eMedicine Specialties > Otolaryngology and Facial Plastic Surgery > Reconstructive Surgery

Mohs Surgery

Author: S Brian Jiang, MD, Associate Clinical Professor of Medicine and Dermatology, Director, Dermatologic and Mohs Micrographic Surgery, University of California School of Medicine, San Diego
Contributor Information and Disclosures

Updated: Aug 7, 2008

Introduction, History, And Training

Mohs micrographic surgery is a procedure in which skin cancers are excised at a 45° angle with subsequent identification of residual tumor using light microscopy. This method provides total histological control of the surgical margins, and it achieves the lowest recurrence rate with maximal preservation of uninvolved tissue. Consider Mohs micrographic surgery the treatment of choice for recurrent or histologically aggressive lesions.

For excellent patient education resources, visit eMedicine's Cancer and Tumors Center. Also, see eMedicine's patient education article Skin Cancer.

History

Frederic E. Mohs developed this technique while still a medical student at the University of Wisconsin. Initially, he used a zinc chloride paste to fix tissue in vivo prior to surgical procedures. This original protocol was called chemosurgery, but now it is more commonly referred to as Mohs micrographic surgery, fixed-tissue technique.

In 1953, while being filmed during a fixed-tissue technique for a basal cell carcinoma (BCC) of the eyelid, Mohs performed the last few layers without fixative in order to speed the process. The horizontal frozen sections he obtained worked so well that Mohs continued this fresh-tissue technique for all eyelid carcinomas. In 1969, he reported a 5-year cure rate of 100% using the fresh-tissue technique to excise eyelid carcinomas. Wide acceptance of the fresh-tissue technique increased substantially after the publication of Tromovitch and Stegman's series in 1974 and Mohs' series in 1976.

Before the 1980s, training in Mohs surgery was informal and without criteria. In current practice, the AmericanCollege of Mohs Surgery (formerly known as AmericanCollege of Mohs Micrographic Surgery and Cutaneous Oncology and the AmericanCollege of Chemosurgery) oversees formal fellowship training. This 1-2 year postresidency training program is invaluable in equipping trainees with competent surgical and dermatopathology skills. The program also equips students with the ability to train and educate other physicians about Mohs surgery. Early pioneers who trained fellows include F. Mohs, T. Tromovitch, S. Stegman, P. Robins, and others. Now, almost all Mohs micrographic surgery is performed using the fresh-tissue technique.

Indications

Indications for Mohs micrographic surgery include the following:

• Recurrent or incompletely excised basal cell carcinoma (BCC) or squamous cell carcinoma (SCC)
• Primary BCC or SCC with indistinct borders
• Lesions located in high-risk areas (ie, those that if shaded resemble the letter H or a mask) involving mainly embryonic fusion planes (eg, eyelids, nose, ear, nasolabial folds, upper lip, vermillion border, columella, periorbital, temples, preauricular and postauricular areas, scalp)
• Cosmetically and functionally important areas, including genital, anal, perianal, hand, foot, and nail units
• Tumors with aggressive clinical behavior (ie, rapidly growing, > 2 cm in diameter)
• Tumors with an aggressive histologic subtype (eg, BCC sclerosing [morpheaform], basosquamous [metatypical or keratinizing], perineural, periappendiceal); perivascular invasion; and infiltrating, adenoidal, or multicentric tumors
• SCCs ranging from undifferentiated to poorly differentiated and SCCs that are adenoid (acantholytic), adenosquamous, desmoplastic, infiltrative, perineural, periadnexal, or perivascular
• Tumors arising in sites of previous radiation therapy
• Tumors arising in immunosuppressed patients
• Basal cell nevus syndrome patients

Preoperative Evaluation

Collect a careful medical history. Give special attention to issues concerning clotting parameters, antibiotic prophylaxis, allergies, epinephrine contraindications, and/or electrocautery.

Clotting parameters

In Mohs surgery, flaps and grafts are occasionally needed to repair resulting defects. If a patient has bleeding diathesis or has been taking aspirin, warfarin, or nonsteroidal anti-inflammatory drugs, flap or graft survival could be compromised. Additionally, these patients are at higher risk for hematomas and infection.

Antibiotic prophylaxis

Antibiotic prophylaxis is not completely standard among surgeons performing the Mohs technique. Prophylaxis is usually given to patients with a history of prostheses (valves or joints), nonphysiologic heart murmurs or valvular disease, or mitral valve prolapse. The most commonly used antibiotics for prophylaxis include dicloxacillin and cephalexin (2 g PO 1 h before surgery). For patients who are allergic to penicillin, the author generally uses azithromycin (500 mg PO 1 h before surgery) or clindamycin (600 mg PO 1 h before surgery).

Allergic reactions

Medication allergies are common in all patients. Besides allergies to oral antibiotics, many patients are allergic to topical antibiotics. The most common topical offenders include bacitracin/polymyxin B sulfate (Polysporin), neomycin/gramicidin/polymyxin (Neosporin), and bacitracin. For patients who are allergic to a topical antibiotic listed above, use an ointment base (Aquaphor), petrolatum, or mupirocin (Bactroban).¹ For those patients who are allergic to penicillin, switch them to macrolides or fluoroquinolones.

Contraindications for epinephrine

In patients taking nonselective beta-blockers or those with a history of severe hypertension, heart failure, or dysrhythmias, the author generally prefers using plain lidocaine without epinephrine.

Electrocautery

For patients with pacemakers, the author generally uses short bursts with the grounding plate placed in the lower extremity or a hand-held heat cautery device. For patients with defibrillators, only use hand-held heat cautery devices.

For all patients, the size, location, and histologic subtype of the tumor dictate the type of resources required. Anticipate the need to consult with colleagues from other surgical or medical specialties when appropriate.

Technique

After local infiltration with anesthesia (0.5-2% lidocaine with epinephrine 1:100,000 or 1:200,000), Mohs surgery often starts with light curettage of the tumor to better delineate the extent of the lesion's horizontal and vertical clinical margins.

Incise the skin at a 45° angle with a small border (1-3 mm) around the clinical margins of the lesion. Completely remove the tissue with horizontal excision of the deep margins. To preserve orientation, scoring the specimen and its corresponding skin edge is strongly recommended.

Divide the specimen into small sections and stain with different color dyes. Draw a map of these sections with colored sides to facilitate localization of any residual skin cancer. The histotechnician then processes and cuts sections using the cryostat and stains them with conventional hematoxylin and eosin stain (see Images 1-7). Sectioning in the Mohs technique differs from sectioning normally practiced in pathology laboratories. Cut Mohs sections horizontally so that they include lateral and deep margins in the same piece. The Mohs surgeon then carefully reviews resulting section slides for the presence of residual tumor. This technique offers complete evaluation of the lateral and deep margins; thus, it renders fewer false-negative results compared with ordinary bread-loaf sections in paraffin slides. In patients with any residual skin cancer, repeat the whole process until the tumor is completely removed.

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 used include primary closure, adjacent tissue transfer (flap), skin graft, and a combination of the previous techniques. An experienced, fellowship-trained Mohs surgeon has extensive experience with all these types of reconstructive surgery techniques.

Postoperative Care

Postoperative care depends on the type of repair used by the surgeon. Many methods of bandaging and cleansing are acceptable. The author's method is described.

In the immediate postoperative period (for wounds left to heal by granulation [secondary intention]), cleanse the lesion with normal saline solution and then apply topical antibiotic 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 antibiotic 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 antibiotic).

For wounds repaired with skin grafts, place the topical antibiotic directly on the graft and apply Xeroform gauze. Place a few layers of sterile 4 X 4-in gauze atop the Xeroform gauze to provide bulk for a good pressure dressing. Place Mastisol dressing adhesive around the skin a few centimeters from the wound, and use 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. For patients with extensive photodamage and actinic keratoses near surgical areas, fluorouracil cream (5%) is recommended after the surgical site completely heals. Reports have recently emerged of carbon dioxide or erbium: YAG laser used for skin resurfacing treatments (as cancer prophylaxis).

Complications

As with any surgical procedure, Mohs surgery has its share of possible complications, such as bleeding, nerve damage, and infection. Repairs (eg, primary, complex, flaps, grafts) are also associated with additional complications (eg, dehiscence, necrosis, hematoma, seroma, ecchymoses).

Bleeding

Minimize bleeding risks by obtaining an adequate preoperative medical history and having a sound preoperative plan (ie, to avoid nonsteroidal anti-inflammatory drugs, warfarin, acetylsalicylic acid [aspirin]). 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.

Nerve damage

Sensory nerve loss often occurs because small sensory fibers are severed during tumor excision. Deficits are usually short-term because the human body regenerates these 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.

Infection

Infections are rare with proper cleansing techniques. For patients with large wounds or diabetes mellitus, oral antibiotics are usually recommended. For wounds involving cartilaginous structures, consider prescribing fluoroquinolones to cover pseudomonal infections.

Prognosis

Five-year recurrence rates for primary basal cell carcinoma (BCC)

• Mohs micrographic surgery - 1%
• Surgical excision - 10.1%
• Curettage and desiccation - 7.7%
• Radiation therapy - 8.7%
• Cryotherapy - 7.5%

Five-year recurrence rates for recurrent BCC

• Mohs micrographic surgery - 5.6%
• Surgical excision - 17.4%
• Curettage and desiccation - 40%
• Radiation therapy - 9.8%
• Cryotherapy - 13% (<5-y period)

Five-year recurrence rates for primary and recurrent squamous cell carcinoma (SCC) treated with Mohs surgery versus other modalities

• Skin and lip - 3.1% (Mohs) versus 10.9% (other modalities)
• Ear - 5.3% (Mohs) versus 18.7% (other modalities)
• Recurrence (Recurrence rate tends to increase with higher-grade tumors.) - 10% (Mohs) versus 23.3% (other modalities)

Future Trends

Confocal laser scanning microscope

The epidermis and part of the dermis can be visualized using this 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 use in Mohs surgery are now underway. The author is currently involved in clinical testing of a prototype designed for Mohs surgery, and the results are encouraging.

Special stains

Several investigators have used immunostaining to assist in tumor visualization. Selective labeling of malignant cells can help unmask tumors within inflammation or can help more clearly determine margins. Examples of these immunostaining techniques for clinical investigation include antidesmoglein for BCC, anticytokeratin for BCC and SCC, and anticarcinoembryonic antigen for extramammary Paget disease.

Melanoma

The use of Mohs technique in superficial melanoma (lentigo maligna and in situ melanoma) is still controversial. Clearly identifying melanoma cells in frozen horizontal sections is not always possible. No clinical evidence to date shows that Mohs surgery is indicated for invasive melanomas.

Multimedia

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Media file 1: Specimen is carefully separated into 4 quadrants.

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Media file 2: Each quadrant is marked with 2 different color dyes.

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Media file 3: Marked tissue is embedded into a chuck for the cryostat.

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Media file 4: Tissue is cut into thin sections.

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Media file 5: Sections are stained with hematoxylin and eosin and placed on slides.

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Media file 6: Slides are viewed under a microscope.

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Media file 7: Residual tumors are marked on a map.

Keywords

Mohs surgery, Mohs micrographic surgery, Mohs chemosurgery, Mohs' surgery, Mohs' micrographic surgery, Mohs' chemosurgery, skin cancer, skin cancer surgery, skin lesion, dermatology, fixed-tissue technique, Mohs, basal cell carcinoma, BCC, basal cell cancer, fresh-tissue technique, squamous cell carcinoma, SCC, squamous cell cancer, basal cell nevus syndrome, MOHS, non-melanoma skin cancer, NMSC, dermasurgeon

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