title: Magnetic resonance imaging contrast enhancement of extra-ocular muscles in dogs with no clinical evidence of orbital disease.
abstract: Enhancement of extra-ocular muscles has been reported in cases of orbital pathology in both veterinary and medical magnetic resonance imaging. We have also observed this finding in the absence of orbital disease. The purpose of this retrospective study was to describe extra-ocular muscle contrast enhancement characteristics in a group of dogs with no known orbital disease. Magnetic resonance images (MRI) from dogs with no clinical evidence of orbital disease and a reportedly normal MRI study were retrieved and reviewed. Contrast enhancement percentages of the medial, lateral, ventral, and dorsal rectus muscles were calculated based on signal-to-noise ratios that were in turn determined from hand-traced regions of interest in precontrast, immediate postcontrast and 10-min postcontrast scans. Comparison measurements were made in the pterygoid muscle. Contrast enhancement of the extra-ocular muscles was observed in all patients (median contrast enhancement percentage 45.0%) and was greater than that of pterygoid muscle (median contrast enhancement percentage 22.7%). Enhancement of the extra-ocular muscles persisted 10 min after contrast administration (median contrast enhancement percentage 43.4%). Findings indicated that MRI contrast enhancement of extra-ocular muscles is likely normal in dogs.
authors.affiliation: Department of Veterinary Clinical Medicine, University of Illinois at Urbana-Champaign, Urbana, IL, 61801.
authors.forename: Stephen
authors.initials: S
authors.lastname: Joslyn
authors.forename: Suzanna
authors.initials: S
authors.lastname: Richards
authors.forename: Susanne
authors.initials: S
authors.lastname: Boroffka
authors.forename: Mark
authors.initials: M
authors.lastname: Mitchell
authors.forename: Gawain
authors.initials: G
authors.lastname: Hammond
authors.forename: Martin
authors.initials: M
authors.lastname: Sullivan
mesh_terms: D000818:Animals; D003287:Contrast Media; D004285:Dogs / Q000033:anatomy & histology*; D005260:Female; D008279:Magnetic Resonance Imaging / Q000662:veterinary*; D008297:Male; D009801:Oculomotor Muscles / Q000033:anatomy & histology*; D012016:Reference Values; D012189:Retrospective Studies
chemical_list: D003287:Contrast Media
keywords: MRI; contrast; enhancement; extra-ocular; muscle