Practical Gastrointestinal Endoscopy

110
CHAPTER 6
Fig. 6.7–Persistent descending
mesocolon or mesentery.
Fig. 6.8 · Inverted cecum.
early embryonic development. An atonic, bulky and dysfunctional
fetal intestine and colon will inevitably be retained longer
than usual outside the abdomen in the umbilical hernia, until the
developing abdominal cavity is large enough to reaccommodate
it. Delayed return of a large colon into the abdomen means that
peritoneal development will be likely to have progressed beyond
the ‘milestone moment’ for fixation and fusion to occur (usually
by 10–12 weeks after conception). The long, mobile and increasingly
dysfunctional colon presents clinically at a later stage, in
childhood with straining at stool and bleeding, in teenage years
with constipation, or in adulthood with hemorrhoids and variable
bowel habit. Endoscopically such a colon is noted to be unusually
capacious, long and often atypically looping—but it can
also be dramatically squashed down and shortened when the
colonoscope is withdrawn at the cecum (typically to a length of
only 50–60·cm), proving the lack of fixations. Further suggestive
evidence that this a genetically determined constitutional abnormality
of development comes from the fact that first-degree relatives
(especially on the female side) are very frequently known
by the patient to have disturbance of habit or constipation; if
endoscoped or imaged their colons are found to be similarly
long and mobile.
How often such failure of fusion, persistent colonic mesentery
and mobility occurs is not clear from the literature. A persistent
descending mesocolon has been found at postmortem in 36%
and an ascending mesocolon in 10%. The persistence of a descending
mesocolon explains most of the strange configurations
caused by the colonoscope in the left colon and splenic flexure
(Fig. 6.7). Occasionally the cecum fails to descend and becomes
fixed in the right hypochondrium (Fig. 6.8); in others, where a
free mesocolon persists, the cecum remains completely mobile
(Fig. 6.9). Peroperative studies that we have undertaken show
that colons in Oriental subjects are more predictably fixed than
those in Western subjects.
Endoscopic anatomy
Fig. 6.9–Mobile cecum.
The anal canal, 3·cm long, extends up to the squamo–columnar
junction or ‘dentate line’. Sensory innervation, and hence mucosal
pain sensation, may in some subjects extend up to 5–7·cm into
the distal rectum. Around the canal are the anal sphincters, normally
in tonic contraction. The anus may be deformed, scarred or
made sensitive by present or previous local pathology, including
hemorrhoids or other conditions—and normal subjects may be
sore from the effects of bowel preparation.
There are two potentially serious consequences from the fact
that the hemorrhoidal veins drain into the systemic (not the portal)
circulation: