Gross and Microscopic Diagnosis by Direct Inspection and Light and Fluorescence Microscopy
Core principle
Diagnosis depends on systematic inspection at both macroscopic and microscopic levels. At the gross level, evaluate color, border, symmetry, and surface change. At the microscopic level, scan at low power to define architecture before examining cytology at high power.
Concepts to master
- Low-power architecture: silhouette, epidermal contour, dermal expansion, infiltrate distribution (superficial vs deep, perivascular vs interstitial).
- Cytologic criteria: nuclear atypia, mitotic figures, pigment, and cytoplasmic features.
- Special stains as needed: Fontana-Masson, Perl's Prussian blue, PAS, mucicarmine, and elastic tissue stains.
- Fluorescence microscopy: DIF patterns (linear vs granular, IgG/IgA/IgM/C3) at the basement membrane zone and perivascular areas.
Traps
- Diagnosing melanoma without assessing architecture at low power.
- Ignoring a deep component on a shave biopsy.
- Misinterpreting DIF granular C3 alone; interpret in clinical context.
- Overcalling atypia in sun-damaged skin without architectural confirmation.
Worked rule of thumb
For any melanocytic lesion, apply the ABCDE plus architecture check: symmetry, circumscription, maturation with depth, and single-cell predominance. Lack of maturation plus confluence favors melanoma.
Key points
- Scan architecture at low power before cytology.
- DIF: linear = bullous pemphigoid/epidermolysis bullosa acquisita; granular = dermatitis herpetiformis/lupus.
- Special stains confirm, they do not replace, H&E interpretation.
- Deep shave biopsies can miss deep pathology.
- Maturation is a key benign feature.