Flexor Hallucis Longus Tenosynovitis
Inflammation of the tendon synovial sheath (tenosynovitis) is seen as an increase in fluid (white) around the tendon (black) as shown below. The flexor hallucis longus tendon acts to plantar flex the great toe. Inflammation of this tendon is not uncommon in ballet dancers.
Axial T2 weighted images from above down: