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22 August 2018 - Case of the Week #462

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Case of the Week #462

Clinical history:
A 30 year old woman, with no significant past medical history or travel history, presented with a breast biopsy for a fluctuant mass-like lesion.

Histopathology images:

What is your diagnosis?

Cystic neutrophilic granulomatous mastitis

Test question (answer at the end):
Which of the following statements is true:

A. Cystic neutrophilic granulomatous mastitis only rarely is painful.
B. Gram positive bacilli are identified in >75% of cases.
C. Diagnosis may require matrix assisted laser desorption ionization–time of flight mass spectrometry.
D. Resolution typically takes days.

Special stains:

Gram stain


Granulomatous lobular mastitis is a rare condition of parous, reproductive aged women which can simulate malignancy based on clinical and imaging features (Am J Surg Pathol 2015;39:1440).

A distinctive histologic pattern, initially described in 2011, is termed cystic neutrophilic granulomatous mastitis (CNGM) and is associated with Corynebacteria infection (Am J Clin Pathol 2011;136:424). In a recent study, affected women had a median age of 34 years (range 25 to 49 years), and all presented with a palpable mass. It was often painful and occasionally was BI-RADS5 (highly suspicious for malignancy by radiology, Am J Surg Pathol 2015;39:1440).

Histologically, CNGM is characterized by lobulocentric granulomas with mixed inflammation and clear vacuoles lined by neutrophils within granulomas. Gram positive bacilli are identified in about half of cases within microcystic spaces (Am J Clin Pathol 2016;145:635). However, diagnosis may require culture, 16S rRNA gene sequencing (Pathology 2017;49:405) or matrix assisted laser desorption ionization–time of flight mass spectrometry (J Clin Microbiol 2016;54:1938).

The differential diagnosis includes granulomatous mastitis due to infection (TB, fungi), sarcoidosis, other systemic granulomatous disease or idiopathic (J Pathol Transl Med 2015;49:279).

Treatment consists of surgical excision or debridement, lipophilic antibiotics with sensitivity testing (J Clin Microbiol 2015;53:2895) and possibly steroids. Resolution typically takes weeks to months (Am J Surg Pathol 2015;39:1440).

Test question answer:
Diagnosis may require culture, 16S rRNA gene sequencing or matrix assisted laser desorption ionization–time of flight mass spectrometry.

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