Diffusion restriction in a superficial breast lesion

Objective: To report the imaging findings of a 22-year-old Asian woman with a freely movable retro-areolar nodule in the right breast, first noticed after a holiday in The Philippines. Material and methods: We preformed clinical examination, mammography and ultrasound with color Doppler imaging. A differential diagnosis of epidermal inclusion cyst, complex cyst, well demarcated carcinoma and echinococcus cyst was proposed. For further differential diagnosis, a MRI of the breasts was performed on a 1.5 superconducting system, with a bilateral breast coil. T2- and T1 weighted images, followed by axial echo-planar diffusion-weighted MRI (DW-MRI) were performed with b values of 0, 500, and 1000 mm(2)/s (trace images and ADC maps). Results: The high signal intensity on T2 weighted images confirmed the cystic character of the lesion. The high signal intensity on T1 FS weighted images can be seen in complex cysts and inclusion cysts, but is less likely in an echinococcus cyst. On DW-MRI there is a marked diffusion restriction in the nodule, which can be seen in complex cysts and inclusion cysts. A well demarcated carcinoma is less likely, unless a tumour with a very high cellularity. Because neither carcinoma nor echinococcus cyst could be ruled out, a surgical excision was performed. Pathological examination revealed normal squamous epithelium with stratification and lamellated keratin, consistent with an epidermal inclusion cyst. Conclusion: We argue that in selected cases DW-MRI can be useful to narrow the differential diagnosis and notable differentiate epidermal inclusion cysts from echinococcus cysts