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1、正常胸腺及胸腺病变的CT表现吕晓飞,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
2、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(thymopharyngeal duct)as the result of failure of descent,sequestration,or failure to involute.Ec
3、topic 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,Figure 1.Normal thymus with a cervical component in a 12-year-old boy.(a)Sagittal ultrasonographic
4、(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 sky”appearance of the thymus;this is created by hyperechoic fat against the background of the remaining hyp
5、oechoic 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 a 3-year-old boy with a strong maternal family history of papillary thyroid carcinoma.The cervical component was
6、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-up studies 2 years later showed no change,and the patient remained asymptomatic.,异位胸腺,Figure 3.Ectopic parapharyngeal thym
7、us 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 parapharyngeal mass(arrow),which is isointense relative to the mediastinal thymus(arrowhead).At needle biopsy,the mass was proved to be ectop
8、ic 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
9、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 this review,we have drawn the following conclusions regarding the appearance of the thymus gland and the detection of thymic abnormalitie
10、s: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 anterior to the aortic arch,superior vena cava,and great vessels throughout life.2.After puberty,parenchymal atrophy within the gland occurs
11、,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 oval focal soft-tissue mass within the thymus gland usually represent a neoplasm.4.Before age 40,differentiation of a small thymoma from normal residu
12、al 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 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(
13、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
14、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
15、。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
16、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
17、区分。在CT上区别胸腺囊肿为先天性或后天性具有一定的意义，因后天性者在手术后可复发、可伴有胸腺瘤或胸腺癌等肿瘤或因与邻近组织粘连而在术中被误认为侵袭性肿瘤。后天性胸腺囊肿表现为边缘欠清楚、密度不均匀、单房或多房的囊性肿块，以多房者多见。如CT上见到有明确的囊壁或伴有钙化时强烈提示为后天性者。,胸腺瘤，纵隔囊性畸胎瘤（皮样囊肿），支气管囊肿,3.胸腺囊肿,CASE 1 Thymic cyst in a 66-year-old woman.(A)Contrast-enhanced CT scan shows an incidentally noted anterior mediastinal le
18、sion(arrow)with well-circumscribed borders and soft-tissue attenuation.The lesion is indistinguishable from a solid mass.(B)On a T2-weighted MR image,the lesion(arrow)is hyperintense and contains a fluid level,findings that indicate a hemorrhagic or mucin-containing cystic lesion.The lesion was surg
19、ically removed,and pathologic analysis demonstrated a thymic cyst.,3.胸腺囊肿,CASE 2 Thymic cyst associated with infection in a 35-year-old woman.Contrast-enhanced CT scan shows an incidentally noted anterior mediastinal cystic lesion with irregular walls and separated areas.The lesion was surgically re
20、moved,and pathologic analysis demonstrated a thymic cyst.,3.胸腺囊肿,CASE 3 Cystic thymoma in a 48-year-old woman.Axial short inversion time inversion-recovery MR image shows hyperintense cystic lesions in the mediastinum abutting the pericardium.Note the hypointense nodular lesion(arrow),a finding that
21、 suggests the presence of a solid component.The nodule demonstrated enhancement after contrast material administration.Surgery was performed,and pathologic analysis helped confirm a cystic type AB thymoma.,3.胸腺囊肿,CASE 4 Cystic change of the thymus in a 28-year-old man with Hodgkin lymphoma treated 3
22、 years earlier.Contrast-enhanced CT scan shows a thymic cyst(arrow)and thymic rebound hyperplasia(arrowhead).,1.胸腺上皮细胞肿瘤：胸腺瘤,（二）肿瘤病变,低危组,高危组,胸腺癌,The WHO classification scheme correlates with invasiveness:Types A and AB are usually clinically benign and encapsulated(stage I),type B has a greater like
23、lihood of invasiveness(especially type B3),and type C is almost always invasive.,胸腺瘤占成人前纵隔肿瘤20%，是成人前纵隔常见的原发肿瘤，好发于40岁者，无性别差异。15%MG病人伴有胸腺瘤，而30%-50%胸腺瘤病人发生MG。胸腺瘤的病理特征为其在组织学上起源于胸腺的上皮性和淋巴细胞性成分，因而常按其上皮细胞和淋巴细胞的比例而分类。以上皮细胞为主的胸腺瘤预后最差。,非侵袭性胸腺瘤:圆形、卵圆形或分叶状肿块;边界清晰;多数密度均匀,也可发生囊变;肿瘤内可见钙化;大部分肿瘤生长不对称,居于前纵隔的一侧；直径2cm的
24、胸腺瘤可仅表现为正常胸腺边缘局部隆起。,Case 1 57岁，女性Case 2 49岁，男性Case 2 58岁，女性Case 2 45岁，男性,不规则轮廓边缘毛糙不清纵隔脂肪层浑浊消失淋巴结肿大胸膜侵犯、血管侵犯、其它脏器侵犯远处转移不均匀强化,低危 高危 胸腺癌,侵袭性胸腺瘤明确的CT征象：纵隔结构的包绕，直接侵犯中心静脉、心包或胸膜种植转移和晚期发生的跨膈肌扩散。,Thymoma tends to spread along the pleural surfaces and may extend into the abdomen via theretrocrural space.(A)Sm
25、all discrete pleural implant(black arrow),visualized to advantage on lung window.(B)Left retrocrural spread(white arrow).(C)Retroperitoneal implant(black short arrow).,胸腺癌,WHO被分为C型，具有胸腺以外的细胞结构特征，缺乏成熟的淋巴细胞。诊断需排除其他部位的原发肿瘤，因其组织学特征类似于起源于胸腺外的癌。少伴有重症肌无力。CT表现为前纵隔大的肿物，具有侵袭性特点，特点与侵袭性胸腺瘤非常相似。但淋巴性及血源性转移几乎仅见于胸腺
26、癌。,胸腺癌,Thymic squamous cell carcinoma in a 40-year-old male.(A,B)Large heterogenous mass extending along the pericardium,with probable invasion(arrows).(C)Six weeks following a Chamberlain procedure(left anterior thoracotomy)there is new chest wall invasion,compatible with tumor seeding in the surgi
27、cal wound.,2.胸腺非上皮性肿瘤,（1）胸腺淋巴瘤,原发于胸腺的淋巴瘤少见，临床上一半以上都是淋巴瘤侵及胸腺，且大多数HD累及胸腺。以结节硬化型、女性多见。原发与继发鉴别困难。CT常表现为胸腺体积增大，前中纵隔多发肿大淋巴结或融合成团块状肿大淋巴结，边界清晰，增强扫描为均匀或不均匀强化。,与胸腺瘤需鉴别：a.胸腺瘤常伴有坏死和囊变，增强扫描除囊变坏死区域，其他区域强化较均匀。b.淋巴瘤放疗前无钙化，25%胸腺瘤有钙化。c.全身淋巴结肿大支持淋巴瘤诊断。d.发病年龄。,鉴别：胸腺瘤，胸腺增生,与胸腺增生鉴别：a.胸腺增生通常为对称性体积增大；b.胸腺淋巴瘤多处淋巴结肿大。,Concur
28、rent thymic and lymph node involvement by Hodgkin lymphoma in a 51-year-old woman.(A)Contrast-enhanced CT scan shows involvement of the left lobe of the thymus(arrow)and subcarinal lymph nodes(arrowhead).(B)Coronal PET image shows asymmetric FDG avidity of the left thymic lobe(arrow)and subcarinal l
29、ymph nodes(arrowhead).,A,B,Case 1,Thymic involvement by Hodgkin lymphoma in an 18-year-old man.Axial PET/CT(A)and coronal PET(B)images show cervical and axillary adenopathy(arrowheads in B)and asymmetric FDG uptake by the thymus(arrow).,A,B,Case 2,（2）胸腺类癌,胸腺类癌是一种较罕见、分化良好的神经内分泌肿瘤。平均发病年龄为40岁，男性发病率为女性三
30、倍。患者通常表现为内分泌紊乱，如Cushing 综合症(25%40%)，MENI,MENII综合症（20%)。切除后易复发。病理上，胸腺类癌表现为巨大肿块，直径范围6-20cm，平均11cm。大约50的病灶有包膜，多数包膜完整。胸腺类癌常侵及邻近的纵隔和其他胸内结构，它们常转移到局部淋巴结、皮肤、肾上腺和骨骼，也见有报道转移到肺、胸膜、颅脑和肾脏。大约50%的病人在发现时已经有侵袭或者转移病灶。,CT表现缺乏特异性，不易与侵袭性胸腺瘤鉴别。需结合临床。,Thymic carcinoid tumor in a 22-year-old man with a 3-month history of a
31、 persistent dry cough.(A)Contrast-enhanced CT scan shows a heterogeneously enhancing thymic mass(arrow).(B)PET image shows intense FDG uptake by the mass(arrow).Note the nodular contour of the mass in both A and B;contrast that appearance with the homogeneous texture and smooth contour in cases of t
32、hymic rebound hyperplasia.,Case 1,A,B,Case 2,Thymic carcinoid in a 74-year-old man.Contrast-enhanced CT scan demonstrates a lobulated,heterogeneously enhancing mass in the anterior mediastinum.Note the loss of the fat plane between the mass and the pericardium,a finding that suggests invasiveness.Ph
33、otomicrograph(original magnification,40;H-E stain)shows tumor cells in a trabecular growth pattern with oncocytic cytoplasm and oval to irregular nuclear contours.,Case 3,Thymic carcinoid in a 62-year-old man.Non-contrast and Contrast-enhanced CT scan demonstrates a lobulated(Fig A),heterogeneously
34、enhancing(Fig B)mass in the anterior mediastinum.Note the loss of the fat plane between the mass and the pericardium,a finding that suggests invasiveness.,A,B,（3）胸腺脂肪瘤,胸腺脂肪瘤是前纵隔少见肿瘤，混合了脂肪、胸腺上皮和淋巴组织，占胸腺肿瘤的5，可发生在任何年龄段，无性别倾向。胸腺脂肪瘤一般预后良好，手术切除后不复发。体积通常较大，典型胸腺脂肪瘤CT扫描表现为前纵隔巨大肿块，其内可见脂肪、纤维分隔、正常胸腺组织。,不典型畸胎瘤，膈
35、疝,Thymolipoma in a 14-year-old girl with a 2-week history of cough and fever.(A)Contrast-enhanced CT scan shows a large,mostly fatty mass(arrows)in the left hemithorax.The mass causes minimal(if any)displacement of the heart.(B)Coronal T1-weighted MR image shows the mass(arrows),which has fibrous se
36、pta and replaces and assumes the shape of the collapsed lung.After resection of the mass,the left lung fully expanded。,A,B,Case 1,Thymolipoma and thymolipoma mimic.(A)Thymolipoma manifesting as a large fatty mass containing small amounts of soft tissue,filling the entire right hemithorax.,(B,C)Morga
37、gni hernia containing omental fat,simulating hymolipoma.Mesenteric vessels(arrowheads)can be tracked into the hernia,suggesting the correct diagnosis.,Case 2,（4）纵隔胸腺生殖细胞肿瘤,生殖细胞肿瘤包括精原细胞瘤、非精原细胞瘤（畸胎瘤、胚胎性癌、内胚窦癌、绒毛膜癌）以及混合型。纵隔生殖细胞肿瘤是最常见的性腺外的生殖细胞肿瘤。多见于儿童和青少年。80%左右为良性，其中良性畸胎瘤占大部分。纵隔生殖细胞肿瘤发病率男性多于女性,其中恶性生殖细胞肿
38、瘤男性发病率远远高于女性。血尿绒毛膜促性腺激素(HCG)、血甲胎球蛋白(AFP)及癌胚抗原（CEA）水平对本病临床诊断有较高的参考价值。畸胎瘤占纵隔生殖细胞瘤的60%70%，由3种胚胎性生殖细胞层中的至少2种组成。通常表现为圆形或分叶状肿块，体积较大，突向中线一侧。前纵隔囊性肿物内有液体、软组织、钙化、脂肪等多种密度,是良性、成熟畸胎瘤的特征性表现。恶性者则边界欠清晰，结节状或团块状软组织密度影为主。,A 43-year-old male with primary malignant mediastinal germ cell tumor demonstrating both fatty co
39、ntent and dense calcification.,Case 1,Mature,benign teratoma in a 35-year-old male presenting with chest pain.(A)Anteriormediastinal heterogeneous mass,containing cystic and enhancing solid areas.(B)The mass appears to encase adjacent mediastinal structures with no apparent separating fat plane.However,at surgery there was no invasion of these structures and complete resection was achieved.,Case 2,
