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8 Spleen and Pancreas
8.3 Retroperitoneum, Other Peritoneal and Retroperitoneal
Structures, Abdominal Vessels and Abdominal Wall
8.3.1 Abdominal Vessels
8.3.1.1 Positioning
Usually assessed in supine position, using topographically defi ned access from
ventral or lateral, depending on position of investigated vessel.
8.3.1.2 Transducers
Depends on position of vessel and patient age as well as size of patient.
Try to use linear transducers for high-resolution anatomic assessment, particu-
larly in neonates, infants and slim children.
Curved arrays preferred with slightly lower frequencies for optimal Doppler.
NOTE : For detailed Doppler studies, good Doppler angle (<60°) essential for
reliable measurements. Patient motion as well as overlying gas may often hinder
continuous visualisation of main abdominal vessels, particularly in middle and
lower abdomen as well as pelvis.
8.3.1.3 How to Investigate
Usually vessel assessed in longitudinal and cross section, including not only vessel wall
and position but also main branches. Always consider normal variants/variations that
may hint at underlying congenital malformation/syndrome (e.g. persisting left IVC).
NOTE : Graded compression may be necessary for access – but may cause
“pseudopathology”
8.3.1.4 US Findings
Typically vessels have echo-poor lumen. With high-resolution transducers, fl oating
particles may become visible. Venous wall thin, arterial wall thicker with muscular
layer and more or less pulsation.
NOTE : Physiologic changes in calibre of abdominal aorta after descending distal to
major upper abdominal parenchymal vessels (coeliac trunk, mesenteric artery, renal
arteries). Similar phenomenon seen in IVC – often larger proximal to renal vein
insertion than distally. Pronounced changes in calibre may hint towards focal steal
phenomena, e.g. by hyperperfusion of specifi c organ system (e.g. high fl ow haemangioma/haemangioendothelioma with signifi cant tapering of abdominal aorta
distal to coeliac trunk) (Fig. 8.18 ).
Anatomy and pathology of various organ vessels described in their respective
chapters – numerous normal variants.
CDS
Aorta : typical high-resistive fl ow patterns with triphasic modulation and negative
early diastolic phase observed.
Peripheral / main arteries of major abdominal organs: low-resistive organ fl ow pat-
tern observed, typical high antegrade diastolic fl ow. Variations with splanchnic activation are seen in coeliac trunk and superior mesenteric artery.
Venous : biphasic and even bidirectional modulation by cardiac action and respiration.
8.3 Retroperitoneum, Other Peritoneal and Retroperitoneal Structures
ab
277
c
d
e
Fig. 8.18 Major abdominal vessels – normal fi ndings. Schematic drawing of normal important
arterial ( a ) and venous ( b ) abdominal vessels. Typical normal US appearance of major abdominal
vessels, sagittal section: ( c ) inferior vena cava ( IVC , × …×), ( d ) upper abdominal aorta and branch-
ing superior mesenteric artery ( arrowheads ) and coronal view using power Doppler demonstrating
aortic bifurcation ( e )
8.3.1.5 Important Variants and Malformations
• Azygos continuation/double IVC, inverted situs (aorta to right, IVC to left)
• Malposition of mesenteric vessel (see Chap. 9 )
• Narrow origin of superior mesenteric artery by compression from crossing
duodenum
• Narrowed (or retroaortic course of) left renal vein with consecutive clinical
obstructive symptoms (see Chap. 10 )
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8 Spleen and Pancreas
NOTE : Graded compression may be needed for removing gas and getting suffi cient
sonographic access – but this technique may also compress vessels and thus decrease
depictability, or cause artifactual pseudo-stenotic fl ow patterns.
8.3.2 Vascular Pathology
8.3.2.1 Thrombosis/Occlusion
General Remarks and US Findings
Thrombosis / embolus : echogenic material within lumen, lack of fl ow on CDS, if
accessible incompressible distended lumen; in long-standing thrombosis revascularisation (of wall as well as thrombus), secondary calcifi cations occur. In tumour
thrombus sometimes vascularisation of thrombus by tumour vessels.
NOTE : Assessment of mesenteric vessels and central renal/splenic vein diffi cult –
no possibility to rule out thrombus or occlusion, particularly if more distally.
Thromboses occur in pelvic veins, renal veins, potentially also IVC and aorta
(e.g. embolic after cardiac or umbilical artery catheterisation).
Causes: central lines, coagulopathies, compression, but also typically for Wilms’
tumour and tumour invasion in renal vein (may progress to right atrium through
IVC). Can usually nicely be depicted by US and CDS (Fig. 8.19 ); sensitivity some-
times better than of other sectional imaging:
• Missing or occluded IVC most often depictable by large paravertebral collateral
vessels or venous plexus that drain into deeper compartments – try to follow
pelvic veins to defi ne normal insertion into normal distal IVC – here lateral
access or access through well-fi lled large bladder helpful, as well as “graded
compression”
NOTE : Defi ne cause of obstruction; evaluate patency of pelvic vessels.
• Stenosis , compression , distortion : congenital malformations (e.g. pre- or
duodenal portal vein) or associated with spinal malformations. Using meticulous
US scanning technique and applying CDS (+ Ce-US?), most conditions can be
recognised. Rarely stenosis of coeliac trunk and mesenteric artery also visible in
children (e.g. after vasculopathies)
• Superior mesenteric artery compression syndrome : diffi cult to diagnose
(positioning manoeuvres)
• Assessment of functional changes : standardised examination conditions essential,
however, large variation with signifi cant systemic infl uence – few important entities
addressed in respective organ systems chapters (portal hypertension, PDA, NEC, etc.)
8.3.2.2 Pelvic Congestion Syndrome
Rare in children – usually secondary to nutcracker anatomy of left renal vein or
compression/occlusion (e.g. retroperitoneal tumour, renal vein thrombus in Wilms’
tumour).
• Enlarged pelvic vessels with inverted fl ow direction on CDS (e.g. draining from
cranial to caudal)
8.3 Retroperitoneum, Other Peritoneal and Retroperitoneal Structures
279
ab
cd
Fig. 8.19 Thrombosis in large abdominal vessels. ( a , b ) Left pelvic vein thrombus, ( a ) longitudi-
nal, ( b ) cross section: no colour signals in large, incompressible pelvic vein (+ +). ( c ) Calcifi ed
rim-like echogenic border around old IVC thrombus (cross section), no colour fl ow. ( d ) Embolic
thrombus to abdominal aorta ( arrowheads )
• Congestive changes of pelvic structures, particularly ovaries
• Collateral circulation may be seen as irregular, tortuous, enlarged pelvic veins
8.3.2.3 Mid-aortic Syndrome
Abdominal aortic coarctation (small calibre) may affect longer segments or just
upper abdominal aorta.
US and CDS Findings
Depend of extent and involved vessels (i.e. coeliac trunk, SMA origin and renal
arteries):
• Causes stenosis with all respective gray scale and CDS/spectral Doppler fi ndings: vessel tapering, increased velocity, distal poststenotic fl ow alterations,
turbulence, etc.
NOTE : If one fi nds tapering of abdominal aorta, always assure that this is not sec-
ondary to signifi cant steal phenomena (e.g. shunt fl ow by large renal AVM, by
hepatic haemangioendothelioma).
280
ab
Fig. 8.20 Aortic aneurysm after renal transplantation. ( a ) Gray scale and ( b ) CDS image of an
aneurysm (+ +) of abdominal aorta at surgical anstomosis of main transplant artery in an infant
after renal transplanation
8 Spleen and Pancreas
8.3.2.4 Retroaortic Left Renal Vein: Nutcracker Syndrome (see Chap. 10 )
8.3.2.5 Compression by Superior Mesenteric Artery (Also Called
Nutcracker or SMA Syndrome)
Narrow angle between SMA and aorta – causing obstruction to duodenum with
respective symptoms.
Most commonly in very slim (female) patients (anorexia, after weight loss):
• Only functional (US/fl uoroscopy) investigations in upright + lying position after fi lling stomach and duodenum with fl uid can aid the diagnosis; the often discussed low
angle between SMA and aorta is uncertain in terms of diagnostic cut-off values
8.3.2.6 Arteriosclerotic Changes and Aneurysms
Practically nonexistent in children.
Sometimes stenosis as well as aneurysmal ectasia may occur postoperatively
(transplant surgery) and in systemic vascular malformations/disease (e.g. Marfan
syndrome, Takayasu and with ADPKD Type II).
Distortion and compression of vessels can be found in numerous conditions such
as tumours, space-occupying enlargement of various organs, malposition of organs
(e.g. diaphragmatic hernia) and congenital malformations.
US fi ndings vary respectively (if area accessible) (Fig. 8.20 ); indirect signs may
be depictable downstream on CDS.
8.3.2.7 Embolic Thrombus to Abdominal Aorta
May occur after cardiac surgery/catheter angiography, as in cardiac malformations
with persisting right to left shunt allowing thrombosis (e.g. from umbilical lines) to
cross from right to left system.
US Findings
• Commonly rather echogenic thrombotic material disrupts anechoic lumen of
aorta with distal tapering due to restricted fl ow
8.3 Retroperitoneum, Other Peritoneal and Retroperitoneal Structures
ab
Fig. 8.21 Mesenteric cystic formations. ( a ) Large mesenteric cyst (+ +) in a girl, reaching from
bladder roof to liver. Size only measurable using extended view US. ( b ) Abdominal (mesenteric)
cystic lymphatic vascular malformation, with multiple cysts and partially sedimented echoes due
to haemorrhage
281
CDS Findings
CDS demonstrates fl ow restriction:
• Similar phenomena hold for emboli to renal/mesenteric arteries, but – due to
vessel size – these embolic entities can usually only be depicted in CDS by lack
of fl ow and interruption of Doppler signals at site of thrombus (with respective
perfusion defi cits of affected organs)
8.3.2.8 Role of US
US – ideal initial investigation when complemented by CDS and spectral analysis
(sometimes ce-US). Complementary imaging: usually CT- or MR angiography.
Catheter angiography mostly used preoperatively or if therapeutic intervention
planned.
8.3.2.9 Complementing Imaging
• US + CDS (ce-US) – ideal initial investigation method
• Diagnostically complementing: CTA/MRA
• Catheter angiography: mostly used if therapeutic option planned for same session
8.3.3 Mesentery
In children peritoneal cavity and slim mesentery usually not seen – only depictable
with ascites and/or if thickened/more echogenic.
8.3.3.1 Mesenteric (Peritoneal) Masses
Cyst
Easy to fi nd on US – usually represent simple mesenteric cyst; exhibits all features
of “simple cyst” and shows “root” at mesentery (Fig. 8.21a ). May become infected –
then differentiation from other entities is diffi cult.
DDx: lymphatic malformation (often with secondary haemorrhage), teratoma
(wall? calcifi cation? nodular-solid compartments?), trapped fl uid/old abscess,
meconium pseudocyst (typically with calcifi ed wall) duplication cyst (gut signature
of wall), ovarian cyst (daughter cyst?), Meckel’s diverticulum, necrotic-cystic other
282
ab
Fig. 8.22 Abdominal/mesenteric abscess. Two examples of abdominal complex cystic pseudotu-
morous formations consistent with (intraperitoneal) abscesses, with a more or less defi ned wall as
depicted by its hypervascularisation on CDS. ( a ) Perforated Meckel’s diverticulum and ( b ) abscess
after bowel perforation
8 Spleen and Pancreas
tumour, etc. – carefully observe additional signs such as debris and sedimentation,
wall thickness and structure, fat or calcifi cations, daughter cyst, relation to other
abdominal structures and vascular supply.
Lymphatic Vascular Malformation and Other Tumours
Same appearance as anywhere else in the body, may become quite large, also arise
from adjacent compartments (e.g. retroperitoneum), not to be differentiated from
other mixed mesenchymal tumours or veno-lymphatic malformation: often show
haemorrhagic cysts with sedimentation (Fig. 8.21b ). Rarely also arterio-venous vas-
cular malformations may occur.
Rarely other tumours may occur – US may depict mass, will not allow defi nitive
diagnosis.
DDx: mesenteric infl ammation and infl ammatory pseudotumors, mesenteric
infarction (echogenic tumour-like mass, in infarction no vascularisation, in infl ammation hypervascular, in abscess hyperemic wall).
8.3.3.2 Abscesses
Relatively rare unless in appendicitis (see there).
Same appearance as everywhere else in the body.
Arise from lymph nodes (see below) or secondary to appendicitis (see above),
fi stulae and perforation.
US and CDS Findings
• Complex mass with complex fl uid in centre, some membrane-like borders in
periphery (Fig. 8.22 )
• Border is usually hypervascular, centre does not exhibit any vessels
Differentiation of abscess from complex/entrapped ascites may be diffi cult (or from
entrapped loops with complex content):
• Sometimes only fi lling of bowel by enema (“US-enema”, “hydrocolon”) will
enable defi nite separation of these entities
• Sometimes fi stula tracts visualised (most commonly in Crohn’s disease, but also
in others, e.g. recurrent appendicitis)
8.3 Retroperitoneum, Other Peritoneal and Retroperitoneal Structures
283
DDx: regional haematoma, necrotic material from omental infarction/twisted
appendix epiploicae, necrotic lymph nodes, necrotic tumours.
NOTE : In all these conditions, secondary infl ammatory component can never be
ruled out, even by other imaging.
Additional Imaging
CT or MR – if not obvious on US for diagnosis/DDx, sometimes (in complicated
cases) preoperatively.
8.3.3.3 Twisted Appendices Epiploica
Physiologic appendices epiploicae not depicted.
If twisted (rare in childhood) – become necrotic due to haemorrhagic infarction –
sudden pain, nonspecifi c laboratory alterations – may pose a DDx to appendicitis.
US Findings
Area close to bowel with increased echogenicity, sometimes hazy margin, local pain
on sonopalpation and noncompressible, some fl uid and mesenteric reaction, no vessels found within on CDS.
8.3.4 Mesenteric Lymph Nodes
Using graded compression technique, typical (normal sized) mesenteric nodes often
seen physiologically.
Present also in gastroenteritis, coeliac disease and other nonspecifi c conditions
(infl ammation, congestion, food intolerance, after intussusception, with tumours, etc.).
US Findings
• Same as described in all other body compartments (see Chap. 4 )
• Typical signs for pathological lymph nodes: large (bigger than 1 cm), spherical,
conglomerated, increased number of nodes, destructed/missing hilus (Fig. 8.23 ).
Usually found along main mesenteric vessels
• Massive pathologic lymph nodes and suspicious confi gurations or bulk needs
work-up (lymphoma? granulomatous disease? specifi c or atypical infection –
Yersinia, Tb? etc.)
• May also have abscesses, necroses and calcifi cations
• For retroperitoneal nodes, mainly focus on assessment along large vessels, again
using graded compression technique
NOTE : In oncology patients always consider potential lymphatic drainage path-
ways – perform focused search at most crucial stations (e.g. nodes at entry of ovarian vein to left renal vein after left ovarian tumour).
8.3.5 Free Intraperitoneal Air
Can be seen sonographically as echogenic spots/bands with reverberation echoes,
typically on highest part of abdomen, below abdominal wall, above ascites, in front
of liver and outside of bowel. Can cause twinkling-like appearance on CDS
(Fig.
8.24 ).
284
8 Spleen and Pancreas
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cd
e
Fig. 8.23 Abdominal/mesenteric lymph nodes. ( a , b ) Reactively enlarged infl ammatory mesen-
teric lymph nodes (in gastroenteritis, EBV infection, etc.). ( c , d ) Hugely enlarged bulks of lymph
nodes in abdominal lymphoma, entire extent can only be conspicuously demonstrated using panoramic imaging ( d ). ( e ) Bulk of enlarged, anechoic unstructured abdominal lymph nodes in a girl
after renal transplantation consistent with post-transplant lymphoproliferative disease (PTLD)
Fig. 8.24 Free intraperitoneal air. Echogenic lines under abdominal wall in front of the liver with
reverberation artefacts, consistent with free intraperitoneal air after bowel perforation in this
neonate with NEC. Note some ascites (+ +) in front of swollen kidney below liver margin (sagittal
right upper quadrant section)
8.3 Retroperitoneum, Other Peritoneal and Retroperitoneal Structures
285
NOTE : If too much transducer pressure applied, air pressed away and missed!
Thus, gentle investigation at highest point of abdomen (e.g. in front of liver)
advised. Depiction of free peritoneal air in constricted spaces more
difficult.
Role of US
Free air can be seen, but more diffi cult to rule out. In suspicion actively search
for it.
8.3.6 Free Intraperitoneal Fluid: Ascites
Defi ned as intraperitoneal fl uid of varying origin.
Simple (clear) or complicated (with echoes, sedimentations, septae) fl uid
between bowel lops, or located behind bladder, in Douglas/Morrison space and
around parenchymal organs (liver, spleen, kidney).
NOTE : Site of fl uid does not necessarily correlate with organ of origin (e.g. in
trauma) – may be shifted by positioning, etc.
Causes: hypoproteinaemia, cardiac disease, portal hypertension, infl ammatory
and neoplastic disease, hypervolaemia, impaired lymphatic drainage, peritoneal
dialysis, shunt, haemorrhage (e.g., trauma, postoperative, vascular rupture and
coagulopathy), and also with gastroenteritis/systemic infection, third space
phenomena, etc.
DDx: fl uid from ruptured cyst, ruptured biliary structures (bilious ascites),
exudative processes (e.g. pancreatitis), localised fl uid versus real cyst (ovarian,
mesenteric, parenchymal organs, duplication cyst, cystic tumours, etc.), fl uid in
constricted compartments/abscess, etc.
Some small amount of ascites may be physiologically present (e.g. after
ovulation), postoperatively, etc.
NOTE : In systemic conditions, simultaneous pleural effusion commonly present –
look for it.
US Findings
• Simple ascites, anechoic fl uid (Fig. 8.25 )
• Complicated ascites, fl oating echoes with more or less sedimentation, fi brin septae and clots
NOTE : Functioning ventriculoperitoneal shunt will cause ascites; often at least
some parts of abdominal shunts visualised. If loculated fl uid collections – always
check for potential obstruction to distal end of drain, within the pseudocyst collection + increasing hydrocephalus (Fig. 8.26 ).
Role of US
Very sensitive when screening entire abdomen, even for small amounts of fl uid.
Actively search in respective compartments (e.g. in FAST ). May be used to guide
diagnostic puncture or drainage.