Idiopathic granulomatous mastitis—our experience

Idiopathic granulomatous mastitis (IGM) is a rare benign chronic inflammatory condition of the breast and is most commonly seen in women of childbearing age. The etiology is uncertain, and an autoimmune association has been suggested with the diagnosis usually made by exclusion. The clinical and radiological features often mimic that of breast cancer and hence confirmed early diagnosis is required to avoid misdiagnosis and unnecessary delay in the treatment. The most common clinical presentation of granulomatous mastitis is unilateral palpable breast lump with or without associated pain. The typical ultrasound finding is an ill-defined, irregular heterogeneous, predominantly hypoechoic lesion with multiple tentacles. Histologic features show a well-defined non-necrotizing epitheloid granulomas along with Langhans type giant cells. Imaging features mimic that of breast cancer, and final diagnosis of granulomatous mastitis always requires specific pathologic findings while excluding other causes.


Background
Idiopathic granulomatous mastitis (IGM) is a rare benign chronic inflammatory condition of the breast, first described by Kessler and Wolloch in 1972 [1], and is most commonly seen in women of childbearing age [1]. It is frequently associated with lactation or hyperprolactinemia, and an increased incidence in non-white women has been proposed [2,3]. The etiology is uncertain, and an autoimmune association has been suggested with the diagnosis usually made by exclusion. The clinical and radiological features often mimic that of breast cancer and hence confirmed early diagnosis is required to avoid misdiagnosis and unnecessary delay in the treatment. In addition, the finding of axillary lymphadenopathy seen in some of the patients with idiopathic granulomatous mastitis is concerning as it is also seen in cases of breast malignancy with nodal metastatic disease. Histologically, idiopathic granulomatous mastitis is characterized by formation of well-defined non-necrotizing granulomas [1,4]. In this article, we discuss the clinical manifestations, imaging findings on ultrasound, and histopathological findings of this rare inflammatory condition of breast.

Methods
A retrospective study of pathology records from January 2013 to December 2017 from our institution was performed.
A total of 35 patients were included in our study, out of which there were 34 female patients and 1 male patient between the age group of 24 to 57 years whose diagnosis of idiopathic granulomatous mastitis was confirmed on histopathology.
Clinical records, imaging findings, and histopathology specimens of these patients were reviewed.
As most of the patients (n = 26) were young and less than 30 years old, ultrasound examination of the affected breast was performed using a high frequency transducer (7-10 MHz).
A definitive diagnosis was obtained by USG-guided FNA using 20-22 gauge needle or percutaneous core biopsy using 14 G-10 cm needle, and an average of 3 cores were obtained. Eight patients underwent surgical excision followed by pathological analysis of the sample. All the cytology and biopsy slides were reviewed and various parameters were noted: the presence of granulomas, giant cells, type of inflammatory cells, and presence of necrosis. The histochemical stains, Zeihl Neelson stain for acid fast bacilli (AFB), Periodic Acid Schiff (PAS) stain, and Gomorri Methenamine Silver (GMS) stain for fungus were also reviewed in all cases which were already done at the time of sample analysis.

Results
A total of 35 cases were diagnosed with idiopathic granulomatous mastitis.
The age group ranged from 24 to 57 years with the peak incidence in reproductive age group ranging from 26 to 35 years of age.

Clinical features
The most common clinical presentation was a unilateral palpable breast lump (n = 23) out of which 14 patients presented with lump associated with pain and 9 patients presented with lump without any associated pain. Isolated nipple discharge and external draining sinuses were noted in 5 and 3 patients, respectively. Three patients presented with mastalgia without any palpable lump. One patient presented with pain and swelling in both breasts at 1 month interval first on right side and then left. USGguided biopsy done on the right side revealed features of idiopathic granulomatous mastitis. Ultrasound showed similar appearing lesions in both breasts. Only 2 patients had family history of breast cancer. None of the women had history of specific infection or any systemic disorder.

Clinical features
No. of patients

Unilateral palpable breast lump 23
With pain 14 Without pain 9 Nipple discharge 5 External draining sinuses 3 Mastalgia without any palpable lump 3 Family history of breast cancer 2

Imaging features
The typical ultrasound finding was an ill-defined, irregular heterogeneous, predominantly hypoechoic lesion with multiple tentacles (Fig. 1

Discussion
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 immunemediated 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 nonmass 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   [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 posttreatment 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.

Conclusion
Idiopathic granulomatous mastitis is a rare inflammatory benign breast disease commonly occurring in women of childbearing age with clinical and imaging features similar to inflammatory breast carcinoma. Final diagnosis of granulomatous mastitis always requires specific pathologic findings while excluding other causes.