title: Diffusion-weighted MRI in a case of nonsuppressing rebound thymic hyperplasia on chemical-shift MRI.
abstract: 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.
authors.affiliation: Department of Radiology, San Luigi Gonzaga University Hospital, Orbassano, Turin, Italy, adriano.priola@inwind.it.
authors.forename: Adriano Massimiliano
authors.initials: AM
authors.lastname: Priola
authors.forename: Dario
authors.initials: D
authors.lastname: Gned
authors.forename: Valerio
authors.initials: V
authors.lastname: Marci
authors.forename: Andrea
authors.initials: A
authors.lastname: Veltri
authors.forename: Sandro Massimo
authors.initials: SM
authors.lastname: Priola
mesh_terms: D003937:Diagnosis, Differential; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008479:Mediastinal Neoplasms / Q000175:diagnosis; D008875:Middle Aged; D013952:Thymus Hyperplasia / Q000175:diagnosis*