Fine-needle aspiration of malignant mesothelioma with unusual morphologic features: A case report

Fine needle aspiration biopsy of metastatic malignant mesothelioma with myxoid change and signet ring cells: A case report and review of the literature

Malignant mesothelioma (MM) is a rare neoplasm, which is most commonly encountered in cytology through effusion specimens. Fine needle aspiration biopsy of MM, particularly the epithelioid subtype, can be a source of diagnostic difficulty and may mimic sampling of an adenocarcinoma. This is the first case report to demonstrate abundant extracellular myxoid material and numerous intracellular vacuoles, including signet ring cells, in a fine needle aspirate of metastatic MM. A review of the literature for myxoid change and vacuoles in fine needle aspiration biopsies of MM discloses that vacuoles are found in up to 35% of aspirates of MM, but myxoid change is very rare, reported in <5% of the cases. Cytologists should be aware of this rare morphologic pattern of metastatic epithelioid MM.

Cytomorphologic findings of malignant mesothelioma in FNA biopsies and touch preps of core biopsies

BACKGROUND

Given the lack of recent literature regarding the aspiration cytology of immunohistochemically confirmed malignant mesothelioma (MM), we were interested in reviewing the experience of our institution and establishing useful morphologic criteria.

METHODS

Seventeen aspiration and touch preparation specimens with a diagnosis of MM obtained between 2002-2013 were reviewed along with 20 cases of adenocarcinoma and 16 cases of squamous cell carcinoma. The utility of a number of morphologic features was evaluated.

RESULTS

In most cases of MM, a consistent pattern emerged. Aspirates and touch preps were cellular with irregularly shaped 2 and 3 dimensional clusters. The individual cells were predominantly angulated and had dense cytoplasm with eccentric nuclei. In every case, a minority of tumor cells contained prominent microvacuoles. The chromatin pattern tended to be fine with small nucleoli. While most cases were cytologically monotonous, five cases displayed striking pleomorphism and three cases contained occasional large atypical cells. Two cases contained metachromatic background material. Features which were most useful in discriminating MM from adenocarcinoma were angulated cell shape(P = 0.0002), dense cytoplasm(P = 0.0001), and cytoplasmic microvacuoles(P = 0.0001). In our material, cases of squamous cell carcinoma were often difficult to distinguish from MM. Useful discriminatory features present in squamous cell carcinoma included ink dot nuclei(P = 0.0003), a "dirty" cystic, necrotic background (P = 0.0027) and tumor balls with peripheral spindling(P = 0.0041).

CONCLUSION

Most cases of MM have a consistent appearance in core biopsy touch preps and FNAs. Distinguishing MM from adenocarcinoma and squamous cell carcinoma can be facilitated by evaluating a few key morphologic features.