A small lump appeared suddenly near the inside of my elbow, about 2 weeks ago. dr said its lipoma, it & area around are painful, could it be sarcoma?

Lump dilemma: Lump inside the elbow which is painful can have several causes starting from lymph node, lipoma, cystic mass and the list goes on if we look at the given info; pain, sudden onset favor tendinitis with fluid collection from a strenous exercise more detailed history and skilful exam can clarify the matter.Sarcoma is very unlikely with this history ultrasound of the mass can provide helpful info.