Hi,
Few more details would be helpful for me:
1. Any pain, itching, discolouration around the swelling? (suggests
varicose veins)
2. Is the swelling pitting type-ie.can be indented on pressing? (suggest obstruction to venous
drainage). Non pitting swelling suggests lymphedema
3. Is it more towards evening, increases on standing/walking or constant throughout the day?
Possibilities of unilateral ankle swelling are varicose veins, enlarged lymph nodes obstructing venous drainage from leg, orthopedic causes and rare causes like
filariasis (here usually swelling extends up the leg). A physical examination after clearing above points will clinch the diagnosis. Your doctor will guide you. We may need few blood tests and a venous doppler study.
Hope I have answered your question. Let me know if I can assist you further.
Regards,
Dr. Muhammed Aslam T. K., Pediatrician