MR imaging of orbital blow-out fractures.

Nineteen patients with orbital blow-out fractures were examined and had CT scans and MR imaging (0.5 Tesla, superconductive). The fractures occurred in the orbital floor in 12 cases, orbital medial wall in 2 cases and both orbital medial wall and floor in 5 cases. Fractures often occur posterior to the eyeball.With a Ti-weighted spin-echo pulse sequence with TR of 500 ms and TE of 20- 25 ms, the fatty component and the muscle component could be identified easily. A good demonstration of the inferior rectus muscle and herniated orbital fat could be obtained with an oblique sagittal view along the optic nerve. The inferior and medial rectus muscle frequently showed cylinder-like hypertrophy. Dislocation or entrapment of the inferior rectus muscle was found in 3 cases.The existence of entrapment (incarceration) of the muscle in a blow-out fracture has been controversial in the past. Orbital MR imaging is recommended to clarify this matter, obtain more accurate diagnosis and to assist in the choice of treatment.