Skin biopsy — Viva

Q1: Indications and selection of biopsy technique (2 min)

Take me through the five core biopsy techniques used in dermatology and tell me when each is the right choice.

The five techniques are punch biopsy (4 mm cylindrical blade reaching epidermis, dermis and subcutaneous fat — the workhorse diagnostic procedure for inflammatory dermatosis, alopecia and blistering disorders, paired with DIF in Michel's medium when autoimmune blistering disease is suspected); shave biopsy or saucerisation (tangential cut with a flat blade reaching epidermis and upper dermis only — for raised benign lesions such as seborrhoeic keratoses, viral warts, skin tags and selected superficial BCC; never for suspected melanoma); excisional biopsy (full-thickness elliptical cut along the skin tension lines with 1-3 mm clinical margin — the rule for suspected melanoma and small lesions where complete removal is curative); incisional biopsy (partial-thickness wedge of the most abnormal area — for large lesions where complete excision is impractical, and for deep processes such as panniculitis where subcutaneous fat must be included); and curettage and electrodesiccation (sharp ring curette scraping away friable tumour followed by electrofulguration of the base and rim — a therapeutic rather than diagnostic modality for small low-risk BCC on the trunk; it destroys the specimen so it is not a biopsy in the strict sense). [1]

Examiner probe: Why is a shave biopsy absolutely contraindicated for suspected melanoma? — Because the shave transects the lesion horizontally; the deepest tumour cell — the basis of Breslow thickness, the most important prognostic factor in melanoma — is left in the patient. AJCC T-stage, sentinel node biopsy threshold, definitive wide local excision margin and adjuvant therapy decision all depend on Breslow thickness, and a shave biopsy cannot measure it. [1]

Q2: Site selection (2 min)

Where on the lesion do you take the biopsy, and why does the location matter for the diagnosis?

For inflammatory dermatosis, biopsy the active edge of a fresh, fully evolved lesion — neither the freshest papule nor the oldest plaque — because the centre of a chronic plaque shows only non-specific chronic change while the edge concentrates the early diagnostic features (spongiosis, vacuolar interface change, leukocytoclastic debris). For an ulcer, biopsy the edge of the lesion where diseased meets normal tissue, not the necrotic base (the base shows only slough). For alopecia, biopsy the active edge of recent hair loss plus a comparison 4 mm punch from clinically uninvolved scalp for control — both submitted for transverse (horizontal) sectioning so the pathologist can calculate the terminal-to-vellus ratio (normal >7:1). For a tumour, biopsy the most indurated, ulcerated or atypical area. For suspected melanoma, excise the whole lesion with a 2-3 mm clinical margin and full thickness — never partial biopsy. For panniculitis, the biopsy must extend into subcutaneous fat (a 4 mm punch usually fails; an incisional ellipse is the rule). [1]

Examiner probe: Why does the depth of biopsy matter for panniculitis? — Because the pattern of inflammation (septal vs lobular, with or without vasculitis) is the diagnostic classifier, and the pattern is in the fat. A 4 mm punch frequently samples only the dermis and the diagnosis is missed. [1]

Q3: Specimen handling and fixative (3 min)

Take me through specimen handling for routine H&E, for direct immunofluorescence, for microbiology and for electron microscopy — and tell me which fixative destroys which test.

H&E — the routine fixative is 10% neutral buffered formalin at a 10:1 formalin-to-tissue ratio; the specimen should be immersed within minutes (no more than 30) of removal to avoid drying artefact. Direct immunofluorescence (DIF) — the specimen goes into Michel's medium, an ammonium sulphate-based transport medium that preserves IgG, IgA, IgM, C3 and fibrinogen at room temperature for up to 5 days; formalin destroys these immunoreactants and a DIF specimen placed in formalin is an irrecoverable waste (the test must be repeated on a fresh biopsy). Microbiology culture — sterile saline, no fixative; standard culture for bacteria, fungi and mycobacteria; PCR for HSV, VZV, mycobacteria, Leishmania, Treponema. Electron microscopy — 2.5% glutaraldehyde in cacodylate buffer; preserves ultrastructural detail for inherited epidermolysis bullosa, viral inclusions and lysosomal storage. [1]

Examiner probe: A 4 mm punch biopsy of perilesional skin from a 70-year-old with tense bullae has been placed in formalin by an inexperienced trainee. What do you do? — The DIF is wasted on that specimen because formalin cross-links the immunoreactants. The patient needs a repeat biopsy from perilesional skin, taken into Michel's medium this time, sent with a paired H&E from the blister edge in formalin. The error is not recoverable on the existing specimen. [1]

Q4: Closure, suture selection, and avoidance of complications (2 min)

Take me through the layered closure of an excisional biopsy on the face of a 60-year-old, including suture selection and removal timing.

Under local anaesthetic (1% lidocaine with adrenaline 1:100 000; wait 5-10 minutes for vasoconstriction), the lesion is excised as a 3:1 to 4:1 ellipse along the resting skin tension lines, extending into subcutaneous fat. The wound edges are undermined laterally by 0.5-1 cm to offload tension. Haemostasis is achieved with bipolar or battery-operated cautery. The closure is two-layered. The deep dermis is approximated with buried interrupted sutures of 5-0 absorbable polyglactin or polydioxanone on a tapered needle; knots are buried deep to the dermis to prevent suture spitting. The epidermis is then approximated with fine interrupted or running sutures of 6-0 non-absorbable monofilament nylon or polypropylene on a cutting needle. Adhesive strips can be used as adjuncts on low-tension wounds. The wound is dressed with non-adherent gauze and a pressure pad. Suture removal is at 5-7 days on the face (because the face heals quickly and tracks less). Photoprotection of the scar is continued for 12 months. [1]

Examiner probe: When would you NOT use adrenaline-containing local anaesthetic? — On digits, nose, ear and penis (the "end-arteries"), the conservative practice is plain lidocaine, although contemporary series suggest low-concentration adrenaline is generally safe; the rule is taught because rare cases of digital tip necrosis leading to amputation have been reported (Arp 2023; Hong 2021). [1]

Q5: Regional differences and evidence base (3 min)

What is the regional delta in the management of cutaneous malignancy, and what is the evidence base?

In the United States (AAD / ACMS / NCCN), Mohs micrographic surgery is the dominant technique for high-risk non-melanoma skin cancer on the H-zone of the face, for recurrent tumours, for aggressive histological subtypes (infiltrative, morpheaform, micronodular BCC, poorly differentiated SCC, perineural invasion), for DFSP, and for specific infiltrative tumours (atypical fibroxanthoma, Merkel cell carcinoma, microcystic adnexal carcinoma). Cure rates are 98-99% for primary BCC, 94-96% for recurrent BCC, 96-97% for primary SCC — the highest of any skin cancer treatment — because Mohs examines 100% of the surgical margin on horizontal en face frozen sections, versus under 1% margin sampling for wide local excision. In the United Kingdom (BAD / NICE NG12) and in Europe / Australia / India, wide local excision (WLE) with predetermined clinical margins is the rule; Mohs is commissioned at specialist skin cancer MDTs and is reserved for H-zone, recurrent, infiltrative and DFSP tumours. [1]

The evidence base for skin biopsy is largely expert consensus and decades of retrospective series — there are few high-quality RCTs because biopsy is the universal reference standard. Key primary literature includes Greenwood 2022, Pickett 2011, Ng 2010 (partial biopsy upstaged 22% of melanocytic lesions in a 218-case series), Kim 2021 (Breslow thickness changed in one-third of melanomas between initial punch biopsy and wide local excision), and the DFSP Mohs meta-analysis (Veronese 2023). [1]

Examiner probe: For lentigo maligna on the cheek of a 75-year-old, would you choose Mohs or WLE? — Mohs with MART-1 immunostaining or slow-Mohs with permanent paraffin sections is increasingly used because subclinical extension on chronically sun-damaged skin defeats standard 5 mm margins; the meta-analysis by Elshot 2023 supports this approach. WLE with wider margins (1 cm) is an acceptable alternative in Europe and Australia. [1]

References

1. [1]Greenwood JD, Merry SP, Boswell CL. Skin Biopsy Techniques Prim Care, 2022.PMID 35125151
2. [2]Pickett H. Shave and punch biopsy for skin lesions Am Fam Physician, 2011.PMID 22046939
3. [3]Ng JC, Swain S, Dowling JP, et al. The impact of partial biopsy on histopathologic diagnosis of cutaneous melanoma: experience of an Australian tertiary referral service Arch Dermatol, 2010.PMID 20231492
4. [4]Kim TH, Shin K, Kim YS, et al. Effect of changes in Breslow thickness between the initial punch biopsy results and final pathology reports in acral lentiginous melanoma patients Sci Rep, 2021.PMID 34615974
5. [5]Jones S, Ho J, Fine J, et al. Clinical Impact and Accuracy of Shave Biopsy for Initial Diagnosis of Cutaneous Melanoma J Surg Res, 2023.PMID 36739830
6. [6]Kumudhini S, Pai R, Shetty A. A comparative study of Michel's medium versus honey as a transport medium for skin specimens prior to direct immunofluorescence microscopy and antigen mapping J Cutan Pathol, 2019.PMID 31087406
7. [7]Meijer JM, Aries JCQ, Diercks GFH, et al. Serration pattern analysis for differentiating epidermolysis bullosa acquisita from other pemphigoid diseases J Am Acad Dermatol, 2018.PMID 29154993
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11. [11]Rutnin S, Somanachan I, Thanomkitti K, et al. Variation of Hair Follicle Counts among Different Scalp Areas: A Quantitative Histopathological Study Skin Appendage Disord, 2022.PMID 35118125
12. [12]Rahman SM, Yoneyama K, Hasan R, et al. Basal cell carcinoma has greater subclinical extension than squamous cell carcinoma: a cohort study Arch Dermatol Res, 2024.PMID 38761227
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14. [14]Arp AS, Le BR, Prabhu N. The Anesthetic Effects of Lidocaine with Epinephrine in Digital Nerve Blocks: A Systematic Review J Am Podiatr Med Assoc, 2023.PMID 37713411
15. [15]Hong IS, Heiner LR. Epinephrine-Containing Digital Nerve Block: A Case of Digital Tip Necrosis Leading to Amputation in a Patient With No Known Vascular, Rheumatologic, or Smoking History J Hand Surg Glob Online, 2021.PMID 35415561
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17. [17]Elshot YS, Ottevanger RR, Bekkenk MW, et al. Lentigo maligna (melanoma): A systematic review and meta-analysis on surgical techniques and presurgical mapping by reflectance confocal microscopy J Eur Acad Dermatol Venereol, 2023.PMID 36652277
18. [18]Noble CA. Clinical-pathologic correlation: The impact of grossing at the bedside Semin Diagn Pathol, 2025.PMID 38336505