Drain in pancreatic bed. Pseudocyst with components in perinephric and anterior Pararenal spaces.
Subcapsular into anterior pararenal space extending along iliac vessels into pelvis. Also via perinephricseptae to upper aspect post pararenal space
Reproteritoneum Anatomy and Pathology
Retroperitoneum Dr. Dhruv Taneja 10/04/2012
Retroperitoneum• The retroperitoneum is the part of the abdominal cavity that lies between the posterior parietal peritoneum and anterior to the transversalis fascia.• It is divided into three spaces by the peri renal fascia (Fascias of Gerota and Zukerlandl) and is best visualized using CT or MRI .The Three spaces are: – anterior pararenal space – perirenal space – posterior pararenal space
Retroperitoneal OrgansRetroperitoneal organs – Duodenum and pancreas – Ascending and descending colon – Kidneys and ureters – Bladder and uterus – Great vessels – Rectum
• ARF = Gerota fascia – thinner• PRF = Zuckerkandle fascia -thicker,• Formed of 2 layers 2 apposition of ARF and lateralconal fascia creating potential space
Interfascial Planes• Tricompartmental anatomy does not completely explain the spread of fluid collections.• Collections tend to escape site of origin into expandable interfascial planes.
Interfascial Planes• These interfascial planes are represented by - Retromesenteric - Retrorenal - Lateroconal interfascial plane, - Combined interfascial planes
Interfascial PlanesThe Retromesenteric plane Expansile plane located between the APR and PRS
Interfascial PlanesThe Retrorenal plane Between the PRS and PPS
Interfascial PlanesThe lateral conal interfascial plane Between layers of the LCF. It communicates with the RMP and RRP at the fascial trifurcation.
Interfascial PlanesThe combined interfascial plane formed by the inferior blending of the RMP and RRP . It continues into the pelvis.
Interfascial PlanesThe fascial trifurcation The point at which the RMP, RRP, and LCF planes communicate mutually
Interfascial PlanesMedial Extension• RMPs and RRS are continuous across the midline.
Interfascial PlanesRight superior extension• The superior PRS is in continuity with the bare area of the liver
Interfascial Planes Left superior extension• The RMP ,RRP and PRS on the left extend to the left hemidiaphragm
Anterior Para Renal Space• Boundaries – Anteriorly: post parietal peritoneum – Posteriorly: ARF – Contents: Ascending and descending colon, duodenum, pancreas – Continuous across midline, with root of small bowel mesentery and inferiorly with perirenal, posterior pararenal and prevesical spaces
Posterior Para renal Space• Boundaries – Anteriorly: PRF and lateral conal fascia. – Posteriorly: transverse fascia. Limited by and parallels psoas muscle. – Open laterally to flank and inferiorly to pelvis – Contents: Fat (no visceral organs) – Continuous (potentially) with each other via pro peritoneal fat of anterior abdominal wall
• Retro mesenteric - between anterior pararenal and perinephric spaces contiguous across midline and laterally with retro renal and lateral conal space.• Retro renal - between peri nephric and posterior pararenal spaces·• Lateral conal – Combined fascial plane continues into pelvis anterolateral to psoas muscle. – Allowing pathway to pelvis. – Trifurcation of 3 planes - anterioposterior location is variable
Peri Renal Space• Anterior and post renal fasciae• Extent: Superior, medial, lateral, inferior• Contents:-
Retroperitoneal Anatomy 3. Perirenal space Kidneys Adrenal glands Upper portion of ureters
Extent of Peri Renal Space• Superior - open to bare area of liver and contiguous with mediastinum.• Medial - above renal hila perirenal spaces are separate, beginning at level of hila there is communication.• Lateral - ARF, PRF fuse to form lateral conal fascia• Inferior - ARF & PRF converge blend about 8 cm below kidney .
Contents of Perirenal SpaceKidney, proximal collecting system, renalsepta, adrenal gland,Renal vasculature and perirenal vesselsLymphaticsBridging septa
Spread via Perinephric Bridging Septe• Thickened septa - nonspecific but may be early sign of renal/perinephric disease• May preclude complete percutaneous drainage of perinephric fluid collections• Serve as conduit for spread of fluid, inflammation, neoplasm• Involvement of septae depends upon rapidity of process
Renal Capsule• Composed of fibrous tissue and smooth muscle.• Forms a firm, smooth investment for the kidney.• Will be sharply deflected over margin of a subcapsular collection/mass with flattening and compression of the kidney.
Pathways of Spread of Disease in the Retroperitoneum• Slowly accumulating, non-aggressive processes confined to 3 main spaces• Rapidly developing collections accumulate and spread within fascial planes, along bridging septae, and lymphatics
Lymphatic Spread of Disease from Perinephric Space Small perirenal lymph nodes Nodes in renal hilum Periaortic/pericaval nodes
Retroperitoneal collections & their extensions
Extension of fluid collections• Fascial planes/adhesions confine retroperitoneal fluid collections to their compartment of origin• Large or rapidly developing fluid collections may decompress along retroperitoneal fascial planes
Extension of fluid collectionsFluid originatingfrom the APSPancreatitisPancreatic injuryAppendicitisabscess of thecolonic wall
Extension of fluid collectionsFluid originatingfrom the PRSRuptured AAARenal injuryHge/urinoma
Extension of fluid collectionsFluid originatingfrom the PPSbleeding after spinaltrauma/surgery
Extension of fluid collectionsPelvic Extension By the infrarenal retroperitoneal space
Extension of Retroperitoneal Fluid into Pelvis• Major route - via fused interfascial planes with dorsal extension, medial to iliac vessels (perinephric collections)• Minor route - dorsal extension lateral to iliac vessels in contact with iliopsoas muscle• Minor route - medially into prevesical space (anterior parerenal collections)
Infections• Most originate from kidney• May spread through all spaces and via bare area to peritoneum and thorax• Xanthogranulomatous pyelonephritis
Collections related to ureteroscopy• Subcapsular• Perinephric• Pararenal
Hematomas• Traumatic- MVA, iatrogenic• Spontaneous- tumor, vascular (AAA,AVM, arteritis), hematologic disorders, end stage kidney• Spread of hepatic or splenic hematomas to perinephric space without renal injury• Leaking aortic aneurysm
Retroperitoneal Tumors• Benign and malignant• Diagnosis is challenging as – determining tumor location (characterizing the retroperitoneal space and identifying the organ of origin) – recognizing specific features of various retroperitoneal tumors (evaluating patterns of spread, tumor compo- nents, and vascularity).
Characterization of the Retroperitoneal Space• The first step is to decide whether the tumor is located within the retroperitoneal space.• Displacement of normal anatomic structures• Anterior displacement of retroperitoneal organs (eg, kidneys, adrenal glands, ureters, ascending and descending colon, pancreas, portions of the duodenum) strongly suggests that the tumor arises in the retroperitoneum.• Major vessels and some of their branches are also found in the retroperitoneal cavity, so that displacement of these vessels can be helpful as well.
Identification of the Organ of Origin• Some radiologic signs that are helpful in determining tumor origin include – the “beak sign,” – the “phantom (invisible) organ sign,” – the “embedded organ sign,” and – the “prominent feeding artery sign”
Beak Sign• When a mass deforms the edge of an adjacent organ into a “beak” shape, it is likely that the mass arises from that organ (beak sign).• On the other hand, an adjacent organ with dull edges suggests that the tumor compresses the organ but does not arise from it
Phantom (Invisible) Organ Sign• When a large mass arises from a small organ, the organ sometimes becomes undetectable. This is known as the phantom organ sign.• However, false-positive findings do exist, as in cases of huge retroperitoneal sarcomas that involve other small organs such as the adrenal gland.
Embedded Organ Sign• When a tumor compresses an adjacent plastic organ (eg, gastrointestinal tract, inferior vena cava) that is not the organ of origin, the organ is deformed into a crescent shape.• In contrast, when part of an organ appears to be embedded in the tumor (negative embedded organ sign), the tumor is in close contact with the organ and the contact surface is typically sclerotic with desmoplastic reaction.• When the embedded organ sign is present, it is likely that the tumor originates from the involved organ.
Prominent Feeding Artery Sign• Hypervascular masses are often supplied by feeding arteries that are prominent enough to be visualized at CT or MR imaging, a finding that provides an important key to understanding the origin of the mass.
Solid Processes• RCC-invasion of peri renal fat, thickening of renal fascia• Lymphoma-multiple renal masses, contiguous retroperitoneal masses, perirenal masses, single renal mass• Metastasis-to perirenal lymphatics - melanoma, RCC, lung (via pleura/mediastinal connections)• Fibrosis-AO, IVC, ureters, peri nephric space• Amyloidosis - perirenal soft tissue collections
Specific Patterns of Spread• Some retroperitoneal tumors have specific patterns of growth and extension that aid in narrowing the differential diagnosis.• Lesions That Extend Between Normal Structures.— Some tumors grow and extend into spaces between preexisting structures and surround vessels without compressing their lumina. Lymphangiomas and ganglioneuromas are examples of such tumors.
Lymphangiomas• 1% of all retroperitoneal neoplasms.• Most cases are detected in the first 2 years of life on the basis of symptoms like abdominal distention or pain; however, they can manifest in older patients as a huge, asymptomatic mass.• At imaging, they appear as fluid-filled, unilocular or multilocular cystic masses with minimal contrast enhancement.• Complete excision is the treatment of choice but is often difficult and has high rates of complication and recurrence
• Lesions That Extend along Normal Structures.—Tumors of the sympathetic ganglia (ie, paragangliomas, ganglioneuromas) tend to extend along the sympathetic chain and have an elongated shape.
Characteristic Tumor Components• Some tumor contents can be clearly demonstrated at CT and MR imaging and provide strong clues that help narrow the differential diagnosis.
Fat• The presence of fat is easily recognized owing to its high attenuation at CT or its high signal intensity at T1-weighted MR imaging with loss of signal intensity on fat-suppressed images. The presence (or absence) of fat limits the differential diagnosis.• A mass that is homogeneous and well defined and consists almost entirely of fat represents lipoma
Lipo sarcoma• When the mass is somewhat irregular and ill-defined but contains fat, the diagnosis of liposarcoma should be considered. L• iposarcomas are the most common sarcomas of the retroperitoneum.• 5th and 6th decades of life, slight female predilection.• They are classified at pathologic analysis into well- differentiated, pleomorphic, myxoid, and dedifferentiated types.• Well-differentiated liposarcomas usually contain an appreciable amount of fat, whereas high-grade liposarcomas may not demonstrate appreciable fat, thereby appearing similar to other sarcomas
Teratoma• Teratomas are also characterized by the presence of fat, and mature teratomas can be characterized by the presence of fluid attenuation or signal intensity, fat-fluid levels, and calcifications
Radiologic Features• The morphologic features of teratoma extend from predominantly cystic to completely solid lesions.• Fat and calcifications,• If the fat appears with the configuration of sebum (ie, fat attenuation or signal that horizontally interfaces with a nonfatty mate- rial), this feature is thought to be nearly pathognomonic for teratoma
• US is highly sensitive teratomas because the lesions are usually quite large at initial presentation. Typical findings include a complex echogenic mass with solid and cystic components that may or may not have acoustic shadowing, depending on the presence of calcification.• CT is more reliable in the unequivocal identification of fat. Calcification was detected in patterns that were characterized as congealed, linear, and shard like. A tooth like structure was seen.• MR imaging demonstrates, A complex mass with both solid and fluid components. The pseudocapsule of the mass is usually easier to identify with MR imaging because of its hypointense rim. This feature is helpful for excluding invasion of adjacent structures. Fat within the lesion characteristically has high signal intensity on T1- weighted images and may be more readily identifiable with MR imaging than with CT. In addition, the chemical shift between fat and water content is a helpful diagnostic finding.
Myxoid Stroma• Myxoid stroma is characterized pathologically by a mucoid matrix that is rich in acid mucopolysaccharides.• Myxoid stroma appears hyperintense on T2-weighted MR images and shows delayed enhancement after injection of contrast medium.• Tumors that commonly contain myxoid stroma include – neurogenic tumors (schwannomas, neurofibromas, ganglioneuromas, ganglion euroblastomas, malignant peripheral nerve sheath tumors), – myxoid liposarcomas, and – myxoid malignant fibrous histiocytoma.
• Schwannomas are the most common tumor of peripheral nerves.• Schwannomas are well encapsulated and contain cells that are identical to Schwann cells.• Their MR imaging appearance depends on the types of tissue they contain. Myxoid tissue is hyperintense on T2-weighted images, cellular tissue is hypointense on both T1- and T2-weighted images, and solid fibrous tissue enhances on contrast-enhanced images.• Neurofibromas tend to have high signal intensity on T2-weighted MR images and are often multiple and associated with neurofibromatosis.• Ganglioneuromas are typically located along the sympathetic chain and tend to be larger, more rounded, and contain calcification more frequently than nerve sheath tumors. The relatively younger age of affected patients may aid in differentiating ganglioneuromas from other neurogenic tumors.
Necrosis• Necrotic portions within tumors have low attenuation without contrast enhancement at CT and are hyperintense at T2-weighted MR imaging.• Necrosis is usually seen in tumors of high-grade malignancy such as leiomyosarcomas.• When they occur in the retroperitoneum, leiomyosarcomas tend to develop massive cystic degeneration. They have central necrosis more commonly than other sarcomas, whereas fat and calcifications are not typically present
Small Round Cells• At T2-weighted MR imaging, tumors composed of small round cells often appear as homogeneous masses with relatively hypointense areas representing densely packed cellular components.• Lymphomas are the most commonly encountered tumors composed of small round cells. They are homogeneous, with minimal contrast enhancement at CT and relatively low signal intensity at T2-weighted MR imaging. An exception is primitive neuroectodermal tumor (PNET), which often appears heterogeneous at MR imaging
VascularityVascularity is another important feature ofretroperitoneal tumors. Extremely hypervasculartumors include paragangliomas andhemangiopericytomas. Moderatelyhypervascular tumors include myxoid malignantfibrous histiocytomas, leiomyosarcomas, andmany other sarcomas. Hypovascular tumorsinclude low-gradeliposarcomas, lymphomas, and many otherbenign tumors
Retroperitoneal Fibrosis• Most commonly idiopathic• Other causes: aortic hemorrhage, aortitis, methysergide toxicity, prior surgery or XRT, collagen vascular disease (Riedel’sthyroiditis, sclerosing mediastinitis)• Clinical: 40-6 0 yrs, males > females• Hydronephrosis, ureteral narrowing, slight medial ureteral displacement
HibernomaHibernoma is a rare, benign, soft-tissue tumorcomposed of brown fat.The name hibernoma is derived from histologicsimilarities between these tumors and thebrown fat identified in hibernating animals.Arise in these locations, which include thethigh, buttock, scapularregion, trunk, neck, mediastinum, chestwall, perirenal areas, breast, scalp, andperiureteric regions
Radiologic Features• At US, the lesions appear echogenic, with both well-defined and ill-defined borders. Vascular analysis with Doppler or color flow US demonstrates that these lesions have increased flow in large surface vessels that are also visible with CT.• At CT, a low-attenuation, well-defined lesion with intratumoral septa is typically seen.• On C +, the septa will enhance, with generalized enhancement throughout the mass occasionally occurring as well.• These soft-tissue septations manifest with attenuation that averages slightly above that of subcutaneous fat.• Calcifications are notably absent
• The spectrum of MR imaging characteristics includes a few cases in which the hibernoma appears very similar to fat (isointense on T1- and T2-weighted images, with minimal if any enhancement).
Neoplastic Cysts• Cystic lymphangiomas are uncommon, congenital benign tumors and occur due to failure of the developing lymphatic tissue to establish normal communication with the remainder of the lymphatic system.• Most occur in the head or neck; a retroperitoneal location is unusual.• Cystic lymphangiomas can occur anywhere in the perirenal, pararenal, or pelvic extra- peritoneal spaces.• Cystic lymphangiomas are more common in men and can occur at any age.• At CT, cystic lymphangioma typically appears as a large, thin-walled, multiseptate cystic mass. Its attenuation values vary from that of fluid to that of fat. An elongated shape and a crossing from one retroperitoneal compartment to an adjacent one are characteristic of the mass.
• Primary mucinous cystadenomas are rare retro- peritoneal cystic lesions that occur in women with normal ovaries.• Primary retroperitoneal mucinous cystadenoma usually manifests as a homogeneous, unilocular cystic mass at CT. Differentiating this mass from cystic mesothelioma, cystic lymphangioma, and nonpancreatic pseudocyst is difficult.
• Cystic mesotheliomas are rare benign neoplasms with a mesothelial origin that originate in the serous lining of the pleural, pericardial, or peritoneal space.• Unlike malignant mesothelioma, cystic mesothelioma is not related to prior asbestos exposure. It does not metastasize but may recur locally and occurs more frequently in women.• Cystic mesotheliomas usually appear as non- specific, thin-walled, multilocular cystic lesions at CT. They may be radiologically indistinguishable from lymphangiomas and other retro-peritoneal cysts.
• Urogenital cysts arise from vestiges of the embryonic urogenital apparatus and can be classified into pronephric, mesonephric, metanephric, and mu ̈ llerian types based on their embryonic lines.• Mu ̈ llerian cyst of the retroperitoneum occurs in women from 19 to 47 years of age.• At CT, mu ̈ llerian cyst manifests as a unilocular or multilocular thin-walled cyst containing clear fluid. The differential diagnosis includes cystic mesothelioma and cystic lymphangioma
Epidermoid cysts• At CT, epidermoid cysts generally appear as thin-walled, unilocular cystic masses with fluid attenuation
Tailgut cysts• Tailgut cysts are rare congenital multicystic lesions that arise from vestiges of the embryonic hindgut and occur between the rectum and sacrum.• Tailgut cyst is more common in women and usually appears in middle age.• At CT, tailgut cyst appears as a well-defined multicystic mass with attenuation values varying from that of water to that of soft tissue.
Pseudomyxoma Retroperitonei• Pseudomyxoma peritonei is a rare condition that is characterized by intraperitoneal accumulation of gelatinous material owing to the rupture of a mucinous lesion of the appendix or ovary• The imaging findings in pseudomyxoma retro- peritonei are similar to those in pseudomyxoma peritonei. At CT, pseudomyxoma retroperitonei appears as multicystic masses with thick walls or septa that displace and distort adjacent structures
Non Neoplastic Lesions• Pancreatic Pseudocyst.• Non pancreatic Pseudocyst.• Lymphocoele.• Urinoma• Hematoma.