Guided biopsy and drainage procedures
Ultrasonography and CT can be used to guide biopsy and drainage procedures. The target can be identified using the imaging modality and the intervention performed in a manner that minimises the risk to organs and vessels. In most instances the only alternative to image guided methods would be operative intervention. Most image guided procedures can be performed without general anaesthesia and are inherently safer than operative alternatives. As only small needles or drainage catheters are utilised these procedures are minimally invasive leaving only a small puncture site and causing minimal damage of healthy tissue.
Biopsies:
Most biopsies in the abdomen and the pelvis are performed preferably with ultrasonographic guidance. This is because ultrasonography facilitates multiplanar access enabling rapid identification of the safest route for biopsy and real time guidance of the needle to ensure accurate placement. However ultrasound beams are attenuated as they traverse tissue so that deeply sited targets may be poorly visualised. Ultrasound is also reflected by gas and bone, making some target lesions inaccessible to the ultrasound beam. In these situations CT guidance is often used, and the needle placed in an incremental manner carefully directed by repeated limited scans. Lung biopsies in which the target lesion is surrounded by gas filled lung nearly all have to be performed using CT.
One of the commonest organs for biopsy is the liver. This can be either for assessment of diffuse liver disease, in which case a biopsy of a representative portion of liver is taken under ultrasound guidance usually from the right lobe, or for focal liver lesions in which the biopsy of the lesion is taken using ultrasound, or occasionally, CT guidance.
Biopsies are performed using local anaesthesia which is also carefully infiltrated down to the lesion under guidance to reduce the discomfort of the biopsy to a minimum. Patients on anticoagulants generally need to stop these prior to the procedure under the monitoring of their physician. Patients on platelet inhibitory drugs (eg aspirin and Clopidegrol ( Plavix)) should stop these a week before the biopsy, again under direction of their physician. Patients will be observed following biopsy for signs of bleeding but usually are allowed home after up to 6 hours if the procedure is being performed as a day case
The risks from image guided biopsies are small. Bleeding is always a possibility but minimised by careful passage of the needle. Puncture of bowel may cause leakage of contents but bowel can usually be avoided. Sometimes it is unavoidable to traverse bowel to reach the target lesion but even then this is usually uneventful.
Drainage Procedures
Collections of pus (or other fluid) can be drained under image guidance using the same principles and having the same risks as image guided biopsies. There are 2 main ways of performing drainages; direct 'stab' techniques in which the drain is inserted directly with a sharp trocar and ' Seldinger' technique in which a needle is put into the collection, a guide wire inserted into the collection and the tract then dilated over the wire. The drain is then inserted over the wire. The former technique is used if access is straight forward as it is quicker with less discomfort.
The latter technique is used if access is difficult and there is a concern of organ or bowel damage if the drain is inserted directly. Drainage is usually performed under antibiotic cover because of the risk of septicaemia.