Summary: Mohs Technique

Fig. 28.4 (a) Bilateral melanoma in situ of the thumbnail nail beds. (b) Removal of nail plate (upper right) and first stage Mohs layer (upper left). (c) Split-thickness skin graft of nail bed

A thorough medical and surgical history, knowledge of the patient’s current medications, and a physical examination are necessary prior to beginning any procedure. Pertinent information that should always be obtained includes a list of medication allergies, whether the patient requires preoperative antibiotics, knowing if the patient has a pacemaker and/or defibrillator, and whether the patient currently takes a blood thinner. Due to the increase prevalence of methicillin-resistant Staphylococcus aureus (MRSA), the patient should also be asked regarding a history of MRSA infections. If there is a positive prior history of a MRSA infection, the surgeon should consider appropriate antibiotic therapy with either doxycycline (VibramycinRx) or trimethoprim and sulfamethoxazole (BactrimRx) during the postoperative period.

Working in conjunction with the patient’s primary care physician may be necessary prior to the patient undergoing surgery. For instance, if working on a diabetic patient’s foot, the patient’s blood glucose

should be well controlled prior to any surgical work. Additionally, patients on a blood thinner like warfarin (CoumadinRx) may need their International Normalized Ratio (INR) adjusted prior to Mohs surgery. Also prior to Mohs surgery, radiographic imaging of the affected digit should be obtained to evaluate for possible bone invasion by tumor. If bone involvement by the tumor is seen on the radiographs, then a hand surgeon should be consulted to consider partial digit amputation. We usually recommend obtaining simple x-ray radiographs with PA, lateral and oblique views.

The surgical site should be inspected, measured, and photographed prior to Mohs surgery. Any unusual clinical features along the nail and adjacent regions should be evaluated. In nail surgery, additional effort should also be made to evaluate the palms and soles for additional pathology. For instance, if pitting on the palms is noted, the patient may have basal cell nevus syndrome and require additional evaluation by his primary care physician after the completion of Mohs surgery. If, for example, multiple palmar and/ or planter keratoses are identified, the patient may have had significant arsenic exposure in the past, and additional work-up is necessary [20]. Examination for epitrochlear and axillary lymph nodes should be done preoperatively. Finally, the risks, benefits, and alternatives of the surgical procedure must be discussed with the patient in order to obtain informed consent.

28.4.2 Anesthesia

A proximal digital block at the proximal lateral sides of the digit is the most common technique used for anesthetizing the region surrounding the nail unit. This procedure minimizes pain and the number of injections required to anesthetize the digit. The main nerves to be anesthetized have both dorsal and ventral branches and run along the radial and ulnar sides of the digit. This distribution results in overlapping sensory innervations at the digit tip; thus, all four nerves should be anesthetized prior to any procedure. Using a 30-gauge needle, the anesthesia should initially be inserted in the region between the dorsal and ventral nerve pathways. After insertion, the needle may be angled dorsally and ventrally to anesthetize each specific nerve branch. The same technique is repeated for the other side of the digit. It is the opinion of the

authors that anesthetizing a longitudinal section of a nerve, as opposed to injecting the anesthesia in a “ring” configuration, provides a more effective nerve block. For a proximal digital block, a maximum of 2–3 mL of 2% plain lidocaine is recommended for each side of the digit. Recent literature suggests that lidocaine with epinephrine may be locally infiltrated into a digit without complications, even if the patient has several comorbidities [32]. However, we feel that lidocaine with epinephrine should be avoided in diabetics, especially when working on the feet. The problem arises that unless one obtains a fasting blood glucose prior to surgery, one cannot be sure the patient is not a diabetic. In some cases, local anesthesia must also be injected into the distal digit to supplement a digital nerve block to provide for patient comfort during surgery. An important aspect of digital blocks is to wait an adequate time for nerve block anesthesia to occur. Usually it takes at least 20 min for nerve block anesthesia to become adequate.

28.4.3 Instruments

For Mohs surgery, our standard instrument trays include: an Adson Dressing Forceps, Bard-Parker #15 scalpel blade on a Bard-Parker #3 standard handle, a Fox 4-mm curette, blunt-tipped Stevens straight tenotomy scissors, a curved hemostat, a skin hook, a nail splitter, and a penrose drain.

When working on a finger, a latex glove fitted over the patient’s hand with the operative fingertip cut and rolled isolates the surgical field and also creates a tourniquet for surgery.

28.4.4 Preoperative Preparation

The digit is cleaned by the patient with soap and water prior to surgery to remove any gross contaminants. The additional application of an antibacterial such as alcohol or povidone-iodine to the surgical site is done prior to Mohs surgery. After anesthetizing the digit, a sterile towel is placed beneath and around the surgical region to delineate the surgical field.

If working on a finger, a latex surgical glove can be used to provide a tourniquet (see Fig. 28.5a–c). After applying a correctly sized surgical glove onto the patient’s hand, the glove fingertip on the operative

c

Fig. 28.5 (a) Finger tip cut off of latex glove. (b) Latex glove finger rolled back proximally to base of finger. (c) Rolled latex glove finger at base of finger provides tourniquet. Note poorly defined scaly patch of distal phalanx. This lesion is a recurrent Bowen’s disease carcinoma that was previously removed by surgery by a plastic surgeon. Prior surgery excised the total nail unit, including the nail matrix, nail bed, and nail folds

Removal of all or part of the nail plate is necessary prior to Mohs surgery. A nail splitter is used to cut the nail prior to removal. The wider shaft of this instrument is inserted between the nail and its bed. It is then slid toward the nail cuticle where the tapered blade of the nail splitter on the top of the nail slips underneath the proximal nail fold. The nail is then cut, and in doing so, split. A hemostat is used to securely grasp the side of the nail plate to be removed, and the nail plate is removed from the digit with a twisting motion. Then, the abnormal tissue in the nail bed or nail fold is curetted to delineate the tumor-involved area. We place the curettings onto the gauze on the Mohs card to be processed as a separate slide with the subsequent Mohs layer. A 2-mm margin of tissue around the curetted region is cut with a scalpel blade cutting tangentially to the tissue. Usually, 3-score marks are then made outward from the Mohs layer onto the surrounding skin to help maintain specimen orientation. The Mohs layer is removed with a scalpel, and care is taken to ensure that the base of the Mohs layer is smooth and complete. The Mohs layer is placed onto the gauze adjacent to the curettings, and Mohs card is brought to the laboratory for processing.

In the laboratory, the tissue is subsectioned and its non-epidermal edges colored by at least two different dyes, and a map is drawn onto the Mohs card to

delineate the location of each removed subsection in relation to the surgical defect. The different color dyes are indicated on the map by colored inks whose colors match the colors of the dyes on the tissue. We feel this reduces the error rate when indicating on the map the location of tumor as seen under the microscope. The tissue is fixed onto glass slides and stained. In our laboratory, the primary stain utilized is hematoxylin and eosin, while a toluidine blue stain is reserved for the management of basal cell carcinomas. The slides are then reviewed by the surgeon. The processing of the frozen sections allows for evaluation of the skin margins as well as the undersurface of the tissue. Any remaining tumor identified on the slides is marked onto the corresponding section of the diagram on the Mohs card. If tumor is identified on the initial stage, a second layer of tissue is removed from the patient at the affected area. These steps are repeated until a tumor-free margin is obtained.

A special problem that occurs when removing tumor that involves the nail matrix is that once the final Mohs layer has been taken, a lateral horn of the matrix must be removed along with the matrix. If this is not done, the lateral matrix horn will regrow as a small spicule which will be a nuisance for the patient.

28.4.6 Dressings and Postoperative Care

Between each Mohs layer, the surgical site is bandaged with a temporary dressing. A piece of nonadherent dressing is cut to fit the defect. Gauze is then cut and folded over the nonadherent dressing. Paper tape is applied in an oblique fashion to secure the temporary dressing, as the vascular supply may theoretically be impeded by winding tape circumferentially around the digit. The tape is also cut so that it does not totally encircle the digit. Tube dressings are another modality that provides a simple pressure dressing. Unfortunately, such dressings may cause complications if not properly used. Ersek demonstrated finger necrosis after the application of an elastic net bandage applied in many layers. The use of the elastic net dressing increased the pressure on the patient’s finger and impeded blood flow after each successive layer [33].

In our experience, postoperative wounds of the periungual/subungual area often go in depth to bare bone and involve a variable amount of matrix. Because it is difficult to always determine the extent of matrix remaining, our bias is to let wounds in this area heal by granulation and epidermization. Second intention healing often produces excellent