[399] Fine Needle Aspiration Biopsy Is a Sensitive Diagnostic Tool for Myxoid Lesions: A Cytohistological Review with Emphasis on Ancillary Studies and Diagnostic Pitfalls

SE Monaco, W Khalbuss. University of Pittsburgh Medical Center, Pittsburgh, PA

Background: The fine needle aspiration biopsy (FNAB) diagnosis of myxoid lesions in soft tissue and bone can be challenging due to overlapping clinical, radiological, and cytological features. The aim of this study is to review benign and malignant myxoid lesions diagnosed by FNAB, to highlight the diagnostic pitfalls, and to assess the utility of ancillary studies.
Design: Myxoid lesions in the soft tissue and bone, diagnosed by FNAB between January 2004 and December 2007, were retrospectively retrieved and reviewed. The cytological material, ancillary studies (immunohistochemical and cytogenetic/FISH studies), and available histological follow-up were analyzed.
Results: A total of 40 cases (5%) of myxoid lesions were identified from 862 soft tissue and bone FNABs, including 26 (65%) malignant lesions and 14 (35%) benign tumors/lesions. The most common malignant neoplasms were myxoid liposarcoma (n=8), metastatic mucinous adenocarcinoma (n=6), and malignant fibrous histiocytoma/myxofibrosarcoma (n=6). The most common benign entities were myxoma (n=5), myxoid fibrolipoma (n=2) and ganglion cysts (n=2). The diagnostic pitfalls on cytology included the reactive myxoid changes surrounding neoplasms, the edematous background of seroma and the cartilaginous background of chondroid lesions (misinterpreted as myxoid background), in addition to pseudo-lipoblast morphology (misinterpreted as lipoblasts). Immunostains were performed in 19 cases (48%) and cytogenetic/FISH studies were performed in 11 cases (28%). Thirty-six cases (90%) had histological follow-up. The correlation analysis between the cytologic diagnoses and histologic follow-up yielded a sensitivity of 100%, specificity of 82%, and diagnostic accuracy of 94% for the malignant myxoid tumors. The six cases of myxoid liposarcoma accurately diagnosed on cytology were positive for t(12;16) or t(12;22) by FISH or cytogenetic analysis. Two false positive cases were interpreted as myxoid liposarcoma on cytology, but were diagnosed on excisional biopsy as schwannoma and hibernoma.
Conclusions: This study shows that FNAB can be helpful in diagnosing myxoid lesions of soft tissue and bone, particularly when used in conjunction with ancillary studies. The presence of myxoid-like material and pseudo-lipoblasts can make the FNAB diagnosis of myxoid liposarcoma difficult; therefore, this diagnosis should be rendered only in recurrent cases or in new cases with FISH confirmation.
Category: Cytopathology

Wednesday, March 11, 2009 1:00 PM

Poster Session VI # 57, Wednesday Afternoon