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Lacrimal canaliculi

The lacrimal canaliculi are small tubular channels in the eyelids that play a crucial role in draining tears from the ocular surface into the lacrimal sac. Their evaluation is important in radiological imaging, especially when assessing causes of epiphora or suspected trauma, infection, or neoplastic processes in the lacrimal drainage apparatus. Understanding their normal imaging appearance on MRI and CT is vital for accurate diagnosis.

Synonyms

  • Canaliculi lacrimales

  • Lacrimal ducts (commonly used but less specific)

  • Lacrimal canalicular ducts

Function

  • Serve as conduits for tear drainage from the puncta at the eyelid margin to the lacrimal sac

  • Each eyelid (upper and lower) contains a canaliculus beginning at the lacrimal punctum

  • The upper and lower canaliculi typically join to form a common canaliculus before entering the lacrimal sac

  • Facilitate tear removal from the eye surface, maintaining ocular surface moisture and protection

MRI Appearance

  • T1-Weighted Images:

    • Lacrimal canaliculi generally appear as linear low-signal intensity structures (due to their fluid content and small caliber).

    • Surrounded by soft tissue of intermediate signal intensity.

  • T2-Weighted Images:

    • The canaliculi may show high signal intensity because of their fluid content, but may be difficult to discern due to small size and partial volume effects.

    • Best appreciated when distended or inflamed.

  • STIR (Short Tau Inversion Recovery):

    • Fluid-filled canaliculi appear with high signal intensity (bright).

    • Adjacent inflammatory changes or edema may also be visible as high signal areas.

    • The lacrimal sac and canaliculi are best visualized if distended (e.g., due to obstruction).

CT Appearance

  • The canaliculi are not typically visualized as distinct structures on standard non-contrast CT due to their small caliber.

MRI images

Lacrimal canaliculi