Sometimes referred to as Fine Needle Aspiration or FNA, needle aspiration is a procedure in which a needle is inserted into a body, most typically into tumours or cysts, to remove fluid. In some cases, needle aspiration is used to completely drain a hazardous area of fluid. In others, needle aspiration is used to remove a portion of fluid from within a tumour or cysts so that studies can be performed.

Typically, a long, thin needle is inserted into the body, and fluid is taken out in a matter of minutes. This is typically outpatient procedure, and no sedation is required. The procedure is generally used in conjunction with CT scan or Ultrasound as a guide. Occasionally, X-Ray is used as well, but this is less common.

Needle aspiration can also be used in the case of a biopsy, and is frequently used in situations involving oncology reports.
Sources: TLC, personal experience, and various internet sites, including http://www.tirgan.com/fna.htm.