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Topic

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Inferior orbital fissure

The inferior orbital fissure (IOF) is a slit-like bony cleft located in the posteroinferior portion of the orbit, formed between the greater wing of the sphenoid bone and the maxilla. It serves as a passageway connecting the orbit with the infratemporal and pterygopalatine fossae, allowing the transmission of neurovascular structures including the infraorbital nerve, zygomatic nerve, and branches of the maxillary nerve (V2). The fissure is oriented obliquely, widening posteriorly and narrowing anteriorly, and is bounded by thin orbital walls. Its precise anatomy is critical for surgical access, fracture assessment, and neurovascular evaluations.

Synonyms

  • Inferior orbital fissure of the orbit

  • Posteroinferior orbital cleft

  • Orbital floor fissure

  • IOF

Function

  • Provides a pathway for neurovascular structures between the orbit and infratemporal/pterygopalatine fossae

  • Supports infraorbital nerve and vessels that supply the midface and orbital contents

  • Contributes to orbital structural integrity, forming part of the posterior orbital floor

  • Acts as a surgical landmark for orbital, maxillofacial, and cranial procedures

MRI Appearance
T1-weighted images:

  • Appears as a thin hypointense linear cleft at the posteroinferior orbit

  • Surrounded by orbital fat, which appears hyperintense, providing natural contrast

  • Contents (infraorbital nerve, vessels) may appear as small intermediate signal structures within the fissure

  • Pathology, such as orbital fractures, nerve entrapment, or tumors, can be detected as disruption of normal anatomy or abnormal signal

T2-weighted images:

  • The fissure remains hypointense, while adjacent orbital fat is hyperintense

  • Edema, inflammation, or masses appear hyperintense, making subtle pathology more conspicuous

  • Useful for evaluating orbital floor injuries or soft tissue extension of tumors

STIR (Short Tau Inversion Recovery):

  • Fat suppression removes orbital fat signal, highlighting edema, inflammation, or masses

  • Normal fissure and nerve structures appear low signal, while pathological changes appear bright hyperintense

  • Particularly helpful for detecting orbital trauma, inflammatory lesions, or infiltrative tumors

CT Appearance

  • The inferior orbital fissure is seen as a well-defined bony cleft at the posteroinferior orbit

  • Orbital fat and soft tissue appear hypodense, contrasting with the hyperdense bony margins

  • Air in the adjacent maxillary sinus provides natural contrast, appearing black (hypodense) on CT

  • CT clearly demonstrates bony defects, fractures, and widening or narrowing of the fissure, which may indicate trauma, neoplasm, or congenital anomalies

  • Neurovascular structures within the fissure are soft tissue density and may be indirectly visualized if abnormal or enlarged

MRI images

Inferior orbital fissure mri axial image -img-00000-00000