Fibropapillomatosis is a common disease identified in wild-caught green turtles in multiple locations around the world.5 The disease commonly manifests itself as multiple benign cutaneous fibroepithelial tumors, which can be found at almost any site on the turtle. Fibrous tumors may also occur in multiple visceral sites.3-5
One method commonly employed for diagnosing internal fibromas is radiography. However, diagnostic capabilities of radiographs are limited by sea turtle anatomy; examination of internal organs is significantly obscured by the bony carapace and plastron. In addition, barnacles or other objects adhered to the shell may appear similar to internal nodules and complicate radiographic interpretation. Magnetic resonance imaging (MRI) is an advanced imaging technique that allows for much more detailed evaluation of soft tissue structures. MRI creates a cross-sectional view of the coelom and the bony outer layer does not affect images. While fluid and soft tissue cannot be differentiated on radiographs, MRI has excellent soft tissue contrast resolution, allowing us to not only identify coelomic organs, but also assess their internal structure.1
This study evaluated the use of MRI as a tool for diagnosis of internal fibropapillomatosis compared to conventional radiographs and, in most cases, findings obtained at necropsy. First, one healthy green turtle was used to establish normal MRI anatomy. Eight additional green turtles were classified as abnormal based upon the presence of external fibropapillomas, abnormal buoyancy or other signs of illness. Each turtle was given a comprehensive physical examination and whole body dorsal-ventral (DV) radiographs were taken. MRI scanning was performed in both dorsal and transverse planes. The radiographs and MRI films were examined for evidence of internal nodules. These results were compared with necropsy findings in five of eight turtles with fibropapillomatosis.
Of the eight turtles with cutaneous fibropapillomatosis, radiographs detected nodules in the lungs of two turtles, while MRI detected nodules in five turtles. While no other visceral nodules could be determined using radiography, MRI detected masses within the stomach and adjacent to the bladder and kidneys in one turtle. However, other extrapulmonary abnormalities observed at necropsy were not visualized on MRI images.
From these results, we concluded that MRI is more sensitive than radiographs and can be a valuable diagnostic tool for determining presence of internal nodules in green turtles with fibropapillomatosis. Nodules were more apparent in the lungs than other organs, though it was also possible to visualize large extrapulmonary nodules on MRI films.
More accurate diagnosis of internal fibromas can help focus rehabilitation efforts in stranded and sick sea turtles. While external fibropapillomas may eventually resolve, there is no evidence of this for internal fibromas. Internal fibromas appear to slowly enlarge, and their presence is used as a prognostic indicator of survival as they cause profound pathology in the organ they originate from or cause mechanical damage in surrounding tissues. Therefore, presence of internal tumors has been used as a criterion to elect euthanasia rather than release. Unfortunately, clinical application of MRI may be limited by cost and availability of the technology.