Hi, Without additional information or a professional examination, it is difficult to determine the exact cause of the dark spot on your chest X-ray. It could be caused by a variety of things such as a benign cyst, a small lung nodule, a lymph node, or even a tiny amount of fluid. It is best to consult with a radiologist or your primary care physician to review the X-ray and perform any additional tests that may be necessary to determine the cause. They may also want to know about your symptoms and medical history. It is also important to note that a chest X-ray is not very sensitive; it is usually used as a screening test or in combination with another test. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Priyanka, General & Family Physician