Ultrasound tests for cancer

ALSO KNOWN AS: Sonogram, echogram, ultrasonography, sonography

DEFINITION: An ultrasound test is a radiologic study that utilizes sound waves to detect an abnormality in an organ of the body under evaluation using a principle similar to sonar used in ship navigation. Ultrasound waves are mechanical pressure waves at a higher frequency than audible sound waves, hence the name ultrasound. These high-frequency sound waves reflect off body surfaces and structures. Different tissues in the body have different acoustic velocities or speeds of sound propagating through them. The time that it takes for a pulsed sound wave to travel from a transducer to a reflector and back again can be measured and then, along with the known acoustic velocity of tissue, can be used to calculate their separation and, thus, the depth from the skin surface of the organ or organ part under study. Bone, for example, has a higher acoustic velocity than soft tissue. One would expect higher-amplitude echoes from soft tissue-bone interfaces and lower-amplitude reflection or echoes from soft tissue-soft tissue interfaces because of the almost matched acoustic velocities among the latter.

The ultrasound transducer converts the amplitude of the mechanical energy received from the organ under study into an electrical signal and vice versa. The emitting and receiving element of an ultrasound transducer is a piezoelectric crystal. The electrical signals from the transducer are fed into a computer and viewed or saved by the sonographer and radiologist, who are responsible for the quality and interpretation of the study.

Cancers diagnosed: Breast, thyroid, testicular, uterine, ovarian, prostate, renal (kidney), bladder, gallbladder, liver, spleen, and pancreatic cancers; cancers associated with pregnancy, such as gestational trophoblastic disease; unsuspected adenopathy often detected as an incidental finding during ultrasound examination, especially during the examination of the thyroid, breast, and abdomen

Why performed: Ultrasounds can diagnose primary and secondary cancers (metastases). It is also used to diagnose ailments depending on the patient’s symptoms, including but not limited to—right-upper-quadrant abdominal pain caused by acute and chronic cholecystitis (calculus and acalculus) and postoperative leaks following cholecystectomy (gallbladder and right-upper-quadrant ultrasound); goiter, Hashimoto’s thyroiditis, and ectopic parathyroid (thyroid ultrasound); mastitis and Paget's disease of the breast (breast ultrasound); pain in the right lower quadrant of the abdomen caused by appendicitis (ultrasound of the appendix); scrotal pain caused by testicular torsion, testicular trauma, orchitis, epididymitis, and hydrocele, as well as undescended testes (testicular ultrasound); pain in the back caused by kidney stones, kidney obstruction, or infection (renal ultrasound); pain and swelling in the legs caused by deep venous thrombosis (DVT study); pain in the epigastric area caused by pancreatitis (abdominal ultrasound); pain in the left upper abdomen caused by splenic infarct or splenic trauma (abdominal ultrasound); pain in the right upper quadrant caused by liver trauma, liver infection, or liver cysts and evaluation for the presence of ascites (abdominal ultrasound); valvular heart disease (cardiac ultrasound or echocardiography); atherosclerosis of the lower-extremity arteries, abdominal aortic aneurysm, and carotid artery atherosclerosis (vascular or arterial Doppler ultrasound); and polycystic ovarian syndrome or pelvic pain or bleeding caused by ovarian torsion, uterine polyps, uterine fibroids, and retained products of conception (pelvic and transvaginal ultrasound).

Additionally, all three trimesters of pregnancy are evaluated by ultrasound. Ultrasound guides amniocentesis, which involves sampling fluid surrounding the fetus to assess possible fetal anomalies like Down syndrome (trisomy 21); sampling and removal of fluid from various body cavities in the adult, such as the lung (pleural effusion tap) and abdominal cavity (ascites); and guiding biopsy of various organs, like the liver, breast, thyroid, and kidney.

Patient preparation: Patients must fast at least four to eight hours before the gallbladder ultrasound, as food causes the gallbladder to contract and minimize the area visible for the ultrasound evaluation. Patients drink at least four glasses of water at least one-half hour before the pelvic ultrasound to distend the bladder, which acts as an acoustic window for the study (sound travels well through water). This enables the sonographer, usually a technologist, to evaluate the baby and the womb during pregnancy and the state of the uterus, cervix, and ovaries in both the pregnant and the nonpregnant state.

Steps of the procedure: The patient is placed on the back of a table, and the technologist or the radiologist applies a clear, water-based conducting gel to the skin over the organ or body part of interest. The gel helps transmit sound waves, which may feel wet and cold. The sonographer rubs a handheld probe or transducer across the surface of the organ of interest. There will be some discomfort from pressure on a full bladder, but the ultrasound waves themselves are painless. Some transducers, such as a transvaginal or transrectal probe, are designed to be inserted inside a body cavity, which may be uncomfortable.

After the procedure: The scan is generated by the computer attached to the ultrasound probe and read by the radiologist the same day. The patient must contact their doctor or healthcare provider for the radiology report and follow-up therapy.

Risks: The study is painless and relatively harmless, as no radiation is involved; transvaginal ultrasound is generally done early in a pregnancy to determine fetal age or to detect a suspected ectopic pregnancy. Use of the transvaginal probe late in pregnancy is a decision made by the healthcare provider, not the sonographer or radiologist.

Results: The results depend on the type of scan performed and the reason for the study. Some ultrasound tests are screening tests and may be normal, while others are ordered by a healthcare provider when an abnormality is suspected.

Bibliography

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Gill, Robert. The Physics and Technology of Diagnostic Ultrasound: A Practitioner’s Guide. High Frequency Pub, 2020.

Hayes, Kevin. Medical Tests Sourcebook. Omnigraphics, Inc., 2022.

Hiam, Deirdre S. The Gale Encyclopedia of Cancer: A Guide to Cancer and Its Treatments. 5th ed., Gale, 2020.

Long, Beverly, et al. "Ultrasound Detection of Endometrial Cancer in Women with Postmenopausal Bleeding: Systematic Review and Meta-analysis." Gynecologic Oncology, vol. 157, no. 3, 2020, pp. 624-633. doi.org/10.1016/j.ygyno.2020.01.032.

Morris, Elizabeth A., and Jin Su Hsieh. Modern Breast Cancer Imaging. Springer, 2022.

Rumack, Carol M., and Deborah Levine. Diagnostic Ultrasound. 6th ed., Elsevier, 2024.

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Szabo, Thomas L. Diagnostic Ultrasound Imaging: Inside Out. 2nd ed. Academic-Elsevier, 2014.

"Ultrasound Scan." Macmillan Cancer Support, www.macmillan.org.uk/cancer-information-and-support/diagnostic-tests/ultrasound-scan. Accessed 20 July 2024.