What causes the teacup sign on mammography?
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Answer:
The teacup sign is the appearance of milk of calcium, calcium precipitated within tiny benign breast cysts, and it depends entirely on the projection. On the craniocaudal view the beam is vertical, so the layered calcium is viewed en face and appears as ill-defined, smudgy, amorphous or round densities that can look suspicious. On a true 90-degree lateral view the beam is horizontal, gravity has settled the calcium into the dependent portion of each cyst, and the layered sediment is seen in profile as a crescentic, linear or concave meniscus, the teacup viewed from the side. Demonstrating this change in appearance between projections is the whole point: calcium that layers with gravity is within cysts and is benign, whereas suspicious calcifications look the same in every projection. Milk of calcium is therefore assessed as BI-RADS 2, benign, and requires no biopsy. A true lateral, not the mediolateral oblique, is essential, because only a horizontal beam demonstrates dependent layering.
Why is it called so?
On the lateral projection the crescent of layered calcium in the base of each cyst resembles the profile of a teacup.
Pathophysiology
Calcium carbonate and calcium phosphate precipitate as a fine suspension within the fluid of small benign cysts in fibrocystic change. The particles are denser than the cyst fluid, so under gravity they sediment to the dependent floor of each cyst. When the X-ray beam is horizontal, as in a true lateral, it passes tangentially through that flat sedimented layer and records it as a sharply defined concave line. When the beam is vertical, as in the craniocaudal projection, it passes through the layer face-on and the same calcium is spread over the whole cyst diameter, producing only a faint amorphous blur.
Alternative names: Milk of calcium, sedimented calcium, layering calcifications
Other associated named signs: Popcorn calcification of an involuting fibroadenoma, rim (eggshell) calcification of fat necrosis or a cyst, rod-like calcifications of secretory disease, and the tram-track vascular calcifications
References
Access all radiology signs posted so far: https://radiogyan.com/radiology-signs/
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