Atlas of breast cancer early detection

An ultrasound beam may penetrate a lesion with no posterior features or it may be attenuated and scattered, producing posterior shadowing. The density of the tissues through which the sound waves travel determines the posterior features seen. When ultrasound waves pass through a lesion completely, they cause posterior enhancement, as is seen in a clear simple cyst that allows all the sound waves to pass and produces strong posterior enhancement. When ultrasound waves are not able to pass through a mass lesion, either partially or completely, it causes posterior shadowing. Posterior shadowing is seen in malignant masses, postsurgical scarring, calcifications, or fibrotic scarring. No posterior features are seen in benign lesions such as fibroadenomas or phyllodes. Note that no posterior features can also be seen in certain histological types of breast cancer, such as mucinous and medullary carcinoma.

The sound transmitted through a solid mass depends on the amount of the fibrotic tissue in the mass. Thus scirrhous carcinomas, which are gritty to cut, show strong posterior acoustic shadowing on imaging with no transmission of sound waves.

Posterior shadowing limits the evaluation of deeper breast structures.

No posterior features

Posterior enhancement

Posterior shadowing

Combined posterior features