Imaging in retroperitoneum presentation.

Imaging of retroperitoneum including anatomy , various Planes, compartments and lesions

1. IMAGING OF RETROPERITONIUM PRESENTER- DR SEEMA MODERATOR- DR ZUBAIR

2. ANATOMY Retroperitoneum Pararenal spaces Perirenal spaces Inter-fascial planes Retroperitoneal hematoma Retroperitoneal mass Identification of organ of origin

3. Retroperitoneum The retroperitoneum is the part of the abdominal cavity that lies between the posterior parietal peritoneum and anterior to the transversalis fascia.

4. BOUNDARIES OF RETROPERITINEUM Retroperitoneum is bounded anteriorly by the posterior parietal peritoneum, posteriorly by the transversalis fascia extends craniocaudally from the diaphragm to the pelvic brim.

5. COMPARTMENTS OF RETROPERITINEUM It is divided into three spaces by the perirenal fascia (Fascia's of Gerota and Zukerkandl ) and is best visualized using CT or MRI .The Three spaces are: Anterior pararenal space Perirenal (or perinephric) space , P osterior pararenal space

6. Anterior Pararenal Space Boundaries – Anteriorly: post parietal peritoneum – Posteriorly : ARF[anterior renal fascia] – 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

7. Peri Renal Space Boundaries • Superior - open to bare area of liver and contiguous with mediastinum. • Medial – anterior and posterior renal fascia fuse • Lateral - ARF, PRF fuse to form lateroconal fascia • Inferior - ARF & PRF converge blend about 8 cm below kidney

8. Contents of Perirenal Space Kidney, proximal collecting system, adrenal gland, Renal vasculature Lymphatics Bridging septa

9. Posterior Para renal Space Boundaries – Anteriorly : PRF[posterior renal fascia] and lateral conal fascia. – Posteriorly : transversalis fascia. – Open laterally to flank and inferiorly to pelvis – Contents : Fat (no visceral organs) Continues anterolaterally into the properitoneal fat,the extraperitoneal fat of the anterior abdominal wall.

10. INTRAPERITONEAL AND RETROPERITONEAL ORGAN Major Intraperitoneal Organ Secondary Retroperitoneal Organ Primary Retroperitoneal Organ Stomach Duodenum 2 nd and3 rd part Kidney Liver and gall bladder Pancreas: head,neck and body Adrenal gland spleen Ascending and descending colon Ureter Duodenum 1 st part Upper rectum Aorta Tail of pancreas Inferior venacava Jejunum , ileum, appendix Lower rectum Transverse and sigmoid colon Anal canal

11. Iliopsoas compartment - located within and immediate adjacent to psoas muscle - posteromedial to the posterior pararenal space

12. Inter-fascial Plane These interfascial planes are represented by - Retromesenteric - Retrorenal - Lateroconal interfascial plane, - Combined interfascial planes

13. The retromesenteric, retrorenal, and lateroconal planes are potential routes of interfascial communication between the retroperitoneal spaces. Retroperitoneal hemorrhage or rapidly expanding fluid collections can spread via these interfascial connections.

14. The Retromesenteric plane Expansile plane located between the anterior pararenal space and perirenal space

15. The Retrorenal plane Between the perirenal space and posterior pararenal space

16. The lateroconal interfascial plane Between layers of the LCF[lateroconal fascia]. It communicates with the RMP[retromesenteric plane] and RRP[retrorenal plane] at the fascial trifurcation.

17. formed by the inferior blending of the RMP[retro mesenteric plane] and RRP[ retrorenal plane] . It continues into the pelvis. The combined interfascial plane

18. The fascial trifurcation The point at which the RMP[retromesenteric plane], RRP[retrorenal plane], and LCF[lateroconal fascia] planes communicate mutually

19. Medial Extension RMPs and RRS are continuous across the midline Inter-fascial Plane Extensions

20. Right superior extension The RMP ,RRP and PRS on the left extend to the right hemidiaphragm The RMP ,RRP and PRS on the left extend to the left hemidiaphragm Left superior extension

21. Retroperitoneal hematoma

22. Anatomic Zones of Retroperitoneum ZONES VASCULAR CONTENTS VISCERAL CONTENTS I[midline Retroperitoneum] Supramesocolic suprarenal abdominal aorta pancreas celiac axis duodenum proximal superior mesenteric artery superior mesenteric vein proximal renal arteries Inframesocolic infrarenal abdominal aorta infrahepatic IVC

23. ZONES VASCULAR CONTENTS VISCERAL CONTENTS II[Upper lateral renal arteries kidneys, adrenal glands Retroperitoneum ] renal veins renal pelvis , proximal ureter III[Pelvic retro- iliac arteries, Peritoneum] iliac veins

24. Zone I Mandates exploration for both penetrating and blunt injury because of the high likelihood of major vascular injury in this area. Zone II Injury to the renal vessels or parenchyma and mandates exploration for penetrating trauma . A nonexpanding stable hematoma resulting from a blunt trauma mechanism is better left unexplored. Zone III Penetrating trauma mandates exploration Blunt trauma are usually with pelvic fractures management is based external fixation or angiographic embolization

25. Goals of Imaging in Retroperitoneal Hemorrhage To identify the retroperitoneal hemorrhage, it’s location and possible source. To assess its relative stability on the basis of the size and presence [or absence] of active extravasation of intravascular contrast material.

26. Retroperitoneal hemorrhages & fluid collections: Below the kidneys, the retroperitoneal spaces- a single space with direct contiguity between the anterior and posterior portions. Retroperitoneal hemorrhage or fluid spread from the abdominal retroperitoneum into the extraperitoneal pelvis along the anterior and posterior perirenal fasciae, which combine to form the fascial plane in the iliac fossa. Superiorly , the perirenal fasciae are attached to the diaphragm. On the right side, the bare area of the liver is directly connected to the anterior pararenal space. Therefore , hepatic lacerations involving the bare area of the liver can be a source of retroperitoneal hemorrhage.

27. IMAGING MODALITIES Multidetector CT is currently the preferred imaging modality for evaluating the retroperitoneum. It clearly defines individual spaces separated by various fascial layers. Multidetector CT angiography (MDCTA) is increasingly being used for assessing diseases affecting the vasculature MRI provide additional information about retroperitoneal abnormalities because of its multiplanar capability and excellent soft tissue resolution. Typical sequences used are precontrast T1-weighted , fat- suppressed T2- weighted and post- gadolinium fat- suppressed T1- weighted SGE images. Positron- emission tomography (PET) with FDG scanning has shown very high sensitivity and specificity for detection of retroperitoneal diseases. can detect small malignant nodes and tumor recurrences

28. PRIMARY NEOPLASMS Primary retroperitoneal neoplasms are rare tumors that originate in the retroperitoneal space but outside the major organs within that compartment. These neoplasms are generally derived from mesenchymal cells, neurogenic cells, or embryonic rests and may be benign or malignant. Diagnosis of these tumors is often challenging and consists of several steps, including tumor location and specific features of various tumors (spread, components and vascularity), displacement of normal anatomic structures

29. The normal anterior and posterior renal fascia measure 1–3 mm in thickness The posterior renal fascia is thicker and more frequently visualized than the anterior. Thickening of the retroperitoneal fascia is a sensitive but nonspecific indicator of adjacent disease and is seen in both inflammatory and neoplastic disorders. Anterior displacement of retroperitoneal organs 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.

30. Figs 20A and B: (A) Anterior displacement of pancreas. Axial CT image shows a large mass that is difficult to localize at first glance. However, anterior displacement of pancreas (arrow) confirms it to be in the retroperitoneal space; (B) Anterior displacement of the IVC. Axial CT image reveals a large, heterogeneous partially cystic right hypochondriac mass with septal calcification on the right. Its retroperitoneal location is suggested by the anterior displacement and stretching of the IVC (arrow). Histopathology revealed a diagnosis of paraganglioma

31. 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”

32. 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

33. Figs 21A and B: Beak sign. Axial CT image shows a large cystic tumor with the beak sign in its contact surface with the pancreas (broken white line). This finding represents mucinous cystadenocarcinoma of the pancreas

34. 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.

35. 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 , 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.

36. Embedded organ sign: CT image shows a huge heterogeneous mass in the right side of abdomen. The lumen of the duodenum is stretched toward the mass, and the wall of the duodenum appears embedded in the mass at the contact surface (arrow). These findings represent gastrointestinal stromal tumor of the duodenum

37. 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. CT angiogram sign” or “floating aorta sign” Retroperitoneal masses arising posterior to the aorta can insinuate between the aorta and the vertebral column and displace the aorta anteriorly; and hence the term floating aorta sign.

38. Retro peritoneal related Abnormality RP Sarcoma RP Neurogenic Tumors RP Fibrotic lesions RP collection Lipo Sarcoma Paraganglioma RP Fibrosis Hematomas Leiomyosarcoma Ganglioneuroma Fibromatosis Urinoma Un differentiated Pleomorphic Sarcoma(MFH) Neuroblastoma Pseudomyxoma Retroperitonei Schwannoma Lymphocele Neurofibroma Ganglioneuroblastoma RP Fat lesions Solid non neoplastic Cyctic neoplastic lesions Lymphnodal mass Vascular related Lipoma Pseudo tumoral lipomatosis Cystic Teratoma Lymphoma Aortic aneurysm Lymphangioma Metastatic Lymph adenopathy Aortic Dissection Pneumo retro peritoneum IVC Thrombosis

39. RETROPERITONEAL SARCOMA Rare mesenchymal neoplasms, accounting for less than 1% of adult malignancies. 15% of sarcomas originate within the retroperitoneum. May develop at any age (M>F), but most present in the 6 th and 7 th decades. Most common histologic subtypes of soft tissue sarcoma: Liposarcoma (40%) Leiomyosarcoma (30%) Undifferentiated pleomorphic sarcoma (UPS) (previously known as malignant fibrous histiocytoma) (15%).

40. LIPOSARCOMA Most common retroperitoneal sarcoma Originate from primitive mesenchymal cells WHO divides liposarcomas into four subtypes: Well- differentiated Myxoid Dedifferentiated Pleomorphic RADIOGRAPHIC FEATURES: CT Heterogenous mass Varying amount of fat and soft tissue Multiple septae Enhancing soft tissue components MRI Myxoid - hyperintense on T2WI with delayed post- contrast enhancement

41. Well differentiated liposarcoma a) CECT huge heterogenous mass with predominant fat attenuation b) T1WI Heterogenous hyperintensity and a partly nodular appearence

42. Well diff Liposarcoma (Myxoid Liposarcoma) A)CECT large mass with fat attenuation B) T2WI High attenuation area with the mass is markedly hyperintense

43. LEIOMYOSARCOMA Retroperitoneum is considered the most common extra uterine site for leiomyosarcoma. Symptoms are often non- specific with abdominal pain They arise from smooth muscle within arteries, veins or bowel . The most frequent site is the IVC (50%), and they are more common in women. They can be: completely extra- vascular: 62% completely intra- vascular: 5% have extra- and intra- luminal components: 33%

44. Retroperitoneal leiomyosarcomas tend to develop massive cystic components which undergo degeneration. Unlike other sarcomas, fat and calcification are not typically present . MRI T1: intermediate to low signal intensity T2: intermediate to high signal intensity

45. Leiomyosarcoma in 8yr A) Heterogenous enhancement with central necrosis and enhanced vessel (arrow) B) T2 WI heterogenous but relatively hypointense mass with central high SI suggests necrosis

46. UNDIFFERENTIATED PLEOMORPHIC SARCOMA UPS, previously known as malignant fibrous histiocytoma 15% of all malignant fibrous histiocytomas occur within the retroperitoneum. Six histological subtypes: ( Storiform,Pleomorphic,Myxoid,Giant cell,Inflammatory,Angiomatoid ) The density of MFH is typically similar to adjacent muscle, with heterogeneous lower density areas if hemorrhage, necrosis or myxoid material is abundant. The soft tissue component enhances . CT

47. MRI They are relatively well circumscribed, located within or adjacent to muscle, exerting positive mass effect on surrounding structures due to their (usual) large size at presentation. T1 intermediate (to low) signal intensity, similar to adjacent muscle prominent enhancement of solid components T2 intermediate to high signal intensity

48. RETROPERITONEAL NEUROGENIC TUMORS Paraganglioma Ganglioneuroma Neuroblastoma Ganglioneuroblastoma Schwannoma Neurofibroma

49. PARAGANGLIOMA a/k/a extra adrenal pheochromocytomas. Arise from highly vascularized specialized neural crest cells called paraganglia. Fourth and fifth decades of life Men and women are affected equally functional or nonfunctional depending on catecholamines secretion .

50. CT Enhancing, well-circumscribed, lobular or round soft tissue–attenuation masses . Homogeneous in attenuation when small or heterogeneous when large . Central areas of low attenuation may be due to central necrosis or cystic change. Punctate calcification and focal areas of high attenuation due to acute hemorrhage may also be seen in some tumors

51. MRI SI and enhancement characteristics of paragangliomas are similar to those of adrenal pheochromocytoma. Low to intermediate SI on T1- weighted images Moderately high SI on T2 relative to skeletal muscle Commonly heterogeneous secondary to foci of intratumoral necrosis or hemorrhage

52. PARAGANGLIOMA: T1- weighted and T2- weighted images show well- circumscribed retroperitoneal mass (M) that abuts right lobe of liver (L) and pancreatic head (P), with heterogeneous low to intermediate T1 SI and intermediate to high T2 SI relative to skeletal muscle

53. NEUROFIBROMA Benign tumors of nerve sheaths of peripheral nerves Commonly occur in deep anatomic locations in patients with NF1 (especially in retroperitoneal and paraspinal locations) and are commonly associated with neurologic symptoms. Neurofibromas are not encapsulated . Localized, plexiform, or diffuse types.

54. When multiple, pathognomonic of NF1, L arge conglomerate infiltrative masses of innumerable neurofibromas diffusely thicken a parent nerve and extend into multiple nerve branches, resulting in a characteristic “bag of worms” appearance

55. Known case of neurofibromatosis type I: Axial T2W fat- saturated images show multiple hyperintense lesions in the pelvis, with a few of them showing central hypointensity suggestive of a ‘ Target sign’

56. SCHWANNOMA Schwannoma, or neurilemoma, is a benign tumor that arises from the perineural sheath of Schwann (neurilemma). Schwannoma accounts for 6% of retroperitoneal neoplasms and is more common than neurofibroma. Females (2:1) 20–50- year age group

57. CT - small schwannomas are round, well defined, and homogeneous, but large schwannomas may be heterogeneous in appearance. Calcification can be punctate, mottled, or curvilinear. The nerve of origin is often difficult to identify. After contrast enhancement, schwannoma demonstrates variable homogeneous or heterogeneous enhancement

58. Axial contrast- enhanced CT show round well- circumscribed retroperitoneal mass with predominantly low attenuation and scattered regions of soft tissue attenuation.

59. Schwannoma: Axial T1- weighted and T2- weighted images through pelvis show round well- circumscribed retroperitoneal mass with slightly low to intermediate T1- weighted SI, high T2- weighted SI relative to skeletal muscle with enhancing regions of lower T2- weighted SI,.

60. “split- fat sign” may be seen when a rim of fat surrounds the tumor, originating from a nerve in an intermuscular location. Schwannoma with a split fat sign: T1W and T2W sagittal images show an oblongated encapsulated lesion, which is isointense on T1 and hyperintense on T2 on the posterior aspect of the arm in the intermuscular plane, with preserved fat at the upper and lower ends.

61. GANGLIONEUROMA rare benign tumor that arises from the sympathetic ganglia . The retroperitoneum (32%–52% of cases) and mediastinum (39%– 43% of cases) The tumor is commonly seen along the paravertebral sympathetic ganglia (59% of cases) or, less commonly, in the adrenal medulla.

62. GANGLIONEUROMA: Axial contrast- enhanced CT images through pelvis demonstrate lobulated hypoattenuating infiltrative lobulated pelvic extraperitoneal mass with low attenuation

63. NEUROBLASTOMA Malignant tumor More commonly seen in males and in the 1st decade of life. Two- thirds of neuroblastomas are located in the adrenal gland, and the remaining neuroblastomas occur along the paravertebral sympathetic chain.

64. CT Neuroblastoma is irregular, lobulated, and heterogeneous and demonstrates coarse amorphous calcifications and variable contrast enhancement, as well as invasion of adjacent organs and encasement of vessels with luminal compression.

65. GANGLIONEUROBLASTOMA Ganglioneuroblastoma is an intermediate- grade tumor that has elements of benign ganglioneuroma and malignant neuroblastoma. Ganglioneuroblastoma is a pediatric tumor occurring in the 2–4- year age group. Imaging appearances vary, and the tumor could be solid or cystic with solid components.

66. RETROPERITONEAL FIBROTIC LESIONS Retroperitoneal Fibrosis Fibromatosis (Desmoid Tumor) FIBROMATOSES The fibromatoses are divided into Superficial (fascial) groups Deep (desmoid tumor ) groups - further subdivided into Extra abdominal, Abdominal wall Intraabdominal (mesenteric, mesocolic , omental, retroperitoneal) subgroups

67. Imaging features Desmoid tumors are typically infiltrative and cross fascial boundaries CT: Homogeneous low to intermediate attenuation Low to intermediate SI on T1- and t2- weighted images relative to skeletal muscle, Tend to appear aggressive although they are not malignant .

68. Desmoid Tunors : Axial T1- weighted (A), T2- weighted (B), images through pelvis show infiltrative left pelvic mass with intermediate T1 and intermediate to slightly high T2 SI relative to skeletal muscle,. Mass infiltrates left bladder wall, left obturator internus muscle, left rectus abdominis muscle, and proximal left thigh musculature, with encasement of left common femoral artery and compression of left common femoral vein.

69. RETROPERITONEAL FIBROSIS Retroperitoneal fibrosis results from proliferation of fibrous tissue in the midline and para- aortic distribution. Approximately 70% cases of retroperitoneal fibrosis are idiopathic and are known as Ormond’s disease. Other causes include drugs (e.g. methysergide ), H/o surgery or radiation, aortic hemorrhage, aortitis, aortic atherosclerosis, extravasation of urine, nonspecific GI inflammation , TB, histoplasmosis, syphilis and actinomycosis. Retroperitoneal fibrosis may be a part of multifocal fibrosclerosis in which fibrous pseudotumor of the orbit, Riedel’s thyroiditis, sclerosing cholangitis and mediastinal fibrosis may also occur.

70. most common between 40 and 60 years of age. M :F = 2:1 . Fibrous plaque typically extends from below the level of the kidneys to the bifurcation of great vessels. The fibrous tissue may involve the IVC, aorta, ureters and occasionally the iliac and renal veins in a symmetric or asymmetric distribution. Microscopically, collagen fibroblasts and inflammatory cells characterize idiopathic retroperitoneal fibrosis. Most patients have impaired renal functions.

71. Excretory urography typically demonstrates bilateral hydronephrosis, which may be asymmetric and sometimes even unilateral. Retrograde studies demonstrate smooth tapering of the ureters that is most pronounced at the pelvic brim. US demonstrates retroperitoneal fibrosis as a poorly demarcated periaortic mass that is echo- free or hypoechoic. Associated hydronephrosis may be seen. CT appearance of the fibrous plaque varies considerably:

72. CT: Retroperitoneal fibrosis is visible as a soft tissue density mass located around the aorta and iliac arteries. Classically, it develops around the aortic bifurcation and spreads upwards where it can envelop the renal hila. Early or active stages - variable enhancement can be seen with intravenous contrast Quiescent disease - no enhancement MRI: low or intermediate signal intensity on T1 and T2 weighted images can have high signal intensity on T2- weighted images when it is in the active, inflammatory stage

73. Figs 30A to C: Retroperitoneal fibrosis. (A) Contrast- enhanced axial CT image shows hypodense, nonenhancing , infiltrating mass surrounding the aorta and IVC and extending into the left perirenal space. Right kidney is shrunken and hydronephrotic; (B) Coronal image shows the entire extent of the plaque like, perirenal soft tissue. Appearance is nonspecific and differentials include malignancy such as lymphoma. Diagnosis was confirmed by biopsy; (C) CT scan through the chest shows evidence of mediastinal fibrosis, a frequent association of retroperitoneal fibrosis

74. Fig. 31: Retroperitoneal fibrosis. Axial T2- weighted MR image shows a very hypointense mass (star), a finding consistent with the presence of mature fibrous tissue with little or no active inflammation

75. LIPOMA Lipomas are benign mesenchymal tumors composed of mature fat and represent the most common mesenchymal neoplasm . They are the most common benign tumor of the retroperitoneum PRIMARY RETROPERITONEAL F A T - CONTAINING LESIONS CT - lipomas typically have homogeneous fat attenuation MRI - SI identical to that of macroscopic fat on all pulse sequences, without enhancing components. Few thin (<2 mm) septae may be seen that have minimal to moderate enhancement Mild enhancement of a thin fibrous capsule

76. RETROPERITONEAL FLUID COLLECTION Haematoma Uriniferous Fluid/Urinoma Lymphocele Chyloretroperitoneum Pseudomyxoma Retroperitonei Fluid Collections (Noninfectious / Infectious)

77. Retroperitoneal fluid collections may result from neoplastic, infectious, inflammatory, and traumatic causes. Simple fluid collections and transudative fluid collections - water attenuation, low SI on T1- weighted images, and very high SI on T2- weighted images. Proteinaceous fluid collections and exudative fluid collections - greater attenuation than water, variably increased SI on T1, and variably decreased SI on T2 .

78. HEMORRHAGE/HEMATOMA Retroperitoneal hemorrhage may be secondary to rupture or leak of an aneurysm or vascular malformation, anticoagulant therapy, a bleeding diathesis, trauma, arterial catheterization, underlying parenchymal organ pathology with rupture, or may be spontaneous.

79. CT - HAEMATOMA Acute clotted hemorrhage - high attenuation (45- 70 HU ) Acute non clotted hemorrhage or more chronic hemorrhage - lower attenuation (20- 45 HU) or fluid attenuation (0- 20 HU) Sentinel clot sign , where areas of higher- attenuation acute clotted hemorrhage are more likely to indicate anatomic sites of hemorrhage

80. Figs 9A and B: Spontaneous retroperitoneal hemorrhage in a patient on anticoagulant therapy. (A) Axial T1-weighted MR image shows a well- defined hyperintense lesion anterior to the left psoas. It is partially decompressing into the parietes; (B) Coronal T2- weighted image shows heterogeneous, predominantly high signal intensity within the mass. There is a markedly hypointense peripheral rim (arrow) due to hemosiderin deposition . These T1 and T2 signalintensities are diagnostic of a subacute hematoma

81. LYMPHOCELES Lymphoceles are fluid- filled cystic lesions that usually occur at least 3 to 4 weeks after pelvic or retroperitoneal lymphadenectomy for urologic or gynecologic malignancies or after renal transplantation . Small lymphoceles - asymptomatic and spontaneously resorb. Large retroperitoneal lymphoceles - symptomatic and may lead to complications related to mass effect upon adjacent structure

82. URINIFEROUS FLUID/URINOMA Most commonly within the perirenal spaces. CAUSE - Due to urinary obstruction but may be due to abdominopelvic trauma, surgery, or diagnostic instrumentation. As urine extravasates into the retroperitoneum, it can cause lipolysis of the surrounding fat, with resultant encapsulation of urine, forming a urinoma.

83. PSEUDOMYXOMA RETROPERITONEI Benign or malignant condition that results in intraperitoneal mucin accumulation. Pseudomyxoma retroperitonei occurs very rarely Caused by retroperitoneal rupture of a primary appendiceal mucinous adenoma in a retrocecal appendix CT - multicystic lesions with low attenuation MRI - low to intermediate SI on T1- weighted images, and high SI on T2- weighted images Thickened walls or septations that displace and distort adjacent structures.

84. PNEUMORETROPERITONEUM Retroperitoneal gas is most often the result of bowel perforation secondary to trauma, iatrogenic causes such as surgery or endoscopy, inflammatory bowel disease, peptic ulcer disease, foreign body, or gas-producing infection. On CT , retroperitoneal gas has very low attenuation and MRI very low SI on T1- and T2- weighted images

85. SOLID NON- NEOPLASTIC MASSES 1 . Pseudotumoral lipomatosis Lipomatosis is a benign metaplastic overgrowth of mature fat Lipomatosis is seen commonly in the pelvis and along the perirectal and perivesicular spaces and is seen less commonly in the abdominal retroperitoneum. CT and MR imaging show excess fat in the pelvis crowding the anatomic structures, with a few fibrous tissue strands but no soft-tissue mass or enhancement.

86. CYSTIC NEOPLASTIC MASSES Cystic Change in Solid Neoplasms : Cystic changes may develop in solid lesions such as paragangliomas and neurilemomas Cystic Teratoma Lymphangioma

87. LYMPHANGIOMA Lymphangioma can be seen in perirenal, pararenal, or pelvic extraperitoneal spaces and can involve more than one compartment. CT - large thin- walled unilocular or multilocular cystic mass with attenuation values ranging from that of fat (caused by chyle) to that of fluid . Calcification is rarely seen. An elongated shape and the involvement of multiple compartments are salient features of lymphangiomas Prone to recurrence . The occurrence of septa, compression of intestinal loops, and a lack of fluid in dependent recesses and mesenteric leaves differentiate lymphangioma from ascites.

88. Lymphangioma : T1- weighted and fat- suppressed T2- weighted images show well-circumscribed lobulated retroperitoneal lesion with low T1 SI and very high T2 SI relative to skeletal muscle, with several thin low- T2- SI internal septations. Note portion of lesion that invaginates between abdominal aorta and lumbar spine , which is characteristic of lymphangioma.

89. Hemangiopericytomas Hemangiopericytomas are highly vascular tumors thought to arise from blood vessel walls. They may demonstrate areas of intratumoral hemorrhage and multiple flow voids on MRI. Hemangiopericytomas enhance rapidly and intensely on dynamic contrast- enhanced CT or MRI Teratomas Teratomas are congenital neoplasms containing components of all three germ layers. CT often shows calcification or even osseous elements. Fat may be seen on both CT and MRI.

90. Fig. 28: Retroperitoneal teratoma. Axial CT image reveals a large heterogeneous mass containing elements that show the attenuation of fluid, fat, soft tissue and calcification

91. Iliopsoas Muscle Compartment Diseases affecting the iliopsoas muscle more commonly originate from adjacent structures and involve the muscle by direct extension. These include hemorrhage, infections and tumors of the spine, kidneys, bowel, pancreas and retroperitoneal lymph nodes. Tuberculous spondylitis and lumbar discitis are the commonest cause of an iliopsoas abscess. Iliopsoas inflammatory masses appearances, ranging from diffuse homogeneous enlargement to discrete masses containing central areas of low CT attenuation or high signal intensity on T2-weighted MR images. Postcontrast images show abscesses as expansile lesions with non- enhancing necrotic centers, intense peripheral enhancement and enhancement of the surrounding tissues.

92. Psoas abscess. CT image shows a well- defined, fluid density lesion in the left psoas muscle. It has a thin, peripheral enhancing rim and large necrotic center

93. Primary neoplasms of the psoas muscle are rare. Iliopsoas malignancies often appear similar to other Retro peritoneal pathologies on imaging. The affected muscle is usually enlarged and may show solid tumoral Contrast enhancement Anaplastic carcinoma iliopsoas. Axial CT image shows a large mass involving the right iliacus muscle. The large, irregular, solid component within the mass raises a possibility of malignancy

94. AORTA The most important abdominal aortic abnormalities are aneurysm formation and aortic dissection. MDCTA and MRA have gradually replaced conventional angiography as the procedures of choice for detailed evaluation of the aorta.

95. Aortic Aneurysm Most abdominal aortic aneurysms result from atherosclerosis. The infrarenal aorta is the most common site of abdominal aortic aneurysms accounting for 95% of cases. If untreated, aneurysms may enlarge and rupture with a mortality of 50–90%. The abdominal aortic aneurysm may show curvilinear calcification on plain abdominal radiography. On ultrasonography (US), CT and MRI the aneurysm is identified as focal area of dilatation exceeding 3 cm in size. Spontaneous rupture is a frequent complication of aneurysms measuring 6 cm or more in diameter.

96. Angiography frequently underestimates Contrast- enhanced 3D gradient echo MRA demonstrates the full extent of the aneurysm and its relationship to aortic branches.

97. Aortic Dissection Aortic dissection usually originates in the thorax but sometimes extends into the abdomen. Multidetector CT has the advantages of shorter scanning times, wide availability and high diagnostic accuracy and has, therefore, classically been the modality of choice for the evaluation of aortic dissection.

98. Fig. 11: Thoracoabdominal aortic dissection. Axial CT angiogram easily demonstrates the linear intimal flap between the anterior true lumen and posterior false lumen. Active extravasation into the retroperitoneum is also seen

99. Morphologic features : The true lumen is usually smaller than the false lumen and would be thin or flat from being pressed, appearing oval in the axial plane. The false lumen is expanded or very large, appearing crescentic or winding around the true lumen in the axial plane. Relationship between the lumina: The lumina may be parallel to each other, the false lumen may wind around the true lumen, or the true lumen may look like a ribbon floating in the false lumen. Appearance of thrombosis: The false lumen usually contains a thrombus, especially at the retrograde end of the initial entry site, whereas the true lumen contains no thrombus in most cases.

100. LYMPH NODES Normal lymph nodes appear as small, rounded soft tissue masses adjacent to the great vessels. Retrocrural , paraceliac , gastrohepatic para- aortic, aortocaval, periportal, peripan creatic , external and internal iliac groups together constitute the retroperitoneal nodes. Presently, CT is the most frequently used imaging technique for evaluation of enlarged retroperitoneal nodes. The retroperitoneal lymph nodes are considered abnormal if their size in their short axis is more than 10 mm, except in the retrocrural space where the upper limit is 6 mm

101. Benign Lymphadenopathy Benign lymphadenopathy may occur secondary to inflammatory or infectious disease. The nodes commonly demonstrate peripheral enhancement with central areas of low attenuation after intravenous contrast administration Calcification is frequently seen in tubercular lymph nodes.

102. Lymphoma Abdominal lymph nodes are involved in 50% of the non- Hodgkin’s lymphoma (NHL) patients as against 25% of those with Hodgkin’s disease (HD) at presentation. Mesenteric involvement is seen in more than half of the NHL patients (versus 5% of those with HD). The patterns of lymphadenopathy are also markedly different, slight enlargement of upper para- aortic nodes and contiguous spread being characteristic of HD. NHL on the other hand manifests with bulky lymph nodes in multiple locations

103. Fig. 17: Non- Hodgkin lymphoma. Contrast enhanced Axial CT image shows large, confluent lymph nodal mass in the preaortic location. The celiac axis branches are engulfed by the mass but their patency is preserved

104. Lymphomas are ‘soft’ tumors and frequently surround the adjacent vessels (floating aorta sign) and ureters without compressing their lumina. Lymphomas are homogeneous, with minimal contrast enhancement and relatively low signal intensity at T2- weighted images representing densely packed cellular components. Nodes are rarely calcified (<1%) in untreated patients . FDG- PET is now considered the most accurate tool for the assessment of treatment response and prognosis in patients with Hodgkin lymphoma and aggressive non- Hodgkin lymphoma.

105. Metastatic Lymphadenopathy Metastatic lymph nodes show varied morphological patterns, but the diagnosis is usually straightforward due to the presence of a known primary. Neoplasms of the stomach, colon, pancreas, kidney, testis, ovary, uterus, bladder and prostate may all metastasize to retroperitoneal lymph nodes.

106. Figs 19A : Metastatic testicular germ cell tumor. (A) Axial CT image shows massive, low attenuation retroperitoneal lymphadenopathy;

107. FDG- PET may be more sensitive and specific than CT for certain retroperitoneal metastases depending on the primary.

108. REFERENCES HAAGA CT & MRI OF WHOLE BODY 5 TH EDITION GRAINGER & ALLISON’S DIAGNOSTIC RADIOLOGY. RADIOPAEDIA

109. THANK YOU