Ryan B. O'Malley, MD
Assistant Professor, Body Imaging
Department of Radiology, University of Washington School of Medicine,
1959 NE Pacific St, Seattle, WA 98195.
 History: 65-year-old female with right lower extremity melanoma
 What is the most likely diagnosis?
a) Mesenteric hemorrhage
b) Mesenteric panniculitis
c) Lymphoma
d) SMV thrombosis with mesenteric edema
1
Findings:
 Mesenteric fat stranding (“misty
mesentery”) surrounding non-enlarged LN
 Preserved fat halo around the vasculature
 Tumoral pseudocapsule
 Benign idiopathic inflammatory process
involving the mesenteric fat
 Commonly incidentally detected in
patients being imaged for other reasons
(including malignancy)
 Autopsy series reported up to 1%
 Does not progress or evolve into
malignancy
 Subtype of sclerosing mesenteritis –
spectrum based on the predominant
imaging findings and tissue type
 Mesenteric panniculitis – ill-defined
inflammation without discrete soft tissue
or mass
 Histology: Heterogeneous chronic
inflammatory infiltrate
 Mesenteric lipodystrophy – fat necrosis
 Histology: Lipid-laden macrophages
 Retractile mesenteritis – fibrotic soft
tissue mass with retraction and distortion
 Histology: Collagen deposition
 Abdominal manifestation of IgG4-related
sclerosing disease




RPF
IPT
AIP
Sclerosing cholangitis
2
 Imaging:
 “Misty mesentery” – nonspecific
term describing increased
attenuation within the mesenteric
fat
 Fluid
 Fibrosis
 Neoplastic infiltration
 Fat-ring sign  preserved fat halo
surrounding the mesenteric
vasculature
 Tumoral pseudocapsule  border
outlining the affected mesentery
Lymphoma
 DDx:
 Lymphoma (after treatment, may be
identical to mesenteric panniculitis)
 Edema (e.g. thrombosis, CHF,
pancreatitis)
 Hemorrhage
 Carcinomatosis
 {separate slide with images of
each?}
 History: 53-year-old female with fatigue
 What is the most likely diagnosis?
a) Lymphoma
b) Sclerosing mesenteritis
c) Carcinoid
d) Metastatic GI stromal tumor
3
 History: 53-year-old female with fatigue
 Findings:
 Clusters of mesenteric and
retroperitoneal LN
 Confluent soft tissue encasing
mesenteric vasculature with lost fat halo
 Most common malignancy
affecting the mesentery
 Primarily spreads via lymphatics
 Most common malignant
retroperitoneal tumor
 Mesenteric LAD more common in
NHL than HD
 ~50% of NHL has enlarged
mesenteric LN at presentation
compared to 5% for HD
 Coexistent retroperitoneal LAD
helps suggest the diagnosis
4
 Imaging:
 Can present with LN with a wide range of
size and morphology
 Characteristically confluent soft tissue
surrounding and encasing vessels (especially
SMA and SMV) with lost fat halo, but no
narrowing
 Sandwich sign – confluent soft tissue on both
sides of mesenteric vessels and perivascular fat
 Following response to therapy, may only
see infiltration of the mesenteric fat +/Ca++
 FDG PET is most accurate modality, 90-95%
sensitive
 DDx:
 Sclerosing mesenteritis
 Misty mesentery and Ca+ usually only seen in
treated lymphoma)
 PTLD
 Can also see sandwich sign
 Metastatic disease
 Typically localized rather than diffuse
 Infectious/inflammatory adenopathy (e.g.
TB, Whipple disease)
 LN may be rim-enhancing with central necrosis
 History: 44-year-old man with enlarging palpable L testicular mass
 Which of the following is considered regional LN
in the setting of testicular CA?
a)
b)
c)
d)
Paraaortic
Common iliac
Internal iliac
Inguinal
5
 History: 44-year-old man with enlarging palpable R testicular mass
 Findings:
 Confluent retroperitoneal LN at the level of the
renal veins
 No pelvic LN
 Right testicular mass
 Metastases from testicular CA most
commonly occur in paraaortic region
 Lymphatics follow gonadal vessels to
level of the renal hilae
 Typically ipsilateral to the primary tumor
 May spread inferiorly toward the aortic
bifurcation
 Frequently skip the pelvic LN (unless
there has been prior inguinal or scrotal
surgery; e.g. post-orchiectomy)
 Always consider testicular CA in DDx
for male patients with retroperitoneal
LN
 Testicular germ cell tumors (95% of
testicular CA)
 Seminoma (60%)
 LN usually soft tissue attenuation
 Nonseminomatous
 LN usually more cystic
 Stage II
 Pure seminoma + regional LN
 Staged based on maximum diameter of
Paño B et al. RadioGraphics. 2011 Jan-Feb;31(1):135-60.
involved LN
 Stage IIA: ≤2 cm  RT
 Stage IIB: >2 and ≤5 cm  RT or chemo
 Stage IIC: >5 cm  chemo (cisplatin-
based)
6
 DDx – retroperitoneal soft
tissue mass(es):
 Lymphoma
 Metastatic LN
 Most commonly pelvic source
(e.g. ovary, testis, prostate,
uterus)
 Mesenchymal tumor
 Leiomyosarcoma
 Liposarcoma
 Retroperitoneal fibrosis
 Hematoma
Paño B et al. RadioGraphics. 2011 Jan-Feb;31(1):135-60.
 History: 60-year-old female with intermittent left flank pain
 Which of the following is an
abdominal manifestation of IgG4related sclerosing disease?
a)
b)
c)
d)
Primary biliary cirrhosis
Whipple syndrome
Castleman’s disease
Retroperitoneal fibrosis
7
 History: 60-year-old female with intermittent left flank pain
 Findings:
 Infiltrative retroperitoneal soft tissue
encasing aorta and IVC, tethering
toward the spine
 Left renal obstruction with delayed
nephrogram and medial deviation of
the left ureter
 Confluent peri-pancreatic soft tissue
 Inflammatory and fibrotic plaquelike
retroperitoneal mass or soft tissue,
which encases aorta, IVC, and ureters
 Presents in middle age (40-60 y/o),
men 2-3x more common than women
 Non-specific presentation – flank or
back pain, fever, fatigue, decreased
urination, malaise
 Majority (>70%) are idiopathic, exact
mechanism uncertain
 Increasingly recognized as systemic
inflammatory condition
 Abdominal component of IgG4-related
sclerosing disease along with other
fibroinflammatory conditions
 Some suggest an immune response to
leaking antigens from atheromatous
plaque within the aorta
 Secondary causes
 Ergot derivatives (e.g. mehysergide) are
most common
 Coexistent malignancy in up to 8%,
possible a desmoplastic reaction to
underlying retroperitoneal metastases
8
 Imaging:
 Infiltrative retroperitoneal
soft tissue, most commonly
along the aorta and common
iliac arteries (centered at the
aortic bifurcation)
 Can be more extensive
 Anteriorly  pancreas and
duodenum
 Craniocaudally  mediastinum
or pelvis
 Bilateral or unilateral ureteral
encasement results in medial
deviation and obstruction
 Enhancement and T2 SI
reflects the degree of
inflammation
 Acute phase – avid
enhancement,  T2 SI
 Chronic/fibrotic – little to no
enhancement, low SI on T1 and
T2
 DDx:
 Lymphoma
 Metastatic disease (e.g. colon,
prostate, testicular)
 Hematoma
 Postirradiation
 Imaging cannot reliably
distinguish benign from
malignant RPF!
 Benign/idiopathic RPF is
classically plaquelike and
tethers the aorta and IVC
toward the spine, reflecting
underlying fibrosis
 Malignancy tends to be bulkier
and lobulated, displacing aorta
and IVC anteriorly and ureters
laterally
 Poor sensitivity and specificity
of these (and other) features
and many exceptions exist
 Biopsy may be required (often
surgical)
9
 Management
 Treat underlying cause and/or
remove causative agent
 Some drug-induced causes also
respond to immunosuppresion
 Glucocorticoids (usually
prednisone) – high-dose
initially, followed by taper and
maintenance therapy
 If renal impairment, PCN and
ureteral stent
 History: 54-year-old female with increasing abdominal girth over 1 year
 What is the most likely diagnosis?
a)
b)
c)
d)
Dermoid
Angiomyolipoma
Myelolipoma
Liposarcoma
10
 History: 54-year-old female with increasing abdominal girth over 1 year
 Findings:
 Large retroperitoneal mass containing fat, soft
tissue nodules, and septations
 Mass effect upon, but separate from,
retroperitoneal structures
 Coarse Ca++
 Most common primary retroperitoneal
malignant tumor
 80% of all retroperitoneal tumors are
malignant (lymphoma most common,
followed by sarcoma)
 >90% of retroperitoneal sarcomas are
liposarcoma or leiomyosarcoma
 2nd most common adult soft tissue
sarcoma (after MFH)
 Malignant from inception  almost never
arise from lipomas
 No fat-containing retroperitoneal lesion
should be dismissed as a lipoma 
retroperitoneal lipomas are exceedingly
rare, more likely represents lipomalike
area of a well-differentiated
liposarcoma
 Grow slowly and are very large at
detection
 Results in longer time to diagnosis 
more likely to dedifferentiate
 15% of well-differentiated liposarcomas
dedifferentiate (median 8 years)
 5 histologic types





Well-differentiated
Myxoid
Dedifferentiated
Pleomorphic
NOS
11
 Imaging:
 Large heterogeneous mass with
varying components of fat,
fibrous strands, & soft tissue
 Mixed (most common) – fat (< -20
HU) and non-lipomatous
components (soft tissue, fluid)
 Solid (myxoid tissue) – T2
hyperintensity with enhancement
 Pseudocystic (-20-20 HU) – mimics
fluid collection
 Displaces retroperitoneal
structures
 Identify kidneys and adrenals
separately to distinguish from
AML or myelolipoma
 Regional LN involvement is rare
 Mets most commonly lung and
liver
 Well-differentiated
 Predominantly fat and fibrous
septations
 Myxoid
Craig WD et al. RadioGraphics. 2009 Jan-Feb;29(1):261-90
 Uniform low attenuation with
increased SI on T2W
 Dedifferentiated
 Discrete nodular soft tissue > 1
cm
 Discrete soft tissue components
are the hallmark of
dedifferentiation
12
Craig WD et al. RadioGraphics. 2009 Jan-Feb;29(1):261-90
 DDx:
 AML
 Large internal vessels, renal
notch, hemorrhage
 History of tuberous sclerosis
 Myelolipoma
 Most (90%) arise from adrenal,
but extra-adrenal type can mimic
sarcoma
 Hematoma
 May be secondary to AAA
rupture or tumor (e.g. RCC, ACC,
AML)
 Management:
 Surgical resection
 Very difficult to obtain clear
margins
 Frequently recurs and
becomes more aggressive
 Recurrence most commonly as
soft tissue rather than fat
13
 History: 60-year-old male with weight loss and facial flushing
Fused CT and OctreoScan
 In what percentage of patients does carcinoid
syndrome occur?
a)
b)
c)
d)
>90%
50%
30%
<10%
 History: 60-year-old male with weight loss and facial flushing
Fused CT and OctreoScan
 Findings:
 Spiculated mesenteric mass in the RLQ with
encasement of vasculature and tethering of
small bowel loops
 Mesenteric mass and liver lesions have uptake
on OcreoScan
14
 Uncommon neuroendocrine tumor
arising from the endocrine system
outside the pancreas and thyroid
 ~2% of all GI tract tumors
 Most common malignant
neoplasm of the small bowel
 Most commonly distal ileum
 Primary tumor is a small (< 3.5
cm) submucosal mass that is
usually occult by imaging
 40-80% spread to mesentery
(directly or via lymphatics)
 Typically the first or only imaging
manifestation (unless there are
hepatic metastases)
 Imaging findings are a result of
extramural spread and resultant
desmoplastic reaction in the
mesenteric fat  retraction and
tethering
 Imaging:
 Enhancing calcified, soft tissue mass with
spiculation of the mesenteric fat, tethering
of adjacent bowel and vasculature
 Metastatic disease becomes more common
with larger tumors (> 1 cm)
 Regional LN
 Liver (usually hypervascular)

5-year survival 79% for <5 lesions vs. 47% for ≥5
 Peritoneum
 Carcinoid syndrome (<10%)
 Refers to a constellation of symptoms – flushing,
diarrhea, wheezing, right heart failure
 90% have metastatic disease, most commonly
patients with liver metastases  tumor products
(e.g. histamine, serotonin) released into systemic
circulation
 Majority originate in midgut (jejunum, ileum,
cecum), bronchial in 10%, rarely distal colon and
rectum
 111In pentetreotide helps distinguish from
other etiologies and predict response to
octreotide therapy (80% have somatostatin
receptors)
 DDx:





Desmoid
Hematoma
Retractile mesenteritis
Treated lymphoma
{more detail for these? Separate slide?}
15
 Management:
 Localized, non-metastatic  resection
 Extent depends on origin and size
 Post-treatment surveillance often
continues for up to 10 years due to late
recurrence
 Carcinoid syndrome
 Somatostatin analogs (e.g. ocreotide) –
bind to somatostatin receptors and block
release of active tumor products
 Hepatic resection
 Considered for select patients with
localized disease, preserved liver
function, and no extrahepatic disease
 Symptomatic relief in most patients,
disease-free survival in up to 20%
 Liver-directed therapy
 Bland or chemoembolization, ablation,
and 90Y have been shown to improve
symptoms in unresectable cases
 Prophylactic octreotide required to
prevent carcinoid crisis
 History: 29-year-old female status post total proctocolectomy with abd pain
 Which of the following describes Gardner
syndrome?
Ectopic gallstone with gastric outlet obstruction
RCC, pancreatic cysts, hemangioblastoma,
pheochromocytoma
c) Lung cysts and RCC
d) Colorectal polyps, skull osteomas, desmoid
tumors, epidermoid cysts
a)
b)
16
 History: 29-year-old female status post total proctocolectomy with abd pain
 Findings:
 Infiltrative mesenteric soft tissue in RLQ
 Tethering and spiculation of surrounding
structures
 AKA aggressive or deep fibromatosis
 Fibromatoses – benign, but locally
aggressive proliferation of fibrous or
connective tissue
 Superficial – smaller, slow-growing,
rarely involve deeper structures
 Deep – larger, more aggressive, grow
rapidly, infiltrate surrounding
structures
 Abdominal wall – classically young
women during pregnancy or within 1 year
postpartum
 Intraabdominal – mesenteric,
retroperitoneal, and pelvic
 Can be familial or sporadic
 Mesenteric desmoids are associated
with patients with FAP (Gardner
syndrome)  18-20% of patients with
Gardner syndrome develop desmoids
 75% develop in patients with prior
abdominal surgery
17
 Variable imaging appearance, frequently
non-specific
 Masslike or ill-defined (and both forms
can coexist in same patient)
 Infiltrative types may encase bowel loops and
vasculature
 Masslike types tend to displace rather than
encase
 Spiculated with radiating strands of soft
tissue and retraction of surrounding
structures
 Similar attenuation/SI to muscle, but can
become necrotic when large
 Usually low SI on T1; If myxoid  high SI
on T2
 Imaging primarily used to plan surgical
resection
 Size and number of lesions
 Local extent – vasculature, bowel, solid
organs
 DDx:




Carcinoid
Sclerosing mesenteritis
Metastasis
Lymphoma
 History: 64-year-old male with LLE numbness, new hemorrhagic brain lesions
 What is the most likely diagnosis?
a)
b)
c)
d)
Desmoid
Metastatic melanoma
Metastatic colorectal cancer
GIST
18
 History: 64-year-old male with LLE numbness, new hemorrhagic brain lesions
 Findings:
 Dominant lobulated sigmoid mass with
eccentric wall thickening
 Multiple round, circumscribed
mesenteric masses
 Numerous tiny subcutaneous nodules
 Skin cancer arising from melanocytes
 Most in sun-exposed areas, but can
develop elsewhere
 Mucosal melanoma  1% of all melanoma
 Primarily head & neck, anorectal,
vulvovaginal
 Worse prognosis than cutaneous primary
 LN disease starts regionally and
progresses contiguously through the
lymphatic chain
 Can metastasize hematogeneously to any
organ
 More common in advanced regional
disease
 Distant metastases can occur even
without regional LN spread
 60% of metastatic melanoma have
abd/pelvis mets
 Most common sites of metastases:
 Regional LN (75%)
 Lung (70%)
 Subcutaneous/soft tissues (67%) – in



transit, between primary and regional LN
Liver (58%) – most common visceral site
CNS (49-73%)
GI tract (40%)
Spleen (5%)
19

Small bowel and mesentery are most common site of
GI metastases

GI tract


Can present anywhere in the GI tract, but usually
multiple
Small bowel more common (75%) than colon (25%)
Intramural, serosal, or polypoid intraluminal masses


Target appearance with central necrosis or ulceration
Aneurysmal SB dilation



Eccentric wall thickening
Mesentery and LN
Mesentery and omentum usually both involved
Lobulated, confluent, or infiltrative patterns (overlap
with lymphoma, carcinoid, and desmoid)
 Rarely result in desmoplastic response (contrast to
carcinoid)





Peritoneal or omental carcinomatosis

LN may bleed
Abdominal LN in 30%
PET/CT (with diagnostic CT) most accurate for
staging and assessing for recurrence



Sensitivity 98%, specificity 94%
Detects unsuspected metastases in 15%
Demonstrates blind spots better than CT alone
 Management
 Metastatectomy – isolated or limited metastatic disease
 Immunotherapy (e.g. IL-2, ipilimumab, anti-PD1 monoclonal Abs)
 Ipilimumab preferred for most patients, produces durable response in 20%
 IL-2 in selected patients can be curative, but severe associated toxicities
 Anti-PD1 monoclonal Abs 2nd line after PD with ipilimumab
 Radiation therapy
 Mostly for brain metastases
 Palliative for symptomatic localized disease
20
 History: 47-year-old male, fall from 27 feet
 What is the most likely diagnosis?
a)
b)
c)
d)
Desmoid
Mesenteric hematoma
Carcinoid
Sclerosing mesenteritis
 History: 47-year-old male, fall from 27 feet
 Findings:
 High attenuation mesenteric fluid
collection displacing adjacent bowel loops
 Active extravasation centrally
 Pelvic fractures
21
 Bowel and mesenteric injuries
found in ~5% of laparotomies for
blunt trauma
 CT is the test of choice with
sensitivity 69-95% and specificity
94-100%
 Mesenteric hematoma should
prompt search for associated bowel
injury
 Imaging:
 Ill-defined mesenteric fat stranding
 May reflect isolated mesenteric injury
or bowel injury
 Highest sensitivity, but nonspecific
 Hematoma
 Specific to mesenteric injury, but does
not always require surgery
 Irregularity of mesenteric
vasculature
 Usually indicates underlying vascular
injury
 Extravasation of IV contrast –
reportedly 100% specific for
significant mesenteric injury
 Usually indicates need for laparotomy
 History: 49-year-old dock worker with increased abdominal girth
 What is the most likely diagnosis?
a)
b)
c)
d)
Malignant peritoneal mesothelioma
Pseudomyxoma peritonei
TB peritonitis
Mesenteric hemorrhage
22
 History: 49-year-old dock worker with increased abdominal girth
 Findings:
 Diffuse infiltrative soft tissue throughout the
peritoneal cavity
 Scalloping of the liver surface
 Small amount of ascites
 No enlarged LN
 Rare aggressive neoplasm
arising from mesothelial cells
lining serosal surface of
peritoneal cavity, spreads
rapidly throughout the abdomen
and pelvis
 Peritoneum is 2nd most
common site of mesothelioma
(after pleura), accounting for
10-15% cases annually
 Most have h/o asbestos
exposure, but the link is less
strong than for pleural
mesothelioma
 Incidence rises sharply at
higher levels of exposure
 20-40 year latency
23
 Imaging:
 Most commonly, diffuse infiltrative




peritoneal soft tissue, including
scalloping of liver or diaphragmatic
surface
Ascites frequently present (60-100%), but
rarely large volume
Pleural Ca++ (50%), thickening, and/or
effusion
Less commonly presents as a dominant
mass with peritoneal nodularity
Distant metastases are rare (consider
alternate diagnosis)
 DDx:
 TB peritonitis
 High attenuation ascites, LN, peritoneal
thickening
 Exposure history
 Carcinomatosis
 Cannot be reliably distinguished by imaging
 Lymphomatosis
 Usually with LN
 Pseudomyxoma peritonei
 Serous carcinoma of the peritoneum
 Primary arising from ovarian epithelial rests
 Management
 No consensus, poor prognosis
 Median survival historically < 1
year, but up to 5 years at
certain centers
 If good performance status
and no extraperitoneal
disease  cytoreductive
surgery + hyperthermic
intraoperative peritoneal
perfusion with chemotherapy
(HIPEC)
 Systemic chemotherapy for
patients who cannot tolerate
surgery + HIPEC or have
extraperitoneal disease
24
 History: 66-year-old female with abdominal bloating and fatigue
 What is the most likely diagnosis?
a)
b)
c)
d)
Pseudomyxoma peritonei
Malignant peritoneal mesothelioma
Simple ascites
Perforated appendicitis
 History: 66-year-old female with abdominal bloating and fatigue
 Findings:
 Dilated tubular structure in the RLQ with
punctate Ca++
 Mucinous implants displacing bowel loops,
scalloping liver surface
 Cystic left ovarian lesion
25

Clinical entity with accumulation of gelatinous
ascites and mucinous implants along peritoneal
surfaces secondary to mucinous epithelial
neoplasia



Histologically bland or low-grade mucinous
epithelium on the peritoneal surface
Most common presenting symptom is increased
abdominal girth
Terminology is confusing and variable, but the
current consensus is that PMP should be used to
describe peritoneal spread in association with
appendiceal mucinous neoplasm
AKA disseminated peritoneal adenomucinosis
(DPAM)
Allows more uniform pathologic and prognostic
classification
 Appendiceal tumor obstructs lumen  ruptures
with tumor cells disseminated throughout
peritoneal cavity
 Appendiceal neoplasm itself is histologically lowgrade, but can result in appendiceal rupture and
peritoneal dissemination, resulting in a more
aggressive clinical scenario




~20% of mucinous tumors of the appendix results
in PMP
Found incidentally in 2/10,000 laparotomies
Disseminated mucin-producing appendiceal
adenocarcinoma (peritoneal mucinous
carcinomatosis) is an aggressive subset with
mucinous epithelium demonstrating features of
carcinoma
 Ovarian mucinous tumors are presumed to be
metastatic (present in 44%)
 Rare metastases to LN or liver parenchyma

 Imaging findings:
 Loculated/mucinous ascites
accumulates throughout the
peritoneal cavity in
characteristic locations
(corresponding to areas of fluid
reabsorption and dependent
accumulation)







Greater omentum
Right subphrenic space
Pouch of Douglas
Right retrohepatic space
Liver and spleen surface
Left para-colic gutter
Ligament of Treitz
 Centrally displaced bowel loops
 Scalloping of liver and spleen
surface
 Mucinous appendiceal +/-
ovarian tumors
 May have curvilinear Ca++ in wall
or lumen
Left ovary
26
TB Peritonitis
Peritoneal carcinomatosis
DDx:
– Peritoneal carcinomatosis
Burrill et al. RadioGraphics 2007 27:5, 1255-1273
– Peritonitis (e.g. TB, bacterial)
– Peritoneal mesothelioma
Pseudomyxoma peritonei
Malignant peritoneal mesothelioma
 Management
 Palliative, intended to manage symptoms by reducing accumulation
of mucus
 Repeated surgical debulking
 Most aggressive approach with curative intent – complete
cytoreduction followed by intraperitoneal heated chemotherapy
 Best results at select expert centers with extensive experience (Sugarbaker)
27