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Mohs Micrographic Surgery

Last updated May 18, 2021

Written by: Lester Fahrner, MD

Reviewed by: Lester Fahrner, MD

Approved by: Krish Tangella MD, MBA, FCAP

Mohs Micrographic Surgery is a procedure designed to remove certain skin cancers with a very high cure rate.


Background Information:

What are the other Names for the Procedure?

  • Mohs Surgery

What is Mohs Micrographic Surgery procedure?

  • Mohs Micrographic Surgery is a procedure designed to remove certain skin cancers with a very high cure rate. It is most frequently used to treat basal cell carcinoma of the skin and squamous cell carcinoma of the skin
  • The procedure is performed with the patient awake, under local anesthetic. The Mohs Micrographic Surgery trained physician sequentially removes skin specimens and then checks the margins of the sections for cancer clearance or persistence 
  • Each specimen is prepared in such a way that the relationship between the specimen and the surgical site is preserved. A hand-drawn depiction of the site, the specimen, and location of residual tumor is kept guiding the proper progression of the surgical session. This is called the Mohs map
  • The specimen is examined under the microscope, checking for skin cancer at all the edges and bottom (deep) section of the specimen. Any areas of residual cancer are marked in colored pencil on the Mohs map
  • If the specimen shows residual cancer, further cut(s) are taken until only normal skin cells are seen at the side and deep margins
  • The entire process, surgery, specimen preparation, pathology evaluation, and sometimes closure of the defect is supervised by the Mohs surgeon

Once the cancer is completely removed, the procedure is stopped. For some cancers, the cure rate approaches 99% when this technique is used.

What part of the Body does the Procedure involve?

  • The Mohs Micrographic Surgery can potentially involve any skin surface on which the skin cancer is found
  • All cancers must be evaluated for the appropriateness of this technique, based on many criteria

Why is the Mohs Micrographic Surgery procedure Performed?

There could be a variety of reasons for performing Mohs Micrographic Surgery. Some of these include:

  • The surgical procedure generally removes less of the surrounding normal tissue that is free of cancer than other treatment methods
  • Mohs Surgery defects are generally smaller than regular excisional techniques, with surgical repair being more easily done. Thus, better outcomes are noted with Mohs Micrographic Surgery
  • It has the highest cure rate for many types of skin cancer. The surgery is most frequently performed on basal cell carcinomas of the skin and squamous cell carcinomas of the skin

What are some Alternative Choices for the Procedure?

Some of the alternative choices for Mohs Micrographic Surgery include:

  • Excisional surgery of skin
  • Curettage and cautery
  • Radiation therapy
  • Hedgehog pathway inhibitor oral medications
  • Any combination of the above treatments

What are the Recent Advances in the Procedure?

Some of the recent advances include the use of a confocal laser microscope to augment or replace preparing frozen and stained microscope slides, for complete cancer removal determination.

What is the Cost of performing the Mohs Micrographic Surgery procedure?

The cost of the Mohs Micrographic Surgery procedure depends on a variety of factors, such as the type of your health insurance, annual deductibles, co-pay requirements, out-of-network and in-network of your healthcare providers and healthcare facilities.

In many cases, an estimate may be provided before the procedure. The final amount depends upon the findings during the surgery/procedure and post-operative care that is necessary.

When do you need a Second Opinion, prior to the Procedure?

  • It is normal for a patient to feel uncomfortable and confused with a sudden inflow of information regarding the Mohs Micrographic Surgery procedure and what needs to be done
  • If the patient needs further reassurance or a second opinion, a physician will almost always assist in recommending another physician
  • Also, if the procedure involves multiple steps or has many alternatives, the patient may take a second opinion to understand and choose the best one. They can also choose to approach another physician independently

What are some Helpful Resources?

https://www.aad.org/ (accessed on 05/16/2021)

https://www.mohscollege.org/ (accessed on 05/16/2021)

https://www.mohssurgery.org/ (accessed on 05/16/2021)

Prior to Mohs Micrographic Surgery procedure:

How is the Mohs Micrographic Surgery procedure Performed?

The Mohs Micrographic Surgery procedure is performed in the following manner:

  • The skin is prepped with an antiseptic, then the extent of the visible and likely margins of the skin cancer is marked with a surgical marker
  • A mark is made at what will be referred to during the remainder of the procedure as “12 o’clock”
  • Local anesthetic is infiltrated into the skin beyond the likely margins
  • The specimen is excised in a distinctive manner. The outline of the lesion is cut first. Instead of holding the scalpel blade perpendicular to the skin, as is usual, it is angled 45 degrees. That is about the angle of the side crust of a pie, for reference. The reason will be clear in a bit
  • The specimen is held up with a forceps, and cut entirely free, with a flat base
  • The “12 o’clock” mark it cut through, so the specimen looks like a small pie, converted into a “Pac-Man” shape with the extra incision
  • Special inks are used to mark the specimen. This permits proper location of any tumor on the specimen and corresponding site on the surgical site
  • Bleeding is controlled, a bandage applied, and the patient sent to the waiting room while the specimen is prepared and examined
  • The specimen is frozen to make it firm, and extremely thin slices made, placed on microscope slides, and stained with two dyes to aid in differentiating cell types
  • The Mohs surgeon examines the slides carefully, looking specifically for any skin cancer at the margins of the specimen. Any residual skin cancer is marked on the Mohs map
  • The patient is brought back into the surgical room and the site injected with anesthetic again if necessary, and the area(s) with residual cancer determined by referring to the Mohs Map
  • Further excisions are made, and the specimen handled in the same manner; the patient is again sent to the waiting room.
  • As many stages as necessary are performed until all the cancer is proven to be removed. The patient is returned to the surgical room, and the defect checked
  • The determination of the options for healing of the subsequent defect is made, and the patient involved in the choice made

At this point, the Mohs Micrographic Surgery is complete. 

  • The most common choices for healing/closure are:
    • Second intention healing
    • Complex skin closure
    • Flap closure
    • Or, skin grafting
  • This might be done the same day, or scheduled for a later date
  • The surgeon may be the Mohs Surgeon, or referral may be made to a plastic surgeon, head and neck (ENT) surgeon, oral and maxillofacial surgeon, or oculoplastic surgeon, or to other healthcare experts
  • In certain high risk cancers, or if an unresectable tumor is discovered in the course of the surgeon, referral to a radiation oncologist may be made

Since the above may be complex to follow, a summary is provided below:

None of the steps of Mohs Micrographic Surgery are particularly complex to understand. The process takes many small repeated steps done meticulously, with attention to the well-being of the patient, and the goal of tumor clearance.

Imagining the cancer to be the berry filling of a pie, and the crust to being the normal skin structures can be helpful. The 45-degree angle “side crust” can be pressed down onto the microscope slide to be in the same plane as the flat “bottom crust”. So, in one view, the Mohs surgeon can check for tumor cells on the slide. If only normal skin is seen on the slide, it means all the cancer was in the upper portion of the specimen, and therefore all gone. If a little cancer is seen just at the middle bottom, that tissue only has to be removed and checked. Or, as another example, the entire bottom is cancer free, but the entire edge has residual cancer, it means the cancer had been just wider than the original estimation. So, the bottom is not made deeper, just a thin round ring of the margin is taken.

The Mohs surgeon must have a thorough knowledge of the anatomy of the skin and underlying tissues. They also must know how to interpret the microscope slide. They must also take into account the biological behavior of the various types and subtypes of skin cancer. In addition, they almost always must have significant surgical skills to perform closures of most of their surgical cases.

Where is the Procedure Performed?

The Mohs Micrographic Surgery is usually performed in a clinic surgical suite specifically configured for the surgical procedure. This typically consists of a number of surgical rooms, a spacious waiting room, and a laboratory for preparation and examination of the microscope slides.

Who Performs the Procedure?

The Mohs Micrographic Surgery procedure is usually performed by a physician specifically trained in the technique. The background of the surgeons is typically dermatology, but may also include head and neck surgeons, plastic surgeons, or oral and maxillofacial surgeons. Physician assistants or advanced practice nurses also assist as team members.

How long will the Procedure take?

The Mohs Micrographic Surgery procedure can be time consuming. Each stage, in which a specimen is surgically removed, takes only about 15 minutes. However, the microscope slide preparation and evaluation take time, with the patient staying in the waiting room.

The ultimate time depends on how many surgical stages are needed to completely remove the cancer. This cannot be known ahead of time. Mohs Micrographic Surgery patients are usually told to expect to spend the entire day in the office.

In addition to the time required to cure the skin cancer, a surgical repair of the resultant defect is also needed. This can consist of wound repair surgery, flap surgery, or a skin graft. These procedures can add up to two hours to the total time needed.

What do you need to tell your Physician before the Procedure?

It is very important to provide the following information to your healthcare provider. This enables your healthcare provider in assessing the risks for the procedure and helps avoid complications.

  • Provide complete medical history such as diabetes, hypertension, heart disease, etc. (if any)
  • Provide a complete list of medications you are currently taking to your physician. This information is useful for a variety of reasons. For example, it can help your healthcare provider prevent complications due to a drug interaction
  • If you are allergic to any specific medication or food items
  • If you are taking blood thinners, such as aspirin, warfarin, herbal supplements, or any other such medications
  • Any medical or family history of bleeding disorders or blood clots
  • If you have ever been diagnosed with blood clots in your leg (deep vein thrombosis) or lung (embolism of lung)
  • Any unusual effects of anesthesia from prior surgery
  • A list of all previous surgical procedures you have undergone, like for example - removal of appendix, gallbladder, or any other part, of your body; surgical repair of any body part, such as hernia repair, perforation of bowel wall, etc.
  • A list of all implanted electronic medical devices. This includes pacemakers, defibrillators, implanted pain devices, deep brain stimulators for Parkinson’s disease or seizure control, etc.

What Preparations are needed, prior to the Procedure?

The physician performing the procedure will evaluate the patient prior to the procedure and discuss the details with risks for complications and obtain his/her permission (termed informed consent).

  • Some medications increase a person’s chances of bleeding and it may be recommended to discontinue them for a period of time, before the procedure is performed
  • Blood tests may be performed to determine if there is a bleeding tendency or any other medical conditions that prevents the person from undergoing the procedure
  • Blood work, glucose, and pregnancy tests (if applicable) will be undertaken per physician recommendations
  • If anesthesia team is involved in the procedure, then they too will discuss details of anesthesia with risks for complications and obtain permission from the patient (informed consent)
  • Avoid application of any deodorant or topical medicines on the area, prior to the procedure
  • It is advisable to quit smoking and the use of any nicotine based products, for a while, before the procedure
  • Consumption of alcoholic drinks must also be avoided for a period of time, as instructed
  • Generally, patients are asked to eat before Mohs Micrographic Surgery. The patient will be awake. Patients who have not had anything for breakfast can become faint as the time needed advances. Many patients will need to have brought something for lunch or a snack
  • Individuals with diabetes, hypertension, or other cardiac conditions, are required to discuss these (including medications being taken) with their attending physician well in advance
  • For individuals with diabetes, it is important that the blood sugar stays within the normal range; if not, their diabetologist may have to control blood sugar by recommending insulin and/or a combination of oral medicines

Pregnant women and individuals with severe underlying sicknesses will need to have a more thorough evaluation before undertaking this procedure.

What is the Consent Process before the Procedure?

The physician will obtain permission for the Mohs Micrographic Surgery using an Informed Consent Form.

Consent for the Procedure: A “consent” is the approval to undergo a procedure. A consent form is signed after the risks and benefits of the procedure, and alternative treatment options, are discussed. This process is called informed consent.

In case of minors and individuals unable to give informed consent, the parent or legal guardian or next of kin can sign the consent for the procedure.

What Tests are needed, before the procedure?

The only tests usually required would be those that involve clotting, such as a CBC and differential, and any others as indicated by history and exam. It is important that the Mohs Surgeon and the primary healthcare provider communicate about the health of the patient.

The physician may suggest further tests depending on the health of the individual and their medical history.

What are some Questions for your Physician?

Some of the questions that you might ask your healthcare provider are as follows:

  • What is Mohs Micrographic Surgery?
  • Why is this procedure necessary?  How will it help?
  • How soon should I get it done? Is it an emergency?
  • Who are the medical personnel involved in this procedure?
  • Where is the procedure performed? 
  • What are the risks while performing the procedure?
  • What are the complications that might take place during recovery?
  • How long will it take to recover? When can I resume normal work?
  • How many such procedures have you (the physician) performed?
  • Are there any follow-up tests, periodic visits to the healthcare facility required, after the procedure?
  • What are the costs involved?

During the Mohs Micrographic Surgery procedure:

What kind of Anesthesia is given, during the Procedure?

Generally, local anesthesia by injection is used.

  • The medication injected for the first stage is chosen to persist until any are needed during subsequent stages, thus minimizing the pain of the next injection
  • Patients sometimes request an anxiolytic, such as a benzodiazepine pill, before beginning the surgical session

How much Blood will you lose, during the Procedure?

  • There will be some blood loss involved as part of Mohs Micrographic Surgery; and, this amount is variable
  • Sometimes small or medium sized arteries may have to be transected. In this case, bleeding is controlled by placing sutures as required

During and at the end of the surgical session, good control of bleeding is necessary. The Mohs surgeon will have electrocautery, suture material, hemostats, and clot promoting materials to perform this important task.  

What are the possible Risks and Complications during the Mohs Micrographic Surgery procedure?

There are general factors that increase one’s risk of getting complications during Mohs Micrographic Surgery, which include:

  • Obesity: Generally greater the degree of obesity, greater is the surgical risk
  • Smoking: Longer the smoking history (in pack years smoked), greater the surgical risk
  • Advancing age
  • Poorly controlled diabetes, as evidenced by a high hemoglobin A1c and a high fasting glucose
  • Poorly functioning kidney, as evidenced by increased BUN (blood urea nitrogen) and blood creatinine
  • Poorly functioning liver, as evidenced by increased blood liver function tests
  • Hypertension (increased blood pressure), especially if it is poorly controlled
  • Poor nutritional status (malnutrition with mineral and vitamin deficiencies)
  • Poor lung function, as evidenced by abnormal lung function tests
  • History of bleeding disorders
  • Poor immune system due to a variety of causes

Some of the possible risks and complications that may arise during a Mohs Micrographic Surgery include:

  • Infection
  • Bleeding
  • Injury to the neighboring structures
  • Pain and discomfort
  • Anesthetic complications
  • Need for further procedures
  • Pneumonia
  • Blood clot formation, affecting blood supply to the buttocks and lower extremities
  • Heart problems

Please note that the complications and risks that may arise during the surgery is governed by factors such as the ultimate size of the Mohs defect.

What Post-Operative Care is needed at the Healthcare Facility after the Mohs Micrographic Surgery procedure?

At the healthcare facility, generally there is no requirement for any post-procedure care, unless any complications arise. However, immediately following the surgery, the patient may be kept in the office suite for further observation.

After the Mohs Micrographic Surgery procedure:

What are the possible Risks and Complications after the Mohs Micrographic Surgery procedure?

The risks and complications that may arise after Mohs Micrographic Surgery include:

  • Excessive bleeding that may sometimes require additional surgical procedures
  • Any symptom that causes uneasiness such as nausea and dehydration
  • Low-grade fever
  • Infection of the surgical wound
  • Pain at or near the surgical site

What is the Prognosis after the Surgery?

The prognosis depends on a set of several factors that include:

  • If the tumor was completely removed
  • The type of skin cancer treated
  • The method of wound healing or closure chosen

When do you need to call your Physician?

Do contact your physician or call 911 (or your local emergency number) based on the seriousness of any of the following symptoms:

  • Fever and chills
  • Severe pain
  • Shortness of breath
  • Bleeding or fluid discharge from the surgical wound
  • Nausea and vomiting
  • Signs of infection
  • Severe fatigue
  • Dizziness

What Post-Operative Care is needed at Home after the Mohs Micrographic Surgery procedure?

At home, the following post-operative care is recommended after a Mohs Micrographic Surgery:

  • Use a cold pack to minimize pain and decrease bleeding risk
  • Keep the bandage in place unless otherwise instructed
  • Take your new prescribed medications following the procedure
  • Avoid any strenuous activity for a period of time, as recommended by the physician
  • Avoid smoking or drinking alcohol post-procedure
  • Continue old prescribed medications after checking with your healthcare provider
  • Do not sign any legal documents post-procedure for a period of 24 hours
  • Specific instructions will be given based on the wound healing or surgical method chosen

How long does it normally take to fully recover, from the Procedure?

The recovery time usually depends on the extensiveness of the surgery. Simple procedures have shorter recovery periods. The healing may take between 2 weeks to a few months.

Additional Information:

What happens to tissue/samples (if any), taken during the Procedure?

The tissue is taken for further examination and later disposed, as per the standard medical procedure. On some occasions, the Mohs surgeon will send a specimen to a pathologist for consultation or confirmation.

When should you expect results from the pathologist regarding tissue taken out, during the Procedure?

  • In a vast majority of cases, only the Mohs surgeon examines the tissue microscopically
  • In the rare cases that a specimen is sent for confirmation, a report will come to the patient within 72 hours to a week’s time 

Who will you receive a Bill from, after the Mohs Micrographic Surgery procedure?

It is important to note that the number of bills that the patient may receive depends on the arrangement the healthcare facility has with the physician and other healthcare providers.

Sometimes, the patient may get a single bill that includes the healthcare facility and the consultant physician charges. Sometimes, the patient might get multiple bills depending on the healthcare provider involved. For instance, the patient may get a bill from:

  • The outpatient facility or hospital
  • The dermatologist
  • A pathologist (if the tissue was sent for analysis)
  • Another surgeon and/or facility if the closure is performed by another physician

The patient is advised to inquire and confirm the type of billing before the Mohs Micrographic Surgery procedure is performed.

Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: May 18, 2021
Last updated: May 18, 2021