Diagnosis:
Cystic breast disease with involution

Findings:
Right Breast: Multiple, rounded, well-circumscribed, smooth surfaced masses demonstrate homogeneous high signal on the proton density fat suppressed sequence (image 1). No enhancement is identified within the lesions on the subtracted images (image 2). Findings are typical for simple cysts.

Study obtained 15 months later demonstrates complete or near-complete involution of all of the previous cystic masses (image 3). One 4mm cyst remains. No contrast enhancement is appreciated within the lesions (image 4).

Left Breast: Multiple, clustered lesions are present within the retroareolar breast parenchyma on the proton density fat suppressed sequence. Signal characteristics are consistent with simple cysts, as seen similarly in the right breast (image 5). No contrast enhancement is demonstrated (image 6).

Study obtained 15 months later demonstrates few small cysts persisting within the same area with normal fibroglandular enhancement, but no enhancement within the lesions (images 7, 8). The majority of the cysts, however, have completely involuted when compared with the previous examination.

Discussion:
Cysts tend to have a variable presentation and may fluctuate in size and symptomatology. Cyclical tenderness may be associated, however cysts typically are asymptomatic. Depending on size, palpable abnormalities may also be appreciated.
The cyclical nature of cystic change is well demonstrated in this case. The study obtained 15 months later demonstrates near-complete involution of the initial findings.
Dynamic contrast-enhanced MRI of the breast can be used as a method of cancer diagnosis as well as differentiating carcinoma from benign disease. This can be especially useful when the underlying fibroglandular tissue is very dense on mammography. Cystic proliferation typically demonstrates homogeneously hyperintense T2 signal characteristics with smooth, non-spiculated margins, as seen in this case. More importantly, contrast enhancement is not demonstrated.
Benign cystic changes may involute or demonstrate interval progression if follow-up imaging is obtained for any reason. In this particular case, the patient’s cystic change decreased over time to near-complete involution bilaterally.

Sources:
Kinkel K, Helbich TH, Esserman LJ, Barclay J, Schwerin EH, Sickles EA, Hylton NM. Dynamic High-Spatial-Resolution MR Imaging of Suspicious Breast Lesions: Diagnostic Criteria and Interobserver Variability. American Journal of Radiology 2000; 175: 35-43
References:

Cardenosa, Gilda. Breast Imaging Companion. Pennsylvania: Lippincott Williams and Wilkins, 2001.