Stomach (258-60)

Muscular bag fixed at both ends with great size variability.

Divided into arbitrary sections (Pl 258):

Cardia (most fixed) where oesophagus enters; T10 level, 2.5cm L of midline, 40cm from teeth; interface with oesophagus mucosa is irregular, extends 1-2cm into oesophagus (‘Z-line)
- ie chances from mucus / glands to squamous epithelium.

Fundus projects above level of entry of oesophagus in contact with diaphragm (air inside)

Body (ends on lesser curve arbitrarily at a line from where angular notch / incisura, seen in vivo where crow’s foot fans out ® 45° line downwards to greater curve)

Antrum and pylorus
Pyloric canal = duodenal junction; to R of midline at L1 level; thickened as pyloric sphincter marked by pre-pyloric vein of Mayo; on head/neck of pancreas.

Mesentery

Fetal stomach is a ventral and dorsal mesentery; differential rotation ledas to ventral forming the lesser omentum; splits to enclose stomach.
Dorsal mesentery passes to gastrosplenic ligament and gastrocolic omentum / greater omentum, including anterior layer over transverse mesocolon.
- remove the greater omentum to take gastric nodes;.
Stomach overlies lesser sac, but peritoneum leaves fundus variably early, leaving part of it 'bare'

Structure (261)

Body mainly parietal & chief cells, antrum mainly G cells (make gastrin) but tongue of antral mucosa extends up lesser curve variable distance.

Outer longitudinal coat & inner circular/oblique coat completely invest stomach.  Thickest in antrum. 

-           reinforced by innermost oblique, loops over fundus (thick at notch) to maintain acute angle of His; clasp fibres play a role in lower GOS.

Pylorus

Complex structure
Circular muscle of distal antrum thickens to form 2 loops:  proximal and distal pyloric sphincters. 
As well, they contain another sheet of circular muscle between them
At lesser curve, the sphincters themselves fuse to form a muscular knob = “pyloric torus”; regarded as primary functional pylorus.
Pyloromyotomy and pyloroplasty (open and sew transversely) attenuate this function.

Gastric Blood Supply (282-3)

Mainly coeliac axis; some supply proximally from aorta via left gastric anastomoses.  Vessels richly anastomotic at mucosal, submucosal and intramuscular levels.

- L gastric off axis; raises the gastropancreatic fold in lesser sac off pancreas.  Gives off oesophageal branch, then divides / descends into major anterior / posterior branches
 - 10% have an accessory L gastric from the splenic travelling through the bare area of the stomach.

- R gastric off proper hepatic. much more variable in size.  Significant for supplying gastric remnant in oesophagectomy. 
-          
fundus & upper left greater curve receive short gastrics
from splenic artery in gastrosplenic lig

-           rest of greater curve by gastroepiploic a’s: right is closer to stomach than left; in partial gastrectomy, supply is divided above left and below right; because left gastro-omental branches are larger, the supply to the omentum is usually preserved.

- L GE is from splenic, passes forward in splenorenal then gastrosplenic ligament to greater curve, runs 1cm off the gastric border.  Hence ends near origin of spleen.
 Gives some ascending br's to fundus as well.

- R GE arises from GDA behind D1. usually anastomosis with the L.

- Short gastrics, including 'posterior gastric artery', which is most proximal short gastric, arches toward stomach through bare area.

Rich anastomoses in gastric wall at 3 levels: mucosally, submucosally and intramuscularly

Venous Drainage (290)

Veins parallel arterial supply, drain to portal or splenic and SMV.  L gastric vein encountered before artery from inferior approach.  Prepyloric vein ® right gastric vein.
Important only really in portal hypertension.

Surgical Points
Distal gastrectomy = well protected by abundant collateral supplies.
High partial gastroectomy = divide left gastric and some of short gastrics
- take care if all short gastrics / posterior gastric taken; be alert for gastric malperfusion prior to joining.

Gastric tubes
- Stomach mobilized except for R gastric and GE arteries
- fundal supply often marginal and usually resected with the specimn.

Lymphatic Drainage and R2 gastrectomy (295)

D0 = no attempt to take nodes
D1 = local nodes in region of cancer
D2 = regional and draining nodes
D3 = secondary nodal groups (pancreatectomy, colectomy, block dissection of SM and coeliac nodes)

There is free anastomosis of lymph vessels in the stomach wall, but valves direct flow (see Last p245): watershed parallel to greater curvature;
Lymph drains to 4 key groups:

i)                       L gastric nodes: drains all of lesser curve

ii)                     Pancreaticosplenic nodes drain high gr curvature (to splenic hilum and along splenic vein)

iii)                   R gastroepiploic drains greater curve (--> pyloric nodes near gastroduodenal artery)

iv)                   Pyloric nodes drain pylorus (--> hepatic nodes)

Gastro-omental nodes may extend several cm into omentum \ omentectomy is included. 

Everything ends up in coeliac nodes eventually; may spread up thoracic duct to Troiser’s sign in the L supraclavicular fossa.

Nerve supply (see 301)

Sympathetics (vasomotor) and pain together run with arterial branches

Parasympathetic more important; controls motility and secretion (and reflexes – 90% of fibres)

Anterior Vagal Trunk (301)

Contains mainly L vagal nerve fibres from oesophageal plexus in posterior mediastinum.  Usually one trunk at the hiatus; may be 2-3 (<10%). 
Two divisions:

(1) greater anterior gastric nerve (of Laterget) runs 1cm away from lesser curve in lesser omentum with left gastric artery ® 1-12 branches to stomach, usually terminating on antrum.

(2) hepatic branches (1-2) arises just below hiatus --> plexuses on hepatic artery / portal vein via lesser omentum; then turns down anterior wall of lesser omentum to reach pylorus.; division of this branch ® problems with gastric emptying. 

Anterior trunk lies to L in thorax ® comes to lie on R at hiatus.  Palpable as a bowstring on oesophagus when this is placed under tension.  Must be mobilized away / upwards in myotomy. 

Posterior Vagal Trunk (301)

Less variable than anterior trunk; formed from mainly R fibres of oesophageal plexus.  Lies further away from oesophagus than anterior trunk.

Divides below diaphragm ® 1 branch runs backwards along L gastric artery to coeliac plexus
And
greater posterior gastric nerve
(posterior nerve of Laterjet), which runs in lesser omentum behind anterior trunk to reach near antrum. 

- May give an ascending branch to fundus that crosses behind the oesophagus = the criminal nerve of Grassi

Posterior trunk does not supply the antrum or pylorus.

Vagotomy Operations

Carried out through abdomen

Truncal Vagotomy

= total abdominal vagotomy.  Usually post trunk bigger than anterior one.  If posterior not found, divide all tissue between oesophagus and aorta and to R and L

Early experience of TV:  1/3 --> impaired gastric emptying requiring drainage procedure.

1/3 --> impaired gastric emptying improving with time.

1/3 --> normal gastric emptying.

Selective Vagotomy

Denervates stomach, leaves innervation of rest of abdominal cavity intact.

Anterior trunk is divided just below hepatic division, post trunk below coeliac division.

Incidence of impaired gastric emptying ~10% (? = those people in whom pyloric nerve supply is via anterior nerve of Laterjet).

Highly selective vagotomy (proximal gastric vagotomy)

Avoids stasis by cutting only branches to fundus and body. 
Any individual nerves are found and cut, and ligating vessels also catches nerves.  Possible because arterial branches run in lesser curve transversely
while nerve branches approach it obliquely.
Very time consuming; equal effect from separating anterior and posterior vagal trunks and Laterjet nerves away from stomach; retain Crows foot.
- must dissect fundus off to left of oesophagus to account for criminal nerve.
Beware lesser curve ulcertation from ischaemia after this procedure if left gastric branches all taken.