Non-obstetric ultrasound scanning

What is a non-obstetric ultrasound?

Ultrasound does not involve ionising radiation and therefore has a significant safety advantage over some of the other imaging modalities. There is no evidence that ultrasound damages tissues or predisposes to malignant change. It does cause a slight heating of tissues and potentially small cavitation in tissues. There is no evidence this causes any harm but, nevertheless, it is advised that imaging which is not medically necessary is avoided and that exposure is limited to the minimum level required.¹

Other advantages of ultrasound include that it is non-invasive and painless. The equipment tends to be much cheaper than, for example, MRI scanners and is potentially portable.

Ultrasound is often considered the best imaging modality for soft tissues.

Ultrasound may also be used for therapeutic purposes but this will not be discussed here. The diagnostic uses below are not a complete list.

See also the separate Obstetric ultrasound article.

How does ultrasound work?

• Ultrasound pictures depend upon reflection of very high frequency sound waves by interfaces between tissues. The frequency is typically 5-10 MHz.

• Ultrasound probes come in various shapes and sizes. It is usually manually moved across the area being examined. A gel is used to provide a non-reflective acoustic link between the probe and the skin or mucus membrane.

• When the sound waves emitted by the probe meet tissues of different densities, the sound waves are absorbed, reflected back to the probe, or transmitted through the tissue at different velocities. When this happens, the ultrasound image is white, or shades of grey, depending on the intensity of the reflection. When the sound waves travel easily through uniform substances such as water or urine, no echoes are produced and the screen is black.

• Transrectal ultrasound is used for assessment of the prostate gland. Transvaginal ultrasound is used for some gynaecological examinations, and devices placed in the oesophagus may be used to get certain images for echocardiography or ultrasound endoscopy.

• Technical advances in ultrasound scanning have been enormous, giving pictures of much greater resolution, as well as real-time scanning and colour Doppler imaging. Nevertheless, the result is still dependent on the operator who performed and interpreted the examination. Interpretation of ultrasound images is normally done at the time by the sonographer rather than using a still image later on.

• Contrast-enhanced ultrasonography further expands the range of use.

Abdominal ultrasound

• X-ray examination of the abdomen gives very limited information. Many renal stones and most gallstones are not radio-opaque.

• Ultrasound has much to offer in the abdomen and may be used to help in the differential diagnosis of abdominal pain.

Liver and gallbladder ultrasound

• The liver appears as a fairly homogeneous area on ultrasound. Tumours tend to be more echogenic. Cysts have a characteristic appearance with bright walls and dark centres.

• Patients with cirrhosis are at risk of developing liver cancer, and six-monthly screening with alpha-fetoprotein and ultrasound is recommended.² Contrast-enhanced ultrasound may be used where standard ultrasound is inconclusive in defining liver lesions.

• Gallstones are more readily demonstrated by ultrasound than by any other technique. Asymptomatic gallstones are common and the frequency increases with age. Fluid around the gallbladder is highly suggestive of cholecystitis.

• Endoscopic ultrasound techniques are also used for upper abdominal pathology.

Pancreatic ultrasound

• Ultrasound is often used in the diagnosis of pancreatic cancer. An ultrasound scan of the liver, bile duct and pancreas may show tumour mass and dilated bile ducts as well as any liver metastases. It is less good at demonstrating tumours in the pancreatic body and tail but endoscopic ultrasound may form part of further investigation.

• In acute pancreatitis, ultrasound may show an enlarged pancreas, dilated common bile duct, and free peritoneal fluid. However, CT scanning is the modality of choice in this scenario.³

• In chronic pancreatitis, ultrasound may show atrophy, calcification, or fibrosis of the pancreas. Cysts may also be seen.⁴

Assessment of appendicitis⁵

• Appendicitis is a common condition but diagnosis can sometimes be difficult.

• Ultrasound assessment is the imaging modality of choice in children and in women of childbearing age, followed by CT if the situation is still uncertain.

Assessment of abdominal aortic aneurysm (AAA)

• An ultrasound can be used to diagnose and measure an AAA and therefore helps to stratify risk and aid management.

• It now used for the national screening programme throughout the UK.^{6 7 8 9}

Urological ultrasound¹⁰

• Ultrasound is very good at showing stones and delineating the outline of kidneys and the collecting system.

• The renal cortex is seen as grey with some darker circles spaced uniformly around the edge. These darker circles correspond to the renal pyramids. In the presence of obstruction, dilatation of the renal pelvis and calyces will be seen. Renal size can be estimated.

• Glomerulonephritis or systemic illnesses such as diabetes, hypertension, arteriosclerosis, or autoimmune diseases result in kidneys that are hyperechogenic (and so a brighter grey) and the kidneys are often smaller than normal.

• If there is a stone in the kidneys or collecting system, it will show as a very bright echogenic area. Other causes of obstruction such as tumour are less intense.

• Ultrasound may be used to assess the residual capacity in a bladder after voiding.

Transrectal ultrasound of the prostate¹¹

• Ultrasound can be a useful means of assessing the appearance and volume of the prostate gland.

• The normal prostate gland of a young man produces a fairly homogeneous image.

• Benign prostatic hyperplasia often produces single, or numerous, cystic structures of various sizes. Cysts appear as anechoic (black) areas surrounded by hyperlucent areas in the walls of the cyst.

• Calcification may produce hyperechoic areas. This tends to follow prostatitis, even in a young man, but there may not be a clinical history of prostatitis.

• Malignant lesions in the prostate gland can be hypoechoic, isoechoic, or hyperechoic. MRI scans are used in diagnosis of prostate cancer but ultrasound scans are often used in biopsy.¹²

Examination of testes using ultrasound¹³

• Ultrasound can be used to assess the scrotum in assessing masses or abnormal examination of the testicles.

• It can also be useful to detect an undescended testis in the inguinal canal.

Gynaecological ultrasound¹⁴

• Ultrasound has shown itself to be especially useful in gynaecology. It can distinguish an ovarian mass from an adnexal mass and a cystic from a solid tumour. Pedunculated or degenerating fibroids may be apparent.

• Abdominal ultrasound of the pelvis is aided by the presence of a full bladder as this elevates the pelvic organs.

• Transvaginal ultrasound is usually more accurate as the probe is nearer to the pelvic organs.

• During infertility treatment involving hyperstimulation of the ovaries to produce several ova, it is important to monitor the production of follicles carefully by ultrasound to achieve the desired result without excessive stimulation.¹⁵

• Ultrasound scan remains the imaging of choice for assessment of the position of an intrauterine contraceptive device (IUCD).

• Ultrasound scan is used for the diagnosis of a hydatidiform mole, showing a classical 'ground glass' appearance.

Echocardiography

See the separate Echocardiography article.

Thyroid ultrasound¹⁶

• The thyroid gland is fairly superficial and amenable to ultrasound examination which can assess the size of the gland and whether any thyroid lumps are solid or cystic.

• Ultrasound scan is used to grade the thyroid gland from U1 to U5.¹⁷

• Ultrasound scan can also guide fine-needle biopsy in thyroid cancer.

• It may also be of value in demonstrating enlarged parathyroid glands in hyperparathyroidism.

Ultrasound of the brain¹⁸

• Normally brain tissue is not suitable for assessment by ultrasound, as it is enclosed in a bony skull that is highly echogenic.

• In the newborn infant, the fontanelles are still open and it is possible to use this for ultrasound to assess the brain.

• Doppler can be used for assessing blood flow and stenosis within the carotid and main cerebral arteries.

Breast ultrasound¹⁹

• Ultrasound may be used to assess lumps in the breast. With clinical examination, mammography and biopsy, it forms part of the initial assessment of women with breast lumps in specialist breast clinics.

• Particularly in pre-menopausal women who have denser breasts, ultrasound may be more useful than mammography in the diagnosis of both breast cancer and benign breast lumps.

Musculoskeletal ultrasound¹

Ultrasound scans are routinely used in the assessment of:

• Achilles tendonitis or rupture.

• Shoulder injuries and tendinopathies including tears, inflammation, thickening, ruptures, calcification of the:

  • Supraspinatus tendon.

  • Infraspinatus tendon.

  • Subscapularis.

  • Long head of biceps.

• Elbow: bursae, tendinopathy, effusion.

• Wrist: tendinopathy, tenosynovitis, carpal tunnel syndrome.

• Knee: effusion, bursae, Baker's cyst, tendinopathies.

• Hip: Screening for developmental dysplasia of the hip in neonates, bursae, effusion, tendinopathies.

• Muscle tears.

• Foot: neuroma, tendonitis.

Other uses for diagnostic ultrasound

Ultrasound is used to distinguish the nature of lumps and lesions almost anywhere in the body - for example, distinguishing lipomas from sebaceous or simple cysts. It may help in establishing whether a lump is a lymph node and, if enlarged, gives an idea if this has an inflammatory or malignant cause.

Ultrasound is widely used to guide biopsy. It is used as a first-line investigation to ascertain the nature of salivary gland swellings.²⁰ It is used to assess vascular conditions, such as deep vein thrombosis. It can be used in the acute diagnosis of pneumothorax.²¹

History

• Ultrasound scanning derives from sonar which was developed during World War I for the safety of navigation after the sinking of the Titanic in 1912 and for the detection of submarines. Further advances saw its use in industry to detect flaws in metal and the development of radar.

• In medicine, ultrasound was used from the 1930s as a therapeutic rather than diagnostic tool.

• Ultrasound for diagnosis started to be developed in around 1948. George Ludwig, who had been in the United States Navy, did much pioneering work on the properties of various tissues in relation to ultrasound. His first publication was in 1949.

• In 1954, the potential of ultrasound in obstetrics was first reported.

• The 1960s saw an explosion of interest in ultrasound and its potential.

• Portable scanners, colour Doppler scanners, echocardiography, use of contrast and many other techniques have developed since the 1960s.