腺囊肿,1.胸腺上皮细胞肿瘤:胸腺瘤 2.胸腺非上皮性肿瘤 (1)胸腺淋巴瘤 (2)胸腺类癌 (3)胸腺脂肪瘤 (4)纵隔生殖细胞瘤,1.胸腺增生,胸腺真性增生
14、的定义是胸腺变大,但是组织结构维持正常的,只是大小超过同一年龄段正常的上限,不涉及任何病理性质的胸腺改变。胸腺真性增生常常见于机体遇到各种应激事件,免疫处于较大的挑战时期,比如肿瘤的化疗、放疗,皮质醇激素治疗,烧伤等应激事件,以后部分患者可恢复到正常大小。 常合并内分泌异常,如特发性甲状腺肿、格雷病(甲状腺中毒)和肢端肥大症。 胸腺弥漫性增大,但仍维持正常形态,两缘对称,呈光滑的不分叶的外形,CT值与正常者相似。,(一)非肿瘤病变,Case 2 胸腺真性增生,14岁,男。原发性T细胞淋巴瘤化疗后。,Case 1 胸腺真性增生,29岁,女性患者,合并Graves病。A. 胸腺体积轻度增大,边缘略
15、膨隆。B。经治疗3年后,胸腺体积缩小如正常。,2.胸腺淋巴样(滤泡性)增生,好发于青壮年,多为15-35岁女性。常见于重症肌无力(MG)患者,65%左右重症肌无力病人显示有淋巴滤泡性胸腺增生。它也被称为自家免疫性“胸腺炎”,较真性胸腺增生多见,此时,胸腺的大小和质量正常,但髓质扩张,而皮质受损。 胸腺可正常或增大,常是在MG病人行胸腺切除中发现并诊断的。据报道,在患MG并经病理证实有胸腺增生的病人中,25% -50 %的病例在CT上胸腺的大小正常;如有增大则可表现为弥漫性增大,使原略内陷的外缘变为隆突;有的则出现局灶性结节或大至5cm 的肿块。CT诊断胸腺淋巴样增生有一定的限度。,36岁,女性
16、患者。胸腺淋巴样(滤泡性)增生,胸轻度增大,边缘稍隆起。,3.胸腺囊肿,胸腺囊肿不多见,占前纵隔肿瘤1%-3%。可为先天或后天获得性,根据病理组织学将胸腺囊肿分为三类: (1)先天性胸腺囊肿,可发生于胚胎期胸腺移行途中颈部至纵隔的任何部位,但最常见于前上纵隔胸腺区。颈部胸腺囊肿最常见于3-8岁儿童,纵隔胸腺囊肿多见于成人。多无症状,偶在查体或因囊肿大有压迫症状,如胸闷不适、胸痛行X线检查时被发现。 (2)获得性胸腺囊肿,常见原因为感染,但也有认为Hassall氏小体扩张构成,好发于无症状的男性。有报道在免疫缺陷病毒感染的无症状的患者中可发生巨大的多房性囊肿。 (3)囊性胸腺肿瘤,此系胸腺肿瘤囊性变。一些胸腺肿瘤,如:何杰金氏病、精原细胞瘤、胸腺癌也可表现为广泛的囊性改变,甚至掩盖了原来的肿瘤,但后者从未见有完全囊变而形成薄壁囊肿者。,3.胸腺囊肿,先天性胸腺囊肿表现为位于前纵隔内一侧性边缘清楚的单房或多房的囊性肿块。囊壁薄或不可见,囊内可有分隔,壁可有钙化。囊内的CT值常为水样密度,但也有高密度者。在儿童中伴有向颈部延伸的先天性胸腺囊肿与淋巴管瘤不能区分。 在