The lymphatic vessels of the abdomen and pelvis can be divided into main categories superficial and deep systems.
The superficial lymphatics originate from the subcutaneous tissue,
and tend to accompany the venous flow to drain into the deep vessels.
While,
on the other hand the deep lymphatics drain deeper structures,
like the internal organs and they tend to accompany the arteries.
The superficial lymphatic system:
It can be furtherly divided into 2 groups according to the level of the umbilicus.
The superficial lymphatics above the umbilicus run superiorly towards the axillary lymph nodes,
while those located below the umbilicus run inferiorly towards the superficial inguinal lymph nodes.
The deep lymphatic system:
They accompany the arteries and are named according to the visceral organs,
they are divided according to their location into:
1.Pre-aortic Group of Lymph Nodes:
The pre-aortic groups tend to lie around abdominal aorta branches.
They are divided into coeliac,
superior mesenteric and inferior mesenteric groups.
They drain the gastrointestinal tract (GIT) starting from the esophagus down to the anus and GIT accessory structures,
namely liver,
spleen and pancreas.
Then,
they form lymphatic vessels,
which drain upwards in the abdominal confluence of lymph trunks.
Coeliac Lymph Nodes:
They lie around the origin of the coeliac artery.
It is the terminal station of gastric,
hepatic and pancreaticosplnic LNS as well as SMA and IMA LNs .
Then they drain into the right and left intestinal lymph trunks.
· Gastric Lymph Nodes: They drain the stomach,
upper duodenum,
abdominal oesophagus and the greater omentum into the coeliac group.
· Hepatic Lymph Nodes: The hepatic nodes extend in the lesser omentum along the hepatic arteries and bile duct,
seated at the junction of the cystic and common hepatic ducts.
They drain the majority of the liver,
gallbladder and bile ducts,
and to lesser extent drains parts of the stomach,
duodenum and pancreas.
· Pancreaticosplenic Lymph Nodes: They drain the spleen,
pancreas and parts of the stomach.
Superior Mesenteric and Inferior Mesenteric Lymph Nodes:
They lie anterior to the aorta near the origin SMA and IMA respectively.
The superior and inferior mesenteric nodes are preterminal groups of the gastrointestinal canal from the duodenojejunal flexure to the upper anal canal.
They collect lymph from the mesenteric,
ileocolic,
colonic and pararectal nodes and drain into the coeliac nodes.
2.
Lateral Aortic Group of Lymph Nodes:
The lateral aortic nodes lie on either side of the abdominal aorta anterior to the medial margins of psoas muscle.
They drains the suprarenal glands,
kidneys,
ureters,
gonads,
uterine tubes,
uterine tubes and upper uterus,
as well as posterior abdominal wall deep tissue.
Then,
they drain into the two lumbar lymph trunks.
3.
Retro-aortic Group of Lymph Nodes:
This is the smallest para-aortic LNs group.
it drains the paraspinal posterior abdominal wall.
Retro-aortic nodes has an important role in interconnections between surrounding groups.
Retro-peritoneal tissues: drains through all para- aortic groups,
namely the pre-aortic,
lateral aortic and the retro-aortic groups.
Being familiar with the lymphatics anatomy help us to widen our scope towards intra abdominal malignancy.
For each tumor we have to examine the primary tumor parse and the regional LNs as follows:
- Gastric cancer:
- Greater curvature of stomach: Greater curvature - Greater omental - Gastroduodenal - Gastroepiploic - Pyloric - Pancreaticoduodenal lymph nodes - Coeliac axis LNs
- Lesser curvature of stomach: Lesser curvature - Lesser omental - Left gastric - Cardio-oesophageal - Common hepatic- Hepatoduodenal ligament- Coeliac axis LNs
- Colorectal cancer: Pericolic/perirectal - Ileocolic - Right colic - Middle colic - Left colic -IMA - Superior rectal (haemorrhoidal) LNs
· Hepatocellular carcinoma : Hepatoduodenal ligament - Caval lymph nodes - Hepatic artery LNs
· Pancreatic cancer : Peripancreatic- Hepatic artery- Coeliac axis LNs
- Renal cell carcinoma: Renal hilar - Paracaval - Para-aortic - Periaortic (lateral aortic) - Retroperitoneal LNs
- Bladder: Perivisceral- Internal iliac - External iliac LNs
- Prostatic tumor: Perivisceral - Internal iliac - External iliac LNs
- Testicular tumors: Perivisceral – Paraaortic LNs
· Ovarian tumors: Perivisceral- Internal iliac - External iliac- Common iliac- Paraaortic LNs
- Endometrial tumors: Perivisceral - Internal iliac - External iliac - Common iliac – Paraaortic LNs.
- Cervix tumors: Perivisceral - Internal iliac - External iliac - Common iliac LNs
Normal LN radiological imaging features are:
Oval, kidney shaped with central fatty hilum (appearing isoechoic on US,
hypodense on CT and high SI on T1 WIs).
Less than 1 cm in its short axis
· US: central vascularity on Doppler imaging.
· CT/MRI: Clear surrounding fat planes.
· MRI: Doesn’t restrict on DWI.
· PET: No SUV value.
Imaging features in different modalities used favoring suspicious LN:
Ultrasound:
· Peripheral,
eccentric or even loss of fatty hilum.
· Increased cortical thickness > 4mm.
· Rounded LN,
with loss of its normal oval kidney shape.
· Cystic appearance of the LN.
· hyperechoic punctuations.
· peripheral vascularization.
· Infiltration to surrounding tissue.
Contrast enhanced imaging criteria:
Morphological criteria that suspect pathological LNs:
1.
increase the diameter of the LN short-axis .
This assessment method has limited accuracy and can't differentiate enlarged hyperplastic benign from malignant lymph nodes.
So lymph node size alone is not a reliable parameter
The normal upper limit of the pelvi abdominal LNs short axis are:
· Gastrohrpatic ligament: 8 mm
· Porta hepatis:8 mm
· Orto caval,celiac axis to reanl artery: 10 mm
· Renal artery to aortic bifurcation: 12 mm
· Common iliac LN: 9mm
· Internal iliac mm
· Obturatot LN: 8 mm
· External iliac and inguinal LNs:10 mm
2.rounded or elliptical shape
3.
eccentric cortical hypertrophy,
with irregular nodal contour
4.Nodal clustering.
5.Hetrogenous nodal density /intensity (particularly cystic or necrotic regions),
having heterogeneity appearance on T2-weighted MR images,
with or without central necrosis.
PET-CT
It has a high sensitivity in detecting metastatic lymph nodes .
The advantage of PET over conventional imaging techniques is its ability to asses nodal function having the ability to distinguish between viable tumor and necrosis or fibrosis in residual mass often present after treatment even if it has a stable size.
Malignant tissues usually present with significantly increased SUV,
which is the single most valuable strength of PET,
due to their higher metabolic rate [5].
The LNs SUV values are compared to the liver SUV value to determine if there is increased activity or not.
Normally LN SUV value should be equal or less than the liver.