Mohs micrographic surgery — SAQ

Stem

A 68-year-old man presents with an 18 mm, slowly enlarging, pearly, telangiectatic nodule on the right nasal ala. A shave biopsy confirms a morpheaform (sclerosing) basal cell carcinoma. He had a BCC on the same cheek excised three years ago. He is otherwise well and takes no regular medication.

Questions

a) What is the diagnosis and which features make this a high-risk tumour? (2 marks)

^[2][3]Recurrent morpheaform basal cell carcinoma of the right nasal ala. High-risk features: aggressive histology (morpheaform/sclerosing subtype has indistinct clinical margins and subclinical extension); recurrent (already recurred after prior treatment); H-zone location (nasal ala — tissue conservation critical, recurrence rates highest); and size over 1 cm on the face.

^[2]b) What is the most appropriate definitive treatment and why? Outline its principle. (3 marks)

Mohs micrographic surgery — the gold standard. Principle: excise a saucerised layer at a bevelled edge; map and colour-code the specimen; process horizontally (en face) on frozen section so that the entire true margin is examined on one slide; the surgeon reads their own slides while the patient waits; if positive, re-excise only the mapped positive area; repeat until clear; reconstruct the same day. Cure rates are higher than standard excision, especially for recurrent disease.^[2][4]

^[1]c) Describe the step-by-step technique of one Mohs stage. (3 marks)

(1) Mark the lesion, debulk with curette, infiltrate local anaesthetic; (2) excise a saucerised layer with a narrow rim at a bevelled edge; (3) cut reference notches and colour-code edges with dyes, draw an anatomical map; (4) orient deep-side up (en face), freeze on cryostat, cut thin sections; (5) stain, the Mohs surgeon reads the slides; (6) re-excise only the mapped positive area; (7) repeat until clear; (8) reconstruct the defect.^[4]

d) What are the key complications and what determines prognosis? (2 marks)

Complications: bleeding, infection, dehiscence, flap/graft failure, site-specific nerve injury (temporal and marginal mandibular branches of the facial nerve), ectropion/alar notching, hypertrophic scar, and recurrence (low for primary BCC). Prognosis depends on tumour biology (histological subtype, perineural invasion), completeness of margin clearance (which Mohs maximises), anatomical site, and immunological status — recurrent facial morpheaform BCC carries a high recurrence risk, exactly why Mohs is indicated here.^[2][4]

References4ShowHide

1. [1]Mullen JT, Feng L, Xing Y, et al. Dermatofibrosarcoma Protuberans: Wide Local Excision Versus Mohs Micrographic Surgery. Surgical oncology clinics of North America, 2016.PMID 27591501
2. [2]Marzuka AG, Book SE. Basal cell carcinoma: pathogenesis, epidemiology, clinical features, diagnosis, histopathology, and management. The Yale journal of biology and medicine, 2015.PMID 26029015
3. [3]Marzuka AG, Book SE. Basal cell carcinoma: pathogenesis, epidemiology, clinical features, diagnosis, histopathology, and management. The Yale journal of biology and medicine, 2015.PMID 26029015
4. [4]Connolly SM, Baker DR, Coldiron BM, et al. AAD/ACMS/ASDSA/ASMS 2012 appropriate use criteria for Mohs micrographic surgery: a report of the American Academy of Dermatology, American College of Mohs Surgery, American Society for Dermatologic Surgery Association, and the American Society for Mohs Surgery. J Am Acad Dermatol, 2012.PMID 22959232