Factors Contributing to Nuclear Bubbling and Clearing Mimicking the Features of Papillary Thyroid Carcinoma
S Ehdaivand, LC Noble, WO Greaves, EN Trudeau, MC Morin, LJ Wang, RA DeLellis. Lifespan Academic Medical Center and Alpert Medical School at Brown University, Providence, RI
Background: The diagnosis of the follicular variant of papillary thyroid carcinoma (FVPTC) depends on the identification of a set of nuclear features, including ground glass chromatin, abundant grooves and pseudoinclusions (PI). Variations in tissue fixation, processing, and sectioning lead to a variety of changes that simulate these features, including nuclear bubbles and disturbed patterns of chromatin distribution leading to nuclear clearing and enlargement. These changes are responsible, in part, for the interobserver variation in the diagnosis of FVPTC. The aim of this study was to identify factors related to the development of these artifacts.
Design: Sections were taken from 10 thyroid adenomatous nodules, 8 formalin fixed for 24 hours and 2 formalin fixed for 1 hour (the latter 2 were essentially alcohol fixed), then routinely dehydrated. Four micron sections were mounted onto Superfrost slides in a 42C waterbath, then air-dried and baked at 65C. Variables tested included incomplete dehydration, use of freeze spray or ammonia water on the block face, varying waterbath temperature, introducing excess water between the tissue and the slide while mounting, varying the air-drying time, and altering the drying method (hot plate vs oven drying). Slides were reviewed for the presence of nuclear bubbles and clearing, as well as cytoplasmic bubbling.
Results: Introducing excess water while mounting the section elicited the most extensive nuclear and cytoplasmic bubbling. Short fixation time, increasing waterbath temperature to 50C, hot plate drying, or immediate oven drying created disturbed patterns of chromatin distribution mimicking nuclear clearing. Incomplete dehydration, freeze spray or ammonia water did not elicit these artifacts.
Conclusions: Short fixation time, excess water introduced while mounting the slide, high waterbath temperature, and incomplete air-drying prior to baking are the main factors that contribute to nuclear bubbling and clearing. In contrast to well-defined PIs, which typically appear eosinophilic with sharply defined margins, nuclear bubbles often appear clear; moreover, they are considerably more common than PIs and are present in adjacent normal thyroid. Disturbed patterns of chromatin distribution and nuclear swelling impart an "empty" appearance to nuclei. Careful attention to tissue preparative methods can circumvent many of the problems associated with the diagnosis of FVPTC.
Tuesday, March 23, 2010 1:00 PM
Poster Session IV # 33, Tuesday Afternoon