Mohs Surgery Treatment & Management

Updated: Apr 29, 2022
  • Author: Shang I Brian Jiang, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Approach Considerations

The cornerstone of Mohs surgery is based on the observation that cutaneous neoplasms often grow contiguously with unpredictable, lengthy, rootlike extensions that can spread deeply or laterally from the clinically apparent lesion. When the tangentially oriented Mohs surgery technique is used to examine surgical margins, almost 100% of tumor margins are microscopically examined, as opposed to less than 1% with traditional histologic methods.

A study by Nätterdahl et al of patients who underwent Mohs surgery for BCC indicated that risk factors for complicated Mohs surgery (defined in the study as Mohs surgery requiring three or more stages) include older age, previous tumor treatment with cryotherapy, and more than one prior surgery. The odds ratios for these factors were 1.02, 2.3, and 3.4, respectively. [70]

Traditional tumor excision methods

Traditional methods of tumor excision involve the removal of the clinically evident tumor along with an additional margin of normal-appearing tissue. The additional margin is removed because malignant extensions are microscopic; the malignant extensions cannot be clinically visualized or palpated.

After the tumor is excised, conventional microscopic processing is used to assess the margins of the specimen for residual tumor. Representative vertical sections may be obtained at 2- to 4-mm intervals throughout the specimen by using the bread-loaf method and in each of 4 quadrants by using the quadrant method. When the tissue sample is microscopically seen to be tumor free, the entire margin from which the sample was obtained is also assumed to be tumor free.

However, a tumor that is determined to have clear margins with the use of these methods may actually have fingerlike extensions in the unexamined intervals, because less than 1% of the interface between the specimen and the patient is actually examined histologically. The failure of these methods to permit consistent identification of residual tumor explains the incidence of local recurrence despite the finding of margins that appear to be tumor free (see the image below).

The conventional bread-loaf technique for checking The conventional bread-loaf technique for checking tissue margins by using vertical sections. Less than 1% of the margin is evaluated, as compared with almost 100% of the margin with the Mohs surgical technique. As illustrated here, residual tumor may not be found and may recur.

Various empiric approaches to surgical removal of skin cancers are recommended on the basis of studies of tumor size, type, and histologic subtype; however, these approaches are not always sufficient for complete tumor removal. For example, although 2- to 3-mm margins are often recommended for the treatment of small nodular basal cell carcinomas (BCCs), such narrow margins are not always adequate.

Although Burg et al showed that 5-mm margins are necessary to ensure adequate excision of clinically well-defined BCCs, and 9- to 10-mm margins are necessary for complete removal of morpheaform BCCs and tumors larger than 2 cm in diameter, [71] this approach assumes that tumor growth is symmetrical in all directions, which is frequently not the case, especially with recurrent, large, or infiltrative tumors. Furthermore, wider surgical margins that lead to reproducibly high cure rates may leave functionally or cosmetically unacceptable results, particularly on the face or scalp, which are common sites of skin cancer.

Confocal laser scanning microscopy

The epidermis and part of the dermis can be visualized using a confocal scanning microscope, based on different refractive indices of various structures in the skin. The US Food and Drug Administration has approved these microscopes, and clinical studies for their use in Mohs surgery are under way.

Special stains

In recent years, immunostaining has facilitated the successful removal of a number of cutaneous malignancies. Selective labeling of malignant cells can help to more clearly delineate tumors that may be masked by inflammation; this is helpful when a tumor presents with subtle or nonspecific histologic features.

Examples of immunostaining techniques include antikeratin for BCCs and squamous cell carcinomas (SCCs), anti-CD34 for dermatofibrosarcoma, MART-1 for malignant melanoma, and anti–carcinoembryonic antigen (anti-CEA) for extramammary Paget disease (EMP). However, the disadvantages and limitations of incorporating immunohistochemistry into a Mohs surgery practice include the additional processing time and cost involved, as well as more time-consuming interpretations.

Nevertheless, progress continues to be made in an effort to make immunostains more cost effective. For example, Kimyai-Asadi and colleagues reported a 20-minute rapid MART-1 immunostaining protocol that has significantly improved the efficiency in the workflow. [52] As research and development advance, the use of immunohistochemistry in Mohs surgery is expected to become a more widely used technique.


Fresh-Tissue Technique

Although the process of performing the fresh-tissue technique of Mohs surgery varies according to individual practices among physicians, the basic procedure is similar, as follows:

  • Step 1: The surgeon begins by outlining the tumor with a marking pen prior to injecting the area with local anesthesia (0.5-2% lidocaine with epinephrine 1:100,000 or 1:200,000), because the anesthesia may distort anatomic landmarks and the tumor's true extent.

  • Step 2: After waiting several minutes for maximal anesthesia and vasoconstriction, some surgeons use a curette to debulk the tumor, which tends to be softer than the surrounding normal skin, to better delineate its extent; however, this method may be less effective with morpheaform basal cell carcinomas (BCCs) or other nonfriable tumors.

  • Step 3: To allow precise orientation of the specimen, some surgeons tattoo the tumor with a substance such as methylene blue, whereas others use hatch marks, sutures, staples, or superficial scalpel incisions at the periphery of the specimen.

  • Step 4: The tissue is then excised with the scalpel angled 45° to the skin to bevel the edge to facilitate histologic processing; the excision is continued circumferentially around the tumor at a 45° angle and under the skin parallel to the surface so that the deep margin is excised horizontally.

  • Step 5: Hemostasis is achieved by using spot electrodesiccation, suture ligatures, oxidized cellulose (eg, Surgicel, Oxycel), pressure, or other methods.

  • Step 6: A 2-dimensional map of the patient's skin defect is drawn, incorporating the hatch marks, sutures, staples, or incisions that were used to orient the specimen.

  • Step 7: The tissue is divided along the tattooed or scored lines and inverted (dermis turned up); then, the edges of the specimen are color-coded with tissue dyes (see examples in the images below).

    A Mohs surgery specimen is carefully separated int A Mohs surgery specimen is carefully separated into 4 quadrants.
    Each quadrant of a specimen undergoing Mohs surger Each quadrant of a specimen undergoing Mohs surgery is marked with 2 different colored dyes.
  • Step 8: The histotechnician mounts the tissue as it is presented, flattening the undersurface in an even horizontal plane; cuts 5- to 7-µm horizontal frozen sections of each tissue specimen with a cryostat (see the images below); and places the specimens on slides. (By compressing each saucerized piece of tissue and sectioning the specimen horizontally from the deep margin upward, the entire undersurface and epidermal margin of the excised specimen is theoretically processed. Histologic preparation for microscopic examination in Mohs surgery requires skill and practice. Minor variations in technique may exist.)

    Marked tissue undergoing Mohs surgical technique i Marked tissue undergoing Mohs surgical technique is embedded into a chuck for the cryostat.
    A Mohs surgery tissue specimen is cut into thin se A Mohs surgery tissue specimen is cut into thin sections.
  • Step 9: The slides are stained (usually with hematoxylin-eosin or toluidine blue), and the Mohs surgeon, who also serves as the pathologist, interprets the results (see the following images).

    Mohs surgery sections are stained with hematoxylin Mohs surgery sections are stained with hematoxylin and eosin and placed on slides.
    Mohs surgery sections are stained with hematoxylin Mohs surgery sections are stained with hematoxylin and eosin and placed on slides.
  • Step 10: Any residual neoplasm is marked on the map in red ink (see the image below); the surgeon can then precisely remove additional tissue where residual tumor is identified—in this manner, uninvolved tissue is preserved, because only the areas with residual tumor are sequentially removed.

    Residual tumors are marked on a map. Residual tumors are marked on a map.
  • Step 11: With the fresh-tissue technique, the resulting defect can be reconstructed immediately (discussed below).

Depending on the size and location of the resulting wound, the surgeon then chooses the most appropriate reconstructive repair to achieve the best functional and cosmetic outcome. These reconstruction techniques include primary closure, adjacent tissue transfer (flap), skin graft, and a combination of the previous techniques.

Many post-Mohs technique defects can be repaired in a linear fashion via primary closure. However, larger defects or anatomically difficult locations warrant repair with a full-thickness skin graft (FTSG) or flaps. For example, due to limited blood perfusion, tightness, and fragility of the overlying skin, FTSG is suggested to be a safe reconstructive option for lower-extremity defects after Mohs surgery. [72] An experienced, fellowship-trained Mohs surgeon has extensive experience with all these types of reconstructive surgery techniques.

Coordinating the roles of the dermatologist, pathologist, cutaneous and/or oncologic surgeon, and reconstructive surgeon ensures the least amount of error when the histopathologic and clinical findings of each patient are correlated.

The following image demonstrates an example of the fresh-frozen technique of Mohs surgery.

An illustrated example of the Mohs surgical techni An illustrated example of the Mohs surgical technique.

Fixed-Tissue Technique

The fixed- and fresh-tissue Mohs surgery techniques are similar. However, with the fixed-tissue technique, the tissue fixation is accomplished before excision, thereby eliminating the need for anesthesia and creating a blood-free surgical field.

Although the fixed-tissue technique is infrequently used, some surgeons find it helpful in certain circumstances. For example, the blood-free field may be useful for penile carcinomas because of the associated vascularity of the tissue.

The fixed-tissue technique consists of the following:

  • Step 1: The tumor is debulked with a curette, and dichloroacetic acid is applied to increase the penetration of the zinc chloride paste and to facilitate hemostasis. (The dichloroacetic acid is a keratolytic agent; therefore, heavily keratinized areas require the application of more of the agent, whereas ulcerated surfaces do not necessarily require application of the acid.)

  • Step 2: A layer of zinc chloride paste is applied, with the thickness of the layer dependent on the desired depth of penetration; this paste consists of a combination of stibnite, bloodroot powder (Sanguinaria canadensis), and a saturated solution of zinc chloride. (The fixative is used sparingly if tissue conservation is critical, such as when the tumor is located on the nasal ala or pinna of the ear. The penetration of this potent fixative depends on many factors, including the amount applied, the duration of application, the vascularity of tissue, and the type of tissue.)

  • Step 3: The fixative paste is covered with an occlusive dressing to protect the adjacent uninvolved skin, and it remains in place for 6-24 hours.

  • Step 4: After tissue fixation, the fixed-tissue technique is performed in a manner similar to the fresh-tissue technique (ie, with the scalpel angled 45° to the skin, thus beveling the edge, an incision is made in the fixed tissue near the border of the unfixed tissue and continued in the fixed tissue parallel to the skin surface.); following microscopic examination of the tissue sections, additional fixative is applied to any remaining areas of tumor involvement for another 6-24 hours.

  • Step 5: Residual tumor is excised in the same manner as the fresh-tissue technique, generally at a rate of one stage of excision per day.

  • Step 6: When a tumor-free defect is achieved, the remaining fixed tissue is allowed to slough; this process generally takes a few days.

  • Step 7: The defect can then be repaired or allowed to heal by means of secondary intention.


Postoperative Care

Postoperative care following Mohs surgery depends on the type of repair used by the surgeon. Many methods of bandaging and cleansing are acceptable. The principal author's method is described in this section.

Immediate postoperative period

For wounds left to heal by granulation (secondary intention), cleanse the lesion with normal saline solution and then apply topical petrolatum ointment. Instruct patients to do the same 1-2 times a day.

For defects reconstructed with linear closure or flaps, cleanse the surgical site with saline and apply topical petrolatum ointment under a pressure dressing. Instruct patients to leave the bandage alone for 24-48 hours. Subsequently, coach patients to change dressings daily using the same routine (ie, saline and topical petrolatum ointment).

For wounds repaired with skin grafts, place the topical petrolatum ointment directly on the graft, and apply a petrolatum gauze dressing (eg, Xeroform). Place a few layers of sterile 4 × 4–inch gauze atop the petrolatum gauze to provide bulk for a good pressure dressing. Use a liquid dressing adhesive (eg, Mastisol) around the skin a few centimeters from the wound; then, apply paper tape to secure the bulky dressing. Advise patients to leave the dressing untouched until the following week.

Patients are usually given oral antibiotics after undergoing more extensive repairs such as flaps and grafts and for larger wounds.

After wound healing

For patients with extensive photodamage and actinic keratoses near surgical areas, fluorouracil cream, imiquimod cream, or photodynamic therapy can be recommended after the surgical site completely heals. Other superficially ablative techniques (eg, carbon dioxide or erbium: YAG laser) can also be used for skin resurfacing treatments (as cancer prophylaxis).



When any surgical procedure is performed, even under ideal conditions, a risk of complications always exists. In general, complications from Mohs surgery are few and usually minor. [73, 74]

Similar to other dermatologic surgical procedures, the most common postoperative complications from Mohs surgery include bleeding, hematoma formation, nerve damage, seroma formation, wound dehiscence, flap necrosis, graft failure, infection, contact dermatitis due to antibiotic ointments or dressing materials, excessive granulation formation, keloid and/or hypertrophic scar formation, hyperpigmentation and/or hypopigmentation, and tumor recurrence (although the likelihood of tumor recurrence is much less with Mohs surgery than with other more routine therapeutic modalities).

A retrospective study by Cowan et al indicated that compared with the results associated with smaller tumors, Mohs surgery on large tumors is 50 times more likely to produce postoperative complications within 6 weeks of the procedure. The report also found that the risk of postoperative complications was not greater in association with aggressive subclinical extension. [75]


Postoperative bleeding rarely occurs in wounds left to granulate, except when patients neglect the wounds. Postoperative bleeding occurs more frequently with repairs, especially large flaps.

Minimize bleeding risks by obtaining an adequate preoperative patient medical history and having a sound preoperative plan in place (eg, avoidance of nonsteroidal anti-inflammatory drugs [NSAIDs] and acetylsalicylic acid [aspirin] when medically safe; monitor and keep international normalized ratio [INR] < 3 for patients on warfarin).

It is of utmost importance to obtain adequate hemostasis and place a pressure bandage in patients who require continued anticoagulation during Mohs surgery. [76] Studies in recent years have shown that continued usage of warfarin and clopidogrel increases bleeding complications during Mohs surgery—although none of the cases had significant long-term complications. Aspirin, NSAIDs, and vitamin E, however, did not show such increases in postoperative bleeding.

Nerve damage

Sensory nerve loss often occurs during Mohs surgery, because small sensory fibers are severed during tumor excision. Such deficits are usually short term owing to regeneration of the nerve fibers.

Avoid motor nerve damage by applying proper knowledge of human anatomy. Allocate extra time to study the anatomy in high-risk areas where motor nerves travel superficially.


Infections from Mohs surgery are rare with the use of proper cleansing and surgical techniques. For patients with lesions in a surgical site area of high infection risk, oral antibiotics are usually recommended. For wounds involving cartilaginous structures, consider prescribing fluoroquinolones to cover pseudomonal infections.

A study by Nasseri indicated that a single set of sterile surgical instruments can be used for both tumor extirpation and reconstruction in Mohs surgery without subjecting patients to an unacceptable risk of surgical site infection. In the study, just seven surgical site infections occurred among 332 patients (infection rate 2.1%) who underwent Mohs surgery using this technique. [77]