Pelvic ultrasound is a procedure in which high-frequency sound waves are used to create images of the pelvic organs by projecting the sound waves into the pelvis and measuring how the sound waves reflect, or echo, back from the different tissues.
Ultrasound is a preferred method of examining the pelvis and functions as an extension of a physical examination, particularly for obese patients. It is a common initial step after physical examination when a patient complains of pelvic pain or abnormal vaginal bleeding. The procedure is performed routinely during pregnancy and examinations to determine the cause of infertility. Ultrasound has the ability to detect the size and shape of pelvic organs, such as the bladder, and is useful in evaluating the cause of bladder dysfunction. In women, pelvic ultrasound is used to examine the uterus, ovaries, and vagina. In general, ultrasound can detect inflammation, free fluid, cysts (abnormal fluid-filled spaces), and tumors in the pelvic region.
A primary use of pelvic ultrasound is during pregnancy. In early pregnancy (at about five to seven weeks), ultrasound may determine the size of the uterus or the fetus to confirm the suspected due date, to detect multiple fetuses, or to confirm that the fetus is alive (or viable). Ultrasound is particularly useful in distinguishing between intrauterine (within the uterus) and ectopic (outside the uterus) pregnancies. Toward the middle of the pregnancy (at about 16-20 weeks), the procedure can confirm fetal growth, reveal defects in the anatomy of the fetus, and check the placenta. Toward the end of pregnancy, it may be used to evaluate fetal size, position, growth, or to check the placenta.
Doctors may use ultrasound to guide the biopsy needle during amniocentesis and chorionic villus sampling. The imaging allows precise placement of the long needle that is inserted into the patient's abdomen to collect cells from the placenta or amniotic fluid.
There are no special precautions recommended before an ultrasound examination. Unlike x rays, ultrasound does not produce harmful radiation so it does not pose a risk to the technologist, patient, or a fetus.
Depending on the goal of the procedure, a pelvic ultrasound can also be called a bladder ultrasound, pelvic gynecologic sonogram, or obstetric sonogram. Ultrasound examinations are often done in a doctor's office, clinic, or hospital setting. Typically, the patient will lie on an examination table with the pelvis exposed. Special gel is applied to the area to make sure that there is no air between the hand-held transducer and the skin and to facilitate moving the transducer. The doctor or technologist will move the transducer over the abdomen. The transducer both creates and receives the echos of the high-frequency sound waves (usually in the range of 3.5-10.0 megahertz). An ultrasound scan reveals the shape and densities of organs and tissues. By performing repeated scans over time, much like the frames of a movie, ultrasound can also reveal movement, like the movement of a fetus. This technique is called real-time ultrasound.
Using a computerized tool, called a caliper, the ultrasound technologist can measure various structures shown in the image. For example, the length of the upper thigh bone (femur) or the distance between the two sides of the skull can indicate the age of the fetus.
Ultrasound technology has been used safely in medical settings for over 30 years, and several significant extensions to the procedure has made it even more useful. A specially designed transducer probe can be placed in the vagina to provide better ultrasound images. This transvaginal or endovaginal scan is particularly useful in early pregnancy or in cases where ectopic pregnancy is suspected. In men, transrectal scans, where the probe is placed in the rectum, are done to check the prostate. Doppler ultrasound has the ability to follow the flow of blood through veins and arteries and can be useful in detecting abnormalities such as abnormal blood flow associated with ovarian torsion, a twisted blood supply that causes pelvic pain. Color enhancement is particularly useful in Doppler imaging, where shades of red signify flow away from the transducer and shades of blue signify flow toward.
Hysterosonography is another variant ultrasound procedure. It involves the injection of saline solution into the uterus during an endovaginal scan. The saline distends the uterine cavity and simplifies the identification of polyps, fibroids, and tumors. The saline outlines the lesion, making it easier to find and evaluate. Hysterosonography can also be used in the testing of patency (openness) of the fallopian tubes during infertility evaluations.
Before undergoing a pelvic ultrasound, the patient may be asked to drink several glasses of water and to avoid urinating for about one hour before the examination. When the bladder is full, it forms a convenient path, called an acoustic window, for the ultrasonic waves. A full bladder is not necessary for an endovaginal examination, sometimes making it a preferred choice for emergency situations. Women usually empty their bladders completely before an endovaginal exam.
For a diagnostic ultrasound, the lubricating gel applied to the abdomen is wiped off at the end of the procedure and the patient can immediately resume normal activities.
Ultrasound carries with it almost no risk for complications.
A normal scan reveals no abnormalities in the size, shape, or density of the organs being scanned. For a scan taken during pregnancy, a normal scan reveals a viable fetus, of expected size and developmental stage. Although ultrasound is an extremely useful tool, it cannot detect all problems in the pelvic region. If a tumor or other lesion is very small or if it is masked by another structure it may not be detected. When used during pregnancy, patients should be advised that all fetal abnormalities may not be seen with ultrasound. Additionally, the reliability of ultrasound readings can depend on the skill of the technologist or doctor performing the scan.
An abnormal scan may show the presence of inflammation, cysts, tumors, or abnormal blood flow patterns. These results may suggest further diagnostic procedures or surgical or pharmacological treatment. Ultrasound examinations in obstetrics may alter the anticipated due date or detect abnormalities or defects in the fetus. This information may reveal that the fetus cannot survive on its own after birth or that it will require extensive treatment or care. The technologist performing the ultrasound should be sure to consult with a radiologist or other doctor if any questionable results appear.
Health care team roles
Ultrasound units are often run by specially trained ultrasound technologists. These technologists are thoroughly trained in the use of the ultrasound unit to produce diagnostically useful images. Nurses aid in patient preparation and education about the procedure. A physician such as a radiologist or gynecologist does the final review and diagnosis based on the results of the ultrasound. The doctor can be present for the exam or may make the final review and diagnosis based on saved images.
It is very important that patients understand the limitations of ultrasound, particularly when it is performed during a normal pregnancy. Many fetal malformations are not detectable, or are unreliably detectable, using ultrasound alone. The patient must understand that a normal ultrasound result does not necessarily guarantee that the fetus is normal.
Acoustic window— Area through which ultrasound waves move freely.
Amniocentesis— A procedure where a needle is inserted through the pregnant woman's abdomen and into the uterus to draw off some of the amniotic fluid surrounding the fetus.
Chorionic villus sampling— A procedure where a needle is inserted into the placenta to draw off some of the placenta's inner wall cells surrounding the fetus.
Ectopic pregnancy— A pregnancy where the fertilized egg becomes implanted somewhere other than in the uterus; if in a fallopian tube it is called a tubal pregnancy.
Real-time— A type of ultrasound involving the taking of multiple images over time in order to record movement.
Sonographer— A technologist who uses an ultrasound unit to takes ultrasound images of patients.
Transducer— The handheld part of the ultrasound unit that produces the ultrasound waves and receives the ultrasound echos.
Ultrasound— Sound above what can be heard by the human ear, generally above 20,000 Hz (cycles per second).
Being hired as an ultrasound technologist to perform pelvic ultrasounds usually involves successful completion of a training program at a two-year college or vocational program. Certification of ultrasound technologists is available through the American Registry of Diagnostic Medical Sonographers as a registered diagnostic medical sonographer (RDMS). Specialty areas within the sonographer credentials that might be useful for performing pelvic ultrasounds include abdomen or obstetrics and gynecology.
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American Institute of Ultrasound in Medicine. 14750 Sweiter Lane, Suite 100, Laurel, MD 20707-5906. (301) 498-4100. (800) 638-5352. 〈http://www.aium.org〉.
American Registry of Diagnostic Medical Sonographers (ARDMS). 600 Jefferson Plaza, Suite 360, Rockville, MD 20852-1150. (301) 738-8401. (800) 541-9754. 〈http://www.ardms.org〉.
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