Diagnostic utility of arborizing stromal meshwork fragments in mucinous tumors

Arborizing stromal meshwork fragments (ASMFs) have been proposed as a useful clue to differentiate mucin associated with mucinous adenocarcinoma from contaminating mucus during endobronchial ultrasound-guided transbronchial needle aspiration. Our aim was to retrospectively review cytology cases with mucinous material to determine the utility of ASMFs in diagnosing mucinous tumors.

Diff-Quik stained smears from archival cytology cases (N = 40) were reviewed, including adenocarcinomas with mucinous features, cystic mucinous neoplasms, and control cases with mucin contamination. Specimens were procured by image-guided fine needle aspiration (FNA) (16 cases), endoscopic ultrasound-guided FNA (22 cases), pathologist-performed FNA (1 case), and fluid drainage (1 case). All cases were reviewed for ASMFs, which were defined as metachromatic, spidery extensions with frayed edges within a background of mucinous material.

ASMFs were identified in 4 (10% of cases, 14% of adenocarcinomas) cases of metastatic gastrointestinal mucinous adenocarcinomas in various locations (liver, lymph node, lung, and bone), but absent in mucin contamination. ASMFs in Diff-Quik stained smears were magenta-colored and corresponded to intervening stroma between dissecting mucin in the tumor. Nonarborizing desmoplastic stroma, inspissated mucus, cartilage fragments, transgressing vessels in renal cell carcinoma, and mucus-like material in pancreatic pseudocysts can morphologically mimic ASMFs.

These data show that ASMFs may be encountered in some (14%) cases of adenocarcinoma with mucinous differentiation. When present, ASMFs can be diagnostically helpful to differentiate adenocarcinoma with mucinous features from contaminating mucus, if reliably distinguished from mimics. Diagn. Cytopathol. 2016;44:805-810. © 2016 Wiley Periodicals, Inc.