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.

Dual-Energy X-ray Absorptiometry Predictors of Vertebral Deformities in Beta-Thalassemia Major.

Vertebral fractures in beta-thalassemia major are increasingly found because of the longer life expectancy of patients, with a major negative impact on their quality of life. We performed a retrospective cross-sectional study to investigate the prevalence of vertebral deformities in thalassemic patients and to identify their best dual-energy X-ray absorptiometry (DXA) predictor among trabecular bone score (TBS), bone mineral density (BMD), and Z-score. Eighty-two outpatients with beta-thalassemia major on regular conventional treatment were studied at a single academic center. All patients underwent plain thoracic-lumbar spine X-rays and lumbar DXA to assess the number and the severity of vertebral deformities (Genant's method), the spinal deformity index, lumbar spine DXA parameters (BMD, TBS, and Z-score), and the presence of platyspondyly. Twenty-nine patients (35%) had vertebral deformities and showed significantly lower TBSs than the remainders (1.141 ± 0.083 vs 1.254 ± 0.072, p < 0.0001). The analysis of variance of the TBS between the group of patients without vertebral deformities (spinal deformity index = 0) and the remaining groups showed a significant difference (p < 0.001). The TBS had better sensitivity (86.2%), specificity (75.5%), and diagnostic accuracy (79.3%) than BMD and Z-score in discriminating patients with and without vertebral deformities. Combining the TBS with the BMD or the Z-score showed that the diagnostic accuracy of the first in discriminating patients with and without vertebral deformities improved from 79.3% to 85.4% and 87.8%, respectively. The presence of platyspondyly was a significant predictor of vertebral deformities in the multivariate model. Vertebral deformities in well-treated patients with beta-thalassemia major are common and are often unrecognized. In our hands, the TBS was better than the BMD and the Z-score in predicting vertebral deformities. Plain X-rays of the spine should be performed also in asymptomatic patients, especially when the TBS is low.

Diffusion-weighted quantitative MRI of pleural abnormalities: Intra- and interobserver variability in the apparent diffusion coefficient measurements.

PURPOSE: To assess intra- and interobserver variability in the apparent diffusion coefficient (ADC) measurements of pleural abnormalities. MATERIALS AND METHODS: Diffusion-weighted magnetic resonance imaging was performed in 34 patients to characterize pleural abnormalities, with a 1.5T unit at b values of 0/150/500/800 sec/mm2 . In two sessions held 3 months apart, on perfusion-free ADC maps, two independent readers measured the ADC of pleural abnormalities (two readings for each reader in each case) using different methods of region-of-interest (ROI) positioning. In three methods, freehand ROIs were drawn within tumor boundaries to encompass the entire lesion on one or more axial slices (whole tumor volume [WTV], three slices observer-defined [TSOD], single-slice [SS]), while in two methods one or more ROIs were placed on the more restricted areas (multiple small round ROI [MSR], one small round ROI [OSR]). Measurement variability between readings by each reader (intraobserver repeatability) and between readers in first reading (interobserver repeatability) were assessed using intraclass correlation coefficient (ICC) and coefficient of variation (CoV). Analysis of variance (ANOVA) was performed to compare ADC values between the different methods. The measurement time of each case for all methods in first reading was recorded and compared between methods and readers. RESULTS: All methods demonstrated good (MSR, OSR) and excellent (WTV, TSOD, SS) intra- and interreader agreement, with best and worst repeatability in WTV (lower ICC, 0.977; higher CoV, 3.5%) and OSR (lower ICC, 0.625; higher CoV, 22.8%), respectively. The lower 95% confidence interval of ICC resulted in fair to moderate agreement for OSR (up to 0.379) and in excellent agreement for WTV, TSV, and SS (up to 0.918). ADC values of OSR and MSR were significantly lower compared to other methods (P < 0.001). The OSR and SS required less measurement time (10 and 21/22 sec, respectively) compared to the others (P < 0.0001), while the WTV required the longest measurement time (132/134 sec) (P < 0.0001). CONCLUSION: ADC measurements of pleural abnormalities are repeatable. The SS method has excellent repeatability, similar to WTV, but requires significantly less measurement time. Thus, its use should be preferred in clinical practice. LEVEL OF EVIDENCE: 4 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;46:769-782.

Apparent diffusion coefficient measurements in diffusion-weighted magnetic resonance imaging of the anterior mediastinum: inter-observer reproducibility of five different methods of region-of-interest positioning.

OBJECTIVES: To investigate inter-reader reproducibility of five different region-of-interest (ROI) protocols for apparent diffusion coefficient (ADC) measurements in the anterior mediastinum. METHODS: In eighty-one subjects, on ADC mapping, two readers measured the ADC using five methods of ROI positioning that encompassed the entire tissue (whole tissue volume [WTV], three slices observer-defined [TSOD], single-slice [SS]) or the more restricted areas (one small round ROI [OSR]), multiple small round ROI [MSR]). Inter-observer variability was assessed with interclass correlation coefficient (ICC), coefficient of variation (CoV), and Bland-Altman analysis. Nonparametric tests were performed to compare the ADC between ROI methods. The measurement time was recorded and compared between ROI methods. RESULTS: All methods showed excellent inter-reader agreement with best and worst reproducibility in WTV and OSR, respectively (ICC, 0.937/0.874; CoV, 7.3 %/16.8 %; limits of agreement, ±0.44/±0.77 × 10-3 mm2/s). ADC values of OSR and MSR were significantly lower compared to the other methods in both readers (p < 0.001). The SS and OSR methods required less measurement time (14 ± 2 s) compared to the others (p < 0.0001), while the WTV method required the longest measurement time (90 ± 56 and 77 ± 49 s for each reader) (p < 0.0001). CONCLUSIONS: All methods demonstrate excellent inter-observer reproducibility with the best agreement in WTV, although it requires the longest measurement time. KEY POINTS: • All ROI protocols show excellent inter-observer reproducibility. • WTV measurements provide the most reproducible ADC values. • ROI size and positioning influence ADC measurements in the anterior mediastinum. • ADC values of OSR and MSR are significantly lower than other methods. • OSR and WTV methods require the shortest and longest measurement time, respectively.

Diffusion-weighted quantitative MRI to diagnose benign conditions from malignancies of the anterior mediastinum: Improvement of diagnostic accuracy by comparing perfusion-free to perfusion-sensitive measurements of the apparent diffusion coefficient.

PURPOSE: To compare perfusion-free to perfusion-sensitive measurements of the apparent diffusion coefficient (ADC) to diagnose benign conditions from malignancies of the anterior mediastinum. MATERIALS AND METHODS: Seventy-six subjects were divided into a "benign conditions" group (A, n = 44) and a "malignancies" group (B, n = 32), based on histological findings. diffusion-weighted magnetic resonance imaging (DW-MRI) was performed at b of 0/150/800 sec/mm(2) . The ADCs were obtained on an ADC map by including (perfusion-sensitive = ADCb0-800 ) and excluding (perfusion-free = ADCb150-800 ) the b = 0 sec/mm(2) . The Mann-Whitney U-test was used to detect differences in ADCb0-800 compared with ADCb150-800 values between all cases, benign conditions, and malignancies. The same test was used to evaluate differences in ADCs between the two groups for each type of measurement (ADCb0-800 and ADCb150-800 ), and receiver-operating characteristic (ROC) curves were obtained to evaluate discrimination abilities with comparison of areas-under-ROC-curves (AUROC). Optimal cutpoints for discrimination between groups were determined by the Youden-Index with computation of accuracy. RESULTS: The median ADCb0-800 was significantly greater compared with ADCb150-800 for all cases (P = 0.0014), benign conditions (P = 0.0412), and malignancies (P = 0.0001). The median percentage of increase was 5.30% for group-A and 22.39% for group-B (P < 0.0001). AUROC of ADC in discriminating between groups was significantly greater for ADCb150-800 (0.932) compared with ADCb0-800 (0.831) (P = 0.001). The optimal cutpoint for distinction between groups was 1.52 × 10(-3) mm(2) /sec (sensitivity = 93.7%, specificity = 88.6%, accuracy = 90.8%) for ADCb150-800 and 1.75 × 10(-3) mm(2) /sec (sensitivity = 75.0%, specificity = 79.5%, accuracy = 77.6%) for ADCb0-800 . CONCLUSION: The use of perfusion-free ADC measurements significantly improves diagnostic accuracy of DW-MRI in differentiating benign conditions from malignancies of the anterior mediastinum. J. Magn. Reson. Imaging 2016;44:758-769.

Diffusion-weighted magnetic resonance imaging of thymoma: ability of the Apparent Diffusion Coefficient in predicting the World Health Organization (WHO) classification and the Masaoka-Koga staging system and its prognostic significance on disease-free survival.

OBJECTIVES: To evaluate the usefulness of diffusion-weighted magnetic resonance for distinguishing thymomas according to WHO and Masaoka-Koga classifications and in predicting disease-free survival (DFS) by using the apparent diffusion coefficient (ADC). METHODS: Forty-one patients were grouped based on WHO (low-risk vs. high-risk) and Masaoka-Koga (early vs. advanced) classifications. For prognosis, seven patients with recurrence at follow-up were grouped separately from healthy subjects. Differences on ADC levels between groups were tested using Student-t testing. Logistic regression models and areas under the ROC curve (AUROC) were estimated. RESULTS: Mean ADC values were different between groups of WHO (low-risk = 1.58 ± 0.20 × 10(-3)mm(2)/sec; high-risk = 1.21 ± 0.23 × 10(-3)mm(2)/sec; p < 0.0001) and Masaoka-Koga (early = 1.43 ± 0.26 × 10(-3)mm(2)/sec; advanced = 1.31 ± 0.31 × 10(-3)mm(2)/sec; p = 0.016) classifications. Mean ADC of type-B3 (1.05 ± 0.17 × 10(-3)mm(2)/sec) was lower than type-B2 (1.32 ± 0.20 × 10(-3)mm(2)/sec; p = 0.023). AUROC in discriminating groups was 0.864 for WHO classification (cut-point = 1.309 × 10(-3)mm(2)/sec; accuracy = 78.1 %) and 0.730 for Masaoka-Koga classification (cut-point = 1.243 × 10(-3)mm(2)/sec; accuracy = 73.2 %). Logistic regression models and two-way ANOVA were significant for WHO classification (odds ratio[OR] = 0.93, p = 0.007; p < 0.001), but not for Masaoka-Koga classification (OR = 0.98, p = 0.31; p = 0.38). ADC levels were significantly associated with DFS recurrence rate being higher for patients with ADC ≤ 1.299 × 10(-3)mm(2)/sec (p = 0.001; AUROC, 0.834; accuracy = 78.0 %). CONCLUSIONS: ADC helps to differentiate high-risk from low-risk thymomas and discriminates the more aggressive type-B3. Primary tumour ADC is a prognostic indicator of recurrence. KEY POINTS: • DW-MRI is useful in characterizing thymomas and in predicting disease-free survival. • ADC can differentiate low-risk from high-risk thymomas based on different histological composition • The cutoff-ADC-value of 1.309 × 10 (-3) mm (2) /sec is proposed as optimal cut-point for this differentiation • The ADC ability in predicting Masaoka-Koga stage is uncertain and needs further validations • ADC has prognostic value on disease-free survival and helps in stratification of risk.

Revisiting nephrocalcinosis: A single-centre perspective. A northern Italian experience.

AIM: Nephrocalcinosis is a clinical-pathological entity characterized by the deposition of calcium salts within the kidney parenchyma. Both the protean presentation and multiple causes may explain the lack of data regarding its prevalence. The aim of this study is to report the prevalence and main clinical features of nephrocalcinosis diagnosed in a newly opened nephrology outpatient unit. METHODS: Analysis on the data we prospectively gathered from the start of activity (2007-2013) was carried out. Clinical and laboratory data were collected from the medical records and from the general laboratory; diagnosis was based upon imaging data reviewed by the same radiologists. RESULTS: Sixty-five of 2695 patients referred to our unit were diagnosed with nephrocalcinosis (2.4%). The affected patients were younger than the overall out-patient population (median: 37.7 (min-max: 8-82) vs 63 years (2-102) P < 0.001), with higher female prevalence (68% vs 51.4%: P < 0.05) and better preserved kidney function (CKD-EPI 103 (23-165) vs 60 mL/min (3.2-169) P < 0.001). Kidney stones were the main reason for referral (35.4%), followed by electrolyte disturbances (22.7%), acute pyelonephritis (4.6%), AKI or CKD (4.6%). Nephrocalcinosis was associated with autoimmune diseases in 29% and with microcythaemia in 23%, while positive family history was present in 23% of patients. Various electrolyte disturbances were observed, with hypercalciuria being the hallmark of beta thalassaemic patients. CONCLUSIONS: Nephrocalcinosis is a rare, but not exceptional disease in nephrology. In Mediterranean countries, microcythaemia would appear to be a major cause of this disease. Greater awareness of nephrocalcinosis is needed for an integrated approach involving various branches of internal medicine and radiology.

Bevacizumab plus octreotide and metronomic capecitabine in patients with metastatic well-to-moderately differentiated neuroendocrine tumors: the XELBEVOCT study.

BACKGROUND: We assessed the activity and toxicity of the XELBEVOCT regimen in patients with metastatic well-to-moderately differentiated neuroendocrine neoplasms (WMD-NEN). Ancillary studies evaluated hypertension, proteinuria, and vascular endothelial growth factor (VEGF) polymorphisms in predicting progression-free survival (PFS) and the predictive role of serum vitamin D in progression-free survival and proteinuria onset. METHODS: This prospective phase 2 study included 45 patients with WMD-NEN arising from various primary sites. The treatment regimen was octreotide long-acting release (LAR), 20 mg monthly, metronomic capecitabine, 2000 mg/daily, and intravenous bevacizumab, 5 mg/kg every 2 weeks, without interruption for 9 months. Bevacizumab was continued until disease progression. RESULTS: Partial response was obtained in 8 patients (17.8%, 95% confidence interval [CI], 6.4%-28.2%); tumor response was more frequent in pancreatic than in non-pancreatic malignancies. The median PFS was 14.9 months; median overall survival was not attained. Biochemical and symptomatic responses were observed in 52.9% and 82.3% of cases, respectively. The treatment was well tolerated. Grade 3 toxicities included hand and foot syndrome (11.1%), proteinuria (4.4%), and renal toxicity (2.2%). Proteinuria (all grades) was correlated with longer PFS (p = 0.017). There was an inverse relationship between proteinuria and vitamin D levels. VEGF polymorphisms were not associated with patient outcome. CONCLUSION: The XELBEVOCT regimen is active and well tolerated in patients with metastatic WMD-NEN. Proteinuria correlated with hypovitaminosis D status and was the best predictive factor of treatment efficacy. TRIAL REGISTRATION: Trial registration number NCT01203306.

Diagnostic accuracy and complication rate of CT-guided fine needle aspiration biopsy of lung lesions: a study based on the experience of the cytopathologist.

BACKGROUND: CT-guided transthoracic needle biopsy is a well-established technique for the diagnosis of focal lung lesions. Fine needle aspiration biopsy (FNAB) requires the presence of a cytopathologist on-site to assess the adequacy of samples. For this reason FNAB is less and less used, and core biopsy is the first-line procedure when an experienced cytopathologist is not immediately available. PURPOSE: To evaluate the accuracy and complication rate of CT-guided FNAB of lung lesions according to the experience of the cytopathologist on-site. MATERIAL AND METHODS: A total of 321 consecutive biopsies were considered. Immediate cytological assessment was performed by an experienced cytopathologist for the first 165 procedures (group A) and by two training pathologists for the remaining 156 biopsies (group B). At the time of FNAB the pathologist assigned a semiquantitative score (0-3) to each specimen to assess its diagnostic quality. All variables between the two groups were analyzed by chi-square and Student's t test. A P value <0.05 was considered statistically significant. RESULTS: For all procedures, overall diagnostic accuracy was 80% for cytology alone, with no statistical difference between the two groups for diagnostic accuracy and sample score assigned. In all, 75% of the cytological samples (75% group A, 74% group B) obtained a higher score with a specific diagnosis of histotype. A post biopsy pneumothorax was detected in 27% of biopsies (25% group A, 28% group B). Thirteen patients (4.0%) required chest tube insertion for treatment. For all cases, the pneumothorax rate was significantly affected by the number of samples obtained (P=0.02), but not by the pleural punctures (P=0.15). There was no statistically significant difference between the two groups concerning the number of needle passes and complication rate (P>0.05). CONCLUSION: The efficacy and safety of CT-guided FNAB is not significantly affected by the training level of the cytopathologist on-site. Moreover, the number of specimens obtained for each procedure is a risk factor for pneumothorax.

Acute abdomen as an unusual presentation of hepatic PEComa. A case report.

Perivascular epithelioid cell (PEC) tumors (or PEComas) are myomelanocytic lesions defined by coexpression of melanocytic and muscle markers, suggesting dual differentiation. They are rare mesenchymal tumors and include subtypes with distinct clinical features: angiomyolipoma, lymphangioleiomyomatosis, and clear cell "sugar" tumors of the lung, pancreas and uterus. Consequent upon the World Health Organization's recognition of PEC-derived tumors as a distinct entity, an increasing number of reports has documented PEComas arising at various anatomical locations. Clear cell myomelanocytic tumors of the falciform ligament/ligamentum teres (CCMTs) represent a rare variant of the PEComas. These hepatic PEComas, different from angiomyolipoma of the liver, pose a clinical, radiological and morphological diagnostic challenge. Because of their rarity, the clinical features and biological behavior of these tumors have yet to be established. We experienced our first case of CCMT in a 36-year-old woman who presented to our emergency department with a 3-day history of abdominal discomfort and progressive growth of an epigastric bulk. Intralesional hemorrhage was causing abdominal distension, which progressed to acute abdomen soon after. The hemoglobin concentration was 9.9 g/dL. Liver laboratory tests showed slight elevation of AST, ALT and gamma-GT. The alpha-fetoprotein level was not elevated. The radiological images showed a hemorrhagic mass with some bizarre features in left hepatic lobe, immediately adjacent to the ligamentum teres and falciform ligament. The patient underwent a left hepatic lobectomy. The diagnosis of CCMT was based on histological and immunohistochemical staining. The postoperative course was uneventful. The patient received no adjuvant treatment and is currently, 34 months after surgery, alive and disease free. In this report we describe a peculiar and hitherto undescribed clinical presentation of this tumor and its further course. Moreover, we discuss previously undescribed diagnostic imaging. We recommend that all unusual carcinomas and mesenchymal tumors of the liver should be tested for HMB-45: when positive, there is a high likelihood of PEComa.

Chemical shift and diffusion-weighted magnetic resonance imaging of the anterior mediastinum in oncology: Current clinical applications in qualitative and quantitative assessment.

Recently, the use of magnetic resonance (MR) in clinical practice for the evaluation of the anterior mediastinum has considerably increased due to technological improvements and standardization of thoracic protocols. Currently, MR imaging is increasingly seen as a useful problem-solving modality, especially in equivocal cases at computed tomography, with the advantage of a higher contrast resolution and no radiation exposure. Chemical shift and diffusion-weighted MR are helpful in tissue characterization and present advantages over conventional MR imaging, first in providing quantitative data, without the need for the administration of contrast medium. By detecting microscopic fat in tissue, chemical shift imaging is useful for differentiating normal thymus and rebound hyperplasia from cancer tissue at diagnosis and after chemotherapy in oncologic patients, and for distinguishing lymphoid hyperplasia from thymoma in autoimmune diseases such as myasthenia gravis. Diffusion-weighted MR reflects diffusivity of water molecules within tissue and is increasingly used as a cancer biomarker, even in the thorax, for the detection and characterization of tumors, for their differentiation from benign conditions, and for monitoring treatment response. In this review, based on the current literature, technical considerations about image acquisition and data analysis of chemical shift and diffusion-weighted MR are discussed along with clinical applications in the field of benign and malignant disease of the anterior mediastinum.

Radiological contribution to the diagnosis of early postoperative complications after lung resection for primary tumor: a revisional study.

In the post-operative course of the interventions of lung resection for primary tumor, complications of different nature and severity can arise, recognizing different pathogenetic mechanisms and differing according to the type of resection performed and to the time elapsed after surgery. The low diagnostic accuracy of chest radiography requires a thorough knowledge of the radiologist about all radiographic findings, both normal and pathological, which can be found in the immediate post-operative period (within 30 days after surgery). This article aims to describe the incidence, the clinical features and the radiological aspects of immediate complications following pulmonary resections, with specific reference to those in which the diagnostic imaging provides a fundamental contribution.

Thymoma of the left thymic lobe with a contralateral small pleural implant successfully detected with diffusion-weighted MRI.

Thymoma is the most common primary neoplasm of the anterior mediastinum. At diagnosis, up to 40% of patients present with advanced disease. Because advanced thymomas receive neoadjuvant chemotherapy, diagnostic imaging is crucial to plan the correct treatment. For characterizing thymomas, CT is the first choice modality, whereas 18F-FDG/PET is reserved for questionable cases and MRI is not routinely employed. Hereby, we describe a case of thymoma with a single contralateral pleural implant in a 30-year-old woman. The small pleural thickening detected at CT was correctly interpreted as pleural seeding related to thymoma at diffusion-weighted (DW)-MRI after a negative 18F-FDG/PET scan, and was subsequently confirmed at surgery. Precise diagnosis and accurate preoperative staging are crucial in managing thymic epithelial tumours in order to design the appropriate treatment and improve prognosis. Indeed, when stage IVa for pleural seeding is diagnosed preoperatively, a multimodality approach including primary chemotherapy followed by surgery and postoperative radiotherapy/chemotherapy is recommended. This is the first report that used DW-MRI for the characterization of pleural seeding in thymoma and demonstrates that DW-MRI could be useful for the correct pre-operatory staging in thymoma patients, especially in cases with indeterminate pleural thickenings at CT, in order to define the correct management.

Diffusion-weighted MRI in a case of nonsuppressing rebound thymic hyperplasia on chemical-shift MRI.

Rebound thymic hyperplasia (RTH) generally retains the quadrilateral or triangular shape typical of the normal thymus. Nevertheless, RTH may rarely appear as a focal mass, a condition that mimics tumors if reveals soft tissue attenuation at computed tomography (CT). In such cases, chemical-shift magnetic resonance imaging (MRI) can demonstrate microscopic fat within tissue, that would be indistinct at CT, by showing signal suppression on opposed-phase images relative to in-phase images, although two cases of nonsuppressing thymus have been described in early adulthood, both of them with minimally fat amount at histology, but none with RTH. Albeit diffusion-weighted MRI could be helpful in cases of nonsuppressing RTH at chemical-shift MRI, considering its capability in differentiating benign from malignant lesions, currently, no data are available on its use in such cases. Hereby, we report a case of atypical RTH at CT with no signal suppression on chemical-shift MRI, arose after corticosteroid treatment for mixed cryoglobulinemia in a 60-year-old woman. Diffusion-weighted MRI demonstrated unrestricted diffusion, as generally seen for benign tissue with no cellular atypia, and thus was helpful to differentiate RTH from malignant mediastinal tumors, especially from B cell lymphoma related to type II cryoglobulinemia.

Chemical-shift and diffusion-weighted magnetic resonance imaging of thymus in myasthenia gravis: usefulness of quantitative assessment.

OBJECTIVES: The objective of this study was to prospectively investigate the usefulness of chemical-shift and diffusion-weighted (DW) magnetic resonance imaging (MRI) in patients with myasthenia gravis (MG) for distinguishing thymic lymphoid hyperplasia (TLH), normal thymus (NT), and thymoma (THY) by using the signal intensity index (SII) and the apparent diffusion coefficient (ADC). MATERIALS AND METHODS: We examined 87 subjects (44 males, 43 females; range, 15-71 years) with generalized MG and antibodies to the acetylcholine receptor seropositivity who underwent surgery. They were divided into a TLH/NT group (A, 64 patients; TLH, 49; NT, 15) and a THY group (B, 24 patients; nonadvanced THY, 15; advanced THY, 9) on the basis of histological findings. One patient with contemporary findings of TLH and nonadvanced THY at histology was listed in both groups (87 subjects, 88 findings). Chemical-shift MRI (CS-MRI) was performed with dual-echo acquisition, and the SII was measured for each subject. Diffusion-weighted MRI was performed at b values of 0, 150, 500, and 800 s/mm, and the ADC value was obtained on the ADC map after excluding the 0-s/mm b value diffusion weighting. All measures were performed independently by 2 radiologists, and interreader agreement was assessed by calculating the intraclass correlation coefficient. Differences on SII and ADC levels between the groups and subgroups were tested using the Student t test. Logistic regression models were estimated, and discrimination abilities were individuated according to the area under the receiver operating characteristic curve (AUROC). The optimal cut points for the differentiation of the groups and subgroups were obtained by using the Youden index. RESULTS: The interreader agreement was excellent (intraclass correlation coefficient: SII, 0.998; ADC, 0.944). For CS-MRI, the mean (SD) SII value was significantly different between the groups (A, 36.37% [12.60%]; B, -0.06% [3.85%]; P < 0.001). No overlap in indexes was found with sensitivity, specificity, and cut point of 100%, 100%, and 6.37%, respectively. Conversely, the mean SII value was not different between the subgroups of each group (A, P = 0.607; B, P = 0.252). For DW-MRI, the mean (SD) ADC values were significantly different between the groups (A, 1.92 [0.21] × 10·mm/s; B, 1.36 [0.33] × 10 mm/s; P < 0.001) and between the subgroups of group A (TLH, 1.86 [0.17] × 10 mm/s; NT, 2.10 [0.23] × 10 mm/s; P = 0.002), although overlapped values were found. The AUROC of ADC in discriminating TLH/NT from THY was 0.931 (95% confidence interval, 0.863-0.998), and the optimal cut point for this distinction was 1.625 × 10 mm/s (Youden index, J = 0.760) with sensitivity of 96.8% and specificity of 79.2%. For the subgroups of group A, the AUROC of ADC in discriminating NT from TLH was 0.794 (95% confidence interval, 0.666-0.923), and the optimal cut point for this distinction was 2.01 × 10 mm/s (Youden index, J = 0.458) with sensitivity of 66.7% and specificity of 79.2%. CONCLUSIONS: CS-MRI and DW-MRI are both useful tools for examining patients with MG. The SII is more accurate than the ADC to differentiate TLH and NT from THY (AUROC, 1.000 and 0.931, respectively). Furthermore, the ADC is a noninvasive parameter that could be used for distinguishing TLH from NT, which is useful in selecting patients for surgery because, for nonthymomatous MG, acceptable rates of complete stable remission after thymectomy are found in TLH but not in NT.