20° oblique projection

20° oblique projection is a troubleshooting projection used in mammography, especially in young women and in follow-up patients.

Technique

The C-arm is turned approximately 20° for a superomedial-inferolateral oblique. With the patient's feet pointing towards the unit and her torso turned slightly outward with the lateral portion of the ipsilateral breast closer to the unit, the breast is placed on the image receptor. The contralateral arm should remain at her side and the ipsilateral hand may grip the lower aspect of the image receptor. Raise the C-arm so that posterolateral tissue comes to rest on the image receptor. Relax the shoulders to better image the upper outer quadrant. To successfully open the glandular structures, try to flatten the breast. Gently pull the breast outward and forward and apply compression.

Clinical application

• demonstrates the entire glandular island with less superimposition than the two projection mammograms
• useful for visualizing the upper outer quadrant of the breast
• preferred position in a follow-up patient of young age
• useful as a third projection when seeking further evidence about a possible abnormality imaged on the MLO projection
• useful as a third view for both the unaffected and the affected breasts in patients who have had breast cancer, as these patients have an increased risk of either developing another carcinoma in the unaffected breast or of recurrence in the affected breast