Imaging findings of expansile lesions of the thymus.

The purpose of this article is to review the imaging findings of the different expansile lesions of the thymus. Almost 50% of all mediastinal masses are located in the anterior mediastinum. The thymus is the most common site of origin of these masses. Several kinds of lesions can arise from this gland because it derives from the three embryonic germ cell layers. Primary neoplasms of the thymus are thymoma, thymolipomas, carcinoma, carcinoid, primary germ cell tumors, and lymphoma. The latter can also involve the organ in a secondary fashion. Other lesions that cause thymic enlargement and that can be confused with neoplasia are thymic cysts and thymic hyperplasia. Even though anterior mediastinal masses are first found on conventional radiographs, computed tomography and magnetic resonance are very useful additional studies for assessing the origin and extension of these masses. The basic concepts regarding embryology, anatomy, and histology relevant for the differential diagnosis of an enlarged thymic gland are also described.

Imaging findings in musculoskeletal complications of AIDS.

Patients with human immunodeficiency virus (HIV) infection and acquired immunodeficiency syndrome (AIDS) are susceptible to a variety of complications that can affect the musculoskeletal system. These complications can be infectious, inflammatory, or neoplastic or can take some other form. Infection (cellulitis, necrotizing fasciitis, soft-tissue abscess, pyomyositis, osteomyelitis, septic arthritis) is the most common complication. Inflammatory processes include various arthritides as well as polymyositis. Non-Hodgkin lymphoma and Kaposi sarcoma are the two most common neoplasms in this patient population. Miscellaneous disorders include osteonecrosis, osteoporosis, rhabdomyolysis, anemia-related abnormal bone marrow, and hypertrophic osteoarthropathy. The underlying mechanisms leading to these diseases are complex and not fully understood but are thought to be multifactorial. Radiology may play an important role in early diagnosis and treatment planning in this population, in whom clinical and laboratory findings are commonly equivocal and nonspecific. Although biopsy is often necessary for the final diagnosis, it is important for the radiologist to be familiar with the different types of musculoskeletal disease in HIV-positive and AIDS patients so that an appropriate differential diagnosis can be established.