Clustered Breast Microcysts

A ‘breast cyst‘ is the most common benign finding in mammograms or ultrasound scans done for breast cancer screening, and as many as 1/3 of all women will develop a cyst at some point in her life.

A cyst is simply an accumulation of fluid within breast tissue, and when it occurs close to the surface and is of enough volume it can form a palpable mass. Sometimes a clinically palpable cyst is called a ‘gross cystic mass‘.

Dr. Halls Dr. Halls
I’ve never heard anyone say ‘gross cystic mass’, ever.

Talking Moose
Talking Moose
Didn’t you write that yourself?

Dr. Halls Dr. Halls
Years ago, when I was young. But I disagree with myself now.


A ‘Microcyst‘ on the other hand, is very small, often less than 2-3 mm. They will only show up on a mammogram or ultrasound, and, they often occur in clusters. Breast clustered microcysts are quite common, estimated to appear in around 6% of all breast ultrasound scans.

cluster of microcysts in the breast

Talking Moose
Talking Moose
Is it lucky to have a cluster of cysts that looks like a 4 leaf clover?

Dr. Halls Dr. Halls
Yes. Yes, that’s correct.


Clustered breast microcysts tend to be observed but not treated

Generally speaking, breast clustered microcysts will not be ‘treated‘ per se, as they are virtually always benign, but will be followed up with annual observation.

Dr. Halls Dr. Halls
Follow-up ultrasound scan, a few times perhaps, but not forever.


Breast microcysts often show microcalcifications

Microcalcifications are not an uncommon finding with clustered breast microcysts.

Although microcalcification brings to mind the possibility of ductal carcinoma in situ (DCIS), luckily the patterns of microcalcification in clustered breast microcysts are very different from DCIS.

Calcifications within clustered breast microcysts tend to develop in ‘layers‘ or ‘sedimentation‘. When these ‘sedimentary‘ calcifications are discovered on a mammogram, it is even more likely that the radiologist will say “do not biopsy, the calcium sediment looks benign“.

breast microcyst cluster ultrasound

Dr. Halls Dr. Halls
This ultrasound of a cluster of microcysts, is the dark area in the middle of the image. Dark is the fluid inside the cysts.


Breast lesions with a combination of fluid and solids is a more complex situation

On ultrasound, clustered breast microcysts may appear as tiny anechoic (dark) round areas, (meaning they don’t reflect ultrasound waves and don’t create echos of sound waves). If the lesion appears to be not entirely made up of fluid, the situation is a bit more complicated. (solid elements might indicate neoplastic cell growth, and would appear to be something more substantial than calcifications).

When the cysts are larger, with ‘thicker‘ portions of the walls, and with indications of some solid particles (most likely floating debris of various kinds on not malignant cells), the cyst might be described as ‘complex‘, and will likely be biopsied.

If some of these more ‘complicated‘ cystic features are present, the radiologist will likely want to make sure that the lesion is not micropapillary ductal carcinoma, which can have a similar appearance. Malignant carcinoma associated with a cyst of microcyst is very unlikely, and usually the comparison of the mammogram and the ultrasound will prove the benign setting.

However, any kind of new fibrocystic change in a postmenopausal women (especially those not taking hormone supplements) will be approached with extra caution, and a percutaneous biopsy is often undertaken.

Breast clustered microcysts are probably benign


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