Retroperitoneal neoplasms include benign and malignant tumors that emerge within the retroperitoneum. These are rarely encountered in the clinical practice. Lymphoma is by far the most important malignant retroperitoneal neoplasm, followed by liposarcoma, leiomyosarcoma and malignant fibrous histiocytoma, whereas a number of benign lesions are described in the literature. Symptoms in the form of abdominal pain, a palpable abdominal mass and distension, usually appear when the tumor is very large. Computed tomography (CT) and magnetic resonance imaging (MRI) are used to make the diagnosis.
Retroperitoneal neoplasms encompass tumors of different origins and nature (benign or malignant) that arise within this anatomical structure, but outside of the organs situated in the retroperitoneum    . Some of the most important retroperitoneal neoplasms are  :
The clinical course of a retroperitoneal neoplasm is predominantly described as insidious, mainly because the tumor needs to grow considerably in size before producing symptoms   . Main complaints, when present, are abdominal pain, distension, and a palpable abdominal mass, while early satiety, abdominal swelling, and gastrointestinal/urinary symptoms, which were thought to be rare, are seen in up to 40-50% of cases    .
Because of a rather nonspecific (or even absent) clinical presentation, the diagnosis of a retroperitoneal neoplasm may be difficult to make. For this reason, the physician plays a crucial role when obtaining a detailed patient history and performing a thorough clinical examination. To identify the exact location of the tumor and determine its subtype, however, imaging studies need to be carried out. CT and MRI are the two main exams used in the assessment of the retroperitoneum     . Several findings that point to a retroperitoneal neoplasm are embedded organ sign (compression of the adjacent organ into a crescent shape), prominent feeding artery sign (hypervascularization of the presenting mass), and the presence of dull edges of the organ adjacent to the tumor . Tumor types may be further discriminated by their distinguishing features: