OBJECTIVE To use high-field and low-field MRI to describe the anatomy of the proximal portion of the tarsal region (proximal tarsal region) of nonlame horses. SAMPLE 25 cadaveric equine tarsi. PROCEDURES The proximal portion of 1 tarsus from each of 25 nonlame horses with no history of tarsal lameness underwent high-field (1.5-T) and low-field (0.27-T) MRI. Resulting images were used to subjectively describe the anatomy of that region and obtain measurements of the collateral ligaments of the tarsocrural joint. RESULTS Long and short components of the lateral and medial collateral ligaments of the tarsocrural joint were identified. Various bundles of the short collateral ligaments were difficult to delineate on low-field images. Ligaments typically had low signal intensity in all sequences; however, multiple areas of increased signal intensity were identified at specific locations in most tarsi. This signal intensity was attributed to focal magic angle effect associated with orientation of collagen fibers within the ligaments at those locations. Subchondral bone of the distal aspect of the tibia was uniform in thickness, whereas that of the medial trochlear ridge of the talus was generally thicker than that of the lateral trochlear ridge. In most tarsi, subchondral bone of the talocalcaneal joint decreased in thickness from proximal to distal. CONCLUSIONS AND CLINICAL RELEVANCE Results generated in this study can be used as a reference for interpretation of MRI images of the proximal tarsal region in horses.

OBJECTIVE To identify signs of tissue-specific cortisol activity in samples of suspensory ligament (SL) and neck skin tissue from horses with and without pituitary pars intermedia dysfunction (PPID). SAMPLE Suspensory ligament and neck skin tissue samples obtained from 26 euthanized horses with and without PPID. PROCEDURES Tissue samples were collected from 12 horses with and 14 horses without PPID (controls). Two control horses had received treatment with dexamethasone; data from those horses were not used in statistical analyses. The other 12 control horses were classified as old horses (≥ 14 years old) and young horses (≤ 9 years old). Standard histologic staining, staining for proteoglycan accumulation, and immunostaining of SL and neck skin tissue sections for glucocorticoid receptors, insulin, 11β hydroxysteroid dehydrogenase type 1, and 11β hydroxysteroid dehydrogenase type 2 were performed. Findings for horses with PPID were compared with findings for young and old horses without PPID. RESULTS Compared with findings for old and young control horses, there were significantly more cells stained for glucocorticoid receptors in SL samples and for 11 β hydroxysteroid dehydrogenase type 1 in SL and skin tissue samples from horses with PPID. Insulin could not be detected in any of the SL or skin tissue samples. Horses with PPID had evidence of SL degeneration with significantly increased proteoglycan accumulation. Neck skin tissue was found to be significantly thinner in PPID-affected horses than in young control horses. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that tissue-specific dysregulation of cortisol metabolism may contribute to the SL degeneration associated with PPID in horses.