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Mohs Micrographic Surgery

The Palo Alto Dermatology Institute Mohs Surgery Unit is directed by double board-certified dermatologic surgeon and Mohs surgeon, Dr. Greg S. Morganroth. Dr. Morganroth has been performing Mohs surgery for over 30 years and has personally performed over 37,000 Mohs surgeries, representing one of highest volumes of Mohs surgery in the history of Mohs surgery in San Francisco Bay Area.  His senior Mohs technician has worked alongside Dr. Morganroth for 27 years.

Mohs Surgery is a complex procedure combining surgical excision with immediate microscopic examination of the entire tissue specimen margin by frozen tissue processing techniques right in the office while you wait. In addition to your physician, who serves as the Mohs surgeon and pathologist, two to three histotechnologists are employed to process, cut, and stain the tissue specimen for proper histological study.

  1. Numbing the skin with a local anesthetic called Lidocaine, marking the skin to create a map, and then surgical removal of a thin layer of skin containing the tumor in the shape of a pie.
  2. Dividing the pie-like specimen into slices that are numbered, mapped, color-coded in the exact same orientation as the map on the patient’s skin and a paper map that will be used during the microscopic examination.
  3. The tissue slices are frozen and sectioned into tissue paper thin slices that are placed on glass slides and stained in our Mohs lab contained by our own staff of four histotechnicians.
  4. Your surgeon examines each section under the microscope to determine if tumor tentacles are left behind in the skin. The tissue is oriented on the slide so that the border of the tissue or the pie crust is examined. This allows your physician to examine 100% of the margin just like he was looking at the entire pie crust of the pie. The filling of the pie or center of the tissue specimen is not examined because the tumor has already been diagnosed by the prior biopsy and the center of the specimen is not helpful for margin control. If the tumor is removed completely, the skin defect is ready to be repaired. If the specimen is positive for residual tumor, steps 1 through 4 are repeated until the skin is clear of tumor (see diagram).

Step-by-Step Pictorial Presentation of an Actual Mohs Micrographic Surgery

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This detailed examination of 100% of the margin by Mohs Micrographic Surgery differs from all other pathology techniques. If you have a skin cancer excised by a physician in the office or hospital, the tissue specimen will be sent to a pathology laboratory for processing and examination by a pathologist. The standard pathology techniques examine only 1% or less of the margin (pie crust). If this 1% is clear of tumor, the pathologist and surgeon assume that the other 99% of the margin is also clear. This approach might work well if skin cancers grew into the skin in a symmetrical manner like a sphere, however most complicated skin cancers grow in an unpredictable manner with tentacles growing in eccentric patterns that may wrap around nerves or track along cartilage planes. Therefore, even though a pathology report indicates clear margins, there may be tumor tentacles left behind on the 99% of the margin that was not examined. This incomplete examination of the margin is the most common cause for a tumor growing back and requiring another surgery. Mohs Micrographic Surgery does a better job of preventing recurrences because the entire margin is examined.

Illustration of Mohs Surgery versus Standard Pathology and Excision Techniques

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The Mohs Surgery technique allows your physician to examine 100% of the surgical margin (or pie crust) and, if tumor is still present, pinpoint the exact location of the residual cancer.* This enables him to return to the treatment area and selectively remove another layer of skin from the positive area only. This minimizes the amount of normal skin that is removed and therefore creates the smallest possible defect in the skin. Guessing the location of residual tumor in the skin is completely eliminated with Mohs Surgery. Since many of the skin cancers removed with Mohs Surgery are complicated, multiple stages are often required to clear the tumor. Please be patient! Examination of each of your stages takes up to 60 minutes. If multiple stages are taken, the Mohs procedure can take up a good percentage of the day. Usually you have been warned if a prolonged procedure is anticipated. The vast majority of this time will be spent sitting in the waiting room watching television or reading a book or magazine.

Advantages of Mohs Micrographic Surgery

In summary, the use of Mohs Surgery significantly increases the chance of complete cure and reduces the unnecessary sacrifice of surrounding normal skin. This minimizes the size of the hole, makes it easier to repair the defect, and will result in a smaller scar.

  • Procedure performed from start to finish by a skin cancer expert
  • Highest cure rate available for skin cancer
  • Visualizes 100% of margin of excision vs. 1% with normal pathology
  • Smallest amount of normal skin is removed
  • Preserves cosmetics and function of the treated area
  • Smallest possible defect results in smallest possible scar
  • Surgery and microscopic examination by the same person
  • Reconstruction performed immediately after tumor removed
  • All done under local anesthesia in the office

Options for skin cancers that do not qualify for Mohs Surgery

Mohs Surgery offers the highest cure rate for skin cancers that qualify for the Mohs Appropriate Use Criteria (Mohs AUC). Tumors that are located in cosmetically sensitive areas, have aggressive growth features under the microscope, are recurrent, or are larger in size are typically candidates for Mohs Surgery.

While the Mohs AUC is useful to capture the majority of challenging tumors, there are gaps in the Mohs AUC where certain tumors (large size, areas of tight skin) need histologic examination of the margins prior to repairing the skin.

For skin cancers that do not meet the Mohs AUC, Palo Alto Dermatology Institute offers excisions with traditional frozen sections. This technique offers immediate histologic examination of the tissue, but does not examine 100% of the margin (Mohs surgery). The standard pathology “bread loaf” or en face tissue sectioning is typical of how surgical specimen are examined by the frozen pathology labs that obtain samples from other surgeons operating in hospitals and surgery centers.   The standard frozen tissue margin examination technique, while not able to statistically reach the high cure rate offered by Moh surgery, significantly increases the cure rate and reduces the chance of incomplete tumor removal necessitating a second surgery.

Mohs Micrographic Surgery Brochure

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