"Thick Section" Gram Stain Yields Improved Detection of Organisms in Tissue Sections of Cystic Neutrophilic Granulomatous Mastitis.

Abstract

Cystic neutrophilic granulomatous mastitis (CNGM) is an uncommon subtype of granulomatous mastitis featuring epithelioid histiocytes/neutrophils rimming discrete cystic spaces. When present, gram-positive bacteria (typically Corynebacterium species) are identified within these cystic spaces, although they can be difficult to appreciate on tissue sections. Based on pilot gram-stained tissue sections of CNGM cases cut on 6 μm thickness (in which bacterial organisms were more readily identifiable) instead of the traditional 4 μm, a formal comparative analysis of 19 CNGM cases was performed on parallel 6-μm ("thick") vs 4-μm sections from one representative block per case. Biopsies (n = 17) and excisional specimens (n = 2) from 19 CNGM cases were included. Gram-positive palisaded rods were identified in seven cases using 4-μm sections and in 11 cases using 6-μm sections (sensitivity of 37% vs 58% in identifying organisms). Among all seven cases of organisms seen on the 4-μm section Gram stain, the paired 6-μm section Gram stain showed a higher number of and more readily identifiable bacteria. Thick section Gram stain of representative tissue blocks performed at 6 μm improves both detection rate and ease of identification of gram-positive organisms in CNGM.