F-18 FDG PET/CT demonstration of thymoma followed by development of lung cancer

It is well-known that thymoma can be associated with diverse extrathymic malignancies. The authors present a case of a 72-year-old man with myasthenia gravis in which F-18 FDG PET/CT demonstrated high FDG uptake in both an anterior mediastinal mass and a lung nodule. The FDG uptake in the lung nodule was significantly higher than that of the thymic lesion, which might suggest the possibility of a second development of lung cancer in this thymoma patient. Surgical resection was done for the 2 tumors, and histologic examination revealed anterior mediastinal thymoma and primary adenocarcinoma of the lung. This case demonstrates the potential usefulness of PET/CT in detecting and assessing the second extrathymic malignancy in a patient with thymoma.     

恶性胸腺瘤的CT与MRI诊断

目的：分析侵袭性胸腺瘤及胸腺癌的CT及MRI表现，探讨其鉴别诊断要点。方法：复习经病理组织学证实的18例侵袭性胸腺瘤及9例胸腺癌的CT、MRI所见，重点观察肿瘤的大小、密度、边缘改变，对周围纵隔结构的侵犯。结果：18例侵袭性胸腺瘤、9例胸腺癌CT、MRI均表现为前纵隔不规则软组织肿块。前者肿瘤直径大于8cm者15例（83％），病灶内密度及信号不均匀12例。心血管受侵16例，后者肿块直径在8cm以上者7例（77.8％),肿块内密度及信号不均6例，心知管受累8例，纵隔肺门淋巴结转移1例，肺内转移3例，双侧肾上腺及肝脏转移1例。结论：虽然侵袭性胸腺瘤和胸腺癌的影像学表现相似，但胸腺癌更具有侵袭性，胸外转移常见，病理组织学检查有助于两者的鉴别。     

原发性胸腺淋巴瘤的CT诊断

目的：探讨原发胸腺淋巴瘤（PTL）的CT表现及诊断价值。方法：回顾性分析1992年3月-2013年4月临床资料齐全且经病理证实的15例原发胸腺淋巴瘤CT表现,所有病例均经CT平扫加增强扫描,并与相同病例的侵袭性胸腺瘤及胸腺癌CT表现进行对照研究。结果：15例原发胸腺淋巴瘤中霍奇金淋巴瘤（HL）8例（8/15）、弥漫性大B细胞淋巴瘤5例（5/15）、T细胞淋巴母细胞淋巴瘤2例（2/15）,女性9例（9/15）、男性6例（6/15）;发病年龄＜40岁13例（13/15）,与侵袭性胸腺瘤（5/15）及胸腺癌（3/15）比较（P＜0．05）。原发胸腺淋巴瘤CT平扫示肿块向两侧生长11例（11/15）,结节状突起、分叶状生长8例（8/15）,密度均匀6例（6/15）,三者分别与侵袭性胸腺瘤、胸腺癌比较差异无显著统计学意义。原发胸腺淋巴瘤CT增强扫描示包绕血管征11例（11/15）,分别与侵袭性胸腺瘤（2/15）、胸腺癌（4/15）比较（P＜0．05）;瘤内小囊肿状改变7例（7/15）,分别与侵袭性胸腺瘤（1/15）、胸腺癌（0/15）比较（P＜0．05）;强化值＜20 HU10例（10/15）,与胸腺癌（1/15）比较（P＜0．05）。结论：原发胸腺淋巴瘤好发年轻女性,CT增强扫描具有一定的特征表现,据之可与侵袭性胸腺瘤及胸腺癌鉴别。     

Thymic lesions and myasthenia gravis. Diagnosis based on mediastinal imaging and pathological findings

Purpose:
To achieve a better understanding of the role of CT and MR imaging in the study of the mediastinum in patients with myasthenia gravis (MG). Material and Methods:
Mediastinal CT and MR findings were correlated with the histopathological results in 104 thymectomized MG patients. Results:
CT was performed in 104 patients; in 11 of them, MR was also carried out. 44 patients had hyperplasia at histology. On CT, thymic hyperplasia was confirmed in 16 cases, thymoma was diagnosed in 10 and a normal thymus in 18 (sensitivity 36%, specificity 95%). Of 52 patients with thymoma at histology, CT showed thymoma in 46, hyperplasia in 1, and normal thymus in 5. CT showed 88.5% sensitivity and 77% specificity for thymoma. In 10 patients with invasive thymoma, CT was indiscriminate, while invasiveness was detected in 7 cases at MR (70% sensitivity) and at CT in 1 case. Both CT and MR detected tumor recurrence in 5 cases, but the exact localization and degree of invasion were best defined by MR. Conclusion:
In MG patients CT is a sensitive, specific and efficient modality for detecting thymoma, but is less so for detecting thymic hyperplasia. MR was shown to be accurate in detecting invasive thymoma both preoperatively and in postoperative follow-up.     

胸腺类癌的CT表现及诊断价值

目的:分析胸腺类癌的CT影像特点,探讨CT的诊断价值。方法:回顾性分析8例经病理证实的胸腺类癌患者资料,所有患者均行CT平扫和增强扫描。结果:胸腺类癌CT均表现为前纵隔肿块,形态不规则,增强扫描明显不均匀强化。本组初始诊断1例为胸腺类癌,7例为胸腺瘤,其中4例为侵袭性。结论:胸腺类癌的最终诊断需依靠病理学,但CT能很好地显示胸腺类癌的形态、范围,指导手术及提示预后。     

Malignant thymic epithelial tumors: CT-pathologic correlation

OBJECTIVE: The purpose of our study was to describe and compare the CT and pathologic findings of atypical thymoma and thymic carcinoma. MATERIALS AND METHODS: Twenty-seven consecutive patients (14 men, 13 women ranging in age from 22 to 77 years [mean age, 52 years]) with pathologically proven atypical thymoma (n = 9) and thymic carcinoma (n = 18) constituted the study population. The chest CT findings in each of the 27 patients were reviewed retrospectively in consensus by two chest radiologists. These findings were correlated with pathologic findings. RESULTS: The tumors were located in the anterior mediastinum, and most tumors had a lobulated margin (24/27, 89%). Atypical thymomas were significantly smaller (mean, 4.7 cm) than thymic carcinomas (mean, 7.2 cm) (p = 0.041) on CT. The findings of invasion of the great vessels, lymph node enlargement, extrathymic metastases, and phrenic nerve palsy were seen only in patients with thymic carcinoma. The frequencies of necrosis, intratumoral calcification, pleural effusion, pleural implants, pericardial effusion, and obliteration of the mediastinal fat plane were not significantly different between atypical thymomas and thymic carcinomas (p > 0.05). Various histologic subtypes were included in thymic carcinoma. The tumor necrosis and calcification seen on CT were confirmed at pathologic examination. CONCLUSION: When a large thymic tumor appears with invasion of the great vessels, lymph node enlargement, phrenic nerve palsy, or extrathymic metastases on CT, thymic carcinoma rather than atypical thymoma should be considered.     

Computed tomography of thymic abnormalities

Computed tomographic examinations of 38 patients with surgically and histologically proven diagnosis were reviewed. Twenty subjects (52%) had an invasive thymoma and 16% an hyperplasic thymus. Myasthenia gravis was present in 6 cases (16%) of thymic abnormalities, four (10.5%) with invasive thymoma and two (5%) with thymic hyperplasia. Graves' disease was also present in one case of thymic hyperplasia. We emphasize the contribution of CT to the diagnosis and the prognosis.     

Mediastinal imaging in myasthenia gravis: correlation of chest radiography, CT, MR, and surgical findings

Chest radiographs and CT and MR images of the mediastinum were studied in 16 patients with myasthenia gravis who underwent thymectomy (two with a final diagnosis of thymoma, seven with hyperplasia, and seven with a normal thymus). The anterior mediastinum was analyzed on imaging studies for thymic morphology and the presence of mass lesions, and the findings were then correlated with the results of surgical resection and pathologic examination. The chest radiographs detected an anterior mediastinal mass in two patients consistent with thymoma on subsequent CT and MR examinations. Chest radiographs in the other 14 patients were normal. In seven patients with a final diagnosis of thymic hyperplasia, both CT and MR demonstrated normal thymic morphology in five, an enlarged thymus in one, and a small thymus in one that was easily identified on CT but was difficult to define on MR. In the other seven patients with a normal thymus on pathologic examination, both CT and MR showed an involuted thymus in four, a normal thymus in two, and an enlarged thymus in one. While both CT and MR were superior to chest radiography for studying the thymus, CT provided better spatial resolution and thymic definition in a much shorter scanning time than MR did. This study suggests that CT should remain the procedure of choice when further imaging of the thymus is needed after the initial chest radiographs in patients with myasthenia gravis.     

Thymus in the superior mediastinum simulating adenopathy: appearance on CT

A soft-tissue nodule was identified in the mediastinum superior to the left brachiocephalic vein in six patients undergoing computed tomography (CT) of the chest. In one case, biopsy of the mass showed that it was thymic tissue. In the remaining cases, the nodule was identified as thymus on the basis of the CT findings. The findings include equal density of the superior mediastinal nodule and the thymic lobes anterior to the ascending aorta, no displacement or narrowing of adjacent arteries, absence of a fat plane between the nodule and the thymic lobes, and parallel reduction in size of the nodule and the rest of the thymus. Two patients were examined with magnetic resonance (MR) imaging. Sagittal MR images demonstrated continuity of the superior mediastinal nodule with the more caudal portion of the thymus. Recognition of this normal variant in children is important in order to avoid unnecessary mediastinal biopsies or overstaging of malignancies.     

胸腺瘤螺旋CT表现与其WHO病理分型对照研究

目的：探讨胸腺瘤螺旋CT影像特征与其WHO病理学分型之间的相关性。方法：分析84例病理证实的胸腺瘤的CT影像特征与其WHO分型之间的相关性。结果：螺旋CT征象上表现有分叶、胸膜、心包及大血管受侵犯及尖角征／锯齿征的胸腺瘤,A型、AB型与B型、胸腺癌两大类之间有显著差异（P〈0．05）,而肿块大小、肿块密度均匀与否、纵隔脂肪线存在与否两者之间无显著差异（P〉0．05）。结论：螺旋CT对A型、AB型与B型、胸腺癌可以做出较为正确的分类,但较难区分A型与AB型、B型与胸腺癌。     

Radiologic detection of thymoma in patients with myasthenia gravis

From 1973 through 1986, 154 consecutive patients who had a transsternal thymectomy for myasthenia gravis had preoperative radiologic evaluation for a possible thymoma. Examinations included posteroanterior and lateral (n = 154) and shallow oblique (n = 126) chest radiography, linear tomography (n = 80), and chest CT (n = 96). At surgery, a thymoma was found in 26 patients (17%). Plain film findings, which often were subtle, correctly predicted a thymoma in 15 (58%) of 26 patients. CT findings correctly predicted a thymoma in 17 of 20 patients (sensitivity, 85.0%; specificity, 98.7%; and accuracy, 95.8%). CT findings failed to detect a thymoma in three patients because a small tumor was indistinguishable from adjacent thymus (n = 2) and respirator motion artifacts (n = 1). Four (15%) of the tumors were invasive, and three (12%) were calcified. The likelihood of a thymoma increased with increasing age (3% for 20 years old and under, 12% for 21-45 years old, and 35% for 46 years old and older). In the youngest group, the thymus is densely cellular and normally relatively large, and therefore a small thymoma may be hidden. In patients 21-45 years old, partial fatty involution leaves parenchymal islands that can mimic a thymoma or obscure a small tumor. In patients over 45 years old, fatty involution enhances recognition of even small thymic tumors. For all patients with myasthenia gravis, we recommend that the initial chest radiographic examination include posteroanterior, lateral, and shallow (20 degrees) oblique views. For those patients under 21 years old, we recommend chest CT only when local symptoms, signs, or radiographic findings suggest the presence of thymic abnormality. For those patients 21 years old and older, we recommend routine chest CT.     

Computed tomography of the thymus gland in myasthenia gravis

Sixteen consecutive patients with myasthenia gravis were examined by computed tomography (CT) before thymectomy. Surgical and histologic findings were compared with those obtained at CT. The results, like those of most other recent studies, indicate that CT is a reliable method for identifying thymoma. In all three patients with thymoma, and in five out of eight patients with hyperplasia, the lesion was observed at CT, giving an overall accuracy of 80 per cent. Although thymic hyperplasia is a basically histologic diagnosis an enlarged gland may give a correct diagnosis of this abnormality.     

重症肌无力的CT诊断

This paper reported 21 cases of myasthenia gravis. All investigated by laboratory tests, conventional chest X-ray study and CT scan, and documented by surgery and pathology. There were 9 cases of thymoma, 2 thymic cyst, 8 normal thymus, 1 atrophic thymus and 1 thymic hyperplasia. In this series, the diagnostic accuracy rate of CT scan was over 90%. Of course, CT is a highly efficient technique for evaluation of abnormalities of thymus, but high resolution CT scanner and the ability of correct interpretation of CT image are even more important.     

Ectopic cervical thymoma located in the carotid triangle

Ectopic cervical thymoma is an extremely rare tumor thought to arise from ectopic thymic tissue caused by the aberrant migration of the embryonic thymus. We present the case of a 44-year-old woman with an ectopic cervical thymoma located in the carotid triangle. A computed tomography (CT) scan detected a mass in her right carotid triangle. On an unenhanced scan, the tumor showed homogeneous isodensity compared with muscles, and neither fat nor calcification was detected. A contrast-enhanced CT image obtained during the arterial phase showed intratumoral septa, while an image obtained during the parenchymal phase showed cystic changes within the mass. The patient underwent a surgical resection. A histological study enabled a diagnosis of type AB thymoma in which foci with the features of type A thymoma are admixed with foci rich in lymphocytes. This subtype is a benign tumor with a good prognosis. Ectopic cervical thymoma should be included in the differential diagnosis of solid masses located in the carotid triangle when the CT findings are typical of a thymoma.     

重症肌无力患者胸腺CT表现与年龄的关系

目的：探讨重症肌无力（MG）患者胸腺CT表现在各年龄组的分布特点。方法：回顾性分析2005年1月～2008年7月住院诊治的241例MG患者的胸部CT影像资料及病理结果。按患者发病年龄分为4组,统计胸腺各种改变在不同年龄组中分布情况。结果：胸腺正常者118例（48．96％）;胸腺增生者34例（14．10％）;胸腺瘤89例（36．9％）。胸腺正常、胸腺增生以及胸腺瘤在四个组中的比例分别为71．05％、48．68％、35．41％、64．51％;23．68％、17．10％、12．50％、0％;5．27％、34．22％、52．09％、35．49％（Х^2值为32．8,P〈0．005）。胸腺正常主要出现在小于20岁年龄组（71．05％）及大于60岁年龄组（64．51％）,胸腺增生主要发生20岁以下年龄组（23．68％）,并且随着年龄增长,比例逐渐降低;胸腺瘤主要出现在40～59岁年龄组（5z．08％）。结论：MG患者的胸腺病变在不同的年龄组中,发病率有所不同。     

Imaging of invasive thymoma in the costophrenic recess presenting as thickening of arcuate ligaments of the diaphragm

Imaging findings in a patient with invasive thymoma in the costophrenic recess are presented, in whom computed tomography (CT) and MRI revealed lateral arcuate ligament thickening. Increased fluoro-deoxy-glucose (FDG) uptake on subsequent positron emission tomography (PET)/CT was helpful in suggesting the correct diagnosis. A second patient with much more obvious invasive thymoma occurring in the costophrenic recess is presented for comparison. It is a well-known fact that thymic malignancies can metastasize to the pleura even years after resection. Rarely, they may present as focal thickening of the diaphragmatic lateral arcuate ligament.     

Differential diagnosis of thymic tumors using a combination of 11C-methionine PET and FDG PET.

We assessed the usefulness of PET studies in making a differential diagnosis of thymic tumors by using 11C-methionine (MET) and 18F-fluorodeoxyglucose (FDG). METHODS: We examined 31 patients with thymic tumors, including 14 patients with thymic cancer, 9 with invasive thymoma, 5 with noninvasive thymoma and 3 with thymic cysts. The histological diagnosis was confirmed by either surgery or biopsy. MET PET and FDG PET were performed in 28 and 29 patients, respectively. Both the MET and FDG uptakes were evaluated by the standardized uptake value (SUV). RESULTS: MET uptake was not substantially different among thymic cancer (4.8 +/- 1.4), invasive thymoma (4.3 +/-1.1) and noninvasive thymoma (4.5 +/- 1.2), bat MET uptake in thymic cysts (0.9 +/- 0.1) was lower than that in the other three tumors (P < 0.01). The FDG uptake in thymic cancer (7.2 +/- 2.9) was higher than that in invasive thymoma (3.8 -/+ 1.3), noninvasive thymoma (3.0 +/- 1.0) and thymic cysts (0.9) (P < 0.01). MET uptake in thymic tumors correlated with the FDG uptake (r = 0.65), whereas MET uptake in thymic cancer was lower than FDG uptake (FDG/MET ratio = 1.52 +/- 0.52) but was higher than FDG uptake in both invasive and noninvasive thymoma (FDG/ MET ratio = 0.86 +/- 0.33). To differentiate thymic cancer from thymoma, a receiver operating characteristic (ROC) analysis was performed. The area under the curve of FDG PET was 0.90, whereas the FDG/MET ratio was 0.87. CONCLUSION: The MET PET, FDG PET and the FDG/MET ratios were unable to differentiate benign thymic tumors from malignant ones, although FDG PET was considered to be useful in the differential diagnosis between thymic cancer and thymoma. Although the difference in the uptake ratio between FDG and MET suggests a different origin of the tumors, the FDG/MET ratio is not considered to be useful as a complementary method for the differential diagnosis of thymic tumors.     

^18F-FDG符合线路显像在胸腺上皮肿瘤诊断中的应用价值

目的探讨^18F-脱氧葡萄糖（FDG）符合线路显像在胸腺上皮肿瘤（TET）诊断中的价值。方法回顾性分析37例TET患者的^18F—FDG符合线路显像结果,图像分析采用视觉分析及半定量方法[肿瘤／正常肺组织放射性比值（TLR）]。按WHO TET病理学分类结果将患者分成3组（高生存率组,包括A、AB、B1型;中生存率组,包括B2、B3型;低生存率组,包括胸腺癌）;同时将^18F—FDG显像结果与增强CT影像进行对比,TLR与免疫组织化学检查所测Ki67标记指数（细胞增殖指标）进行相关性分析。组间TLR比较采用方差分析。结果（1）^18F—FDG符合线路显像阳性率91．9％（34／37）;（2）3个不同生存率组TLR间差异有统计学意义（高、中、低生存率组TLR依次为：1．42±0．27,2．13±0．74,3．00±1．19,F=9．99,P〈0．05）;（3）TLR与Ki67标记指数有明显相关性（r=0．613,P=0．002）;（4）^18F-FDG显像发现2例增强CT未发现的病灶,病灶分别位于前胸壁和右锁骨上淋巴结;（5）共有4例伴发重症肌无力。结论^18F—FDG符合线路显像有助于WHO TET病理学分类和发现更多的TET侵犯、转移灶;可以用^18F—FDG在TET的浓聚程度反映细胞的增殖活力。     

Anterior mediastinal tumors: diagnostic accuracy of CT and MRI

Purpose

To compare the diagnostic accuracy for anterior mediastinal tumors among CT, MRI, and both CT and MRI, and to determine the optimal CT and MRI procedures for the diagnosis of anterior mediastinal tumors.

Materials and methods

Both CT and MRI were performed in 127 patients with pathologically diagnosed anterior mediastinal tumors. The patients included 48 cases of thymoma, 12 cases of thymic carcinoma, 12 cases of thymic cyst, 20 cases of mature teratoma, 13 cases of malignant germ cell tumor, and 22 cases of malignant lymphoma. The CT and MRI scans were assessed by two chest radiologists without knowledge of their clinical and pathologic data. The observers recorded various CT and MRI findings and their first choice of diagnosis.

Results

The two observers made a correct first-choice diagnosis in an average of 78 (61%) of 127 cases on CT, 71 (56%) of 127 cases on MRI, and 85.5 (67%) of 127 cases on both CT and MRI. These included 83% cases of thymoma on CT, 84% on MRI, and 85% on both CT and MRI; 38% cases of thymic carcinoma on CT and 13% on MRI, and 33% on both CT and MRI; 46% cases of thymic cyst on CT and 71% on MRI, and 63% on both CT and MRI; 58% cases of mature teratoma and 38% on MRI, and 78% on both CT and MRI; 35% cases of malignant germ cell tumor on CT and 27% on MRI, and 31% on both CT and MRI; and 55% cases of malignant lymphoma on CT and 43% on MRI, and 61% on both CT and MRI. There were significant differences between the diagnostic accuracy by CT and MRI in the cases with both thymic cysts and thymic carcinoma (p < 0.05).

Conclusion

CT is equal or superior to MRI in the diagnosis of anterior mediastinal tumors except for thymic cyst. CT should be considered the modality of choice following chest radiography, however, in certain circumstances, such as thymic cyst with hemorrhage or inflammation which mimic solid tumor despite low enhancement, MRI may be better in distinguishing anterior mediastinal tumors. For more helpful information in the diagnosis of mature teratoma after CT, MRI may follow.     

CT findings in primary thymic carcinoma

Computed tomography of five cases of thymic carcinoma was reviewed. The subtypes of thymic carcinoma were squamous (two cases), lymphoepithelioma-like (one case), undifferentiated (one case), and basaloid (one case). The patients ranged from 52 to 72 years of age. Computed tomography showed anterior mediastinal tumors infiltrating along the pleura or mediastinum with frequent internal necrosis or calcifications. The three nonsquamous cell cases developed extrathymic metastases to the mediastinal lymph nodes, lung, or chest wall. Although the CT features of thymic carcinomas were similar to those of invasive thymoma, the former showed more aggressive behavior. Among the four variants of thymic carcinoma, squamous carcinomas were less aggressive and had less tendency to develop necrosis than the others.