Mediolateral oblique view

The mediolateral oblique (MLO) view is one of standard mammographic views. It is the most important projection as it allows to depict most breast tissue. 

Adequacy

The representation of the pectoral muscle on the MLO view is a key component in assessing the adequacy of patient positioning and therefore, the adequacy of the film. 

The amount of visible pectoral muscle determines the amount of breast tissue included in the image, resulting in a decisive quality factor, very important to reduce the number of false negatives and increase the sensitivity of the mammography. Furthermore, as most breast pathology occurs in the upper outer quadrant, it is important that this area is clearly visible on MLO views. 

Technique 

The patient is positioned in front of the mammography arm of the hand in question lying at the top of the table top, usually at 45°. There will be a uniform compression on the breast and armpit, making sure that the skin is flat and that there are no skin folds.

It must be noted that the standard 45° is not always suitable for all women.  In certain disease processes, the angle can be altered to between  40° and 60°, to maximize the quality of imaging.  Examples of conditions that require angle change includes scapula-humeral disease, kyphosis, scoliosis, pectus.

Correctness criteria

• nipple well aligned
• pectoral muscle displayed until the level of the posterior nipple line (PNL)
• presence of submammary angle free 
• folds and the absence of artifacts

Errors to avoid

• projected behind the line nipple skin
• inframammary fold not lying visible in mammograms
• overlapping structures
• inclusion of other body parts, e.g. nose, chin, ear, shoulders and hair