الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
CT is the most important imaging modality for the retroperitoneum and is superior to other imaging modalities in defining the characteristics of the mass and the condition of neighboring organs and structures.
The aim of this work is to determine the role of multi detector computed tomography (MDCT) in assessment of retroperitoneal lesions based on imaging appearance as either cystic or solid or neoplastic and non-neoplastic and the characteristic imaging findings, such as the composition, enhancement pattern, location, and relationship to adjacent structures.
The study was conducted on 52 patients 26 males and 26 females with a mean age of 51.2 referred to the Radio-diagnosis department at Alexandria Main University Hospital diagnosed with retroperitoneal lesion during the time period starting from December 2016 to May 2018.
All patients were subjected to full history taking, thorough clinical examination, laboratory investigations and MDCT.
Thirty two cases (61.5%) were malignant lesions, eleven cases (21.1%) were benign lesions and nine cases (17.3%) were retroperitoneal collections.
The first step is to confirm whether the tumor is located within the retroperitoneal space. Before a tumor can be described as primary retroperitoneal, the possibility that the tumor originates from a retroperitoneal organ must be excluded. Some radiologic signs that are helpful in deter¬mining tumor origin include the “beak sign,” the “phantom (invisible) organ sign,” the “embedded organ sign,” and the “prominent feeding artery sign.
Twenty five cases of retroperitoneal lymphoma showed hypo-attenuating hypo-enhancing mostly homogenous (except in cases who were on chemotherapy) pre/para aortic nodal masses showing variable degrees of amalgamation. The diagnosis achieved by contrast enhanced MDCT using some of the characteristic imaging findings of lymphoma like anterior aortic displacement, anterior ureteric deviation and floating vessel sign with some associated imaging findings as splenomegaly.
Ten cases of lymphoma were presented as retroperitoneal soft tissue mantle similar to retroperitoneal fibrosis. Contrast enhanced MDCT helped to differentiate between the two entities based on some imaging findings; anterior aortic displacement was found much more common with lymphoma than with RPF, ureteric tethering and medial ureteric bowing were found with RPF while anterior ureteric displacement was with lymphoma. Invasion of the renal parenchyma was found with lymphoma and not RPF.
Six cases of retroperitoneal sarcoma, 3 of them were retroperitoneal liposarcoma appeared as sizable fatty retroperitoneal mass with enhancing intra-tumoral soft tissue nodules as well as coarse calcification, their diagnosis achieved by contrast enhanced MDCT and confirmed by histopathology. The other three cases appeared by contrast enhanced MDCT as solid retroperitoneal soft tissue mass showing areas of necrosis, in close proximity IVC or the renal vein and the presumed diagnosis given by contrast enhanced MDCT was retroperitoneal soft tissue sarcoma and two of them confirmed by histopathology to be leiomyosarcoma while the last one was malignant fibrous histocytoma.
Renal angiomyolipoma (AML) and retroperitoneal liposarcoma are both common retroperitoneal masses containing adipose tissue. The study excluded 3 cases of renal angiomyolipoma and the main differentiating imaging findings between the two entities were renal parenchymal defect at the site of tumor contact, renal artery vascular supply and tumoral vessels extending through the renal parenchyma, all of them were found with renal AML and not with the perirenal liposarcoma.
Three cases of retroperitoneal cystic lymphangioma showed trans-spatial cystic retroperitoneal lesion with enhancing internal septations presenting commonly in the first decade of life. The diagnosis achieved by MDCT confirmed by histopathology.
Two cases of retroperitoneal paraganglioma, showed retroperitoneal mass in classical location near the aorta and its major branches (para-aortic location) with arterial phase hyperenhancemnt and rapid washout in the delayed phase, the diagnosis achieved by contrast enhanced MDCT and confirmed by clinical examination and laboratory investigation of elevated serum level of catecholamines and urinary VMA as well as recurrent bouts of hypertension not responding to the usual antihypertensive agents.
One case of retroperitoneal MPNST, showed paraspinal heterogeneous soft tissue mass with foraminal widening and intraspinal extension associated with bone destruction. The diagnosis was achieved by contrast enhanced MDCT and confirmed by histopathology.
Other rare cases include one case of retroperitoneal mature cystic teratoma and one case of extrameduallry hematopoiesis. The diagnosis achieved by contrast enhanced MDCT in the former by the presence of retroperitoneal cystic mass showing internal fat density as well as calcifications in adolescent female patient confirmed by histopathology. In the latter the diagnosis achieved by both clinical history of myelofibrosis on treatment and MDCT which revealed the presence of paraspinal soft tissue lesions containing fat density present in the posterior mediastinum as well as the abdomen.
Regarding retroperitoneal collections, three cases of retroperitoneal hematoma found in patients on long term antiplatelet therapy, showed initially hyper-dense retroperitoneal hematoma with active contrast extravasation, the diagnosis achieved by contrast enhanced MDCT. Five cases of retroperitoneal inflammatory collection either pyogenic or tuberculous, appeared on contrast enhanced MDCT as ring enhancing fluid collections with or without psoas muscle involvement and showing foci of calcifications. One case of retropeitoneal urinoma after pelvic surgery showed delayed contrast extravasation on contrast enhanced MDCT in delayed phase.
So, based upon the MDCT characteristics of the lesion such as tissue density, tissue composition, enhancement pattern and vascularity, MDCT helped to narrow the differential diagnosis