Cystic neutrophilic granulomatous mastitis

A 44-years-old woman with no significant past medical history and without recent breastfeeding presented with complaints about a 3-week history of left-breast inflammation and pain. At physical examination, left breast was enlarged with a hard mass in the upper quadrants suspicious of malignancy but without axillary lymphadenopathy.

A mammogram revealed a global asymmetry in the left breast. (Fig. 1).
Correlated ultrasound showed a hypoechoic irregular mass with no circumscribed margins, tubular extensions and some abnormal lymph nodes with diffuse cortical thickening. (Fig. 2).
MRI demonstrated enlargement and deformity of the left breast and a heterogeneous mass with little cystic areas. The kinetic map showed increased perfusion of the mass with rapid early contrast enhancement and plateau on the late phase. (Figs. 3-5).
These findings were suggestive of malignancy, therefore a core needle biopsy (CNB) of the lesion and lymph node were performed. Histopathology showed empty cystic vacuoles within lobulocentric granulomas. The vacuoles were surrounded by a rim of neutrophils and a well-defined granuloma composed of histiocytes and multinucleated giant cells. The Ziehl, Gram and PAS were negative. The final diagnosis was cystic neutrophilic granulomatous mastitis (CNGM). Lymph node biopsy was negative for malignancy. (Fig. 6).
The patient was treated with antibiotics (ciprofloxacin) and steroids without clinical improvement.
A new MRI after four months revealed a radiological worsening with an increase of the cystic areas within the mass with restricted diffusion, compatible with abscessing of the mass and the presence of a cutaneous fistulous tract of which the culture was also negative. (Figs. 7-9).
The culture of the fistulous content was also negative. The patient underwent new treatment with methotrexate, and there was a significant clinical improvement after two weeks.

Granulomatous mastitis (GM) is an uncommon, chronic benign inflammatory condition with a variety of causes including infections (bacterial, fungal, mycobacterial), sarcoidosis, autoimmune process and idiopathic. [1-4]
Idiopathic granulomatous mastitis or granulomatous lobular mastitis (GLM) is a GM of unknown aetiology characterised by sterile non-necrotising lobulocentric granulomas. The diagnosis of GLM is made by exclusion of other causes of granulomatous lesions and histological findings. [2,3]
A distinct histological pattern of GLM termed CNGM has been described recently and seems to be associated with gram-positive coryneform bacilli. The species most frequently found are the lipophilic Corynebacterium Kroppenstedtii. [5-9]
The clinical and radiological presentation of CNGM are similar to idiopathic GLM and usually mimic malignancy.
Patients are young parous women of reproductive age with a history of lactation and are more likely to be Hispanic. [6]
GNGM usually presents as a palpable mass combined with signs of inflammation or malignancy.
Mammography usually shows an asymmetric density or irregular mass without microcalcifications. Ultrasound findings include irregular hypoechoic lesions with fluid collection or tubular structures. [7,8]
MRI can show a heterogeneously enhancing mass or rim-enhancing lesions that may also show segmental or regional non-mass enhancement associated. The masses may have ill or well-circumscribed margin and oval or irregular shape. The majority of the lesions demonstrate restricted diffusion and T2 hyperintensity that represents oedema. The kinetic analysis usually shows progressive or plateau pattern of enhancement. MRI may be useful when mammography and ultrasound are inconclusive, to monitor the evolution and to assess the extent of the disease. [3,4,10]
All imaging modalities can reveal accompanying findings like parenchymal oedema, skin thickening, nipple retraction, and lymphadenopathy.
These radiological and clinical imaging findings are non-specific and suspicious of malignancy, therefore a CNB must be done to rule out malignancy.
Histology is characterised by lobulocentric granulomas with mixed inflammation and clear vacuoles lined by neutrophils within granulomas. These vacuoles that represent dissolved lipid show a thin rim of neutrophils that are surrounded by histiocytes, lymphocytes, plasma cells and Langhans giant cells forming granulomas. The cystic vacuoles are not present in all granulomas. Bacteria may be identified in only 1 or 2 vacuoles and never outside of the vacuoles. [5,6,7,8,9]
The histologic and microbiologic identification of Corynebacteria in patients with CNGM can be difficult because the number is often very low and limited to the cystic vacuoles. [7,8]
There is no consensus for the treatment and patients are usually treated with a combination of antibiotics, steroids, and surgery. The recognition of this histologic pattern in a CNB sample and its possible association with Corynebacterium infection, despite the negative result of histologic and microbiologic studies, may help guide treatment. [7,8]

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