Duodenum (261) and Associated Veins

10in long (2+3+4+1) tube lying in front of IVC and aorta. C-shaped loop around head of pancreas.

First 2.5cm is between peritoneum of lesser and greater omentum (rest is retroperitoneal)

1st Part (5cm) Superior; L1 level

Runs up, back & to R.  Overlies gastroduodenal artery (284), bile duct, portal vein and beneath = IVC.  

D1 often adherent to neck of GB ( lies over its ‘cap’) & is common site of biliary-enteric fistula. 

Next 2.5cm passes back and up on upper part of head of pancreas to medial border of R kidney (261)

-           covered in front by peritoneum, and inferior surface of liver lies over this.
Blood supply is from GD and CHA, other superior arteries.

2nd Part (7.5cm) Descending; L2 level (though frequently lower in life)

Curves down over hilum of R kidney with head of pancreas snug inside. 
Anterior aspect crossed by transv mesocolon (so half in infracolic, half in supracolic) (261)
Mobilized by Kocher manoeuvre; does not disrupt blood supply coming in from HOP

Posteromedial wall contains ampulla of Vater at halfway; minor papilla enters 2cm cephalad.  (285)

3rd Part (10cm) Horizontal; L3 level

Curves forwards from R paravertebral gutter over R psoas, gonadal vessels, R ureter
 SMV and SMA emerges over it, and mesentery of small intestine cross anteriorly (so that it is in both right
and left infracolic compartments)
;
D3 hardest to mobilise due to these anterior relationships.
Blood supply is from uncinate process.

4th Part (2.5cm) Ascending; L2 level

Ascends to L of aorta, over L psoas, L lumbar sympathetic trunk (250) to reach lower border of pancreas.  Covered by peritoneum and coils of jejunum.

Breaks free from peritoneum to form duodenojejunal flexure, pulling up a mesentery for the small intestine; ‘the inferior duodenal fold’. 
Further supported by
Ligament of Treitz
(a thin band of fibrous tissue +/- smooth muscle), suspends superior and left DJ flexure to right crus.

Internally thrown into folds plicae circulares or valvulae conniventes, but first 2.5cm are smooth at duodenal cap (smooth on barium swallow)

Paraduodenal recess lies beneath upper end of IMV; herniation --> IMV thrombosis (253); exceedingly rare.

Inferior and Superior duodenal recesses formed by folds of peritoneum raised between floor of infracolic compartment and lower & upper convexities of D-J flexure.  Retroduodenal recess may form between these. 

Mouths of recesses all face towards each other cf caecal recesses face away; herniae may spread to involve all 4 sites; exceedingly rare.

 Blood supply: superior and inferior pancreaticoduodenal arteries (283)

But first 2cm (usual site of ulceration) by hepatic, gastroduodenal, supraduodenal, right gastric, and right gastroepiploic branches.
- hence D1 can be readily dissected away from the pancreas

Veins ® superior mesenteric and portal veins (290)

Lymph ® with superior and inferior pancreaticoduodenal vessels ® coeliac and SMA nodes (295)


Associated Major Veins

Splenic Vein
Origin in hilum, initially superior then behind the body of the pancreas.
Receives left gastroepiploic vein near its origin.
3-13 pancreatic veins usually entering anterior and superior surface before joining the SMV behind the neck of the pancreas.
Recieves IMV in 3/4 behind body of pancreas; in rest IMV goes to SMV; only tributary entering it from below.
Occasionally receives gastric vein/s, instead of these going to the portal vein.

SMV
Drains midgut
Originates in distal sm bowel mesentery, ileal, caecal then ileocolic, ileal and jejunal branches, right coli, and middle colic veins.
Variable length below the pancreatic border; usually 2-3cm before tributaries from right colic, inferior PD, R gastroepiploic join.
Surgically significant here as site of shunt anastomoses; not always possible.
The ileocolic artery usually passes posteriorly to it.
Under pancreatic head, receives pancreas tributaries, can be reasonably sizeable
Right gastric vein may enter near its jx into portal; at risk when dissecting the GDA off anterior portal vein when mobilizing for pancreaticoduodenectomy.

PV
Forms behind neck of pancreas by union of SM and splenic
ascends in free margin of the epiploic foramen behind bile duct (to right) and hepatic artery (to left);
IVC related posteriorly
- but a difficult shunt option as not very mobile, not always parallel, and IVC often distorted in liver disease due to enlargement of Segment I
GDA overlies portal vein behind D1; dissecting behind artery opens plane between PV and neck of pancreas
Has no tributaries in margin of lesser omentum; only above and below.
Right branch receives a cystic vein.

Portal Hypertension
Numerous collateral channels form;
Submucosal veins of upper stomach and esophagus
- drain to azygos system
Inferior rectal veins; not the same as haemorrhoids
Ligamentum teres, umbilical vein, paraumbilical veins to abdominal wall
Retroperitoneum with multiple small veins enlarging --> diaphragm, adrenal, renal v's.