A malignant Schwannoma is a type of soft tissue sarcoma. It often affects the sciatic nerve that begins in the lower back and runs through the leg. You can also find these tumors at the brachial plexus, or nerves at the top of the arm and the sacral plexus, a bundle of nerves in the lower back. The most common type of Schwannoma is called acoustic neuroma, because it grows on the eighth cranial nerve, which controls hearing. An acoustic neuroma can cause deafness.
Though exact causes remain unknown, it’s said to be associated with genetic factors. As for its symptoms, the patients may experience: dizziness and/or loss of balance, pain or discomfort: numbness, burning, or "pins and needles”, soreness localized to the area of the tumor or in the extremity, swelling in the extremities (arms or legs), also called peripheral edema; the swelling often is painless. In some cases, they may even find it difficult to move in the extremity that has the tumor, including a limp.