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

Osseous cyst‐like lesions of the proximal sesamoid bones (PSBs) 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 PSBs 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.