13.1 Craniocaudal (CC) Positioning

Why the CC is a screening essential

A screening mammogram is four images: right and left craniocaudal (CC) plus right and left mediolateral oblique (MLO). ARRT Procedures 2.A Views tests those projections as a pair, not as two interchangeable pictures of the same tissue. The CC is the superior-to-inferior projection: the C-arm sits at 0°, the image receptor (IR) is horizontal under the breast, and compression is applied from above. Its clinical job is to show posteromedial tissue the MLO is anatomically poor at including, and to give a second plane so a finding can be placed medial or lateral to the nipple.

The positioning standard ARRT still uses is the Clinical Image Evaluation chapter of the ACR 1999 Mammography Quality Control Manual. ACR accreditation still scores positioning from that chapter (the first of eight clinical-image parameters). The ACR Learning Network Mammography Positioning Improvement Collaborative later converted the same ideas into a meets / does not meet table for quality improvement — not the accreditation score sheet, but the language departments use to fail an image.

Set the C-arm, then set height from a lifted fold

Detector height vs seeing the IMF

Rotate the C-arm to 0° before the patient steps in so the detector is horizontal and the beam is vertical. Height is not a remembered number on the column. Lift the breast and elevate the inframammary fold (IMF) with your hand, then bring the detector up to that raised crease. If the detector is too low, the breast slumps, posterior tissue falls off the chest-wall edge, and the nipple points toward the floor. If the detector is too high, the IMF is over-elevated and you lose inferior and posterior tissue — a classic items-style trap.

Hold two facts at once:

• You use the elevated IMF as a height landmark.
• You do not need to see the IMF on the finished CC. An open fold is an MLO criterion. Chasing a visible IMF on the CC usually means the detector is in the wrong place or you have turned the patient into a mock-oblique.

Stance, two-handed lift, and the dropped shoulder

The patient stands slightly off the unit, both feet facing the machine, weight even, hips back, torso leaning in. Shoulders are relaxed — relaxed is not dropped. A dropped ipsilateral shoulder drags posterior tissue off the detector and can project the shoulder, chin, or upper arm over the breast. ACR Learning Network treats "other body parts projected over breast" (contralateral breast, hand, shoulder, chin) as a major fail with no partial credit.

Stand on the medial side of the breast you are imaging. Turn the patient's head toward you (away from the side being examined) so the mandible and ipsilateral shoulder clear the field. With both hands, pull the breast up and away from the chest wall onto the detector and anchor it. Do not let go until the paddle has fully compressed. The same early release that creates camel-nose sagging on the MLO also lets posterior CC tissue sneak back toward the chest wall.

The nipple should point straight at the back center of the detector. That alignment is how you know the breast is not rolled and not exaggerated.

Medial (cleavage / sternal) tissue is the CC's non-negotiable

Cleavage and sternal contact

The medial breast is relatively fixed at the sternum. It cannot be stretched the way lateral tissue can, so on the MLO it is the tissue most likely to be excluded. Therefore the CC must include posteromedial, cleavage, and sternal-contact tissue. Drape the contralateral breast over the corner of the detector so the sternum meets the IR. Skin-to-skin cleavage on the image is the proof you reached midline. If medial tissue is missing on the CC, it is often missing from the entire screening study.

Do not trade medial tissue for a photogenic lateral margin. If far-posterior lateral glandular tissue is still off the detector after a correctly centered CC, add a dedicated exaggerated craniocaudal lateral (XCCL). Do not rotate a "standard" CC until the nipple sits in the medial third of the image.

Lateral tissue without excessive exaggeration

Once medial contact is locked, pull lateral posterior tissue onto the detector as the paddle comes down. Keep the paddle flush with the chest wall so retroglandular fat is not left behind. ACR Learning Network scores CC exaggeration as a minor criterion: nipple midline with no exaggeration meets; a slight medial or lateral offset with no posterior tissue lost partially meets; nipple off midline and lost medial or lateral posterior tissue does not meet.

Pectoralis on the CC is a bonus, not a requirement. The 1999 manual notes that even with correct positioning the pec appears on only about 30–40% of CC images (the Learning Network rounds this to about 30%). Chasing pec on every CC is how technologists rotate laterally, lose cleavage, and still fail the posterior nipple line. Posterior tissue on the CC is judged by the retroglandular fat plane and by PNL, not by whether a strip of muscle happened to come along.

Posterior nipple line: the 1 cm rule

How to measure PNL

The posterior nipple line (PNL) is the only numeric check that the CC included comparable depth to the MLO. Measure from the base of the nipple (from the skin line if the nipple is rolled) back to the pectoralis at 90°. If no pec is visible, measure to the posterior edge of the image. On the MLO, draw from the nipple perpendicular to the anterior margin of the pec, or to the posterior image edge if the muscle is short.

ACR 1999 and the Learning Network agree: PNL on the CC must be within 1 cm of PNL on the same-side MLO. The usual failure is a CC that is more than 1 cm shorter than the MLO, meaning posterior tissue was left on the chest wall. Fix it with a higher-quality lift, correct detector height, sternal contact, and a shoulder that is not dropped. PNL is a Learning Network major criterion: fail it on either breast and the exam fails that collaborative's "all 14 majors" bar.

A matching PNL does not prove you pulled as far as anatomy allows. If both views are equally shallow, both can pass the 1 cm rule and still miss posterior tissue. Always look for retroglandular fat and compare with prior depth.

Nipple in profile, motion, and what the CC is not

The nipple must be in profile on at least one view of each breast (CC or MLO). Ideal is both views; the scored minimum is one per breast. A buried nipple superimposes retroareolar ducts and can hide a retroareolar mass or calcification. If forcing profile on the CC would drop posterior tissue, keep the posterior tissue and obtain a dedicated nipple-in-profile image.

Motion is a major fail with no partial credit. On the CC it usually means the patient breathed, the shoulder crept down, or you released the breast before the paddle locked. Ask for a still breath-hold — not a deep inspiratory chest-lift that pulls tissue out of the field. Left-to-right compression on the same projection should be comparable; a large mismatch is a clue that one side was under-compressed.

CC critique: meets vs does not meet

Use this table when you hang a CC. "Meets" language follows ACR 1999 plus the Learning Network major/minor split. IMF is listed so you remember it is out of scope for this view.

High-yield CC errors

1. Lateral exaggeration that loses medial tissue — nipple migrates medially, cleavage disappears, and a medial cancer can sit off the film.
2. Dropped shoulder — posterior tissue walks off; shoulder or chin may overlay the breast.
3. Motion — blur of ligaments and calcifications; always a major fail.
4. Detector too high or too low — over-elevating the IMF loses inferior/posterior tissue; a low detector lets the breast slump.
5. Letting go before lock — posterior tissue retracts and PNL shortens.
6. Treating IMF visualization as a CC goal — use the raised fold only to set height.

If lateral glandular tissue is still missing after a midline CC that already meets PNL and medial criteria, the next image is an XCCL, not another rotated "CC."