Principles and techniques of biopsy with special reference to fine-needle aspiration cytology

Fine-needle aspiration (FNA) cytology is an inexpensive, effective and (generally) safe procedure for diagnostic sampling of superficial masses. In the UK, it has attained central importance in the management of palpable lesions of the breast and thyroid gland. The use of image guidance means that aspiration of impalpable and deep-seated lesions is routine in radiological practice in the UK. The aim of the FNA procedure is to collect sufficient representative material from the lesion to enable a cytological diagnosis 'i.e. based on the appearance of dispersed individual cells and cell groups' to be made. As well as its role in the primary diagnosis of tumours, FNA cytology in very useful in the staging of malignant tumours. For example, endoscopic ultrasound-guided FNA of a paraoesophageal lymph node can detect metastatic oesophageal carcinoma. Another useful role for FNA is in diagnosing recurrence of malignancy, particularly lymphoma. Clinical FNA procedures are described and potential causes of an inadequate 'i.e. non-diagnostic' aspirate are discussed. Various modalities of image guidance are discussed and methods of slide preparation compared. The role of special techniques such as immunocytochemistry and fluorescence in situ hybridization is illustrated by means of diagnostic scenarios. The uses and limitations of FNA cytology of the breast, thyroid, lymph nodes and salivary glands are discussed.