Comparison of CT and chemical-shift MRI for differentiating thymoma from non-thymomatous conditions in myasthenia gravis: value of qualitative and quantitative assessment

Clinical application of standardization right thoracic incision for thoracoscopic thymic tumor resection

BACKGROUND

With the continuous development of minimally invasive thoracic surgery, thoracoscopic thymectomy has become a routine operation. This method, now widely recognized, better protects lung function, reduces intraoperative blood loss and pain, and shortens postoperative hospital stay. We now introduce a standardized right thoracic incision for thoracoscopic thymic tumor resection, which has achieved favorable clinical outcomes.

METHODS

This retrospective study involves 63 patients who underwent standardized right thoracic incision for thoracoscopic thymic tumor resection from October 2022 to January 2024. We analyzed the relevant clinical data, including postoperative pathological diagnosis, operation time, intraoperative blood loss, chest tube drainage duration, postoperative hospital stay, and follow-up data.

RESULTS

All 63 patients underwent thoracoscopic surgery. Thoracoscopic surgery excised thymic tumors and mediastinal fat in 62 cases, while 1 case of thymic carcinoma underwent thoracoscopic biopsy due to invasion of the superior vena cava and innominate vein. Postoperative pathological diagnosis revealed thymoma in 35 cases (33 cases of thymoma and 2 cases of thymic adenocarcinoma). R0 resection was achieved in 33 cases and R1 resection in 1 case. Additionally, 2 patients diagnosed with thymic adenocarcinoma were advised to undergo postoperative radiotherapy. Postoperative pathological diagnosis of the other 28 cases showed thymus hyperplasia in 13 cases and thymus cysts in 15 cases. The mean operation time was 57.3 ± 14.2 min, and intraoperative blood loss was 22.5 ± 14.7 ml. The mean chest tube drainage duration was 2.7 ± 1.3 days, and the postoperative hospital stay was 3.7 ± 1.4 days. No secondary operations were required, and no severe complications or mortality were observed during the perioperative period. All patients were discharged smoothly after surgery. Ten patients were not followed up due to recent surgery. The remaining 53 patients were followed up for 6 to 12 months, with no recurrence or distant metastasis observed.

CONCLUSION

The standardized right thoracic incision for thoracoscopic thymic tumor resection simplifies the procedure of thymectomy. The operation's risk points are relatively fixed, making it safe and feasible. It is easy for the operator to master, and the thymic tumor resection rate is high. It possesses characteristics of being minimally invasive, enabling rapid recovery, having fewer complications, and requiring simple perioperative management.

Cine-MRI and T1TSE Sequence for Mediastinal Mass

Background/Objectives: Contrast-enhanced computed tomography (CT) is the standard radiologic examination for evaluating the extent of mediastinal tumors. If tumor infiltration into the large central thoracic vessels, the pericardium, or the myocardium is suspected, cine magnetic resonance imaging (cine-MRI) can provide additional valuable information. Methods: We conducted a retrospective study of patients with mediastinal tumors who were staged with CT, cine-MRI, and a T1-weighted turbo spin echo (T1TSE) prior to surgical resection. Imaging was re-evaluated regarding tumor infiltration into the pericardium, myocardium, superior vena cava, aorta, pulmonary arteries, and atria and compared with intraoperative findings and postoperative histopathological reports (gold standard). Unclear CT findings were further investigated. Results: Forty-seven patients (29 female and 18 male patients; median age: 58 years) met the inclusion criteria. Cine-MRI was able to predict infiltration of the aorta in 86%, pulmonary arteries in 85%, and atria in 80% of unclear CT cases. Aortic tumor infiltration in unclear CT cases was significantly more often correctly diagnosed with cine-MRI than with T1TSE sequence. Conclusions: Additional cine-MRI is of crucial benefit in unclear CT cases. We recommend performing cine-MRI if infiltration into the large central vessels and atria is suspected. T1TSE sequence is of very limited additional value.

Myasthenia gravis and congenital myasthenic syndromes

Myasthenia gravis is an autoimmune disorder caused by antibodies against elements in the postsynaptic membrane at the neuromuscular junction, which leads to muscle weakness. Congenital myasthenic syndromes are rare and caused by mutations affecting pre- or postsynaptic function at the neuromuscular synapse and resulting in muscle weakness. MG has a prevalence of 150-250 and an annual incidence of 8-10 individuals per million. The majority has disease onset after age 50 years. Juvenile MG with onset in early childhood is more common in East Asia. MG is subgrouped according to type of pathogenic autoantibodies, age of onset, thymus pathology, and generalization of muscle weakness. More than 80% have antibodies against the acetylcholine receptor. The remaining have antibodies against MuSK, LRP4, or postsynaptic membrane antigens not yet identified. A thymoma is present in 10% of MG patients, and more than one-third of thymoma patients develop MG as a paraneoplastic condition. Immunosuppressive drug therapy, thymectomy, and symptomatic drug therapy with acetylcholine esterase inhibitors represent cornerstones in the treatment. The prognosis is good, with the majority of patients having mild or moderate symptoms only. Most congenital myasthenic syndromes are due to dysfunction in the postsynaptic membrane. Symptom debut is in early life. Symptomatic drug treatment has sometimes a positive effect.

CT-Based Radiomics Nomogram for Differentiation of Anterior Mediastinal Thymic Cyst From Thymic Epithelial Tumor

Objectives

This study aimed to distinguish preoperatively anterior mediastinal thymic cysts from thymic epithelial tumors via a computed tomography (CT)-based radiomics nomogram.

Methods

This study analyzed 74 samples of thymic cysts and 116 samples of thymic epithelial tumors as confirmed by pathology examination that were collected from January 2014 to December 2020. Among the patients, 151 cases (scanned at CT 1) were selected as the training cohort, and 39 cases (scanned at CT 2 and 3) served as the validation cohort. Radiomics features were extracted from pre-contrast CT images. Key features were selected by SelectKBest and least absolute shrinkage and selection operator and then used to build a radiomics signature (Rad-score). The radiomics nomogram developed herein via multivariate logistic regression analysis incorporated clinical factors, conventional CT findings, and Rad-score. Its performance in distinguishing the samples of thymic cysts from those of thymic epithelial tumors was assessed via discrimination, calibration curve, and decision curve analysis (DCA).

Results

The radiomics nomogram, which incorporated 16 radiomics features and 3 conventional CT findings, including lesion edge, lobulation, and CT value, performed better than Rad-score, conventional CT model, and the clinical judgment by radiologists in distinguishing thymic cysts from thymic epithelial tumors. The area under the receiver operating characteristic (ROC) curve of the nomogram was 0.980 [95% confidence interval (CI), 0.963–0.993] in the training cohort and 0.992 (95% CI, 0.969–1.000) in the validation cohort. The calibration curve and the results of DCA indicated that the nomogram has good consistency and valuable clinical utility.

Conclusion

The CT-based radiomics nomogram presented herein may serve as an effective and convenient tool for differentiating thymic cysts from thymic epithelial tumors. Thus, it may aid in clinical decision-making.

CT texture analysis in evaluation of thymic tumors and thymic hyperplasia: correlation with the international thymic malignancy interest group (ITMIG) stage and WHO grade

OBJECTIVES

To evaluate the effectiveness of CT texture analysis (CTTA) in (1) differentiating Thymoma (THY) from thymic hyperplasia (TH) (2) low from high WHO grade, and (3) low from high Masaoka Koga (MK)/International Thymic Malignancy Interest Group (ITMIG) stages.

METHODS

After institute ethical clearance, this cross-sectional study analyzed 26 patients (THY-18, TH-8) who underwent dual energy CT (DECT) and surgery between January 2016 and December 2018. CTTA was performed using TexRad (Feedback Medical Ltd., Cambridge, UK- www.fbkmed.com) by a single observer. Free hand regions of interest (ROIs) were placed over axial sections where there was maximum enhancement and homogeneity. Filtration histogram was used to generate six first-order texture parameters [mean, standard deviation (SD), mean of positive pixels (MPP), entropy, skewness, and kurtosis] at six spatial scaling factors "SSF 0, 2, 3, 4, 5, and 6". Mann-Whitney test was applied among various categories and p value < 0.05 was considered significant. Three-step feature selection was performed to determine the best parameters among each category.

RESULTS

The best performing parameters were (1) THY vs TH- Mean at "SSF 0" (AUC: 0.8889) and MPP at "SSF 0" (AUC: 0.8889), (2) Low vs high WHO grade - no parameter showed statistical significance with good AUC, and (3) Low vs high MK/ITMIG stage- SD at "SSF 6" (AUC: 0.8052 and 0.8333 respectively]).

CONCLUSION

CTTA revealed several parameters with excellent diagnostic performance in differentiating thymoma from thymic hyperplasia and MK/ITMIG high vs low stages. CTTA could potentially serve as a non-invasive tool for this stratification.

ADVANCES IN KNOWLEDGE

This study has employed texture analysis, a novel radiomics method on DECT scans to determine the best performing parameter and their corresponding cut-off values to differentiate among the above-mentioned categories. These new parameters may help add another layer of confidence to non-invasively stratify and prognosticate patients accurately which was only previously possible with a biopsy.

The Value of CT and MRI for Determining Thymoma in Patients With Myasthenia Gravis

The aim of the study was to evaluate the usefulness of computed tomography (CT) and magnetic resonance imaging (MRI) for differentiating thymoma from nonthymoma abnormalities in patients with myasthenia gravis (MG). A cross-sectional study of 53 patients with MG, who had undergone surgical thymectomy, was conducted at 103 Hospital (Hanoi, Vietnam) and Cho Ray Hospital (Ho Chi Minh City, Vietnam) during August 2014 and January 2017. The CT and MRI images of patients with MG were qualitatively and quantitatively (radiodensity and chemical shift ratio [CSR]) analyzed to determine and compare their ability to distinguish thymoma from nonthymoma abnormalities. Logistic regression was used to identify the association between imaging parameters (eg, CSR) and the thymoma status. The receiver operating curve (ROC) analysis was used to determine the differentiating ability of CSR and radiodensity. As results, of the 53 patients with MG, 33 were with thymoma and 20 were with nonthymoma abnormalities. At qualitative assessment, MRI had significantly higher accuracy than did CT in differentiating thymoma from nonthymoma abnormalities (94.3% vs 83%). At quantitative assessment, both the radiodensity and CSR were significantly higher for thymoma compared with nonthymoma groups (P < .001). The ROC analysis showed that CSR had significantly higher sensitivity (Se) and specificity (Sp) than radiodensity in discriminating between the 2 groups (CSR: Se 100%, Sp 95% vs radiodensity: Se 90.9%, Sp 70%). When combining both qualitative and quantitative parameters, MRI had even higher accuracy than did CT in thymoma diagnosis (P = .031). In conclusion, chemical shift MRI was more accurate than CT for differentiating thymoma from nonthymoma in patients with MG.

Comparison between CT and MRI in the Diagnostic Accuracy of Thymic Masses

Purpose: The aim of this study was to compare diagnostic accuracy between CT and MRI for thymic masses.

Methods: We searched literature and collected information on first author, publication year, cases of different types of thymic lesions, correct diagnostic cases of CT and MRI and results of quantitative analysis of CT and MRI. The ROC curve was applied to compare the diagnostic performance of different imaging modalities.

Results: Eight literatures were finally included and analyzed in this study. There were 253 cases examined by CT and 340 cases by MRI in total. We showed outcomes of quantitative analysis of each study in this article. The sensitivity of CT and MRI was both 100%, while the specificity was 75% and 80%, respectively. AUC of CT was 0.875 [95%CI: 0.473, 0.997] and that of MRI was 0.880 [95%CI: 0.531, 0.995].

Conclusion: The diagnostic accuracy of MRI is superior to CT in detecting thymomas, thymic cysts or thymic hyperplasia but that of CT and MRI is still unclear in differentiating thymic carcinomas and lymphomas/germ cell tumors.

Myasthenia gravis

Myasthenia gravis (MG) is an autoimmune disease caused by antibodies against the acetylcholine receptor (AChR), muscle-specific kinase (MuSK) or other AChR-related proteins in the postsynaptic muscle membrane. Localized or general muscle weakness is the predominant symptom and is induced by the antibodies. Patients are grouped according to the presence of antibodies, symptoms, age at onset and thymus pathology. Diagnosis is straightforward in most patients with typical symptoms and a positive antibody test, although a detailed clinical and neurophysiological examination is important in antibody-negative patients. MG therapy should be ambitious and aim for clinical remission or only mild symptoms with near-normal function and quality of life. Treatment should be based on MG subgroup and includes symptomatic treatment using acetylcholinesterase inhibitors, thymectomy and immunotherapy. Intravenous immunoglobulin and plasma exchange are fast-acting treatments used for disease exacerbations, and intensive care is necessary during exacerbations with respiratory failure. Comorbidity is frequent, particularly in elderly patients. Active physical training should be encouraged.

Multislice computed tomography performance in differential diagnosis of high-density thymic cyst and thymoma in lesions less than 3 cm

Background

This study was conducted to evaluate the performance of multislice computed tomography (MSCT) to diagnose high‐density thymic cysts and thymomas in lesions measuring < 3 cm.

Methods

The records of 42 patients admitted to Ningbo No. 2 Hospital with an anterior mediastinal mass (diameter < 3 cm) suspected of carcinoma originating from the thymus were retrospectively analyzed. All patients underwent surgery and pathological examination. Twenty‐eight were diagnosed with thymic cysts and 14 with thymoma. The features of thymic cysts and thymomas revealed on MSCT were compared.

Results

Mediastinal masses with a triangular or teardrop shape and a straight mediastina–lung border were more likely to be diagnosed as thymic cysts (P < 0.05), while those with a bulging nodule–lung border were more likely thymomas (P < 0.05). Using the CT value as a reference for differential diagnosis, the diagnostic sensitivity, specificity, and area under the receiver operating characteristic curve for CT values of non‐contrast CT images, enhanced CT values, and ΔCT values were 0.65 (0.47–0.84), 0.95(0.86–1.00), and 0.96 (0.89–1.00), respectively.

Conclusion

MSCT of high‐density thymus gland nodules (maximum diameter ≤ 3 cm) can reveal specific features that could be helpful for differential diagnosis.

The added value of chemical shift MRI in the preoperative diagnosis of thymolipoma

Thymolipoma is a rare tumor of the thymus. Classic radiologic findings of thymolipoma include fatty masses of the anterior mediastinum in conjunction with the thymus. Differential diagnosis with other more aggressive entities like liposarcoma and teratoma can be challenging. We report a case where chemical shift magnetic resonance imaging helped in the differential diagnosis.

Nonsuppressing normal thymus on chemical-shift MR imaging and anterior mediastinal lymphoma: differentiation with diffusion-weighted MR imaging by using the apparent diffusion coefficient

OBJECTIVES

To prospectively evaluate usefulness of the apparent diffusion coefficient (ADC) in differentiating anterior mediastinal lymphoma from nonsuppressing normal thymus on chemical-shift MR, and to look at the relationship between patient age and ADC.

METHODS

Seventy-three young subjects (25 men, 48 women; age range, 9-29 years), who underwent chemical-shift MR and diffusion-weighted MR were divided into a normal thymus group (group A, 40 subjects), and a lymphoma group (group B, 33 patients). For group A, all subjects had normal thymus with no suppression on opposed-phase chemical-shift MR. Two readers measured the signal intensity index (SII) and ADC. Differences in SII and ADC between groups were tested using t-test. ADC was correlated with age using Pearson correlation coefficient.

RESULTS

Mean SII±standard deviation was 2.7±1.8% for group A and 2.2±2.4% for group B, with no significant difference between groups (P=.270). Mean ADC was 2.48±0.38x10^-3mm²/s for group A and 1.24±0.23x10^-3mm²/s for group B. A significant difference between groups was found (P<.001), with no overlap in range. Lastly, significant correlation was found between age and ADC (r=0.935, P<.001) in group A.

CONCLUSIONS

ADC of diffusion-weighted MR is a noninvasive and accurate parameter for differentiating lymphoma from nonsuppressing thymus on chemical-shift MR in young subjects.

KEY POINTS

• SII cannot differentiate mediastinal lymphoma from nonsuppressing normal thymus at visual assessment • ADC is useful for distinguishing nonsuppressing normal thymus from mediastinal lymphoma • ADC is more accurate than transverse-diameter and surface-area in this discrimination • ADC of normal thymus is age dependent and increases with increasing age.

The Effect of Diagnostic Imaging on Surgical Treatment Planning in Diseases of the Thymus

Accurate imaging of the thymus is essential in the diagnosis and surgical treatment of both neoplastic and nonneoplastic conditions. Imaging of the thymus is a rather complex task, which affects both initial diagnosis and further surgical treatment planning. Imaging techniques include a wide armamentary of possibilities, from the most frequently used computed tomography (CT) to 18-fluorodeoxyglucose positron emission tomography- (18-FDG-PET-) CT and chemical shift magnetic resonance imaging (CS-MRI). In cases where surgical treatment is involved diagnostic imaging is of pivotal importance, not only in distinguishing benign from malignant disease but also in making a way among subtypes of thymic conditions. The article presents a current review of the advantages and backdrops of different imaging techniques used in the diagnosis of benign and malignant thymic conditions, with emphasis on differential imaging of thymic hyperplasia (TH), ectopic thymic tissue (ETT), and thymic epithelial tumors (TETs), with special attention to the importance of MR imaging according to the new TNM classification of thymic epithelial tumors.