14.3 Tangential (TAN) and Rolled Views (RL, RM, RS, RI)

Tangential (TAN): Putting Skin in Profile

A tangential view skims the beam along the skin at a chosen spot so skin and the fat immediately beneath it project at the edge of the image, free of overlapping fibroglandular tissue. Two jobs dominate ARRT items:

1. Prove calcifications are dermal (in the skin), not intraparenchymal.
2. Put a palpable lump in tangent, usually over subcutaneous fat, so its margins are not buried in dense tissue.

Neither job is accomplished by another whole-breast CC or MLO. You must first know where on the skin the area of interest sits, mark it, and then build the projection around that mark.

Dermal calcification workflow

Skin calcifications are often lucent-centered. They cluster near the inframammary fold, parasternal skin, areola, or axilla, and they may show the tattoo sign — the same geometric cluster on two projections, as if stamped on the skin. When morphology is not enough, prove location:

1. Use a fenestrated (biopsy / alphanumeric) paddle over the suspected skin, from the approach that puts that skin toward the paddle (CC for superior skin, caudocranial / from-below for inferior skin).
2. Place a BB on the skin over the calcifications using the grid coordinates.
3. Reposition so the BB sits at the crest of the curve — the beam is tangent to that skin. Imagine a line from nipple to BB; mound the tissue so that line is parallel to the detector face and the beam skims it.
4. On the TAN image, dermal calcifications sit at the skin line, typically with the BB. Intraparenchymal calcifications remain inside the breast, deep to the skin line.

Label the image RTAN or LTAN. Do not label it RCCTAN, RMLOTAN, or "lateral TAN." Tube angle may resemble those views; the projection name is still TAN. A mole already marked with an open-circle skin marker does not need a TAN to prove it is on the skin — the marker is the proof. TAN is for calcifications or lumps whose dermal versus parenchymal location is the actual question.

Palpable lump in tangent

Place the facility's palpable-mass marker (commonly a triangle) on the lump. Rotate the breast and C-arm so the marker is in profile and the lump is projected over fat just beneath the skin. The radiologist can then see whether a mammographic correlate exists at that skin site. TAN does not replace ultrasound for a palpable finding; it answers a mammographic location question: is there a density at the marked skin, and is it in the skin or in the breast?

Digital breast tomosynthesis has reduced how often TAN is needed just to "unstack" tissue. The exam still tests the 2D logic: if the question is "is it in the skin?", TAN is the view. If the question is "is this one-view density real, and is it upper or lower?", that is a rolled-view problem, not a TAN problem.

Rolled Views: RL, RM, RS, RI

Rolled views do two things. They throw overlapping tissue off a questionable density so a pseudomass disappears. If the finding is real, they tell you which half of the breast it lives in when it is seen on only one projection.

The ACR abbreviation names the direction you roll the tissue you can hold — on CC, that is the superior surface.

Label with laterality + parent view + roll, for example RCCRM (right CC rolled medial) or LMLRS. The roll is a position, not a new beam path. The central ray remains craniocaudal for RL and RM, and remains a 90° lateral for RS and RI. Hold the rolled orientation while you apply compression; if the breast slips back, you have a poorly labeled CC, not a rolled view.

How a finding moves on a CC roll

Think of the breast as two stacked layers. When you roll the top (superior) layer one way, the bottom (inferior) layer goes the opposite way.

Rule: a superior lesion moves with the superior roll. An inferior lesion moves opposite the superior roll.

Worked example: A density is seen only on the CC, slightly lateral to the nipple. You obtain RCCRM (superior tissue rolled medially). The density moves laterally. That is opposite the superior roll, so the finding is in the inferior half. You now know to look in the lower breast on the MLO or 90° lateral, and you can target ultrasound there. If that same density had moved medially on RM, it would be superior — it traveled with the top layer.

If the density vanishes on both RL and RM, it was overlapping tissue (a pseudomass). If it persists and merely changes position, it is a real finding that still needs an orthogonal view before biopsy planning. Rolled views localize a one-view finding; they do not replace CC plus a true lateral for wire localization.

RS and RI from a true lateral

On a 90° ML, the lateral breast is against the detector, so the movable "away" surface is medial. RS rolls that medial tissue up; RI rolls it down. A medial lesion then moves with the roll; a lateral lesion, already against the detector, moves opposite or stays relatively fixed. Use RS or RI when the finding is seen on the lateral or MLO plane and you need to throw superimposed tissue off it, or to decide medial versus lateral when the CC is unrevealing.

Rolled views are harder to reproduce than a small tube angle, which some radiologists prefer for the same unstacking job. For the exam, know the named rolls and the superior-with / inferior-opposite rule on CC. Do not invent a roll code such as "rolled anterior."

Exam traps: reversing superior versus inferior movement; labeling RM when you rolled the top laterally; using TAN to localize a mid-breast finding that is not a skin question; expecting rolled views to replace a true orthogonal pair for needle localization; labeling a TAN as a CC because the C-arm happened to be at 0°.

Exam Tip: Two questions, two views. "Is it in the skin?" → BB plus TAN, look at the skin line. "Is this CC-only density upper or lower?" → RM or RL, then apply with-the-roll versus opposite-the-roll. Mixing those tools is how otherwise good positioning answers get marked wrong.