• Patient selection

Relevant history should be obtained, including any history of prior hypertrophic scarring, keloids, allergies, or herpes simplex virus infection. Before performing CROSS, preconditioning the skin with agents such as tretinoin cream are not recommended due to the risk of unpredictable and excessive TCA penetration. A history of drugs that depress adnexal glands, such as isotretinoin, is a relative contraindication to medium to deep chemical resurfacing because of the increased risk of developing hypertrophic scars. However, we believe that a drug history of isotretinoin is not a contraindication and does not influence the clinical results because CROSS spares the adjacent normal skin.

• Expected benefits

After five or six courses of treatment, about 80–85% of the patients experience good clinical responses using 65% TCA, whereas 90–95% of the patients present with good clinical responses using 100% TCA. To achieve a pronounced clinical improvement, five or more courses of CROSS treatment must be delivered at a 4–6week intervals. According to the results of an animal study, treatment using the CROSS method is more effective than simple application of TCA in activating fibroblasts in the dermis and increasing the amount of collagen. These changes were more prominent in the areas treated with a CROSS method, particularly when 100% TCA was used, than the areas treated with simple application of TCA.

Traditionally, due to higher rate of pigmentary or scarring complications in Asian skin, many dermatologists use one or two TCA applications of lower concentration, 10–30%, using a cotton-tipped applicator until even white frostings form. However, multiple, deep, and firm applications are needed to treat a single scar using the CROSS method in contrast to a single or double simple applications in the traditional method. While more effort and time are needed compared to conventional chemical resurfacing methods, the CROSS technique is being widely used due to the superior clinical results, rapid healing time, and lower complication rate.

Major side effects, such as persistent erythema, permanent hyperpigmentation, hypopigmentation, herpes simplex flare-up, scarring, or keloids, have not been reported at the treatment sites when using 65% TCA CROSS treatment. Even when 100% TCA was used, only transient side effects have been noticed; posttreatment erythema, which usually fades over 2–8 weeks, and transient postinflammatory hyperpigmentation, which spontaneously disappears in 6 weeks.

A split-face trial, in which one side of the face was treated with the nonablative 1550 nm erbium-doped fractional laser and the other side treated with the CROSS method, has been undertaken. In rolling-type acne scars, the objective and subjective improvement rates have been reported to be significantly higher in the sides treated with nonablative erbium-doped fractional laser than the CROSS method. However, in ice pick type of acne scars, there have been no statistically significant differences between the nonablative erbium-doped fractional laser and the CROSS treatment sides. In the CROSS sides, grades of pain were significantly less than that of the sides treated with laser. However, downtime and duration of erythema were reported to be longer in the sides treated with the CROSS method than with the nonablative erbium-doped fractional laser.

• Equipment

TCA with various concentrations (% weight/volume, unbuffered) can be purchased (e.g., Sigma-Aldrich, St. Louis, MO) or made by order in a local pharmacy. Clinical efficacy is more pronounced with higher concentrations of TCA. Usually, sharpened wooden applicators are used for CROSS and cotton-tipped wooden applicators are more suitable for the treatment of large and multiple scars (Figure 10.1, Table 10.2).

Figure 10.1 Sharpened wooden applicators (created by shaving the end of a cotton tip applicator to a point with a 10-blade)

Table 10.1 Summary of expected clinical course in CROSS treatment

When a large area or numerous enlarged pores have to be treated, multiple repetitive dipping of the wooden applicator in TCA is required which results in the prolongation of the treatment time. Therefore, to shorten the treatment time, we use a method using a 1 mL syringe and a fine-gauge needle as described below. Firstly, a 1 mL syringe is filled with 0.1–0.2 mL of 100% TCA. Secondly, a disposable fine-gauge needle, preferably a 30- or 31-gauge needle for acne scars and a 33-gauge for enlarged pores (Figure 10.2) is inserted. Thirdly, remove the piston gently with caution to prevent spilling of TCA along with the piston (Figure 10.3).

Figure 10.2 A 1 mL syringe is filled with 0.1 mL of 100% TCA and a disposable a 30-gauge needle is used

Figure 10.3 Removal of the piston gently with caution

However, despite its convenience and effectiveness, it is difficult to regulate the flow of TCA from the needle tip compared to a TCA-soaked wooden applicator. To address this problem, the 31-gauge, 8 mm needle on a 1 mL insulin syringe can be gently bent using a mosquito forceps (Figures 10.4–10.6). The flow rate of TCA can be regulated according to the individual needs by the degree of the needle bending and therefore controlling the resistance to the flow.

Figure 10.4 Gently bending a 31-gauge, 8-mm needle on a 1-mL insulin syringe using a mosquito forceps

Figure 10.5 Needle on an insulin syringe bent for CROSS

Figure 10.6 Bent needle of an insulin syringe (lower) compared with a straight needle of an insulin syringe (upper)

• Treatment algorithm

Local anesthetics or sedation are not required for the CROSS. Generally, patients feel bearable prickling and burning sensation during the procedure. If needed, a topical anesthetic cream, such as EMLA cream (eutectic mixture of 2.5% lidocaine-HCl and 2.5% prilocaine; AstraZeneca AB, Södertälje, Sweden), can be applied prior to treatment. After facial washing with soap, the skin is cleansed with alcohol. Either 65% or 100% TCA is focally applied on the entire depressed area of atrophic scars or enlarged facial pores with pressure using various applicators (Figures 10.7–10.10). The skin is monitored carefully until it reaches a ‘frosted’ appearance after a single application of TCA, which usually occurs within 10 seconds. The frosted appearance is the result of coagulation of epidermal and dermal proteins and is used mainly to monitor the peel depth. After the procedure, the treated areas are cooled down with ice packs to reduce excessive inflammation and pain.

Figure 10.7 Treatment of chicken pox scars with CROSS method by using a sharpened wooden applicator.

Figure 10.8 Frosted appearance of the lesions on the cheek after CROSS treatment by using a sharpened wooden applicator

Figure 10.9 Treatment of enlarged pores with CROSS method by using a straight needle of an insulin syringe

Figure 10.10 Frosted appearance of the lesions on the nose after CROSS treatment by using a straight needle of an insulin syringe

After CROSS, application of ointment-based antibiotics for moisturizing effect instead of an occlusive dressing is recommended. The use of an ointment is discontinued after crust formation in order to avoid the risk of detaching the crust. Use of dressing materials, such as hydrocolloid plaster, is not recommended. Generally, oral prophylaxis consisting of antibiotics and antiviral medications are not needed for the CROSS. Patients are instructed to use a bland moisturizer (e.g., Physiogel^™ Cream, Stiefel Laboratories, Sligo, Ireland or Cicaplast^®, La Roche-Posay, Paris) several times for a few days after treatment to promote wound healing and to minimize dryness. Patients are also instructed to use a broad-spectrum sunscreen and to avoid overexposure to sunlight in order to minimize the formation of postinflammatory hyperpigmentation.

• Troubleshooting

Overflow of TCA should be removed by immediate and careful dipping motion with a Q-tip or gauze. Scarring associated with the TCA overflow is usually prevented by proper management of the crusts. However, post-treatment erythema and transient postinflammatory hyperpigmentation can develop.

Safety should be emphasized when treating periocular areas with high concentration TCA, because the eye is particularly vulnerable to acid injury. Therefore, the use of proper eyewear (goggles, wrap-around glasses, or eye shields) is crucial. If TCA inadvertently gets into the eye, emergency irrigation using 1 to 2 liters of running 0.9 % normal saline for 10 minutes is necessary. Then, prompt referral to an ophthalmologist for proper management should be followed.