Extremely rare, occur in patients with neurofibromatosis I.
GU is involved in ~20% in patients with neurofibromatosis.
Bladder is most commonly involved in GU tract, and involvement can be extensive.
Typically involves young patients (~1/3 pediatric patients); male>female (3:1).
Mainly of plexiform type (involves multiple fascicles of nerve).
Loose spindle cells with tapered wavy nuclei (image A).
Associated with irregular collagen bundles ("shredded carrot" appearance) (image B).
No nuclear atypia or mitosis.