Image guided biopsies

Abstract

Image-guided biopsy is widely performed in all organ systems for tissue sampling, either of abnormal tissue that has been identified, or indiscriminate biopsy in cases of organ dysfunction to obtain representative tissue for histological diagnosis. The use of real-time image guidance allows targeted biopsy of even small lesions, and the avoidance of adjacent organs, vessels or collecting systems. The most commonly employed imaging modality is ultrasound, which is ideal for superficial organs like the thyroid, or solid organs such as the liver or kidneys. In addition, special ultrasound probes used transrectally, transvaginally, or endoscopically allow the biopsy of lesions within genitourinary, gastrointestinal and respiratory tracts. Ultrasound is limited by poor transmission of sound waves through air and bone however. CT gives excellent visualisation of structures within aerated lung, bone, and where loops of air-filled bowel are located. This permits biopsy of lung, bone or structures deep within the abdomen or pelvis. Fluoroscopy may also be used for bone biopsy. Other techniques such as MRI or PET guided biopsy are performed on occasion, however are limited by availability and cost. The risks of biopsy depend on systemic factors such as coagulopathy, and regional factors such as adjacent organs with can be inadvertently injured. In addition, certain specific malignant lesions carry a risk of seeding along the biopsy tract, such as osteosarcomas and certain salivary gland tumours. Where such lesions are within the differential diagnosis, biopsy should be planned in conjunction with the relevant oncological surgeon to ensure the biopsy tract will be included in any primary oncological resection, thus preventing the need for additional resection. Where multiple lesions exist, such as in cases of suspected metastatic malignancy, biopsy should target the lowest-risk area, such as superficial lymph nodes. Occasionally, dedifferentiated cytology within distant metastases may necessitate additional biopsies for definitive identification of the primary tumour. The size and number of biopsy cores required vary with organ and local practice. Biopsies of solid organs such as the liver and kidney are typically performed with 16-20 G core needles, with smaller gauge needles often requiring additional cores. Certain lesions such as in the parotid or thyroid may only require fine needle aspiration for diagnosis. Traditionally, a diagnosis of lymphoma required a surgical excision of a node, however there is increasing acceptance of image-guided biopsy in the first instance (Figs. 14.1 and 14.2).