Imaging Characteristics of Pathologically Proven Thymic Hyperplasia: Identifying Features That Can Differentiate True From Lymphoid Hyperplasia

Abstract

OBJECTIVE The purpose of this article is to investigate the imaging characteristics of pathologically proven thymic hyperplasia and to identify features that can differentiate true hyperplasia from lymphoid hyperplasia. MATERIALS AND METHODS Thirty-one patients (nine men and 22 women; age range, 20–68 years) with pathologically confirmed thymic hyperplasia (18 true and 13 lymphoid) who underwent preoperative CT (n = 27), PET/CT (n = 5), or MRI (n = 6) were studied. The length and thickness of each thymic lobe and the transverse and anterior-posterior diameters and attenuation of the thymus were measured on CT. Thymic morphologic features and heterogeneity on CT and chemical shift on MRI were evaluated. Maximum standardized uptake values were measured on PET. Imaging features between true and lymphoid hyperplasia were compared. RESULTS No significant differences were observed between true and lymphoid hyperplasia in terms of thymic length, thickness, diameters, morphologic features, and other qualitative features (p > 0.16). The length, thickness, and diameters of thymic hyperplasia were significantly larger than the mean values of normal glands in the corresponding age group (p < 0.001). CT attenuation of lymphoid hyperplasia was significantly higher than that of true hyperplasia among 15 patients with contrast-enhanced CT (median, 47.9 vs 31.4 HU; Wilcoxon p = 0.03). The receiver operating characteristic analysis yielded greater than 41.2 HU as the optimal threshold for differentiating lymphoid hyperplasia from true hyperplasia, with 83% sensitivity and 89% specificity. A decrease of signal intensity on opposed-phase images was present in all four cases with in- and opposed-phase imaging. The mean maximum standardized uptake value was 2.66. CONCLUSION CT attenuation of the thymus was significantly higher in lymphoid hyperplasia than in true hyperplasia, with an optimal threshold of greater than 41.2 HU in this cohort of patients with pathologically confirmed thymic hyperplasia.

Thymic Measurements in Pathologically Proven Normal Thymus and Thymic Hyperplasia

“…In our previous study of 31 patients with pathologically proven thymic hyperplasia, the size of the thymic gland with hyperplasia was significantly larger compared to the age-matched mean values of normal thymus [10]. The study also demonstrated that the thymic CT attenuation higher than 41.2 HU on contrast-enhanced CT is suggestive of lymphoid hyperplasia rather than true hyperplasia.…”

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

“…17,34 Indeed, because diffusion-weighted imaging provides information related to the cell density and cellular architecture of tissues based on the random translational molecular motion of water molecules, it has been used in different organs for distinguishing benign from malignant lesions through the measurement of the apparent diffusion coefficient (ADC), which is significantly lower in malignant tumours (e.g., high-grade THY and mediastinal lymphoma) compared with normal tissues or hyperplastic thymus (e.g., NT and TLH, which do not suppress on opposed-phase imaging because of the low lipid content within the thymus, as generally seen in young patients Quantitative analysis: unenhanced and contrast-enhanced CT For unenhanced and contrast-enhanced CT, no difference was found in the attenuation of the NT compared with TLH. Conversely, in their cohort of 15 patients, Araki et al 45 re-ported higher attenuation of the thymus in the TLH group compared with the true hyperplasia group (a condition indistinguishable from NT at histology) at contrast-enhanced CT, although these data were not confirmed at unenhanced CT. In the present study, a significantly higher intensity of enhancement was demonstrated for the NT/TLH group compared with the THY group and for advanced THY compared with early THY.…”

Approach to Chest Computed Tomography

“…6C). 11 Heart failure with mediastinal edema can cause haziness of the normally dark mediastinal fat and can cause mild enlargement of the mediastinal lymph nodes. 12 Fluid in a variety of pericardial recesses can mimic enlarged mediastinal lymph nodes.…”