Method	Level of evidence	Strength of recommendation
1.1	Diagnostic method
1.1.1	Ultrasound[2]	I	A
1.1.2	Detection of pathogenic microorganisms[3]	II	A
1.1.3	Pathological diagnosis[2],∗	I	A
1.2	Type of biopsy
1.2.1	Core needle biopsy[4,5]	I	A
1.2.2	Vacuum-assisted breast biopsy[6]	II	B

^∗On microscopic examination of hematoxylin and eosin-stained sections, periductal mastitis is characterized by greatly dilated ducts filled with pink material, abundant fatty acid crystals, and infiltration of lymphocytes, plasma cells, and neutrophils around the dilated ducts. Granulomatous lobular mastitis manifests as multifocal non-caseating granulomas centered on lobular units of the breast and composed mainly of epithelioid cells, Langhans giant cells, neutrophils, and lymphocytes. They vary in size and may be accompanied by microabscesses.