A middle aged man presented with a swelling over the neck since childhood. Neck swelling has a bag of worm appearance. Most probable diagnosis is:

Plexiform neurofibroma- special type of neurofibroma, is the plexiform variant,which involves an entire large nerve and its branches,forming a mass of tangled,rope like structures that feel like a "bag of worms" on palpation and that can reach enormous size and be associated with massive soft tissue overgrowth leading to significant functional impairment.A plexiform neurofibroma is considered to be pathognomic of NF1