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De Hertogh et al’s autopsy study of the fetal gastro-oesophageal region provides valuable insight into the development of foregut epithelium in the 13–24 week gestational period (Gut 2003;52:791–6). Coincidentally, two other studies appeared on the same subject in April 2003.1,2 These studies were stimulated by our hypothesis that cardiac mucosa does not exist as a normal structure in humans.3,4
Three columnar epithelial types are reported between squamous epithelium and parietal cell containing gastric mucosa in De Hertogh’s study (Gut 2003;52:791–6). These are called “primitive oesophageal mucosa”, “primitive stomach mucosa”, and “cardiac mucosa”. Careful anatomical correlation place all of these mucosae in the oesophagus, proximal to the gastro-oesophageal junction. “Primitive oesophageal mucosa” is a ciliated epithelium that disappears at 24 weeks. “Proximal stomach mucosa” is a layer of flat columnar cells containing depressions that correspond to early gland pits distally. “Cardiac mucosa” is composed of foveolar and surface epithelium overlying glandular structures containing no parietal cells. The description of “cardiac mucosa” and figs 2 and 4 show a very thin columnar epithelium composed of uniform mucous cells with foveolar pits and rudimentary sac-like structures devoid of any inflammation. Derdoy et al’s “cardiac mucosa”2 and Park et al’s “transitional zone”1 are identical in appearance. I have never seen this fetal epithelium in any adult patient. The fact that these authors call it “cardiac mucosa” does not make it identical to the more conventional cardiac mucosa seen in adults. The only similarity is that it is a glandular mucosa composed of mucous cells only. It is much thinner than adult cardiac mucosa, it has no inflammation, and its glands are much less developed if present at all.
I would like to propose an alternate explanation for the changes seen in all three papers that I believe provides a better explanation of the data in the papers. The early fetal oesophagus is lined by primitive undifferentiated ciliated columnar epithelium. It begins differentiating into squamous epithelium proximally and gastric mucosa distally. Gastric differentiation is marked by the appearance of true glands containing parietal cells. In the second trimester, the oesophageal squamous epithelium is separated from parietal cell containing gastric mucosa by a columnar epithelium composed of foregut columnar stem cells forming a flat surface and a foveolar pit. This is uncommitted fetal columnar epithelium. This continues to develop into either squamous epithelium proximally or parietal cell containing gastric mucosa distally, so that its overall length decreases as fetal age increases (as shown in De Hortogh et al and Derdoy et al’s studies2). With completion of the development of the lower oesophageal sphincter in early infant life, the physiological gastro-oesophageal junction is defined and the uncommitted columnar foregut epithelium completes its development into squamous in the oesophagus and gastric mucosa with parietal cells distal to the lower oesophageal sphincter. The uncommitted foregut columnar epithelium disappears. The only normal mucosae seen after development is complete are squamous and gastric with parietal cells. This is proven by illustrations that show children with a direct transition of squamous epithelium to gastric mucosa with parietal cells (Chandrasoma and colleagues4 and fig 2A of Park and colleagues1). The absence of cardiac mucosa in these illustrations is proof that cardiac mucosa is not universally present in children. Adult-type cardiac mucosa is also absent universally in fetuses. The only reason why De Hertogh et al reach the conclusion that it is universally present in fetal life is that they erroneously apply the term “cardiac mucosa” to the uncommitted fetal columnar epithelium that is universally present in fetal life.
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