Fine needle aspiration cytology (FNAC) is an important diagnostic tool in the clinical investigation. FNAC, as we know it today, dates back to around 1950. However, the idea to obtain cells and tissue fragments through a needle introduced into the abnormal tissue was by no means new. FNAC is now part of the service of all sophisticated departments of pathology. Fine needle aspiration cytology was initially conceived as a means to confirm a clinical suspicion of local recurrence or metastasis of known cancer without subjecting the patient to further surgical intervention. This remains one of the most important contributions of the technique from a practical point of view. Following success in this area, the interest focused on the preliminary preoperative diagnosis of all kinds of neoplastic processes, benign or malignant, in any organ or tissue of the body and on definitive, specific diagnosis in inoperable cases as a guide to rational treatment. The expansion of FNAC in the primary diagnosis of tumors in the last 30 years or so has been impressive and generally successful. This development is to a large degree the result of the consistent, continuous and critical correlation between cytological assessment and histopathological diagnosis facilitated by the organizational coordination of laboratory resources.
The clinical value of FNAC is not limited to neoplastic conditions. It is also valuable in the diagnosis of inflammatory, infectious and degenerative conditions, in which samples can be used for microbiological and biochemical analysis in addition to cytological preparations. This is of particular importance in patients with acquired immunodeficiency syndrome (AIDS) and in other immunocompromised patients. FNAC has proven useful in the diagnosis and monitoring of graft rejection in transplantation surgery.
Advantages and limitations
The technique is minimally invasive, produces a speedy result and is inexpensive. Its accuracy in many situations, when applied by experienced and well-trained practitioners. A definitive specific diagnosis may not be possible by cytology in a proportion of cases, but a categorization of disease and a differential diagnosis with an estimate of probability can usually be provided to suggest the most efficient further investigations, saving time and resource. The method is applicable to superficial lesions that are easily palpable, in the skin, subcutis and soft tissues, thyroid, breast, salivary glands, and superficial lymph nodes.
Fine needle biopsy (FNB) is less demanding technologically than surgical biopsy, has a low risk of complications and can be performed as an office procedure, in outpatient departments and in radiology theaters, saving expensive days in the hospital. It is also highly suitable in debilitated patients, is readily repeatable and allows biopsy of multiple lesions in one session.
Practitioners of FNAC must be aware that the technique has certain inherent limitations.
Firstly, results and accuracy are highly dependent on the quality of samples and smears. Appropriate training and experience is essential to consistently achieve optimal material for diagnosis.
Secondly, many pathological processes are heterogeneous, and the tiny samples obtained with a fine needle may not be representative even when the biopsy is guided by imaging. Multiple biopsies help, but the number of passes is limited by the need to minimize trauma.
Thirdly, some lesions are recognized mainly on the specific microarchitectural pattern, which may not be sufficiently represented in cytological preparations.
Fourthly, the small FNB sample may not allow the full armamentarium of ancillary techniques to be drawn upon, for example, batteries of immune markers. Finally, precise cytological criteria have not yet been defined in some rare conditions.
The practice of FNAC
The success of FNAC depends on four fundamental requirements:
1) Samples must be representative of the lesion investigated.
2) Samples must be adequate in terms of cells and other tissue components.
3) Samples must be correctly smeared and processed.
4) The biopsy must be accompanied by sufficient and correct clinical/radiological
In the major hospital, on the other hand, FNB is an essential component of the preoperative/pretreatment investigations on which clinical management is based. The aim is to establish a precise and, if possible, type-specific diagnosis, and prognostic indicators if required. The full armamentarium of laboratory techniques may be called upon to achieve this goal and the supplementary use of core needle biopsy may also be considered. The information obtained by FNB may be of decisive importance in the planning of surgery, radiotherapy, chemotherapy, etc.
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