FNA or core needle biopsy? Why not both?

November 2007
PAP/NGC Programs Review

Camilla J. Cobb, MD

Like other initially competing methods, fine-needle aspiration and core needle biopsy have achieved not only individual but also combined utility in the diagnosis of mass lesions. Fine-needle aspiration, or FNA, is quick, safe, accurate, and inexpensive, and outcomes compare well with the results of tissue biopsy when the FNA is performed and interpreted by skilled individuals.^1-5 However, with fewer skilled individuals performing and interpreting the FNAs and making themselves available for on-site adequacy assessment, the use of core needle biopsy, or CNB, has increased, for not only deep-seated nonpalpable lesions but also for palpable masses in the breast, thyroid, lymph nodes, and soft tissue. This shift was welcomed (and in some cases encouraged) by many pathologists, whose training in anatomic pathology and daily work consists mainly of surgical pathology, which brings in considerably more revenue than comparable time spent on cytopathologic activities.

CNB procedures are usually performed by radiologists, who are also trained to perform FNAs but who will generally provide the specimen type that the pathologists prefer, and in recent times that specimen is often a CNB. The Catch-22 in this, so to speak, or the unanticipated outcome, is that radiologists are not simply dropping the cores into formalin and sending them to the pathology laboratory for processing and interpretation the next day. As with the FNA, radiologists also want an adequacy assessment on the CNB. Like the FNA, CNBs are time-consuming procedures (for the radiologist, not the pathologist) that, even for palpable lesions, are usually performed with image guidance. The CNB is also expensive and time-consuming for patients and is uncomfortable as well. Also like the FNA, CNBs, even with image guidance, can "miss" the lesion. Radiologists, therefore, want to ensure that the CNB is adequate and that any specimen triage needed (for example, for microbiologic culture or flow cytometry) is accomplished during the single procedure. Adequacy assessment of a CNB is, therefore, reasonable, and pathologists, despite their grumblings, are generally complying with this new responsibility.

Unfortunately for some pathologists, assessing the adequacy of a CNB is more challenging than assessing the adequacy of an FNA sample. Problems are related to the nature of cell transfer from the CNB to the glass slide, which is accomplished by (gently) making multiple touches of the core to the slide or (gently) rolling the core over the slide. Compared with an FNA specimen, these procedures typically transfer significantly fewer cells and can cause cellular distortion and promote air-drying, which challenge adequacy assessment and specimen triage. Furthermore, the physical manipulation of the tissue core and the delay in placing the small core into fixative sometimes lead to tissue disruption and poor preservation that can cause difficulty in histologic interpretation.

No doubt, a well-sampled CNB specimen usually has greater diagnostic accuracy and provides more tissue for ancillary testing compared with the typical FNA sample,^1,2,6,7 but the manipulations required to assess the adequacy of the CNB can compromise the interpretive outcome significantly, yielding equivocal diagnoses. After a period of struggle at my own institution, our pathologists and radiologists collectively found a solution to this dilemma. When the pathologist is called upon to assist a radiologist in the minimally invasive retrieval of tissue for diagnosis, an FNA is done initially for adequacy assessment, followed by CNB, only if (based on adequacy assessment) additional tissue is needed. We find this to be an efficient and cost-effective approach that also parallels a recent shift in the literature from the almost exclusive advocation of CNB over FNA to a renewed recognition of the benefits of FNA, including the value of FNA compared to, and combined or in tandem with, CNB.^1,3-5,7,8-18 Thus, should you encounter problems regarding the utility of FNA versus CNB, a discussion among pathologists and radiologists about the advantages of doing both may be helpful. A reasonable alternative, if it is possible, is to limit adequacy evaluations of CNBs and FNAs to pathologists in the group who practice cytopathology.

References

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