Neoplastic and proliferative disorders of the perinephric space.

The perinephric space is a well-marginated central compartment of the retroperitoneum, located between the anterior and posterior pararenal spaces. Various neoplastic and proliferative disorders can affect the perinephric space, and there is a wide array of imaging findings. Although many perinephric lesions may extend directly from the kidney and adrenal gland, other lesions occur in the perinephric space due to haematogenous spread, as part of a systemic disease, or by extension from an adjacent retroperitoneal compartment. Imaging plays a pivotal role in the diagnosis of perinephric diseases, as many of the disease processes affecting this space will not result in clinical signs or symptoms until the disease is at an advanced stage. Despite the often shared non-specific clinical and imaging findings among these disease processes, application of a categorical differential diagnosis based on the imaging characteristics will serve to narrow the differential diagnosis and direct further evaluation and treatment. In this article, the lesions have been categorized as soft-tissue rind [nephroblastomatosis, fibrosis, Erdheim-Chester disease (ECD), extramedullary haematopoiesis, lymphoma, infiltrating metastases], focal solid lesions (extension of renal or adrenal malignancies, melanoma metastases, treated lymphoma), fat-containing lesions (angiomyolipoma, liposarcoma, myelolipoma), and cystic lesions (lymphangiomas, abscesses). The aim of this article is to demonstrate and describe the key imaging features of several neoplastic and proliferative disorders that affect the perinephric space.