Idiopathic granulomatous mastitis is a rare benign chronic inflammatory disease of the breast. The etiology had been uncertain, and it had been postulated that IGM results from a localized autoimmune response to the retained or extravasated fat- or protein-rich secretion in the breast ducts during childbearing age due to a previous hyperprolactinemia [5]. The response to steroids supports this autoimmune nature of the disease [6]. However, histological features of an immune-mediated inflammation, such as vasculitis and predominantly plasma cell and lymphoid aggregates, are not seen in IGM [7]. Idiopathic granulomatous mastitis is not associated with trauma, specific infections, or foreign material [1].
Idiopathic granulomatous mastitis is most commonly seen in premenopausal women, most often in women of childbearing age. The mean age at presentation in our study was 31 years [8]. The most common presentation was unilateral breast lump with or without pain. The distribution of IGM is usually unilateral, with bilateral cases reported less often, in 1–9% of cases [9,10,11]. Prevalence of peripheral, subareolar, and diffuse IGM lesions of 50%, 25%, and 25%, respectively, has been reported [8, 10].
Imaging features of idiopathic granulomatous mastitis have not been described frequently. It manifests in a variety of non-specific appearances. The most common imaging finding of idiopathic granulomatous mastitis in our study was an ill-defined, heterogeneous predominantly hypoechoic lesion with irregular margins and tentacle-like extensions (Fig. 1) (23/35). The tubular extensions demonstrate that idiopathic granulomatous mastitis insinuates around the breast lobules rather than destroys them [2]. These findings were similar to those previously reported by Han et al. [12], Yilmaz et al. [13], and Lee et al [10]. Nine patients had associated dilated ducts. Doppler ultrasound showed the lesion and the surrounding tissue to be hypervascular (Fig. 1c) as stated by Fazzio et al. [9] and Al-Khawari et al. [14].
Ultrasound is also useful in guiding fine needle aspiration (FNA) and core needle biopsy.
Fazzio et al. [9], Yilmaz et al. [13], and Memis et al. [15] identified a focal asymmetric density as the most frequent pattern. Han et al. [12] described multiple small masses or a large focal asymmetric density. A study in 11 women by Lee et al. [4] showed an irregular ill-defined/obscured mass to be the most common finding. One patient in our study showed an equal density irregular lesion (Fig. 5) with obscured margins, while other patient had normal mammography.
MR findings of idiopathic granulomatous mastitis are variable. Heterogeneous ill-defined masses and non-mass enhancement with mixed kinetics were described by Fazzio et al. [9] as the most common pattern in their study. One patient in our study showed similar findings of regional non-mass-like enhancement with prominent duct with wall thickening and surrounding inflammatory changes (Fig. 6). Irrespective of kinetics, the affected parenchyma demonstrates intense enhancement compared to uninvolved tissue. Another patient showed multiple round to oval well defined lesions appearing predominnatly hypointense on T1WI & hyperintense on T2WI. All these lesions showed peripheral enhancement after the administration of intravenous gadolinium. Surrounding parenchyma showed inflammatory changes. Few non-mass-like enhancing foci were also seen with adjacent focal skin thickening (Fig. 7). These findings were similar to those described by Gautier et al. [2] and Oztekin et al. [16]. In advanced disease, larger fluid collections can be seen interspersed within abnormal enhancement, with or without sinus tracts extending to the skin surface [2]. Involved parenchyma displays restricted diffusion in the majority of cases with consistently lower mean ADC values (1.0 × 10−3 mm2/s) than what is observed for normal breast parenchyma (2.3 × 10−3 mm2/s). Although ADC values in IGM are falsely positive for malignancy, time intensity curves are more benign, consistent with inflammation. Additional MR imaging findings include axillary lymphadenopathy, nipple and/or skin thickening, nipple retraction, sinus tracts, and parenchymal distortion [2, 9]. Importantly, MR provides the best estimate of disease extent and contralateral breast involvement.
Pathologically, idiopathic granulomatous mastitis is characterized by well-defined non-necrotizing granulomas with collection of epithelioid cells, Langhans type of multinucleated giant cells, and lymphocytes with no evidence of microorganisms. The presence of non-caseating granuloma is the characteristic finding in a biopsy. At times, there can be a coalescence of the granulomas and microabscess formation. But usually, these granulomas lack caseation necrosis. The presence of neutrophils and microabscess formation warrants a careful search for fungal hyphae and spores, which again needs to be confirmed by histochemical stains. Foreign body type of giant cells should prompt a search for refractile foreign body material.
It should be differentiated from other causes of chronic inflammatory breast diseases such as tuberculosis, Wegener’s granulomatosis, sarcoidosis, fungal infection, duct ectasias, carcinoma, and fat necrosis, where again granulomas may be the presenting feature under the microscope [17].
Pluguez-Turull et al. [18] described the role of a breast radiologist in the surveillance, pre-surgical, and post-treatment evaluation of HPE-confirmed idiopathic granulomatous mastitis is as follows:
- (a)
Establish the multiplicity and location of IGM lesions
- (b)
Document the size of the lesion(s)
- (c)
Identify abscess formation and the related possibility for intervention
- (d)
Evaluate the treatment response by assessing the stability or interval change in the lesion(s)
- (e)
Identify metachronous disease and local recurrence at imaging surveillance
A definite diagnosis of idiopathic granulomatous mastitis always requires a histopathological analysis since the clinical and imaging features of granulomatous mastitis are very non-specific [1, 8]. As FNA is more easily available and more cost-effective, it is often the first option for tissue sampling and gives faster results than core biopsy. FNA is useful in the initial differentiation of an inflammatory breast process from malignancy. However, biopsy is more superior and specific than FNA in distinguishing malignancy from inflammatory condition and for accurate tissue diagnosis.
