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Topic

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Retrobulbar fat

Retrobulbar fat refers to the specialized adipose tissue located within the orbit, posterior to the globe and surrounding the optic nerve and extraocular muscles. This fat is a critical component of the orbital contents, occupying the intraconal and extraconal spaces and providing structural support and cushioning to the globe and neurovascular structures. Its abundance and distribution play a crucial role in both the functional dynamics of ocular movement and the radiological appearance of the orbit.

Synonyms

  • Orbital fat

  • Intraconal fat

  • Periorbital fat (less specific)

  • Retro-ocular fat

Function

  • Acts as a cushion for the globe, protecting the eye from trauma and external forces

  • Provides a medium through which nerves and vessels can safely traverse the orbit

  • Maintains positioning and alignment of the eyeball within the orbital cavity

  • Facilitates smooth movement of the extraocular muscles during ocular motion

  • Serves as an energy reserve in metabolic conditions

MRI Appearance

  • T1-Weighted Images:

    • Retrobulbar fat appears hyperintense (bright), similar to subcutaneous or other body fat

  • T2-Weighted Images:

    • Retrobulbar fat remains hyperintense but is usually slightly less bright compared to T1 images

  • STIR (Short Tau Inversion Recovery):

    • Retrobulbar fat is hypointense (dark), as the STIR sequence suppresses fat signal for better visualization of adjacent structures and pathology

CT Appearance

  • Appears as areas of low attenuation (dark/black) with Hounsfield units typically between -80 to -100, consistent with adipose tissue

MRI images

Retrobulbar fat mri image