Changes in the Valvulae Conniventes

Normal mucosal folds are the result of the action of the muscularis mucosa. In the jejunum and duodenum, they form 1 to 2 mm folds of invagination as they lie along the long axis of the gut in a random fashion, producing a feathery mucosal pattern; the intervening sulci are of equal width. In the ileum, these mucosal folds taper gradually until the terminal ileum resembles a smooth tube. However, there is considerable variation in these fold patterns. The villi are present on these folds and are too small to be appreciated radiologically. The finger-like microvilli with their brush borders are present like a carpet on the villi and can be seen only under a microscope.

In sprue, there is loss of these finger-like villi, with ridges of flattened mucosa. The crypts of Lieberkühn are filled with an excess number of goblet cells and there are chronic inflammatory cells and edema in the lamina propria. There is no overall loss of thickness of the mucosa. The carpet of mucosa and lamina propria becomes less flexible and less pliable. This appears to produce thickening of the transverse mucosal folds during contraction of the muscularis mucosa and presents radiographically as rigid, cogwheel-like, sparse folds instead of the normal feathery appearance (Figs. 16.7 and 16.13A). The folds may measure 4 to 5-mm in thickness and may protrude more than 4-mm into the lumen from the wall of the gut. When the muscularis mucosa atrophies, these folds will disappear.

The normal local response of the muscularis mucosa to intestinal chemical reaction, and the stretching due to a bolus, help in contraction. The mucosal folds and the villi are thought to function like the ciliary action of the respiratory tree. The transit of the bolus through the small bowel is aided by this action of the muscularis mucosa. When there is disruption of the normal function of Meissner's plexus, this motility is altered.

Fig. 16.7 Thickening of the valvulae conniventes (primary and secondary mucosal folds, valves of Kerckring) produces a cogwheel mucosal appearance of the proximal small bowel. There is also an increase in caliber of these loops caused by loss of tone and slowing of peristalsis.