Table 2.

Differential diagnosis of breast pilomatrixoma

Lesion	Imaging modality
	Mammography	Ultrasound	MRI
Skin calcifying lesions (seborrheic keratosis, inclusion cysts)	Well circumscribed superficial mass. Heterogenous calcifications.	Inclusion cysts have a solid or hypoechoic appearance with or without hyperechoic spots due to calcifications. Surrounding vascularity may be seen if inflammation is present.	T1WI: hypointense cystic component. T2WI FS: hyperintense cystic component. T1 C.E.: rim enhancement when inflammation is present.
Fibrocystic changes (usual ductal hyperplasia, adenosis, apocrine metaplasia)	Circumscribed lobulated low density mass with pleomorphic calcifications. Clustered pleomorphic, punctate or amorphous calcifications without mass.	Simple, complicated, clustered cysts or complex cystic and solid masses showing scattered echogenic foci due to microcalcifications and fibrosis.	T1WI: cysts typically isointense to parenchyma. Variable signal when cysts contain proteinaceous or hemorrhagic fluid. T2WI FS: hypointense to hyperintense signal due to the content of the cysts. T1C.E. FS: possible smooth rim enhancement of cysts when inflamed. Scattered and diffuse foci (< 5 mm) of enhancement.
Lobular neoplasia	Amorphous calcifications. Spiculated mass or architectural distortion. Multifocal/multicentric lesions.	Irregular hypo- to anechoic mass with or without hyperechoic spots due to calcifications.	T1 C.E. FS: non-mass ductal enhancement or irregular enhancing mass.
Papilloma	Oval or round mass centrally or peripherally located with/without clustered pleomorphic calcifications.	Intraductal mass near nipple with lobulated margins. Dilated ducts around the lesion. Internal vascularity on Doppler analysis.	T2WI: hyperintense duct with intraductal hypointense mass. T1C.E. FS: variable weak enhancement to malignant enhancement profile.
Fibroadenoma	Oval or lobulated mass with/without coarse calcifications (clustered or “pop-corn” shaped).	Hypoechoic circumscribed oval mass with/without internal hyperechoic spots.	T2WI FS: isointense with parenchyma or moderately hyperintense when myxoid. T1 C.E. FS: oval or lobulated mass showing generally rapid, homogeneous intense enhancement.
Fat necrosis	Round, oval or lobulated radiolucent mass. Pleomorphic calcifications. Spiculated or irregular mass.	Anechoic/irregular hypoechoic/complex cystic/solid mass. Posterior shadowing once fibrosis and calcifications develop. Internal flow may be seen up to 6 months after surgery due to granulation tissue.	T1WI: high signal. T2WI FS: low signal with fat suppression. T1 C.E. FS: thin rim of peripheral enhancement may persist up to 18 months post-surgery. Rarely contrast enhancement may persist for years.
Invasive ductal carcinoma (IDC)	Dense mass with spiculated/lobulated margins. Focal asymmetric mass/distortion. Clustered irregular, branched, pleomorphic calcifications.	Irregular hypoechoic mass with posterior shadowing. “Taller than wide”. Architectural distortion with/without hyperechoic halo Rarely lobulated, rounded hypoechoic nodule.	T2WI FS: usually hypointense focal mass if visible. Central necrosis can be hyperintense. T1 C.E. FS: usually rapid and intense enhancement. May show rim enhancement, internal enhancing septations and rapid washout.
Pilomatrixoma	Round, lobulated nodule with pleomorphic, irregular microcalcifications.	Hypoechoic nodule with lobulated/irregular margins and hyperechoic internal spots.	No data available.