2. 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 (Fascia's of Gerota and Zukerlandl) and is
best visualized using CT or MRI .The Three spaces
are:
– anterior pararenal space
– perirenal space
– posterior pararenal space
5. • ARF = Gerota fascia – thinner
• PRF = Zuckerkandle fascia -thicker,
• Formed of 2 layers 2 apposition of ARF and
lateralconal fascia creating potential space
6.
7. Interfascial Planes
• Tricompartmental anatomy does not
completely explain the spread of fluid
collections.
• Collections tend to escape site of origin into
expandable interfascial planes.
8. Interfascial Planes
• These interfascial planes are represented by
- Retromesenteric
- Retrorenal
- Lateroconal interfascial plane,
- Combined interfascial planes
11. Interfascial Planes
The lateral conal interfascial plane
Between layers of the LCF. It communicates with the
RMP and RRP at the fascial trifurcation.
12. Interfascial Planes
The combined interfascial plane
formed by the inferior blending of the RMP and
RRP . It continues into the pelvis.
17. Interfascial Planes
Left superior extension
• The RMP ,RRP and PRS on the left extend to
the left hemidiaphragm
18. 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
20. 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
22. • 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
23.
24. Peri Renal Space
• Anterior and post renal fasciae
• Extent: Superior, medial, lateral, inferior
• Contents:-
26. 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 .
27. Contents of Perirenal Space
Kidney, proximal collecting system, renal
septa, adrenal gland,
Renal vasculature and perirenal vessels
Lymphatics
Bridging septa
28. 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
30. 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.
31. 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
32. Lymphatic Spread of Disease from
Perinephric Space
Small perirenal lymph nodes
Nodes in renal hilum
Periaortic/pericaval nodes
35. 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
36. Extension of fluid collections
Fluid originating
from the APS
Pancreatitis
Pancreatic injury
Appendicitis
abscess of the
colonic wall
37. Extension of fluid collections
Fluid originating
from the PRS
Ruptured AAA
Renal injury
Hge/urinoma
38. Extension of fluid collections
Fluid originating
from the PPS
bleeding after spinal
trauma/surgery
39. Extension of fluid collections
Pelvic Extension
By the infrarenal
retroperitoneal
space
40. 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)
41. Infections
• Most originate from kidney
• May spread through all spaces and via bare
area to peritoneum and thorax
• Xanthogranulomatous pyelonephritis
55. 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).
56. 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.
59. 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”
60. 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
64. 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.
65. 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.
69. 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.
70. 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
71. 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.
72. 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
75. • Another entity with this growth pattern is
lymphoma. This neoplasm tends to surround
adjacent vessels, manifesting with the “CT
angiogram sign” or “floating aorta sign”
77. • 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.
78. 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.
79. 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
83. 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
86. 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
87. 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
88. • 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.
91. 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.
92. • 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.
98. 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
101. Cystic Portion
• Some tumors are completely cystic in
appearance. These include lymphangiomas
and mucinous cystic tumors.
• Solid tumors with a partially cystic portion
include neurogenic tumors
103. 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
106. Vascularity
Vascularity is another important feature of
retroperitoneal tumors. Extremely hypervascular
tumors include paragangliomas and
hemangiopericytomas. Moderately
hypervascular tumors include myxoid malignant
fibrous histiocytomas, leiomyosarcomas, and
many other sarcomas. Hypovascular tumors
include low-grade
liposarcomas, lymphomas, and many other
benign tumors
111. Hibernoma
Hibernoma is a rare, benign, soft-tissue tumor
composed of brown fat.
The name hibernoma is derived from histologic
similarities between these tumors and the
brown fat identified in hibernating animals.
Arise in these locations, which include the
thigh, buttock, scapular
region, trunk, neck, mediastinum, chest
wall, perirenal areas, breast, scalp, and
periureteric regions
112. 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
113. • 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).
114.
115.
116. 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.
117.
118. • 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.
119.
120. • 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.
121. • 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
122.
123. Epidermoid cysts
• At CT, epidermoid cysts generally appear as
thin-walled, unilocular cystic masses with fluid
attenuation
124. 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.
125. 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
126. Non Neoplastic Lesions
• Pancreatic Pseudocyst.
• Non pancreatic Pseudocyst.
• Lymphocoele.
• Urinoma
• Hematoma.
