An adult female Mata Mata (Chelus fimbriatus) presented to the animal health department of the John G. Shedd Aquarium for evaluation of reported unusual behavior and possible swelling in the neck region. This animal was accessed into the collection two years previously. Prior medical treatment was limited to a course of oral pyrantel pamoate for presumed oxyuroid nematodiasis, topical treatment of minor plastron dermatitis, and passive interrogatable transponder placement during the quarantine period. The turtle was housed in a mixed species Amazon-themed exhibit along with a male and female conspecific, a pair of dwarf caiman (Paleosuchus palepebrosus), and a variety of Amazon fishes. Water quality in the system remained stable with all parameter values within expected ranges. A variety of frozen fish species were fed two to three times per week, and thiamine and d-alpha tocopherol were provided once per week as a supplement. Several days prior to presentation aquarists noted the animal to be spending more time than usual at the water surface, and the turtle did not consume its entire expected ration. A swelling at the neck base was suspected but difficult to confirm by visual observation.
On presentation the animal weighed 7.852 kg, was alert, and demonstrated expected responses to handling. Physical examination was unremarkable except for a slight distention of the cervical skin at the left axillary inlet that was easily displaced and appeared non-painful. Ultrasonography of the region was consistent with subcutaneous gas reverberation. Radiographs confirmed moderate gas density along the base of the neck and extending halfway into the coelomic space. Association of the gas density with intra-coelomic anatomy was undetermined. Twenty milliliters of liquid barium suspension was administered via large olive-tipped feeding catheter into the distal esophagus, the majority of which the turtle immediately regurgitated. Radiographs after the barium administration revealed a nice "snorkelogram" (positive contrast image of external nasal passages) but were inconclusive. The following day, after deliberation, percutaneous aspiration of gas was conducted by using a 19-gauge butterfly catheter and 60-ml syringe. Multiple 60-ml syringes of gas were removed (total volume approximately 240 ml) and the turtle was kept dry docked with frequent misting in a reserve area overnight. The turtle was given 120 ml of reptile ringers solution intracoelomically and started on parenteral ceftazidime at 22 mg/kg every 3 days for three doses. The next day the turtle was noted to have marked subcutaneous emphysema of the entire cervical region.
A complete blood count and plasma chemistry panel was obtained with unremarkable results. Whole body computed tomography scans and respiratory endoscopy were performed under sedation. No lesions to explain the etiology for the third-spacing of gas were discovered. The animal was returned to a reserve enclosure and kept dry docked until some reduction (approximately 10%) in cervical distension was noted two days later. Nearly complete resolution took several months. Although the animal was once again able to submerge and was eating well, a small but decreasing amount of subcutaneous gas remained in the cervical region at the time of abstract preparation.
Third-spacing of gas is not uncommon in aquatic chelonians, but is most often reported in sea turtles. The etiology is speculative and includes a rent in the respiratory or gastrointestinal tracts or a cutaneous lesion that allows gas to enter the coelomic cavity and migrate rostrally. The authors were unable to locate any scientific investigations into causation or response to treatment in chelonians. The etiology in this case remains unknown in spite of aggressive diagnostic assessment.