Lower Oesophagus

Anatomical Relations

Normally 3cm of oesophagus lies within abdomen; is retroperitoneal but peritoneum invests anterior and L lateral aspects only (257) (runs to diaphragm on R as uppermost lesser omentum). 
Lies on L crus, with aorta behind that. (253); then comes to run to left of aorta as it enters stomach.

-           anterior and posterior trunks of vagus are related to relative oesophageal surfaces.

-           L lobe of liver is anterior (grooved), caudate lobe to R. (258); retract liver cranially and to right to access.; may need to divide the left triangular ligament. (not usually)

Enters stomach at cardiac orifice, right margin continuous with lesser curve. 
Left makes an acute angle (of His = 30-70°); height of fundus above this angle = 2-5cm.

Lower oesophageal sphincter: no morphological thickening to correspond with measurable zone of ­P.  
Guarding against reflux assisted by i) R crus fibre contraction; ii) entry angle of oesophagus; iii) long folds of oesophageal mucosa; iv) high pressure zone in lower oesophagus, v) positive intra-abdominal pressure.

Structure
Outer longitudinal and inner circular (thicker). 
Smooth.
Opinion is divided about whether there is an anatomical LOS; may have some distal thickening but not where LOS is manometrically.

Submucosa is loose c.t. so can be lifted off muscle easily.

Phreno-oesophageal ligament
Is a condensation of fascia off the diaphgram.
Attaches oseophagus anteriorly to the peritoneum and endo-abdominal fascia.
Viewed as the fibrous tissue binding the oesophagus to the edges of teh oesophageal hiatus.

Hiatus
Probably only important for reflux prevention during sharp increases in intra-abdo pressure.
T10 level, 1cm posterior to central tendon; formed by L and R crus.
Oblique opening; deeper posteriorly
Tissue at inferior margin of hiatus froms the median arcuate ligament, crossing over the aorta.
Crura sling the hiatus; from anterior surfaces and discs of L1-L3 and anterior longitudinal ligament.
- R is longer
- Innervated by R and L phrenic respectively.
- Cross each otehr variably, commonly R crus forms hiatus
In reflux surgery:
- inferior binding of R and L crus limbs is not always clear; just pick up general tissue here during repair
- crura are musculotendinous; important to try to stitch the tendinous portions when narrowing the hiatus.

Mobilization
Distal approach:
- enter lower mediastinum through phreno-oesophageal ligament
- then enter loose areolar tissue over oesophagus; encircle it with a finger, passing from L to R behind oesophagus.
- fibroareolar tissue posteriorly must be broken; weaker as you go superiofly.
--> this approach almost always includes the anterior vagal and excludes the posterior vagal; beware anterior vagus and separate off.
If needed, can enlarge hiatus vertically, will encounter L inferior phrenic vein.
Lap approach
Open window in lesser omentum, above hepatic branch of vagus.
A triangular fat pad lies over the right pillar of the hiatus
Here, posterior vagal nerve tends to stay with oesophagus and needs to be protected.
Fundo
Ligate and divide short gastrics first.
Where gastrosplenic becomes the gastrocolic ligament, serves as a landmark to distal dissection.

Blood Supply

Cardia & lower oesophagus mainly from below by ³1 branch of L gastric and branches of splenic artery (282-3) and posterior gastric artery (~most proximal short gastric)
Lower thoracic oesophagus gets aortic branches.  There is a rich intramural arterial anastomosis in the subcutaneous layer.

Nerve Supply (301)

Vagal inhibitory fibres --> sphincter relaxation (swallow, belching, vomiting).

Vagal excitatory fibres --> resting sphincter tone. 

- these supply branches run within the muscle layer so skeletonisation of lower oesophagus doesn’t disrupt LOS function. 

Sympathetic adrenergic fibres --> relaxation, (?function).