Diagnosis
The cystic nature of a breast lump can be confirmed by ultrasound examination, aspiration (removal of contents with needle), or mammogram. Ultrasound can also show if the cyst contains solid nodules, a sign that the lesion may be pre-cancerous or cancerous. Examination by a cytopathologist of the fluid aspirated from the cyst may also help with this diagnosis. In particular, it should be sent to a laboratory for testing if it is blood-stained. Commonly, cysts are detected with the help of mammograms. However, the medical history and physical examination also play an important role in establishing an accurate diagnosis. During these tests, the doctor will try to find out as much information as possible regarding the symptoms the patient has experienced, their intensity and duration and the physical examination is performed regularly to check for other abnormalities that may exist within the breast. As mentioned above, cysts are often undetectable at touch. Therefore, a mammogram can provide valuable and clear images of the breast tissue. Generally, if there is any abnormality within the breast tissue, it will be shown on the mammogram. There are two types of mammograms available. One of them is primarily used in screening, and are ordered for patients who do not show any symptoms and these are called screening mammograms. Diagnostic mammograms are used on patients who developed certain symptoms of a breast condition or in patients whose screening mammograms showed abnormalities. Patients suspected of breast cysts will normally be given a diagnosing mammogram, although they are not suspected of cancer.
Signs and symptoms
Signs and symptoms of breast cysts include: 

A smooth, easily movable round or oval breast lump with distinct edges
Breast pain or tenderness in the area of the lump
Increased lump size and tenderness just before menstruation
Decreased lump size and resolution of other signs and symptoms after menstruation
Having one or many simple breast cysts does not increase a persons risk of breast cancer.Lumps in the breast are often not found during self-examinations or physical exams. However, in some cases they can be felt at touch, especially if they are larger. Breasts are usually lumpy or nodular as a result of the hormonal changes that women go through during their menstrual cycle. However, new breast lumps should always be referred to a specialist. Cysts can also be confused with infections that form on the nipple or the areola. A common cyst look-alike is a localised infection of a duct in the nipple. These can happen whether youre breast feeding or not, (if you are breast feeding it could also be a bleb) this becomes a bump that may then start to look yellow and white (pus filled). Check with your doctor if you are unsure or have other symptoms that are worrying you. Fluid leaking from a cyst, as may happen due to puncture or vigorous compression during mammography, or due to seat belt injury in the course of an automobile accident, may trigger an aseptic inflammation in the surrounding breast tissue.