Intraneural sclerosing perineuroma of the posterior interosseous nerve (neuromuscular ultrasound)

(Top left) There is a focal well-circumscribed, avascular enlargement of the posterior interosseous nerve as its origin at the level of the elbow, measuring 1.35 cm in length and 0.56 cm in diameter. Distally, at the level of the supinator muscle, there is fascicular distortion and enlargement of the posterior interosseous nerve. Contralaterally, there is normal posterior interosseous nerve echogenicity, fascicular architecture and cross-sectional area at the same levels (right panel). The patient underwent surgical exploration with neurolysis, and it was determined that the lesion was an intraneural sclerosing perineuroma with presence of spindle cells on pathology that stained positive for perineuroma markers. (Contributed by Dr. Elina Zakin.)