Fine needle aspiration cytology of granulomatous mastitis

Granulomatous mastitis (GM) is an uncommon breast lesion that mimics carcinoma. The fine needle aspiration cytological (FNAC) features of GM have rarely been discussed in the literature. These features are reported in eight histologically confirmed cases of GM.

A retrospective study was undertaken in which a diagnosis of GM had been made on histopathology, and the FNAC slides were reviewed and assessed for the presence of granulomas, necrosis, multinucleated giant cells, and inflammatory background cells. Polymerase chain reaction (PCR) for Mycobacterium tuberculosis was performed on the histological material to exclude tuberculosis.

All cases were confirmed histologically and PCR for mycobacterial DNA was negative. In the FNACs, varying numbers of granulomas composed of epithelioid histiocytes were present in four cases. The same four cases showed giant cells of either foreign body or Langhan's type. No necrosis was noted. Six cases showed many histiocytes, some plump and others epithelioid, in the background. The number of epithelioid histiocytes corresponded to the presence of granulomas. Neutrophils were the predominant background inflammatory cells in most cases (six).

The cytological diagnosis of GM is difficult because the features overlap with other aetiologies, including tuberculosis. Specific features are absent. The absence of necrosis and a predominantly neutrophilic infiltrate in the background favour a diagnosis of GM. This diagnosis should also be considered when abundant epithelioid histiocytes are seen in smears, even in the absence of granulomas. However, the definitive diagnosis of GM depends on histology from fine needle biopsies and negative microbiological investigations.