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Sonographic features of breast abscesses with emphasis on "hypoechoic rim" sign.

BACKGROUND
There are only limited reports on the ultrasound (US) features of breast abscess. The purpose of this paper is to review the US features of breast abscess with emphasis on "hypoechoic rim" sign which is more commonly seen in chronic abscess.


METHODS
In a period of 10 years, 20,998 patients were referred for breast US examinations. Medical records identified 204 patients in whom breast abscess was diagnosed. All patients were examined using high-resolution real-time US scanners. The initial ultrasound reports and hard copy images were all carefully reviewed. The grading of the echogenicity of the abscess was classified from grade 0 to grade 5. The contours of the lesions were described as smooth, macrolobulated, microlobulated, irregular, zigzag, spiculate or indistinct. The wall thickness was measured to document the presence of "hypoechoic rim" which denoted a wall thickness greater than 2 mm. The associated findings and other acoustic phenomena related to the lesion were recorded.


RESULTS
One hundred and thirty-six patients (136/204) having specific aspiration and/or biopsy/histopathological results were included in the study. All of the 136 patients showed abnormal US findings (100%). Most lesions showed grade 1 or grade 2 echogenicity (117, 86%). The contour of the abscess was usually smooth (42, 31%), macrolobulated (42, 31%), or irregular (22, 16%). A hypoechoic rim was noticed in 18 lesions (13%). Focal skin thickening was chiefly noticed in 91% of superficial abscesses (39/43) and 17% of intramammary abscesses (14/84). Diffuse skin thickening was exclusively evident in the breasts coexisting with mastitis. Hypoechoic interstitial streaks were not a common finding (7%), occurring in acute abscesses. The other findings included surrounding hypoechoic amorphous tissue (26%), posterior wall enhancement (71%), distal enhancement (60%) and lateral shadows (57%).


CONCLUSIONS
US plays an important role in confirmation of the clinical diagnosis of breast abscess and aids significantly in the management of inflammatory breast diseases. Presence of the hypoechoic rim surrounding a fluid space or a central area of low-level echoes (i.e., grade 1 to grade 3) is indicative of a chronic abscess.