ABD Mohs Surgery cheat sheet

Basal cell carcinoma subtypes with aggressive behavior: morpheaform, infiltrative, micronodular, and basosquamous; superficial and nodular are less aggressive.

Squamous cell carcinoma high-risk features: depth >2 mm, perineural invasion, poorly differentiated, recurrent, immunosuppression, and ear/lip location.

Melanoma Breslow thickness drives prognosis; mitotic rate and ulceration are independent adverse prognostic factors in the AJCC staging system.

Mohs appropriate for basal cell carcinoma and squamous cell carcinoma with high-risk features, dermatofibrosarcoma protuberans, and microcystic adnexal carcinoma.

Perineural invasion spreads along nerve sheaths; named-nerve involvement (e.g., trigeminal, facial) warrants imaging and multidisciplinary planning.

Field cancerization from cumulative ultraviolet exposure produces multifocal subclinical disease; margin control exceeds visual estimation.

Microcystic adnexal carcinoma and dermatofibrosarcoma protuberans show subclinical extension, requiring Mohs over wide local excision in cosmetically sensitive sites.

Immunosuppressed patients (transplant, chronic lymphocytic leukemia) have higher recurrence and metastasis rates for cutaneous squamous cell carcinoma.

Mohs stages: debulk, take thin peripheral and deep margins, map and ink, frozen section, then re-excision of positive areas only.

Complete margin assessment in Mohs approaches 100% of the peripheral and deep margin, versus less than 1% sampling with standard vertical sections.

Indications: high-risk histology, recurrent tumors, ill-defined borders, anatomically sensitive sites (face, ears, digits, genitalia), and large size.

Relaxed skin tension lines guide elliptical excision orientation; in Mohs the defect is mapped before reconstruction planning.

Inking scheme (e.g., two-color or quadrant) must be recorded on the map to correlate frozen-section findings with the surgical defect.

Debulking specimen is sent for permanent section to confirm diagnosis and assess deepest invasion.

Curettage before margin excision can help define tumor extent but must not compromise the mapped margin.

Frozen-section artifact (folds, chatter, freeze artifact) can mimic or obscure tumor; correlate with clinical and map findings.

Frozen sections are cut at 4–6 micrometers; thicker sections impair nuclear detail and increase false-negative risk.

Basal cell carcinoma on frozen section: nests of basaloid cells with peripheral palisading and retraction artifact from stroma.

Squamous cell carcinoma: keratinizing nests with intercellular bridges and keratin pearls; perineural invasion requires tracking along nerve.

Tumor islands smaller than one high-power field at the margin may be missed; serial sections and careful scanning reduce false negatives.

Inflammatory infiltrate and fibrosis after prior treatment can obscure residual tumor; examine deeper levels when suspicious.

Melanoma is generally not evaluated by frozen section due to difficulty distinguishing atypical melanocytes; permanent sections preferred.

Dermatofibrosarcoma protuberans: uniform spindle cells in storiform pattern infiltrating subcutis; CD34 positive, factor XIIIa negative.

Margin positivity definition: tumor at the inked edge; close margins (within one high-power field) prompt additional excision.

Reconstruction ladder: secondary intention, primary closure, split-thickness or full-thickness graft, local flap, regional flap, free flap.

Fusiform (elliptical) closure length-to-width ratio of 3:1 to 4:1 reduces dog-ear formation; orient along relaxed skin tension lines.

Bilobed and rhomboid flaps redistribute tension; Limberg rhomboid uses 60/120-degree angles.

Full-thickness skin grafts rely on vascularized bed; cartilage-exposed or irradiated beds have poor graft take.

Nasal reconstruction: local flaps (bilobed, nasolabial) preferred; cartilage framework needed for alar or tip defects.

Ear defects: wedge closure for helical rim; composite graft for small full-thickness defects; chondrocutaneous advancement for larger.

Antibiotic prophylaxis is not routine for clean Mohs defects; consider for high-risk (immunosuppression, prosthetic valve, large contaminated defects).

Suture removal timing: face 5–7 days, scalp 7–10 days, trunk/extremities 10–14 days; tension-bearing areas longer.

Local anesthesia maximum doses: lidocaine 7 mg/kg without epinephrine, 4.5 mg/kg with epinephrine; bupivacaine 3 mg/kg.

Epinephrine-containing solutions reduce bleeding and prolong anesthesia; avoid in distal digits and areas with compromised perfusion.

Anticoagulation (warfarin, direct oral anticoagulants) is generally continued during Mohs; stopping increases thromboembolic risk.

Complications: bleeding, hematoma, infection, dehiscence, hypertrophic scar, keloid, nerve injury, and flap/graft necrosis.

Hypertrophic scars occur within weeks; keloids extend beyond original wound and recur; intralesional triamcinolone is first-line.

Vasovagal syncope during injection: supine positioning, cool compress, monitor vital signs; most resolve spontaneously.

Postoperative bleeding management: pressure, cautery, suture; severe or expanding hematoma requires evacuation to prevent flap compromise.

Document informed consent, allergies (lidocaine, epinephrine, latex), and anticoagulant use before the procedure.

Facial nerve branches: temporal, zygomatic, buccal, marginal mandibular, cervical; marginal mandibular injury causes asymmetric smile.

Temporal branch runs superficial to the zygomatic arch; danger zone is the region anterior to the tragus.

Trigeminal divisions: ophthalmic (V1), maxillary (V2), mandibular (V3); mental nerve exits the mental foramen.

Danger triangle of the face drains via the angular vein to the cavernous sinus; infection risk warrants prompt treatment.

Nasal blood supply: internal carotid (anterior and posterior ethmoidal) and external carotid (angular, infraorbital, sphenopalatine) anastomoses.

Eyelid anatomy: anterior lamella (skin and orbicularis), posterior lamella (tarsus and conjunctiva); defects >50% of lid margin need reconstruction.

Ear: blood supply from superficial temporal and posterior auricular arteries; cartilage framework lacks intrinsic blood supply.

Neck levels I–VI guide nodal staging; level I submental/submandibular, level II upper jugular.

Mohs appropriate use criteria (AUC) score guides case selection; higher scores support Mohs over excision.

Quality metrics: recurrence rate, margin positivity, complication rate, and patient-reported outcomes.

Time-out and surgical site verification reduce wrong-site errors; verify patient, site, and procedure before incision.

Pathology specimen tracking: unique identifiers, map documentation, and chain of custody for each stage.

Sterilization and instrument handling per OSHA and infection-control standards; sharps injury protocol includes post-exposure prophylaxis.

Coding and documentation: CPT codes for Mohs stages, repair, and grafts must match operative notes.

Electronic health record documentation of consent, photographs, and pathology results supports billing and quality audits.

Safety checklists and team briefings reduce adverse events and improve communication in office-based surgery.

Informed consent requires disclosure of risks, benefits, alternatives, and the right to refuse.

Confidentiality is protected by HIPAA; minimum necessary standard governs disclosure.

Conflicts of interest must be disclosed, including industry relationships and self-referral.

Professionalism includes honesty in documentation, avoiding upcoding, and respecting patient autonomy.

Health policy: Medicare reimbursement and prior authorization affect access to Mohs; documentation must support medical necessity.

Ethical billing requires accurate coding of stages and repairs; fraud includes unbundling and upcoding.

Patient privacy extends to photographs and case discussions; de-identification before any publication or teaching use.

Advocacy for appropriate use of Mohs balances access, cost, and quality; overuse raises ethical and policy concerns.