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Meinoshin Okumura
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MS03 - Workup and Management of Small Anterior Mediastinal Masses/Lesions (ID 66)
- Event: WCLC 2019
- Type: Mini Symposium
- Track: Thymoma/Other Thoracic Malignancies
- Presentations: 5
- Now Available
- Moderators:Meinoshin Okumura, Pier Luigi Filosso
- Coordinates: 9/08/2019, 13:30 - 15:00, Amsterdam (2011)
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MS03.01 - Differentiation of Small Anterior Mediastinal Lesions Using Imaging (Now Available) (ID 3449)
13:30 - 15:00 | Presenting Author(s): Edith Michelle Marom
- Abstract
- Presentation
Abstract
Mediastinal masses are relatively uncommon in the general population and no specific algorithm exists for the evaluation and diagnosis of these lesions. Most mediastinal masses occur in the anterior, or prevascular compartment and these lesions demonstrate tremendous heterogeneity in clinical and pathologic features. The selection of laboratory tests, whether to perform a biopsy, immediate surgery, follow-up imaging or order further imaging investigation varies between medical disciplines, and patients’ clinical features. The use of CT has grown exponentially over the last decade. This has led to an increasing amount of incidental prevasscular mediastinal lesions encountered, often smaller than those encountered in symptomatic patients.
There is no agreement as to what defines a mediastinal lesion as ‘small’. For the radiologist, this usually constitutes a lesion, which is too small to characterize, perhaps smaller than 1cm. For the surgeon, this may be a lesion, which could be approached with minimally invasive surgery, or perhaps a lesion which one may suspect is benign. When dealing with the incidental prevascular lesion, the most important role for the radiologist is to correctly identify a “no touch lesion”: a benign lesion or normal variant that should not be treated. The second task the radiologist must face is diagnose correctly a lesion or at least narrow the differential to tailor the diagnostic approach causing minimal harm in the process.
The imaging modality of choice for identifying, localizing, and characterizing most mediastinal masses is CT. Most clinicians and radiologists are most familiar with this imaging modality and it has the ability to accurately locate, identify densities such as fat, bone, calcification and fluid. There are some prevascular mediastinal lesions that have a pathognomonic appearance on CT, which may obviate the need for a biopsy, such as goiter, mature teratoma or thymolipoma. However, CT has two major drawbacks: it does expose individuals to a relatively large amount of ionizing radiation, and it is not as good as MRI in tissue characterization. Thus, when a prevascular lesion measures as fluid, it is sometimes difficult to identify nodular thickening within the fluid to distinguish a benign cyst for example, from a cystic thymoma. Similarly, cysts may seem solid on CT. Proteinaceous cyst, when measured by CT, have Hounsefield Units, which measure as soft tissue rather than fluid. MRI overcomes these issues, with its better contrast resolution.
MR imaging is not routinely performed to evaluate all mediastinal masses; however, it is the best modality for distinguishing cystic from solid masses (e.g., thymic cysts from solid tumors), identifying cystic and/or necrotic components within solid lesions, demonstrating septations and/or soft tissue within cystic lesions, and distinguishing thymic hyperplasia and normal thymus from soft tissue tumors.
Tissue characterization, whether using CT or MRI, relies on visible assessment or measuring the density/intensity of the lesion. When a tissue is measured, a region of interest (ROI) is placed in the lesion. For the measurement to be accurate, the ROI should include more pixels, should be about 1cm in diameter and not include soft tissue around the lesion. It is because of this, that in small lesions, smaller than 1cm, the density/intensity cannot be accurately measured. Another example is the use of MRI to distinguish thymic hyperplasia from a soft tissue malignancy. The MRI chemical shift sequence shows a signal drop when fat and soft tissue abut each other. This causes the fat-soft tissue interface to appear as a dark linear outline on this sequence. Since thymic hyperplasia contains a combination of fat and soft tissue, there is a signal drop in thymic hyperplasia using this sequence, not seen with other masses in the prevascular mediastinum. However, when a soft tissue lesion in the prevascular mediastinum is too small, chemical shift imaging is not useful. The periphery will drop out due to the soft tissue interface with the surrounding mediastinal fat, leaving insufficient amount of tissue centrally for investigation.
Positorn emission tomography (PET) integrated with CT using fluorodeoxyglucose as the isotope, is commonly used in staging different malignancies. Its role however in differentiating benign from malignant masses is limited. That is because some benign entities, such as thymic hyperplasia may be FDG avid, whereas some malignancies, such as some types of thymoma, are sometimes not FDG avid. Also, the FDG uptake of commonly encountered malignancies in the prevascular mediastinum is high, so that it is impossible to distinguish between them. For example thymic carcinoma, paraganglioma and non-seminomatous germ cell tumor show similar FDG uptake. In addition, the spatial resolution of PET is low, much lower than CT or MRI so that small lesions, those smaller than 1cm, are not accurately assessed by this modality.
We will review the imaging approach to the incidentally discovered, usually small, prevascular mass. How to identify the ‘no touch lesion’, when to order additional imaging and which imaging modality to select in order to prevent futile surgery.
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MS03.02 - Resection, Biopsy or Observation of Small Anterior Mediastinal Lesions (Now Available) (ID 3450)
13:30 - 15:00 | Presenting Author(s): Frank Detterbeck
- Abstract
- Presentation
Abstract
With greater prevalence of CT scanning for many reasons, the incidental detection of a prevascular lesions has increased markedly. 3 sources of data show the incidence to be around 0.5-1% in asymptomatic adults. There is no accepted standard for how to manage these patients, and until recently there was little data to base an approach on. Recently, examination of scans done for lung cancer screening provide some answers. The majority of these lesions have CT characteristics that are consistent with a thymic epithelial tumor (TET). However, the vast majority are stable over a median follow-up of approximately 5 years. While a minority exhibit growth, on further observation most of these do not continue to grow or decrease in size. It is well documented that thymic cysts and other benign lesions sometimes grow slightly. The overall incidence of a malignancy is around 2%. Even after a prolonged period of observation, when resection is undertaken for a TET, the vast majority are stage I (8th edition of TNM) and there have been no recurrences over a median follow up of approximately 5 years. This has been the case even with thymic carcinoma. In summary, simple observation of incidentally discovered prevascular lesions appears to be safe, without losing a window for intervention in the small percentage of patients that need this.
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MS03.03 - Minimally Invasive Surgical Strategies and Considerations for Small Anterior Mediastinal Lesions (Now Available) (ID 3451)
13:30 - 15:00 | Presenting Author(s): Benny Weksler
- Abstract
- Presentation
Abstract
Minimally Invasive Surgical Strategies and Considerations for Small Anterior Mediastinal Lesions
Thymomas are the most common anterior mediastinal masses. These are slow growing relatively indolent tumors that are often curable with surgical resection. Thymomas are often detected in asymptomatic patients who had a computed tomography of the chest for other reasons. Until recently, the surgical standard of care for curative surgery was resection of the thymus en-bloc with the mass through an open sternotomy. Advances in video surgery have allowed resection of the thymus and the anterior mediastinal masses through small incisions.
Currently, there are multiple minimally invasive approaches to the anterior mediastinum, including thoracoscopy though the chest wall, thoracoscopy through a subxiphoid incision, and robotic assisted thoracoscopy. Although data comparing the techniques is sparse, there is no reason to believe that one has oncologic or survival advantages over the other. Data comparing minimally invasive approaches with open approaches have shown better short-term outcomes such as postoperative complications and blood loss, and similar long-term survival.
Several authors have questioned the need for a complete thymectomy in patients with small anterior mediastinal lesions, hence the term thymomectomy. Thymomectomy involves the removal of the thymoma only, with margins around it, but without a formal complete thymectomy. Data comparing complete thymectomy with thymomectomy is sketchy and likely unreliable. Another area of intense investigation is the role of nodal dissection or sampling in the surgical management of thymomas. Data from multiinstitutional database suggests that the incidence of nodal metastases is higher than previously thought. Although data is lacking, removal of enlarged nodes, or sampling of nodes in the anterior mediastinum is likely indicated.
In summary, small anterior mediastinal masses can be removed using minimally invasive techniques. The need for complete thymectomy, and nodal sampling are areas of investigation. Until more data is available, complete thymectomy with nodal sampling appears prudent.
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MS03.04 - Followup/Surveillance of Small Anterior Mediastinal Lesions (Now Available) (ID 3452)
13:30 - 15:00 | Presenting Author(s): Wentao Fang
- Abstract
- Presentation
Abstract
With increasing popularity of CT screening for early stage lung cancers, there is a tendency toward increased detection of small anterior mediastinal nodules. However, work-up and management strategy for such incidentally found small mediastinal lesions remains to be established.
During 2013-2018, 415 patients with incidentally found small anterior mediastinal mass less than 3 cm in diameter were retrieved from a prospectively kept database at the Division of Mediastinal Surgery, Shanghai Chest Hospital. A marked increase was seen in the annual number of such cases detected (Figure 1). MRI was used in addition to CT scan for differential diagnosis in 413 cases. The other 2 patients could not receive MRI because of metal implantation at previous surgery.
Eight-nine patients received surgery, 82 (92.1%) of them turned out to have thymic epithelial tumors (Table). Among thymic tumor patients, 36 had a follow-up history for a median of 18 months, and 27 (75%) of the lesions increased in size. Thymic carcinomas and neuroendocrine tumors enlarged more rapidly than type B2/B3 thymomas, and the latter more rapidly than type A/AB/B1 tumors (Figure 2). Two of the seven thymic carcinomas were upstaged to UICC T3 lesions, and nodal involvement was found in two thymic carcinoma and one atypical carcinoid patients. The other 33 tumors were all in UICC stage Ia. Seven patients turned out to have bronchogenic cysts (3) or thymic cysts (4). None of them had follow-up history and 5 of them received surgery because of MR suspected thymomas. Thus the accuracy of MRI for diagnosing thymic tumors was 94.1% (80/85).
Three-hundred-twenty-six patients are still under follow-up, 311 of them were diagnosed of having benign lesions (cysts, hyperplasia, lymph nodes) by MRI. With a median follow-up of 33 months, none but one MRI diagnosed cyst increased by 0.3 cm after 3 years. Two MRI diagnosed cystic and two hyperplasic lesions decreased in size during follow-up. Thirteen patients with MRI diagnosed clinical stage I thymomas refused surgery. Only two of the lesions increased in size by 0.2-0.3 cm after 2 years (Table).
In conclusion, MRI is highly useful in differential diagnosis of small anterior mediastinal lesions. Follow-up could be safely recommended for those MRI diagnosed benign lesions.
Table. Change in size during follow-up for small anterior mediastinal lesions.
Diagnosis
Patient
Size
Follow-up
Size (+)
Size (-)
(Number)
(Mean, cm)
(Median, month)
(Number)
(Number)
Surgery (TET)
36
2.4
18
27
0
AB
11
2.4
36
2
0
B
11
2.5
12
4
0
Ca
7
2.3
24
6
0
NETT
3
2.3
15
3
0
Metaplastic
2
1.1
36
2
0
Micronodular
2
2.1
5
0
0
No-surgery
326
2.2
33
3
4
TET
13
1.5
18
2
0
Cyst
267
2.3
36
1
2
LN
24
1.2
24
0
0
Hyperplasia
22
2.4
24
0
2
Figure 1. Increasing incidence of incidentally detected small anterior mediastinal lesions at Shanghai Chest Hospital.
Figure 2. Trends of increase in size during follow-up in different subtypes of thymic epithelial tumors.
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MS03.05 - Relevance of Nodal Involvement and the Thymic Lymph Node Map (Now Available) (ID 3453)
13:30 - 15:00 | Presenting Author(s): Jhingook Kim
- Abstract
- Presentation
Abstract
Thymic epithelial tumors (TET) including thymoma, thymic carcinoma, and thymic neuroendocrine tumors are rare cancers, accounting for less than 1% of all tumors. No official staging system was defined by the Union Internationale Contre le Cancer and the American Joint Commission on Cancer (AJCC) until 2017. This led to several proposals being published over the years, but few received clinical validation. Unlike lung cancer, where regional spread through the lymphatics has been proved, most common patterns of recurrence in TET are local failure, or dissemination into the pleural or pericardial spaces. Therefore, the role of additional intraoperative nodal assessment is uncertain in TET, for which total thymectomy is the standard procedure.
Lymph node metastasis in TET is more common with thymic carcinoma. Kondo et al. reported in their retrospective study (n=1320) that lymphogenous spread with or without distant metastasis was found in 3.2% of thymomas, and more commonly in 33% of thymic carcinomas.1 In particular, anterior mediastinal lymph nodes were thought to be the primary drainage location for TET. Anterior mediastinal lymph nodes were involved in approximately 90% of thymomas, 70% of thymic carcinomas, and 90% of thymic neuroendocrine tumors with lymph node metastasis. Furthermore, a cadaveric study found that the anterior mediastinal nodes are the primary drainage basin and the intrathoracic lymph node group are secondary.2
In 2017, the first TNM classification of TET was announced in the 8thedition of the AJCC Cancer Staging Manual, based on proposals made through a collaboration between IASLC and ITMIG.3 A new N category was presented based on the lymph node drainage pattern found in anatomic studies and international databases. Prominent nodes defined by anatomic studies are included as regional nodes in the lymph node map (Table 1).2 In addition, the IASLC lymph node map of lung cancer and AAO-HNS/ASHNS node map were referenced to define boundaries. This new N category classifies the node involvement into three groups according to a region-based system: N0, N1 (anterior region: anterior mediastinal and anterior cervical nodes), and N2 (deep region: middle mediastinal and deep cervical nodes) (Fig. 1). However, this classification is limited by the fact that the amount of data included was too limited to determine statistical significance.2,4,5
Although the first official N category has been published, controversy still remains over the lymph node involvement in TET. The prognosis with nodal metastasis is clearly poor, but the clinical significance of the criterion dividing the current N1, and N2 groups is uncertain. Moreover, the treatment strategy according to each stage is not yet fully defined. ITMIG recommends removal of anterior mediastinal nodes at the time of resection for thymoma.6 This fits into the generally accepted definition of an extended thymectomy which includes anterior mediastinal nodes. For locally advanced thymomas (Masaoka stage III or IVA) and thymic carcinoma, a systematic removal of intrathoracic nodes is encouraged (i.e., those corresponding to the deep region). However, for minimally invasive surgery, which is currently in widespread use, the extent and level of lymph node removal should be discussed further. It also remains to be determined whether different treatment strategies should be adopted according to the histological classification of thymomas, as well as whether it is appropriate to apply the same staging for the different TET pathological entities (i.e. thymoma, thymic carcinoma, and thymic neuroendocrine tumor). Therefore, the current official staging system will play a major role in settling these debates through collection from appropriate databases under uniform definitions. Further research is needed to establish the relevance of the node map, the prognostic role of nodal involvement, and the clinical implications of node dissection.
Reference
1. Kondo K, Monden Y. Lymphogenous and hematogenous metastasis of thymic epithelial tumors. Ann Thorac Surg. 2003;76(6):1859–64
2. Bhora FY, Chen DJ, Detterbeck FC, et al. The ITMIG/IASLC Thymic Epithelial Tumors Staging Project: A Proposed Lymph Node Map for Thymic Epithelial Tumors in the Forthcoming 8th Edition of the TNM Classification of Malignant Tumors. J Thorac Oncol. 2014;9(9):S88–S96.
3. Amin MB, Edge SB, Greene FL, et al, eds. AJCC Cancer Staging Manual. 8th ed. New York:Springer; 2017
4. Detterbeck FC, Stratton K, Giroux D, et al. The IASLC/ITMIG Thymic Epithelial Tumors Staging Project: Proposal for an Evidence-Based Stage Classification System for the Forthcoming (8th) Edition of the TNM Classification of Malignant Tumors. J Thorac Oncol.2014;9(9):S65–S72.
5. Kondo K, Van Schil P, Detterbeck FC, et al. The IASLC/ITMIG Thymic Epithelial Tumors Staging Project: proposals for the N and M components for the forthcoming (8th) edition of the TNM classification of malignant tumors. J Thorac Oncol. 2014;9(9 Suppl 2):S81–7.
6. Toker A, Sonett J, Zielinski M, et al. Standard Terms, Definitions, and Policies for Minimally Invasive Resection of Thymoma. J Thorac Oncol. 2011;6(7):S1739–42.
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MA20 - Thymic Tumors: From Molecular to Clinical Results and New Challenges in Other Rare Thoracic Tumors (ID 149)
- Event: WCLC 2019
- Type: Mini Oral Session
- Track: Thymoma/Other Thoracic Malignancies
- Presentations: 1
- Now Available
- Moderators:Kazuya Kondo, Edith Michelle Marom
- Coordinates: 9/10/2019, 11:30 - 13:00, San Francisco (2009)
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MA20.08 - Discussant - MA20.05, MA20.06, MA20.07 (Now Available) (ID 3802)
11:30 - 13:00 | Presenting Author(s): Meinoshin Okumura
- Abstract
- Presentation
Abstract not provided
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