Dermatology Coding Alert

Question: One of our dermatologists reports malignant lesion excision by stating the dimension of the excised tissue, not the lesion itself. For instance, the dermatologist documented an “excised diameter” of 11 cm by 3.1 cm for a melanoma on the patient’s left leg. How should we code this?

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Answer: Without talking to the dermatologist, the best code you can choose for this case is 11604 (Excision, malignant lesion including margins, trunk, arms, or legs; excised diameter 3.1 to 4.0 cm). However, you might be under- or over-billing because the dermatologist’s documentation doesn’t give you the information you need.

Take the measure: The dermatologist should measure the lesion before excision and report the dimension of the lesion as the widest diameter, such as 4.5 cm. It’s important to measure before excision because the tissue will shrink after excision when the tension on the tissue is released, and will further shrink as it dries and is placed in formalin for preservation.

Add the margin: The dermatologist should also document the smallest surgical margin required to completely excise the lesion, such as 0.1 cm. To get a more satisfactory closure, dermatologists often excise a skin lesion in an elliptical shape, involving far larger margins in two directions than is required to completely excise the lesion. You can’t use the larger margin to select the CPT® code.

Do this: Select the CPT® code based on the largest diameter of the lesion, plus two times the smallest required margin. You count the margin twice because it occurs on both sides of the lesion. So in this example, you should select the code based on 4.5 cm plus 2 x 0.1 cm, which equals 4.7 cm. The correct code is 11606 (…excised diameter over 4.0 cm).

Notice: The dermatologist could have removed this lesion with the same “excised diameter” as the original example of 11 cm by 3.1 cm. That would be the case if the longer dimension (4.5 cm) paralleled the elliptical cut and the smaller dimension (such as 2.9 cm) paralleled the minimum required margin of 0.1 cm (2.9 + 2 x 0.1 = 3.1). While accurate documentation allows you to bill the case as 11606, reporting only the “excised diameter” means you’re stuck with 11604. The payment difference will cost your practice $138.70 (based on the 2015 Medicare fee schedule national non-facility amount, conversion factor 35.9335). It’s also possible to overbill this procedure as 11604, if dermatologist had used a long elliptical excision to remove a smaller lesion.

Bottom line: The dermatologist must measure and report the largest lesion diameter and the smallest required margin if you want to accurately report these services.