Radiological imaging in Retroperitoneum

1. Imaging in Retroperitoneum
M LAXMI KANTH

2. RETROPERITONEUM
The retroperitoneum is the compartmentalized space
located posterior to the posterior parietal peritoneum.

3. 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.

4. COMPARTMENTS OF RETROPERITINEUM
• It is divided by fascial planes into three compartments
• Anterior pararenal space
• Perirenal (or perinephric) space
• Posterior pararenal space

5. ANTERIOR PARARENAL SPACE
• Anterior pararenal space contains
• retroperitoneal portions of the colon, duodenum, and
pancreas
• confined by the posterior parietal peritoneum anteriorly, the anterior
renal fascia posteriorly, and the lateroconal fascia laterally

7. PERIRENAL SPACE
• The perirenal space contains the kidney, renal vessels, adrenal gland,
renal pelvis, proximal ureter, perirenal lymphatics, and perirenal fat.
• Confined by the anterior renal fascia and posterior renal fascia

9. POSTERIOR PARARENAL SPACE
• Posterior pararenal space almost always contains only fat.
• posterior renal fascia anteriorly,
• transversalis fascia posteriorly,
• psoas muscle medially,
• continues laterally external to the lateroconal fascia as the
properitoneal fat of the abdominal wall.
• Inferiorly the posterior pararenal space is open to the pelvis
• superiorly it continues as a thin subdiaphragmatic layer of
extraperitoneal fat.

11. RETROPERITONEAL ANATOMY: PLANES
• Retromesenteric planes are major routes by which effusions are
distributed in the extraperitoneal abdomen.
• The route of escape for common pathologic entities, such as pancreatitis
and colitis.
• Lateroconal planes are relatively small. They extend down the length of
the ascending and descending colon just lateral to the colonic lumen.

12. RETROPERITONEAL ANATOMY: PLANES
• Retrorenal plane extends inferior to the cone of renal fascia, it joins the
retromesenteric plane to become a combined plane that is situated on
the anterolateral surface of the psoas muscle,
• lateral to the ureter and medial to the iliac vessels. It continues into the
pelvic extraperitoneum.

14. • The Combined interfascial plane formed by the inferior blending of
the RMP and RRP and it continuous in to the pelvis

15. 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.

16. • 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

17. • 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.

18. 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

19. • 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.
• Some radiologic signs that are helpful in determining tumor origin
include the “beak sign,” the “phantom (invisible) organ sign”, and the
“embedded organ sign”.
• When there is no definite sign that suggests an organ of origin, the
diagnosis of primary retroperitoneal tumor becomes likely.

20. • 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

21. • 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. 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.

22. • 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

23. • Embedded organ sign: When a tumor compresses an adjacent plastic
organ (e.g. 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 (positive embedded organ sign) at the contact surface, it is
likely to be the organ of origin.

24. • 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

25. • Prominent Feeding Artery Sign.—Hypervascular masses are often
supplied by feeding arteries that are prominent enough to be
visualized at CT or MR imaging.

26. • The role of imaging is to determine the tumor location and extent. It
is essential to determine which organs are definitely or possibly
invaded by the tumor for planning appropriate therapy.
• Primary retroperitoneal sarcomas have a high rate of recurrence after
local resection, even when the surgical margins are negative for
tumor.
• 75 % of recurrences typically appear within 2 years of initial surgery.
• All patients should undergo baseline imaging CT or MRI 6 months
after the initial surgical resection.

27. Retro peritoneal related Abnormality
RP Sarcoma RP Neurogenic Tumors RP Fibrotic lesions RP collection
LipoSarcoma 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

28. RETROPERITONEAL SARCOMA
• Rare mesenchymal neoplasms, accounting for less than 1% of adult
malignancies.
• 15% of sarcomas originate within the retroperitoneum.
• Maydevelop at any age (M>F), but most present in the 6th and 7th
decades.

29. • Most common histologic subtypes of soft tissue sarcoma.
•Liposarcoma (40%)
•Leiomyosarcoma (30%)
•Undifferentiated pleomorphic sarcoma (UPS) (previously known as
malignant fibrous histiocytoma) (15%).

30. LIPOSARCOMA
• Most common retroperitoneal sarcoma
• Originate from primitive mesenchymal cells
• World Health Organization (WHO) divides liposarcomas into four subtypes:
• Well-differentiated
• Myxoid
• Dedifferentiated
• Pleomorphic

31. • 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

32. • Well differentiated liposarcoma 9a) CECT huge heterogenous mass with
predominant fat attenuation
• 9b) T1WI Heterogenous hyperintensity and a partly nodular appearence

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

34. 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%

35. • 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

36. • 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

38. UNDIFFERENTIATED PLEOMORPHIC SARCOMA
• UPS, previously known as malignant fibrous histiocytoma
• 15% of all malignant fibrous histiocytomas occur within the retroperitoneum.
• Sixhistological subtypes: (Storiform,Pleomorphic,Myxoid,Giant
cell,Inflammatory,Angiomatoid)

39. CT
• The density of MFH is typically similar to adjacent muscle, with
heterogeneous lower density areas if haemorrhage, necrosis or
myxoid material is abundant.
• The soft tissue component enhances.

40. 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 solidcomponents
• T2
• intermediate to high signal intensity

42. RETROPERITONEAL NEUROGENIC TUMORS
• Paraganglioma
• Ganglioneuroma
• Neuroblastoma
• Ganglioneuroblastoma
• Schwannoma
• Neurofibroma

43. 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.

44. 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

45. 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

46. 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

47. NEUROFIBROMA
• Benign tumors of nerve sheaths of peripheralnerves
• 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.

48. • When multiple, pathognomonic of NF1,
• large 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

49. • Known case of
neurofibromatosis type
I: AxialT2W fat-
saturated images show
multiple hyperintense
lesions in the pelvis,
with a few of them
showing central
hypointensity
suggestive of a
‘Target sign’

50. 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

51. • 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

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

53. 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,.

54. • “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.

55. 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.

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

57. 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.

58. 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.

59. 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.

60. RETROPERITONEAL FIBROTIC LESIONS
• Retroperitoneal Fibrosis
• Fibromatosis (Desmoid Tumor)

61. FIBROMATOSES
• The fibromatoses are divided into
• Superficial (fascial) groups
• Deep (desmoid tumor) groups - further subdivided into
• Extraabdominal,
• Abdominal wall
• Intraabdominal (mesenteric, mesocolic, omental, retroperitoneal) subgroups

62. 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.

63. DesmoidTunors:AxialT1-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.

64. 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.

65. • 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.

66. • 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:

67. • CT:
• Retroperitoneal fibrosis is visible as a soft tissue density mass located around the aorta
and iliacarteries. 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

68. • 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

69. • 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

70. 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 FAT-
CONTAINING LESIONS

71. • CT - lipomas typically have homogeneous fat attenuation
• MRI - SI identical to that of macroscopic fat on allpulse
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

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

74. RETROPERITONEAL FLUID COLLECTION
• 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 .

75. 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.

76. 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 likelyto indicate anatomic sites of hemorrhage

77. • 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

78. 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

80. 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.

82. PSEUDOMYXOMA RETROPERITONEI
• Benign or malignant condition that results in intraperitoneal mucin
accumulation.
• Pseudomyxoma retroperitonei occurs very rarely
• Caused byretroperitoneal rupture of a primary appendiceal mucinous
adenoma in a retrocecal appendix

83. • CT - multicystic lesions with low attenuation
• MRI - low to intermediate SI on T1-weighted images, and high SI on T2-
• weighted images
• Thickened wallsor 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

86. SOLID NON-NEOPLASTIC MASSES
1. Pseudotumoral lipomatosis

87. 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.

88. Apear-shaped bladder is
produced by symmetric
compression and displacement
of the bladder caused by pelvic
lipomatosis.
The lower portions of the
ureters may be pinched medially,
with resultant
hydroureteronephrosis.

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

90. LYMPHANGIOMA
• Lymphangioma can be seen in perirenal, pararenal, or pelvic
extraperitoneal spaces and can involve more than one
compartment.
• CT - large thin-walled unilocular ormultilocular cystic mass
with attenuation values ranging from that of fat (caused by
chyle) to that of fluid.
• Calcification is rarely seen.

91. • 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.

92. 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.

93. 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

94. 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.

95. • 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

96. 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.

97. • 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.

98. • 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

99. • 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

100. • 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

101. 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.

102. 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%.

103. • 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.

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

106. Aortic Dissection
• Aortic dissection usually originates in the thorax but sometimes
extends into the abdomen.
• Mortality rate of untreated dissection is very high approaching 25% at
1 day, 50% at 1 week and 75% at 1 month.
• 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.

107. • 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

108. • 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.

109. • 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.

110. 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

111. • Fat-suppressed T2-weighted images are very sensitive for the
detection of lymph nodes and perform better than CT, particularly in
pediatric patients or other patients with paucity of retroperitoneal
fat.

112. 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.

113. 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

114. • 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

116. • 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

117. • 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.

118. 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.

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

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

121. THANK YOU