Idiopathic granulomatous mastitis (IGM) is an uncommon, non-malignant, inflammatory disorder of the breast characterized by the formation of granulomas in the breast tissue. It often presents with symptoms that closely mimic infectious conditions such as acute mastitis or breast abscesses, making diagnosis difficult. IGM is predominantly seen in women of reproductive age, especially those who are postpartum or lactating, although it can occur in non-lactating women as well.

The etiology of IGM remains unclear but is hypothesized to involve an immune-mediated or inflammatory response. It is characterized by the presence of granulomatous inflammation with multinucleated giant cells, which often leads to the formation of breast lumps, pain, and, in some cases, abscess formation. Due to its similarity to acute mastitis, IGM may initially be misdiagnosed, delaying appropriate treatment.

This report presents a case of IGM in a 29-year-old pregnant woman, who presented with symptoms suggestive of acute mastitis but was ultimately diagnosed with IGM after unsuccessful treatment with antibiotics and drainage.

A 29-year-old female in her third trimester of pregnancy (7 months of amenorrhea, expected delivery date: March-April 2025) presented to the outpatient department (OPD) with complaints of pain in her left breast for the last 10 days. She described the pain as localized, with no associated nipple discharge, axillary lymphadenopathy, or external draining sinuses. The patient denied fever or any other systemic symptoms.

She reported a history of similar complaints 7 months prior, for which she had undergone an incision and drainage procedure at a local hospital. There was no significant medical history, and she was not taking any regular medications. She was in good health otherwise, with no history of autoimmune disorders or chronic diseases.

On physical examination, the patient was found to have a tender, firm, and poorly defined mass in the left breast. The overlying skin was normal, and there was no erythema or ulceration. No axillary lymphadenopathy was noted. The right breast was unremarkable, with no lumps or signs of infection.

Figure 1:  Ultrasound showing retroareolar collection.

Figure 2: Ultrasonography showing collection in lateral part of breast.

Figure 3: Incision and drainage of abscesses done with frank pus drained as shown.

Ultrasound Imaging

To assess the extent of the breast involvement, an ultrasound (USG) was performed on the left breast. The ultrasound revealed a heterogeneous, ill-defined area measuring approximately 6.59 x 5.34 x 1.44 cm (volume: 26.5 cc), located in the retroareolar region at the 9 o'clock position. The area showed surrounding fat stranding, indicative of an inflammatory process. There were also regions of soft tissue breakdown with altered echotexture, including hyperechoic and hypoechoic areas, suggesting a possible mastitis or abscess formation. The right breast showed mild dilation of the lactiferous ducts, but no other significant findings were noted. No axillary lymphadenopathy was observed.

A follow-up ultrasound, performed to further evaluate the breast masses, showed multiple ill-defined fluid collections:

• A 26 cc collection in the inner upper quadrant (Retroareolar Region at 10-11 o'clock) with a tract extending downwards.
• A 7-8 cc collection in the upper outer quadrant at 2-3 o'clock, approximately 1.36 cm from the skin.
• A 6-7 cc collection in the lower inner quadrant, approximately 2 cm from the skin (5-6 o'clock).

These findings suggested an inflammatory process with abscess formation in multiple areas of the left breast.

Cytology and Microbiological Testing

Given the clinical presentation and imaging findings, the patient underwent fine-needle aspiration (FNA) of the breast mass. The aspirated fluid was sent for microbiological testing, including bacterial culture. The results were negative for bacterial growth after 48 hours, ruling out a bacterial infection. Repeated fungal cultures, acid-fast bacilli (AFB) staining, and Gene Xpert (CBNAAT) were also negative, suggesting the absence of tuberculosis, fungal infections, or other infectious agents.

The cytology of the aspirated material showed a predominance of neutrophils, with degenerating cells in a hemorrhagic background, which was indicative of an acute suppurative inflammatory process. However, due to the failure of antibiotic therapy and continued worsening of symptoms, further investigation was warranted.

Histopathological Examination

Due to the lack of response to antibiotics and the patient's persistent symptoms, a biopsy of the abscess wall was performed. Histopathological examination revealed granulomatous inflammation, with the presence of epithelioid cells, multinucleated giant cells, and necrotic tissue. These findings were consistent with idiopathic granulomatous mastitis (IGM), confirming the diagnosis.

Management

Upon diagnosis of IGM, the patient was prescribed oral corticosteroids, which are commonly used to reduce inflammation in cases of granulomatous mastitis. However, due to her pregnancy, the decision was made to avoid systemic steroids in favour of more conservative management. The patient was instead treated with antibiotics and antipyretics, but her symptoms continued to worsen.

Given the failure of medical management, a decision was made to proceed with surgical intervention. The patient underwent incision and drainage of the breast abscess under local anesthesia, which led to significant improvement in her symptoms. The patient was closely monitored for any signs of complications such as recurrence of abscess formation or new granulomatous lesions.

Idiopathic Granulomatous Mastitis (IGM) is a rare, benign, and often challenging condition to diagnose. It typically presents with symptoms similar to acute mastitis or breast abscess, including breast pain, tenderness, and the formation of masses. The condition most commonly affects women of reproductive age, particularly in the postpartum or lactating period, although it can occur in non-lactating women as well. The etiology remains unclear, but IGM is thought to be an autoimmune or inflammatory disorder.

The differential diagnosis of IGM includes infectious mastitis, breast abscess, tuberculosis, and inflammatory breast cancer. In this case, the patient initially presented with symptoms consistent with acute mastitis, but the failure to respond to antibiotic therapy and the negative microbiological cultures led to further investigation. The presence of granulomatous inflammation on biopsy confirmed the diagnosis of IGM.

Management of IGM is challenging, particularly in pregnant women. While corticosteroids are commonly used to reduce inflammation, their use during pregnancy is limited due to potential risks to the fetus. In this case, conservative management with antibiotics and drainage was employed. Surgical drainage is often necessary in cases of large or recurrent abscesses, and it can provide significant symptomatic relief.

This case illustrates the diagnostic challenges and complexity of managing idiopathic granulomatous mastitis, especially in pregnant women. The condition’s initial presentation can mimic acute mastitis, and failure to respond to conventional treatments should prompt further investigation. Biopsy and histopathological examination remain essential for confirming the diagnosis. Early recognition and appropriate management, including drainage and possible medical treatment, can lead to a favorable outcome.

The management of IGM in pregnant women requires careful consideration of treatment options to minimize fetal risks while effectively addressing the inflammatory process. This case emphasizes the importance of a multidisciplinary approach, combining surgical, medical, and imaging techniques, to ensure the best possible outcome for both the mother and the fetus.

Nil.

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