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It is difficult to comment without examination. Long standing lump behind the ear could be lipoma (localized collection of fat), a cyst, an inflamed lymph node or a neurofibroma (localized harmless swelling in of nerve and connective tissue). You may not have been sick but local infections like dandruff or dermatitis too can cause a lymph node to swell. Since it has increased in size, you can ask for a CT scan of the lump. In all probability it will be a swollen lymph node. Take care!