Analgesia

For the vast majority of biopsy procedures a local anaesthetic is administered following localization of the biopsy site with ultrasound. Lidocaine (1% or 2%) is commonly used; the volume will depend on patient build, depth of lesion, patient anxiety, etc. It is also useful to inject the anaesthesia under ultrasound guidance, so that lidocaine can be targeted exactly to the biopsy route, enabling effective pain relief throughout. Usually a short period of time, commonly 3–4 minutes, is allowed to pass so that the anaesthetic can work, after which, a small scalpel incision is made in the skin to facilitate the biopsy needle’s introduction, with little or no discomfort to the patient. In cases of simple aspiration with a 22G needle or smaller, local anaesthetic is usually unnecessary.

Patients who are particularly apprehensive may require pre-procedure medication with a sedative such as diazepam or similar anxiolytic agent, however, this is uncommon. Very occasionally intravenous analgesia and/or sedation may be required during the procedure; it is often a good idea to have an intravenous cannula in situ prior to biopsy.

The use of general anaesthesia for children is common practice to enable the procedure to be carried out quickly and accurately while the child remains still.

Methods of ultrasound guidance

There are various ways of performing ultrasound-guided procedures i.e. guided, freehand or ‘blind’. The choice of method depends on the procedure in question, equipment and the experience and skill of the operator.

Biopsy guidance

Most manufacturers provide a biopsy guide which fits snugly onto the transducer head and provides a rigid pathway for the needle (Fig. 11.1) These are now common and a widely accepted method of biopsy. The fixed biopsy guide contains a groove for a series of plastic inserts ranging from 14G to 22G size, depending upon the size of the biopsy needle. It is usual to use one size greater than the needle (i.e. a 16G insert for an 18G needle) as the needle tends to move more freely. The guide is sterilized and fitted onto the transducer over a sterile sheath.

Fig. 11.1 • (A) Necessary component parts to perform an ultrasound-guided biopsy procedure. A series of plastic inserts (Ai) range in size from 14G to 22G. The appropriate insert is inserted into a fixed biopsy guide (Aii). The procedure is performed with sterile jelly (Aiii) and a sterile probe cover (Aiv) if required.

(B) The assembled biopsy guide.

The needle pathway is displayed on the ultrasound monitor electronically – as a line or narrow sector – through which the needle passes. The operator then scans in order to align the electronic pathway along the chosen route, the needle inserted, and the biopsy taken. These attachments should be tested regularly to ensure the needle follows the correct path (Fig. 11.2).

Fig. 11.2 • Testing the alignment of the biopsy guide. The electronic pathway is activated on the image and the needle is scanned as it is passed into a jug of water.

Equipment and needles

The core of tissue for histological analysis is obtained with a specially designed needle consisting of an inner needle with a chamber or recess for the tissue sample and an outer, cutting needle which moves over it i.e. the Tru-cut needle. The biopsy is obtained in two stages – first the inner needle is advanced into the tissue, then the outer cutting sheath is advanced over it and the needle withdrawn containing the required tissue core (Fig. 11.3). The use of a spring-loaded ‘gun’ to operate these needles is now commonplace (Fig. 11.4). It is designed to enable operation of the needle with one hand, (whilst being able to hold the probe with the other) and has the advantage of being sterile and disposable.

Fig. 11.3 • Biopsy needle closed (top) and open (bottom).

Fig. 11.4 • Non-disposable spring-loaded gun designed to operate the cutting needle.

The whole needle is advanced into the tissue, just in front of the area to be biopsied. By pressing the spring-loaded control, the inner part is quickly advanced into the lesion, followed rapidly by the cutting sheath over it. Needles can be obtained in a variety of sizes, generally 14, 16, 18 or 20G. Most focal lesions are biopsied with a standard 18G needle. As a general principle, as the needle advances approximately 1.5–2.0 cm during biopsy, it is advisable to position the needle tip on the edge of a lesion to obtain a good histological sample as most lesion necrosis tends to be centrally located. Because the gun enables the operator to scan with one hand and biopsy with the other, the needle can be observed within the lesion, yielding a high rate of diagnosis with a single pass technique,¹ and minimizing post-biopsy complications.

Fine needle histology, involving the use of needles of 21G or less, reduces even further the possibility of post-procedure complications. These are generally not used as only small amounts of tissue are obtained for analysis and as thin needles they are apt to bend more easily, and are therefore more difficult to see and retain within the plane of the scan. Biopsy of deep lesions is therefore more difficult if not impossible.

Liver biopsy

The most common reason for ultrasound-guided biopsy is for metastatic disease. The liver is one of the most common sites for metastases and histology may be required to confirm the diagnosis, or, more usually, to identify the origin of an unknown primary lesion (Figs 11.5–11.7). Biopsy of suspected HCCs is generally avoided, as it is associated with a poorer treatment outcome and there is a small risk of tumour seeding. CEUS and/or MRI can now characterize many lesions, avoiding the need for biopsy in an increasing number of cases. Focal lesion biopsy is generally safely and accurately performed with an 18G needle which yields reliable tissue for histological analysis. In general, an accuracy of 96% should be achievable.²

Fig. 11.5 • (A) A liver lesion is identified in the right lobe prior to biopsy.

(B) A route is chosen avoiding the adjacent hepatic vein.

Fig. 11.6 • The needle is introduced into the liver, just in front of the lesion under ultrasound guidance.

Fig. 11.7 • The gun is fired, propelling the needle tip into the lesion . This visually confirms the biopsy has been taken from the correct area.

In addition to focal lesion biopsy another common reason for liver biopsy is to assess the presence/absence of parenchymal liver disease, severity of disease and where appropriate, the aetiology of the disease process. This is often performed in patients with abnormal liver function tests with no evidence of biliary obstruction. The clinical history and serological analysis can be helpful in determining aetiology however biopsy is often required. This is usually performed with a 14G or 16G Tru-cut needle. Often the liver is simply identified with ultrasound and a suitable mark made on the skin, often in the mid axillary line and the biopsy performed through the right lobe. Although this is acceptable for this type of biopsy, ultrasound guidance during the procedure is still preferable to the ‘blind’ technique in order to avoid large vessels and reduce the subsequent risk of haematoma. Biopsy may also be performed for patients with suspected rejection following hepatic transplantation.

Where coagulation profiles are not correctable (and most generally are) liver biopsy can be performed using a ‘plugged’ technique or, more commonly, by the transjugular route (Fig. 11.8).

Fig. 11.8 • Transjugular biopsy of the liver. Access is via the right internal jugular vein, through the right atrium and into the IVC and hepatic veins. Once the catheter is wedged in the hepatic vein the cutting needle is released and a biopsy is taken.

Pancreatic biopsy

The commonest reason for biopsy of the pancreas is in patients presenting with obstructive jaundice due to a mass in the head of the gland. A fine needle technique enables the mass to be accessed through the stomach and left lobe of liver without complications, however, an 18G needle biopsy is advisable to try to reduce false-negative results due to the well-known situation of a carcinoma being associated with an element of peripheral inflammation. Pancreatic biopsies are often better performed under CT control (Fig. 11.9) particularly when lesions are small, patients big and/or the lesion is difficult to identify with ultrasound. In those patients with negative biopsies very often interval CT scans are performed to see if the lesion is static or progressive.

Fig. 11.9 • (A) CT-guided biopsy of a pancreatic head mass. The tip of the biopsy needle (arrow) is positioned in the periphery of the lesion so that when the biopsy is taken a good core of tissue is obtained. Note the artefact from the needle tip.

(B) CT-guided biopsy of a retroperitoneal lymph node mass (arrowheads). The mass lies adjacent to the aorta (arrow) however this is protected from the needle by the angle of approach and its relationship to the vertebral body. CT is the preferred biopsy method of choice for deep structures within the retroperitoneum.

Native kidney biopsy

Histology is frequently required in order to direct further management of diffuse renal disease. Biopsy of solid, renal masses are rarely performed as the diagnosis of renal cell or transitional cell carcinoma is usually clear from imaging. Biopsies are still performed, however, in those patients who are not having surgery to confirm the diagnosis, as this is often required prior to chemotherapy or new therapeutic regimens.

Biopsy of the native kidney is performed in the majority of centres under ultrasound guidance. Contraindications to biopsy include hydronephrosis, which may be more appropriately treated with catheterization or nephrostomy, or small kidneys, i.e. <8 cm longitudinal axis, these appearances being indicative of chronic renal impairment. Kidneys >9 cm can potentially be biopsied, however, other factors including cortical thickness, age, clinical history and the requirement for definitive diagnosis will all have a bearing on whether biopsy is performed or not. Hydronephrosis and kidney size are easily assessable with a pre-biopsy scan.

In most cases the biopsy is performed with the patient prone over a small bolster to maximize access to the kidney. The shortest route, avoiding adjacent structures, is selected – subcostally, traversing the cortex of the lower pole and avoiding the collecting system and major vessels is recommended. With ultrasound guidance, either kidney may be chosen and accessibility will vary between patients. The depth of penetration and angle of approach are carefully assessed. Biopsy is normally with a 16G needle.

The patient’s cooperation is required in suspending respiration at the crucial moment. This avoids undue damage to the kidney as the needle is introduced through the capsule. The needle should be positioned just within the capsule prior to biopsy so that the maximum amount of cortical tissue is obtained for analysis as the throw of the needle may be up to 2 cm (Fig. 11.10).

Fig. 11.10 • Ultrasound-guided biopsy of the native left kidney. The tip of the needle was positioned on the outer aspect of the kidney. With a 2 cm jump of the needle on firing, a good core of renal parenchyma is obtained.

Renal transplant biopsy

Biopsy is a valuable tool in the post-operative management of a transplant recipient (Chapter 7), enabling the cause of graft dysfunction to be identified, in particular differentiating acute tubular necrosis from acute rejection. Ultrasound guidance is essential in order to reduce complications such as haematoma, vascular damage (which may result in an AV fistula or pseudoaneurysm formation) and laceration of the renal collecting system.

A single pass technique, using the spring-loaded biopsy gun with an 18G needle is usually sufficient for histological purposes, however two passes may be required so that electron microscopy and immunofluorescence can also be performed. The procedure is well tolerated by the patient and the complication rate low at less than 5%.³

Related posts:

Ultrasound of the acute abdomen Optimizing the diagnostic information Ultrasound of the spleen and lymphatic system Pathology of the gallbladder and biliary tree Ultrasound of the renal tract Pathology of the liver and portal venous system

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