Morphological imaging of thymic disorders.
ABSTRACT The thymus is a bilobed lymphoid organ the morphology of which varies considerably with age as a result of a process of fatty infiltration occurring after puberty. Although several diseases can arise in the thymic parenchyma, including germ cell and neuroendocrine tumours, primitive epithelial neoplasms (thymomas) are the most common neoplasms and account for almost 10% of mediastinal masses. Thymomas are usually benign but can be locally invasive. Up to 30% of patients with a thymoma have myasthenia gravis, which is more commonly associated with thymic hyperplasia. The latter results in a symmetric diffuse enlargement of the thymus. However, thymic hyperplasia can be histologically found in up to 50% of normal-sized thymuses on computed tomography (CT). CT is much more accurate in detecting thymomas than it is in detecting thymic hyperplasia, although CT findings may be unspecific. CT can be exhaustive in the case of an encapsulated thymoma (65% of all thymomas), which appear as a solid homogeneous mass with a slight contrast enhancement and a well-defined surrounding fat plane. These tumours rarely recur after surgery. CT can also accurately detect a spread through the capsule into the adjacent mediastinal fat, which characterizes invasive thymomas (35%). These, however, are best evaluated by magnetic resonance imaging (MRI). On T1-weighted MR scans the thymus is well delineated against the mediastinal fat, whereas marked inhomogeneity of the signal may appear on T2-weighted images as a result of areas of cystic degeneration in the tumour mass. The superior contrast resolution of MRI and the multiplanar images that can be produced with it are well suited for documenting the mediastinal spread of invasive thymomas. MRI depicts accurately pleural and/or pericardial implants as well as the involvement of great vessels, offering considerable aid in the planning of surgery.
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ABSTRACT: To evaluate the imaging appearance of the thymus in the myasthenic patients by using chemical shift magnetic resonance imaging, and, to correlate the chemical shift ratio (CSR) with pathologic findings after surgical excision. In the past year, a total of 11 myasthenic patients (4 males, 7 females; age range of 26-65 years), have been investigated by MRI centered at the thymic lodge. Our protocol included a Dual-Echo technique, T1-weighted In-phase/Opposed-phase MR images in all patients. A chemical shift ratio (CSR) was calculated by comparing the signal intensity of the thymus gland with that of the chest wall muscle for quantitative analysis. For this purpose, we have used standard region-of-interest electronic cursors at a slice level of the maximum axial surface of the thymus. We have identified two patients groups: a thymic hyperplasia group and a thymic tumoral group. With the decrease in the signal intensity of the thymus gland at chemical shift, the MR imaging was evident only in the hyperplasia group. The mean CSR in the hyperplasia group was considerably lower than that in the tumor group, 0,4964 ± 0,1841, compared with 1,0398 ± 0,0244. The difference in CSR between the hyperplasia and tumor groups was statistically significant (P=0,0028). MR imaging using T1-weighted In-phase/Opposed-phase images could be a useful diagnostic tool in the preoperative assessment of the thymic lodge and may help differentiate thymic hyperplasia from tumors of the thymus gland.Journal of medicine and life 06/2012; 5(2):206-10.