Abstract

Flexible endoscopes are commonly used to examine, biopsy, and remove foreign objects from the oral pharynx, esophagus, and first chamber (or forestomach) of cetaceans. On rare occasions, examining the second or fundic chamber is necessary; however, due to its unusual position among the stomach chambers, locating the entrance can be rather tricky. The author will describe the anatomic location and proper orientation of an endoscope to safely enter the fundic chamber of the stomach of bottlenose dolphins (Tursiops truncatus) and Commerson's dolphins (Cephalohynchus commersoni).

The digestive system of the odontocete is unique among mammals; its three stomach chambers functionally correspond to regions of the single stomach of most other mammals.^1,2 The first is the distensible forestomach, an enlargement of the distal esophagus, which is lined with thick squamous epithelium that appears lighter in color than the esophagus. The second is the glandular or fundic main stomach, which is deep pink to red in color where chemical breakdown of food occurs. The fundic stomach then leads to the "U-shaped" pyloric stomach via a connecting channel. The opening to the fundic chamber is immediately lateral to the gastroesophageal sphincter and is distinguished by a relatively large ostium at the junction of the distal esophagus and the cardia of the forestomach.

The keys to endoscopically locating the fundic stomach are proper anatomic positioning of the individual, determining orientation of scope within the esophagus and forestomach, recognizing the location of the ostia leading to the fundic stomach, and distinguishing mucosal differences.

In the author's opinion, the optimum position is right lateral recumbency, which places the stomach chambers in an upward/lateral position with the fundic chamber lateral to the forestomach. In order to orient the endoscope within the forestomach, first locate a pool of gastric juice, deflect the endoscope tip approximately 75 degrees in the direction away from the pool, and then slowly pull the endoscope out of the forestomach. If the stomach is properly insufflated the fundic chamber will fill with air, and as the endoscope is pulled near the gastroesophageal sphincter, the ostium and the red colored mucosal surface of the fundic chamber should come into view. Insertion into the fundic stomach is quite easy, allowing the operator to perform a complete examination.

Other methods employed to examine the fundic chambers of odontocetes include: 1) ventral recumbency with slow careful insertion of the endoscope searching for the ostium before entering the forestomach; 2) retroflexion of the endoscope from the insufflated forestomach; and 3) serendipity. The author prefers the present technique because it offers precise anatomic orientation to the ostium once a pool of gastric juice is located within the forestomach and easier access to the fundic chamber because positioning the individual in right lateral recumbency allows maximal insufflation of the forestomach and fundic chambers.

References

1.  Dover SR, Van Bonn W: Flexible and Rigid Endoscopy in Marine Mammals: In Dierauf LA, Gulland FMD (eds.) CRC Handbook of Marine Mammal Medicine, 2nd ed. Boca Raton, CRC Press, pp 621-642, 2001.

2.  Reidarson TH, Cetacean Medicine. In Fowler M, and Miller ER (eds): Zoo and Wild Animal Medicine V. Orlando, WB Saunders. (in press)