Fat-containing Retroperitoneal Lesions: Imaging Characteristics, Localization, and Differential Diagnosis.

The complex anatomy of the retroperitoneum is reflected in the spectrum of neoplastic and nonneoplastic conditions that can occur in the retroperitoneum and appear as soft-tissue masses. The presence of fat within a retroperitoneal lesion is helpful in refining the differential diagnosis. Fat is easily recognized because of its characteristic imaging appearance. It typically is hyperechoic at ultrasonography and demonstrates low attenuation at computed tomography (-10 to -100 HU). Magnetic resonance imaging is a more ideal imaging modality because it has better soft-tissue image contrast and higher sensitivity for depicting (a) microscopic fat by using chemical shift imaging and (b) macroscopic fat by using fat-suppression techniques. Whether a lesion arises from a retroperitoneal organ or from the soft tissues of the retroperitoneal space (primary lesion) is determined by examining the relationship between the lesion and its surrounding structures. Multiple imaging signs help to determine the organ of origin, including the "beak sign," the "embedded organ sign," the "phantom (invisible) organ sign," and the "prominent feeding artery sign." Adrenal adenoma is the most common adrenal mass that contains microscopic fat, while myelolipoma is the most common adrenal mass that contains macroscopic fat. Other adrenal masses, such as pheochromocytoma and adrenocortical carcinoma, rarely contain fat. Renal angiomyolipoma is the most common fat-containing renal mass. Other fat-containing renal lesions, such as lipoma and liposarcoma, are rare. Fatty replacement of the pancreas and pancreatic lipomas are relatively common, whereas pancreatic teratomas are rare. Of the primary retroperitoneal fat-containing lesions, lipoma and liposarcoma are common, while other lesions are relatively rare. (©)RSNA, 2016.

Abdominal twists and turns: part I, gastrointestinal tract torsions with pathologic correlation.

OBJECTIVE: The gastrointestinal tract is secured in place by various suspensory ligaments. Laxity or incomplete development of these anchoring ligaments can lead to hypermobility and predispose the patient to torsion-related ischemic pathology. A prompt diagnosis is necessary to avoid life-threatening consequences of prolonged visceral ischemia. Abdominal torsions are rarely diagnosed clinically, and it is often the responsibility of the radiologist to recognize and make the diagnosis through radiography, fluoroscopy, or cross-sectional imaging. This article reviews the imaging spectrum (with radiologic-pathologic correlations) and therapeutic implications of gastrointestinal tract torsions. CONCLUSION: Torsion-related ischemic pathology may involve any portion of the gastrointestinal tract from the stomach to the colon. The clinical presentation of gastrointestinal tract torsion is nonspecific, and radiologists are relied on to make this diagnosis. Recognition of the predisposing factors and imaging spectrum of gastrointestinal tract torsions is essential to help direct timely intervention in these potentially life-threatening entities.

Abdominal twists and turns: part 2, solid visceral torsions with pathologic correlation.

OBJECTIVE: The solid abdominal viscera are secured in place by various suspensory ligaments. Laxity or incomplete development of these anchoring ligaments can lead to hypermobility and predispose the patient to torsion-related ischemic pathology. The clinical symptoms of solid visceral intraabdominal torsions are nonspecific. A prompt diagnosis is critical to avoid life-threatening consequences of prolonged visceral ischemia. Abdominal torsions are rarely diagnosed clinically, and it is often the responsibility of the radiologist to recognize and make the diagnosis through cross-sectional imaging. This article reviews the imaging spectrum, radiologic-pathologic correlations, and therapeutic implications of solid visceral intraabdominal torsions, including some unusual solid organ and abdominal fat torsions. CONCLUSION: The clinical presentation of solid visceral intraabdominal torsion is nonspecific and radiologists are relied on to make this diagnosis on cross-sectional imaging studies. Recognition of the predisposing factors and imaging spectrum of intraabdominal torsions is essential to help direct timely intervention in these potentially life-threatening entities.