Assessment of mediastinal tumors with diffusion‐weighted single‐shot echo‐planar MRI

Abstract

Purpose:To assess the role of diffusion-weighted singleshot echo-planar magnetic resonance imaging (MRI) in patients with mediastinal tumors. Methods:Prospective study was conducted on 45 consecutive patients (29 male, 16 female, age 22-66 years, mean 41 years) with mediastinal tumor. They underwent diffusion-weighted single-shot echo-planar MRI of the mediastinum with a b-factor of 0, 300, and 600 sec/mm 2 . The apparent diffusion coefficient (ADC) value of the mediastinal tumor was correlated with the histopathological findings. Results:The mean ADC value of malignant mediastinal tumors was 1.09 Ϯ 0.25 ϫ 10 Ϫ3 mm 2 /sec, and of benign tumors was 2.38 Ϯ 0.56 ϫ 10 Ϫ3 mm 2 /sec. There was a significant difference in the mean ADC value between malignant and benign tumors (P ϭ 0.001) and within different grades of malignancy (0.001). When an ADC value of 1.56 ϫ 10 Ϫ3 mm 2 /sec was used as a threshold value for differentiating malignant from benign tumor, the best results were obtained with an accuracy of 95%, sensitivity of 96%, specificity of 94%, positive predictive value of 94%, negative predictive value of 96%, and area under the curve of 0.938. Conclusion:The ADC value is a noninvasive parameter that can be used for differentiation of malignant from benign mediastinal tumors and grading of mediastinal malignancy.

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

“…13,[25][26][27][28] In contrast with Abdel Razek, that distinguished Masaoka-Koga stage I disease (non-invasive THY) from higher stages (II-IV, invasive THY), we assessed whether DW-MRI could distinguish stage I-II (non-advanced THY, no neo-adjuvant therapy before surgery required), from stage III-IV (advanced THY, neo-adjuvant treatments needed). 11 Although we found a significantly higher mean ADC in non-advanced THY compared to advanced THY, this finding may have been influenced by the higher percentage of type B3 THY in advanced THY subgroup (56% versus 7% of nonadvanced THY subgroup). Indeed, the lower ADC values generally found in malignant tumors compared to benign conditions are related to a combination of higher cell density, tissue disorganization, and increased extracellular space tortuosity, all contributing to reduced motion of water.…”

“…8 reported for non-invasive THY in previous studies. 10,11 This discordance could be related to the "perfusion bias" with a consequent overestimation in ADC measurements of those studies. Indeed, as both the investigators used also the images obtained with b values of 0 s/mm 2 for the ADC computation, the ADC value was determined not only by diffusion (related to cell density and cellular architecture) but also by tissue perfusion.…”

“…For children and adolescents, this finding is consistent with a previous study that evaluated the fatty replacement of the normal thymus with chemical-shift MRI in 95 healthy volunteers. 20 Those investigators found that chemical-shift MRI can detect physiological fatty infiltration of the normal thymus in all subjects ≥16 years, in half of adolescents aged [10][11][12][13][14][15][16] years, but in none <10 years, although a microscopic and gradually increasing amount of fat in the normal thymus exists from birth. 20 In addition, a recent report described a case of non-suppressing normal thymus in a 21-year-old woman.…”

“…Unfortunately, there is no perfect correlation among Jeong and Masaoka-Koga classifications because, although low-risk thymomas are frequently grouped in the earlydisease group, percentages of high-risk thymomas are reported at a rate up to 45 % in the early stage disease group [10]. Limited data are available on quantitative assessment of thymic epithelial tumours (TETs) by using diffusionweighted magnetic resonance imaging (DW-MRI) from small cohorts of studies which considered various anterior mediastinal tumours, although those studies did not attempt to differentiate thymomas based on WHO and MasaokaKoga classifications by using the ADC [11][12][13][14][15][16][17][18]. More recently, a study involving 30 patients with TETs has demonstrated the ability of ADC in differentiating low-risk from high-risk tumours, and early from advanced disease [19].…”

CT and MRI findings of thymic carcinoid

“…T 2 weighted MRI was superior to pre-contrastenhanced CT in the depiction of the internal heterogeneity of the tumour. Razek et al 15 and Gumustas et al 16 reported that the mean apparent diffusion coefficient (ADC) of malignant mediastinal masses was significantly lower than that of benign mediastinal masses. They also mentioned that cystic or necrotic parts interfered with ADC value.…”