Going deeper: Fine needle aspiration cytology of internal organs (Proceedings)
Cytology of internal organs as a diagnostic tool
Fine needle aspiration (FNA) cytology is an excellent adjunctive tool for evaluating internal organs. It is often diagnostic, requires little specialized equipment, and can rapidly provide useful information. While aspiration of internal body cavities, organs, and masses is considered an invasive procedure and has greater risk of complications than does sampling of superficial sites, it often provides diagnostic information that would otherwise require surgery. Current ultrasound techniques allow guided placement into the lesion of question and visualization of the site both prior to and after aspiration which has substantially improved the information that can be gained from cytologic evaluation of FNA samples. However, understanding the limitations of FNA cytology of abdominal organs is equally as important.
The limitations of FNA cytology of internal organs are amplified because of the relatively 'blind' sampling technique, even with ultrasound guidance. The sample may be inadequate because of low cellularity; a limitation often associated with more fibrous tissues or tissues of relatively low parenchymal cell density, e.g., kidney and lung, respectively. Even if cellularity is adequate, the sample may not represent the primary lesion. In contrast to a biopsy sample, FNA does not preserve tissue architecture. A well differentiated malignant neoplasm may not demonstrate morphologic features of malignancy necessary for cytologic diagnosis. However, by combining interpretive expertise with appropriate site selection, ultrasound guided aspirates correlate well with histologic diagnosis,The primary use of cytology of internal organs should be to differentiate inflammatory from neoplastic lesions. Cytology is not as useful as histology for determining the origin of epithelial or mesenchymal cells, however discrete cell tumors can often be accurately diagnosed. The type of inflammation and etiologic agents can be identified.
General approach to cytology of internal organs
Some types of disease processes, such as those with mesenchymal proliferation or fibrosis do not exfoliate well and repeated aspiration is not useful. Cells should be evaluated to determine if they are consistent with the expected sample. If not, the challenge is to determine if the specimen represents the site of interest or is an unexpected finding. Although an organ may be effaced by a neoplastic or inflammatory lesion, another possibility is that non-representative tissue was sampled. This is more likely to occur with 'blind' aspirates but occasionally happens with ultrasound guided FNA.
Inflammatory cells are evaluated as at other sites. Their presence should prompt a search for infectious agents at both low and high magnifications. Small lymphocytes and plasma cells are often present as part of an inflammatory response and lymphoblasts may be seen if long standing inflammation allows the formation of lymphoid follicles. Thus if the lymphoid population is heterogeneous, the presence of lymphoblasts should be interpreted with caution. Caution should be taken when interpreting mesenchymal or epithelial pleomorphism when there is evidence of inflammation, necrosis, or hemorrhage as reactive cells can be moderately pleomorphic in appearance.
Neoplasia can develop from any of the normal cell populations that comprise an organ. Neoplastic changes include anisokaryosis, variable nuclear to cytoplasm ratio, multiple nuclei, coarse chromatin, large variable sized or angular nucleoli, abnormal mitotic, increased cytoplasmic basophilia and the presence of punctate vacuoles. Pleomorphism is a 'hallmark' of neoplasia however some tumors, such as neuroendocrine tumors, are notable for their bland appearance. In most cases, an attempt should be made to categorize neoplastic cells as epithelial, mesenchymal, or discrete (round) although poorly differentiated and anaplastic tumors defy classification.