Skin Involvement of Idiopathic Granulomatous Mastitis: Sonographic, Clinical, and Histopathological Features

<b>Objectives:</b> Idiopathic granulomatous mastitis (IGM) is a rare benign breast disease in which cutaneous involvement is insufficiently characterized. This study aimed to evaluate the sonographic, clinical, and histopathological features of skin manifestations in IGM. <b>Methods:</b> We retrospectively analyzed 138 women with biopsy-proven IGM who underwent breast and skin ultrasonography between 2023 and 2024. Clinical cutaneous findings were documented, and 14 patients with visible skin lesions underwent additional punch biopsy for histopathological evaluation. Sonographic and clinical features were stratified according to symptom duration (0-3, 4-6, 7-9, and ≥ 10 weeks). <b>Results:</b> Cutaneous lesions were identified in 84/138 patients (60.9%). Sonographic findings followed a sequential distribution: fibrous echogenicity loss in early disease (11/14, 78.6%), vacuolar structures at 4-6 weeks (11/19, 57.9%), dermo-subcutaneous blurring at 7-9 weeks (9/34, 26.5%), and advanced features such as fistula formation (11/17, 64.7%) and dermo-subcutaneous disruption (11/17, 64.7%) beyond 10 weeks. Clinical findings paralleled imaging, with erythema and papulopustular lesions predominating early (13/14, 92.9%), erythema nodosum peaking at 4-6 weeks (7/19, 36.8%), and ulceration and fistula formation emerging after ≥ 7 weeks (11/17, 64.7% at ≥ 10 weeks). Histopathological analysis of 14 skin biopsies demonstrated nonspecific inflammatory changes without granuloma formation. <b>Conclusions:</b> IGM demonstrates sequential sonographic and clinical cutaneous patterns associated with symptom duration. Early erythematous and papulopustular changes progress to ulceration and fistula formation in prolonged disease. Although supportive in suggesting cutaneous involvement, these features are not diagnostic, and histopathological confirmation remains essential. Prospective studies are warranted to further define the clinical and histological course of cutaneous changes in IGM.