Mohs Micrographic Surgery: Design and Execution of Secondary Intention

Anatomy and Physiology

SIH was the preferred method for treating high-risk tumors because of its superior control of recurrences before the introduction of the fresh tissue technique for MMS in the late 1960s to early 1970s.[7] In 1983, Zitelli et al evaluated the cosmetic outcomes of SIH across various facial regions and concluded that excellent results could be achieved on concave surfaces, whereas outcomes on convex areas were less predictable. Zitelli further classified the expected cosmetic outcomes of SIH following MMS into 3 categories.

Excellent outcomes were typically observed in what he termed "NEET areas," which included concave nose, ear, eyes, and temple surfaces. Satisfactory outcomes involved relatively flat regions in the "FAIR areas," composed of the forehead, anthelix, eyelids, and the remaining portions of the nose, lips, and cheeks. Variable outcomes were associated with NOCH areas, comprising convex surfaces of the nose, lips, cheeks, chin, and ear helix.[8]

Mott et al later examined the relationship between these categorized anatomic regions and the percentage of wound contraction. The group reported that NEET and FAIR areas exhibited identical contraction rates of 74% and high cosmetic acceptability scores of 97%. In contrast, NOCH areas showed a lower contraction rate of 66% and a reduced cosmetic acceptability of 74%. Except for the temples, most cutaneous defects across NEET, FAIR, and NOCH regions contracted in a fusiform pattern rather than a circular one.[9]

Snow et al identified a well-functioning circulatory system as the most important predictive factor for favorable outcomes in SIH. This finding is particularly relevant given that most MMS procedures are performed in highly vascularized regions such as the scalp and face. Granulation tissue reflects healthy perfusion and is critical in protecting underlying structures, including bone, cartilage, and subcutaneous tissue.[10]

Wound healing progresses through 4 phases: hemostasis, inflammation, proliferation, and remodeling. The proliferative phase includes granulation and contraction and is characterized by the formation of new vessels, deposition of collagen, and epithelial regeneration.[11] Granulation tissue forms through fibroblast-driven collagen synthesis and angiogenesis. This phase is essential for initiating epithelialization, which begins at the wound margins.[12] Prominent granulation typically occurs in areas with dense populations of hair follicles and sebaceous glands. The remodeling phase proceeds once granulation is complete and epithelial migration has begun.

Wound diameter is the second most important determinant of SIH success following MMS. Healing duration is directly proportional to wound size. Early assumptions held that wounds exceeding 20 mm in width could not successfully undergo SIH. However, Mohs later demonstrated that defects up to 100 mm may still heal by this approach, although these wounds exhibit reduced stability during the process.[13]

Since 1980, several authors, including Bloom, Vanderveen, and Snow, have reported that facial and cranial bones denuded of periosteum can still support granulation tissue formation when mechanically stimulated using a chisel or rongeur. This response enables subsequent epithelialization and complete healing. Reports have also noted that granulation tissue typically covers exposed bone for a duration proportional to twice the width of the exposed surface, while full epithelialization requires approximately 3 times that width.

Preserving normal anatomical structures during reconstruction is essential in functionally important regions, such as the hands. SIH facilitates the preservation of extensor function in the fingers.[14] Schwartzman et al emphasized the need to account for the undefined nature of anatomical boundaries when evaluating SIH as a wound care strategy in cosmetically sensitive regions. These boundaries lack consensus, making standardized assessment challenging. Furthermore, post-MMS SIH produces epithelium devoid of skin appendages such as hair follicles and eccrine glands, potentially altering the visual characteristics of the reconstructed area.[15]

Indications

Frederic Mohs was the first to identify SIH as a preferred method for wound healing. In 1983, Zitelli expanded on this foundation by emphasizing that the anatomical location of the defect is the primary consideration when selecting SIH following MMS. Facial regions were categorized according to expected cosmetic outcomes, as previously discussed. Zitelli also observed that older patients generally experience better aesthetic results regardless of wound location. Increased skin laxity in this population favors healing by contraction over reepithelialization and improves the concealment of scarring and contour irregularities.

Building upon the earlier NEET, FAIR, and NOCH classification that links anatomical location to outcome quality, Moreno et al proposed 2 general clinical indications for using SIH. Recommended indications include tumor recurrence after non-MMS treatment, recurrence after MMS, and tumors with distinct biological behavior. Advisable scenarios include high-risk or concave regions, the posterior auricle, temples, and the lip when the vermilion is not involved. Other suitable cases include forehead defects, antihelix involvement, wounds crossing anatomical subunits symmetrically, tumors requiring more than three MMS stages, coagulation disorders, and advanced age.

Skin color should also inform the decision to use SIH after MMS, as hypopigmentation is a common outcome. Lighter skin tones tend to yield better cosmetic results. One of the most frequently treated convex regions using SIH is the forehead. In a case series by Deutsch et al, forehead defects were assessed using a visual analogue scale, where 0 indicated poor, 1 fair, 2 good, and 3 excellent. The average rating for color match between the healing wound and surrounding skin was 2.2, while the overall cosmetic outcome averaged 2.4.[16]

Nonconcave Regions of the Face

In 1994, Snow and colleagues reported a prospective cohort study involving 115 wounds in 91 patients treated between 1982 and 1991 with SIH following MMS for defects with exposed bone on the face and scalp. While SIH was historically limited to concave facial areas, later findings expanded its role. Donigan et al described their experience with SIH after MMS of the lips, observing excellent functional outcomes and good-to-excellent cosmetic results in partial-thickness defects. In 2002, Gloster and colleagues published a case series of 13 patients who underwent MMS involving the lips. Beyond favorable aesthetic results, the SIH group demonstrated lower costs, with savings of up to 50%, more straightforward follow-up for cancer recurrence, reduced postoperative pain, and a low incidence of surgical site infections when wounds were appropriately managed.[17]

Defects With Exposed Bone

In 1992, Becker and colleagues presented a cohort of more than 200 patients with MMS defects involving exposed bone on the scalp and face. The authors concluded that SIH is a safe and effective strategy for managing wounds with exposed bone, particularly on the scalp and forehead, where tissue regeneration was successful without complications.

Eyelid Region

In 2019, Trieu et al reported a case series of 17 patients who underwent SIH after MMS for eyelid defects. A total of 88% of cases resulted in very-good-to-excellent outcomes in both partial- and full-thickness wounds. No major complications, including entropion, ectropion, or corneal scarring, were observed. These findings reinforce Zitelli’s earlier conclusion that the palpebral region is highly favorable for SIH. Trieu et al also supported using SIH in lower eyelid defects involving up to 25% of the lid.[18] In a 5-year retrospective study, Kibbi et al evaluated SIH outcomes in the eyelid region and found that lesions smaller than 1.04 cm² achieved better cosmetic results compared to larger ones.[19] Defects involving the internal canthus were associated with lower rates of favorable aesthetic outcomes.

Extensor Surface of the Hand

In 2012, Bosley et al described a series of 59 cases treated with SIH after MMS on the dorsal surface of the hands. The authors emphasized that SIH preserves normal anatomical structures more effectively than primary closure, which may increase the risk of functional compromise. Preservation of finger extension and hand movement was prioritized over cosmetic concerns in this functionally critical region. Defects exceeding 1 cm on the dorsal extensor surfaces of the fingers were considered unsuitable for primary closure because of the elevated risk of contracture and stricture formation.

Auricular Region

In 2021, Gonzalez and colleagues reported a case series involving 4 patients with secondary auricular cartilage defects treated using the auricular fenestration technique. This approach involved micro-perforation of the cartilage, followed by SIH supported with hydrocolloid dressings. Cosmetic outcomes were comparable to those achieved with grafting, and the authors concluded that the auricular region is a suitable candidate for SIH. [Gonzalez et al, 2021]

In 2015, Hochwalt et al conducted an observational study that included 37 patients who underwent MMS of the helix for various cutaneous tumors. Of the total defects, 29 were managed by SIH and 18 with full-thickness skin grafts (FTSG). Notching, particularly after cartilage removal, was documented by several authors as a potential aesthetic complication.[20][21]

In 2023, Shahwan et al performed a systematic review of surgical repairs following MMS. The review identified 1100 articles, of which 378 cited SIH as the preferred method of reconstruction, compared with 203, 221, and 294 articles that favored skin grafts, flaps, and linear closures, respectively. These findings highlight the persistent underutilization of SIH in clinical practice.[22]

Nasal Defects

In 1983, Zitelli documented excellent cosmetic outcomes using SIH for concave facial surfaces, including nasal wounds in the alar groove. In 2022, Kim et al published a retrospective cohort study involving 96 patients with nasal defects treated by MMS and subsequently managed with SIH. The study aimed to identify factors influencing the cosmetic success of this approach. Smaller defects (<1 cm) were more likely to produce superior aesthetic results, chiefly because larger wounds tend to involve multiple nasal subunits, increasing the likelihood of anatomical distortion. Lesions on the nasal sidewall often extended above the superficial fat plane, and defects addressed in a single MMS stage or fewer were more likely to result in acceptable cosmetic outcomes.[23]

Lower Extremities

In 2024, Renzi et al published a prospective clinical trial enrolling 51 patients treated between November 2017 and July 2020 with post-MMS SIH for defects below the knee. Among these patients, 25 developed clinically infected wounds, while 26 did not. The analysis found no statistically significant correlation between surgical site infections and factors such as microbial pathogen, wound size, number of MMS stages, comorbidities, or type of skin malignancy.[24]

Schoenfeld et al reported a case series involving 25 patients with plantar melanomas managed using MMS and SIH. Compared with FTSG, SIH improved cosmetic and functional outcomes, although healing time was longer (12 weeks for SIH versus 8 weeks for FTSG).[25] The Healing Evaluation After Lower-Extremity Surgery (HEALS) study evaluated 53 patients with malignant tumors of the lower legs treated by MMS and allowed to heal by second intention. The mean healing time was 81 days. Faster wound healing was observed when subcutaneous fat remained intact. This study's results also reported a higher rate of surgical site infections with SIH (30%) compared with other reconstructive options in the same cohort.[26]

Contraindications

Several patient-related contraindications should be evaluated before selecting SIH as the wound healing strategy following MMS. Patients in vulnerable social situations or those unable to adhere to the prescribed wound care regimen should not undergo SIH. Bosley et al concluded that lesion size does not contraindicate the use of SIH on the dorsal surface of the hands. Depending on clinical context and physician judgment, this observation may extend to other anatomical regions.

Gloster and colleagues advised against using SIH when the vermilion-cutaneous junction is involved, due to the risk of significant anatomical distortion. In such cases, wedge excision with layered repair is more appropriate to achieve favorable cosmetic outcomes. Gloster et al also identified several relative contraindications to SIH, including active anticoagulation, use of platelet inhibitors, or both, which may increase the risk of postoperative bleeding in larger wounds. This recommendation contrasts with Moreno et al, who support the use of SIH in patients with coagulation disorders.

In alignment with Gloster and Bosley, Moreno et al emphasized the following relative contraindications that warrant careful consideration when planning post-MMS SIH:

• History of aggressive radiotherapy to the surgical site
• Exposure of major blood vessels or nerves
• Inability to ensure adequate postoperative wound care
• Necessity of immediate return to daily activities
• Likelihood of suboptimal functional outcomes

Gil-Lianes et al added further relative contraindications to SIH. These contraindications include Fitzpatrick skin phototypes IV or greater, vasculopathy, tobacco use, malnutrition, poorly controlled diabetes, and increased risk for endocarditis or prosthetic infection.

Equipment

No additional specialized instruments are required beyond the standard equipment needed for MMS, including scalpels, local anesthetics, syringes, gauze, wound dressings, needle holders, surgical scissors, skin hooks, hemostats, electrocautery, aluminum chloride or Monsel solution, sterile drapes, sutures, surgical marking pens, color-coded tissue dyes, a cryostat for frozen sectioning, and a microscope with appropriate slides and stains such as hematoxylin and eosin. Certain cases may warrant the use of specialized wound dressings containing prophylactic antibiotics or hemostatic agents, based on clinical judgment and patient-specific factors. A purse-string suture technique may also be employed to decrease wound diameter and reduce healing time when appropriate.

Technique or Treatment

No specific technique has been established to initiate the granulation phase in SIH. However, several technical considerations have been described in the literature. Zitelli noted that, regardless of size, depth, or degree of tissue, nearly all surgical wounds may be suitable for SIH. Semiocclusive dressings have been recommended to enhance healing, particularly in areas with exposed cartilage or bone. Although MMS defects smaller than 2 cm are generally managed using primary closure, flaps, or grafts, provided no contraindications are present, Gloster suggested in a 2002 publication that defect size alone should not preclude the use of SIH after MMS.

Kircik et al evaluated hemostatic options for SIH in patients who underwent MMS. In the study, group 1 received a potassium-based salt preparation, while group 2 was treated with a sterile, compressed surgical sponge. No significant differences were observed between groups regarding ulceration, inflammation, necrosis, desquamation, contact dermatitis, or other cutaneous adverse effects. However, group 1 demonstrated reduced scarring and erythema.[27]

Sams et al described the bolster dressing as an alternative approach for post-MMS SIH. Although traditionally used in skin grafts, this dressing consists of an antibacterial or gauze, layered with cotton balls and antibiotic ointment or petroleum jelly. The gauze is secured to the wound margins using a continuous suture technique applied in sections. The remaining suture is then tied over the gauze and cotton ball layers, providing compression and containment. According to Sams et al, this technique offers multiple advantages, including preventing postoperative bleeding, minimizing patient manipulation, and maintaining a moist wound environment.[28]

Moreno et al recommended simplified wound care using physiologic saline for cleansing, dry gauze for mechanical debridement, and hydrocolloid dressings when available. Petroleum jelly and gauze are preferred in the absence of hydrocolloids. Dressing frequency and type should be adjusted to the patient’s clinical needs and wound characteristics.

Becker advised against early decortication of wounds with exposed bone; however, in cases where no granulation tissue forms after several weeks, selective decortication of the bone may be performed to stimulate granulation. This approach was not associated with an increased risk of osteomyelitis. In certain cases, SIH may be complemented with a delayed intervention involving application of a partial-thickness skin graft over mature granulation tissue. This strategy requires periodic follow-up to monitor progress and outcomes. Gonzalez et al monitored patients receiving SIH treatment with evaluations at 24 hours postoperatively and then weekly for a month. Subsequent follow-ups were conducted at 3, 6, and 12 months to assess healing and long-term results. 

Other surgical and nonsurgical techniques are frequently combined with SIH following MMS. Defects involving 2 or more cosmetic subunits of the face are more often considered for combined surgical approaches. Among the most commonly applied techniques are purse-string closure and partial primary closure. A second-stage surgical intervention may also be considered for scar revision. This procedure is generally less morbid because the SIH process reduces the overall size of the wound.

When used with SIH, the purse-string suture technique has significantly shortened healing time, with reductions ranging from 40% to nearly 100%, depending on the degree of tension applied. In addition, postoperative resurfacing using carbon dioxide or long-pulsed erbium-doped yttrium aluminum garnet lasers has been reported to enhance cosmetic outcomes in areas where spontaneous epithelialization is unlikely or incomplete.[29] Some study results have also demonstrated that adding skin columns, either as allografts or xenografts, may accelerate the healing process and further decrease total healing time.

Complications

Overall, complication rates associated with SIH are low, estimated at less than 3%. A 2019 retrospective observational study involving over 1000 patients treated with MMS for various conditions reported that individuals undergoing SIH were more likely to contact their clinician postoperatively than those treated with flaps or grafts. However, this increased contact frequency was not associated with higher complication rates.[30]

Several factors may interfere with the wound healing process. In general, wound diameter and infection are the most frequently cited causes of delayed healing. Snow et al identified specific contributors to complications and delays in SIH following MMS, including open defects adjacent to the nose or exposed sinus cavities, prior radiation therapy, and postoperative manipulation of the surgical site. Despite these concerns, Kim et al noted that granulation tissue rarely becomes infected.

Sams et al reported in 2004 that the infection rate associated with SIH was approximately 0.2% when antibiotic dressings were used. Without antibiotic dressings, infection rates ranged from 2.5% to 4.3%. More recent data, however, suggest that infection risk for post-MMS SIH may reach up to 10%. Moreno et al recommended the use of prophylactic antibiotics in cases involving high-risk anatomical sites such as the oral cavity, nasal vestibule, axilla, perineum, and plantar surfaces, as well as in situations where breaks in aseptic technique have occurred. Nevertheless, recent evidence has not demonstrated significant differences in surgical site infection rates, supporting the routine use of prophylactic antibiotics in SIH.

Common complications associated with SIH vary by anatomical region and are often related to differences in healing time caused by trauma or mechanical stress specific to each site. Lip defects, for example, are subject to frequent movement during speech and mastication, which can prolong healing. Gloster et al noted that lip reconstruction presents distinct challenges due to its proximity to large vessels and the oral cavity, increasing the risk of both local and systemic infection. Retraction of the vermilion border also remains a significant concern in these cases. Moreno et al identified the most concerning complications in the eyelid region, which include ectropion, eyelid notching or webbing, and trichiasis.

In the context of SIH applied to the hands, Bosley reported no significant complications following post-MMS SIH. This finding contrasts with more commonly observed complications in this anatomical area when primary closure is used, such as hematoma, stricture formation, dehiscence, and infection. Hochwalt et al reported slightly prolonged postoperative pain in patients treated with SIH of the helix compared to those treated with FTSG. However, this difference was neither statistically nor clinically significant (mean 2.3 days, standard deviation= 2.1, P = 0.22).

Miller reported that deep surgical defects often heal with prominent hypopigmentation and atrophic scarring, particularly when the wound extends to the subcutaneous tissue or deeper layers. Additional complications include bone necrosis, osteomyelitis, hyperplastic granulation, and chronic pain. Arrested SIH, although uncommon, represents a clinically significant complication characterized by failure to initiate the proliferative phase of wound healing. Affected wounds appear glossy and lack granulation tissue.

Nonsteroidal anti-inflammatory drugs have demonstrated efficacy in inducing the proliferative phase in these cases, suggesting a critical role for arachidonic acid in the underlying pathophysiology. Despite these concerns, several advantages have been identified with SIH following MMS. These benefits include improved surveillance for tumor recurrence, absence of seroma or granuloma formation, elimination of risks associated with graft or flap failure, and a reduction in the need for complex reconstructive procedures.

Clinical Significance

Several studies' results have evaluated cosmetic and functional outcomes in post-MMS SIH. However, publications specifically assessing quality of life after SIH are limited. Stebbins et al published a letter to the editor summarizing over 10 years of experience from the Department of Dermatology at Vanderbilt University. In this letter, the authors concluded that although no definitive recommendation could be made, SIH appeared equivalent to other closure methods regarding patient satisfaction and cosmetic outcomes.

Findings by Hochwalt et al were consistent with those of Stebbins. In their series, SIH and full-thickness skin grafting demonstrated comparable cosmetic results based on visual assessment scores of postoperative photographs reviewed by blinded Mohs surgeons. Patient satisfaction was also reported to be similar across both treatment groups. Despite these positive findings, important limitations of post-MMS SIH include prolonged healing duration, delayed return to daily or occupational activities, and psychological distress related to the presence of an open wound.

Regarding patient-reported experience with SIH following Mohs surgery, a recent survey conducted in the United Kingdom evaluated nearly 70 patients treated with SIH between 2018 and 2019. The mean satisfaction score was 4.3 on a Likert scale ranging from 1 (least satisfied) to 5 (most satisfied). Perception of wound healing time received a mean score of 3.7, where 1 represented "too long" and 5 "very short." The majority of respondents indicated a willingness to undergo SIH again if indicated [Gajebasia et al, 2022].

In summary, SIH following MMS remains an established yet underutilized wound healing alternative. Clinical evidence has demonstrated that SIH yields excellent cosmetic and functional outcomes, comparable to those achieved with other surgical repair methods. Additional advantages include improved surveillance for tumor recurrence and reduced risk of anatomical distortion in anatomically sensitive regions.

Enhancing Healthcare Team Outcomes

Individualizing patient care is essential in surgical decision-making, particularly in determining how each procedure is managed. The choice of surgical closure technique, including whether SIH is appropriate, should consider factors such as anatomical location, patient age, comorbidities, and recurrence risk. Study results have demonstrated that SIH is a well-tolerated and effective option following MMS and should be considered when clinically appropriate. Recent reports have also highlighted high levels of patient satisfaction with SIH after MMS—an important consideration, particularly because MMS is often performed in cosmetically sensitive areas.

Additionally, SIH offers a cost-effective alternative that may contribute to healthcare system savings. This economic advantage could improve access to treatment in uninsured communities, where out-of-pocket payment is often the most feasible option. Anderson et al highlighted several additional benefits of SIH, including fewer postoperative activity restrictions due to the absence of wound dehiscence risk, lower incidence of hematoma, and improved surveillance for tumor recurrence.

SIH has been widely used following MMS since the procedure was first introduced. When applied to appropriately selected patients, SIH provides a safe and effective healing method without introducing additional ethical concerns. Post-MMS SIH also facilitates interprofessional collaboration during the healing process. Nurses, pharmacists, general clinicians, and dermatologists can all contribute meaningfully to wound care. Sometimes, family members may be trained to assist with at-home dressing changes and monitoring. This coordinated approach minimizes errors, reduces delays, and enhances patient safety, ultimately supporting improved outcomes.