Clinical and low field magnetic resonance imaging features of osseous cyst‐like lesions of the proximal sesamoid bones in seven horses

Summary Osseous cyst‐like lesions of the proximal sesamoid bones ( PSB s) were diagnosed in 7 horses. The diagnosis was achieved radiographically prior to magnetic resonance imaging ( MRI ) in only one horse, and in the other 6 horses the diagnosis was made using low field MRI (retrospective evaluation of the radiographs after the MRI revealed ill‐defined radiolucencies of the PSB s in 4 of these horses). The horses ranged in age from 3 to 12 years, and the affected limbs included 3 forelimbs and 4 hindlimbs. The onset of lameness was reported to be sudden in 6 horses and insidious in one, and the duration of lameness at the time of MRI ranged from 0.3 to 11 months. The degree of lameness in the 6 horses with sudden‐onset lameness was moderate to severe. Pain on flexion of the affected metacarpo(tarso)phalangeal (fetlock) joint or exacerbation of the degree of lameness following fetlock flexion was recorded in 4 of the 7 horses. The MRI findings in all cases included a focal high signal intensity lesion (all magnetic resonance sequences) at various locations in one PSB . Both septic and nonseptic aetiologies were identified. Four of the 7 horses were subjected to euthanasia due to persistent lameness, one remained chronically lame and only 2 were able to return to their previous level of exercise.