Page 107 - Clinical Anatomy

ECA2 7/18/06 6:42 PM Page 92

92 The abdomen and pelvis

Numerous anomalies may occur in the highly complex developmental
process.
1◊◊Atresia or stenosis of the bowel may result from failure of recanalization of
the lumen. Another cause of this may be damage to the blood supply to the
bowel within the fetal umbilical hernia with consequent ischaemic
changes. Imperforate anus—see page 83.
2◊◊Meckel’s diverticulum represents the remains of the embryonic vitello-
intestinal duct (communication between the primitive mid-gut and yolk
sac) and is, therefore, always on the anti-mesenteric border of the bowel. As
an approximation to the truth it can be said to occur in 2% of subjects, twice
as often in males as females, to be situated at 2 feet (62cm) from the ileocae-
cal junction and to be 2in (5cm) long. In fact, it may occur anywhere from 6
in (15cm) to 12 feet (3.5m) from the terminal ileum and vary from a tiny
stump to a 6in (15cm) long sac. Occasionally the diverticulum ends in a
whip-like solid strand.
As well as a diverticulum—the commonest form—this duct may persist
as a fistula or band connecting the intestine to the umbilicus, as a cyst
hanging from the anti-mesenteric border of the ileum or as a ‘raspberry
tumour’ at the umbilicus, formed by the red mucosa of a persistent umbili-
cal extremity of the diverticulum pouting at the navel (Fig. 70).
The mucosa lining the diverticulum may contain islands of peptic
epithelium with oxyntic (acid-secreting) cells. Peptic ulceration of adjacent
intestinal epithelium may then occur with haemorrhage or perforation.
3◊◊The caecum may fail to descend; the peritoneal fold which normally
seals it in the right iliac fossa passes, instead, across the duodenum and
causes a neonatal intestinal obstruction. The mesentery of the small intes-

Fig. 70◊Abnormalities
associated with
persistence of the vitello-
intestinal tract. (a)
Meckel’s diverticulum.
(b) Patent vitello-
intestinal duct. (c) Cyst
within a fibrous cord
passing from the anti-
mesenteric border of the
intestine to the
umbilicus. (d) Meckel’s
diverticulum with
terminal filament passing
to umbilicus.