IS case 520: Inferior rectus muscle entrapment

Jeremy Sykes, MD

University of Rochester

Imaging Sciences URMC 2010
Publication Date: 2010-09-10

History

Patient is a 46-year-old male status post assault with facial trauma.

Findings

See figures

Diagnosis

Inferior rectus muscle entrapment

Discussion

When an object strikes the orbit, the transmitted forces result in increased intra-orbital pressure. If the increase in pressure is sufficiently large, orbital "blow-out" fractures may occur whereby the bones of the orbit are disrupted. The weakest portions of the orbit include the medial wall and floor and are the most likely regions in which such fractures may occur. Although most pure orbital fractures affect the region medial to the infraorbital groove, any fracture type, size, or geometry is possible.

With such fractures, orbital contents may herniate through the defect. One complication of such herniation is entrapment of the extraocular muscles within the defect. This may manifest clinically as abnormal extraocular movements and possible enophthalmos (retraction of the globe). As in the case above, the inferior rectus muscle may become entrapped after orbital floor fractures. With these fractures, attention should be paid to the shape and position of the inferior rectus muscle on coronal CT images. If the muscle remains flattened in cross-section, then significant entrapment is unlikely. However, if the muscle has a rounded appearance in cross-section and is inferiorly displaced, significant entrapment is present. Such trauma requires surgical intervention to release the entrapped contents and restore bony anatomy.

References

  1. Hopper RA, Salemy S, Sze RW. Diagnosis of midface fractures with CT: what the surgeon needs to know. Radiographics. 2006 May-Jun;26(3):783-93. PMID: 16702454
  2. Cohen A, Mercandetti M. Facial trauma, orbital floor fractures (blowout). eMedicine. Updated: May 20, 1010. http://emedicine.medscape.com/article/1284026-overview

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