PHOTOS 1-2: Bone biopsies and histopathological evaluation are the only ways to establish a definite diagnosis of a bone tumour. Bone biopsies are also used to evaluate bone tissue abnormalities characteristic of certain diseases and to evaluate the effects of therapeutic regimes on bone. Bone biopsies have the disadvantages that they are invasive and that there is a question of how representative the specimen is of the whole bone tissue. These disadvantages can be overcome by careful surgical procedure in which the muscle is cut as little as possible, working aseptically and controlling infection and bleeding with antibiotics and packing. Closed biopsy techniques are preferred for bone biopsies because they have a lower complication rate and are less expensive. Bone can be biopsied with a trephine instrument or a jamshidi biopsy needle. The biopsy needle is a small bone trephine instrument without cutting serrations on the tip.
PHOTOS 3-6: The site of bone biopsy is usually at the junction of lytic and normal bone and another biopsy is done in the centre of the lytic area. Multiple biopsies can be done without weakening the bone if only one cortex is penetrated. The rib and iliac crest are often used for bone biopsies. The rib is not the best site as it could cause a fracture. The iliac crest is mostly used as biopsy in this area does not result in fracture, the proportion of trabecular to cortical bone is similar to that of the whole skeleton and the procedure is almost painless. PHOTOS 7-16: The lesion is located radiographically and the area to be biopsied is determined. The animal is placed under general anaesthesia. The skin over the biopsy site is clipped and the surgery site is prepared with a surgical scrub. The region is draped and an incision is made. Blunt dissection is used to reach the bone to be biopsied. The biopsy needle is inserted with its stylet in position through the incision and advanced through the overlying muscles to the bone. The stylet is removed once bone contact has been made. The instrument is rotated back and forth along its longitudinal axis to reach the required depth in the bone. The entire medullary cavity of the bone should be crossed. Once the desired depth is reached the instrument is rotated 360º in one direction several times. It is then rocked back and forth several times to break off the core. The end of the shaft is covered with the thumb to create a vacuum to hold the sample in and the instrument is gently removed. The sample is cleared from the shaft with a stylet. If using a jamshidi needle the shaft of the needle is cleared retrograde. Suture the skin as necessary. A light wrap can be applied to decrease the chances of haematoma formation. Post operative radiographs are made to confirm the location the biopsy sample was taken from. PHOTOS 17-18: The bone sample is transferred to a biopsy cassette for histopathology and measurement of the sample.
REFERENCES: PHOTOS 1-18: 1. Jowsey, J 1977, ‘The bone biopsy’, Plenum Medical Book Company, New York, pp. 59-89. 2. Morrison, WB 2001, ‘Cancer in dogs and cats : medical and surgical management’, 2nd ed., Teton New Media, Jackson, Wyo, pp. 118-121.
Metadata assigned by Dr. M. van Schoor, Senior Lecturer, Dept. of Companion Animal Clinical Studies