Case ReportInitial Experience Using Contrast Magnetic Resonance Imaging in Laminitic Horses: 18 Studies
Introduction
When properly performed, the standing radiographic digital venogram is a reliable diagnostic tool to evaluate the digital vasculature in horses [1], [2], [3], [4]. The venogram has been used to evaluate a variety of pathologies in the equine digit, including laminitis [5], [6], [7]. Serial radiographic venograms (RVs) performed after experimentally induced laminitis show the progression of pathology associated with distal displacement of the distal phalanx as the hoof transitions from normal to chronically laminitic [5], [8]. Characteristic filling deficits of contrast solution on the radiographic digital venogram are similar in appearance to the corrosion casts of chronic laminitic patients, corresponding to areas of venous compression secondary to distal phalanx displacement [9], [10]. In clinical practice, serial standing RVs evaluate effectiveness of therapy and direct treatment [11], [12], [13]. Because the availability of magnetic resonance imaging (MRI) is increasing in horses, it has been shown to be a superior diagnostic modality to evaluate soft-tissue and bone in the foot [14], [15], [16]. However, its use in the live laminitic patient has not been described. This article describes how contrast MRI of the digital venous system was performed and interpreted on a group of laminitic horses, together with a few additional pertinent soft-tissue findings associated with the laminitic horse which have not been previously reported (most of the soft-tissue pathologies delineated by MRI will be detailed in a different publication).
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Materials and Methods
In this study, a 0.25-Tesla open magnet (Esaote S.p.A., Genoa, Italy) was used. This system requires general anesthesia, with all studies related to forelimbs performed in right lateral recumbency. Before the induction of anesthesia, radiography is performed on the foot to be evaluated to ensure the absence of any metal within the hoof capsule, then a complete blood count is performed, a jugular catheter is placed, and the hair is clipped off of the medial and lateral pastern. The horse is
Results and Diagnostic Findings
We began to develop this technique in 2007 using horses with normal standing RVs from our embryo transfer recipient mare herd. These mares were primarily grade mares, weighing an average of 425 kg. Initially RVs were performed on all healthy horses and laminitis cases within 48 hours of MRI. Two RVs were performed immediately after MRI, using the same intravenous catheters, while the horses were still in lateral recumbency. Both cases developed pastern inflammation after this procedure, and
Discussion and Conclusion
Recently, MRI of cadaver hooves in the initial active stage of laminitis, using a 4.7-T magnet, revealed it to be both more sensitive and specific than digital radiology in predicting laminitis [14]. Criteria were also established, independent of field strength, to predict laminitis reliably using a laminae-to-dermis ratio. Because of the expense of MRI and the necessity of anesthesia, the use of this modality on clinical laminitic cases will be limited. However, the benefits of MRI for these
Acknowledgments
The authors thank The Animal Health Foundation, St. Louis, MO, for the generous gift in helping offset some of the costs we have incurred during the development of the technique used in this study.
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