should extend through to the level of the dermis in order to provide sufficient tissue for diagnosis; ideally, it would extend to the mid-reticular dermis. Punch biopsy usually extends to the subcutaneous fat when the entire length of the punch blade is utilized. Histopathology On histologic examination, actinic keratoses usually show a collection of atypical keratinocytes with hyperpigmented or pleomorphic nuclei, extending to the basal layer of the epidermis. A "flag sign" is often described, referring to alternating areas of orthokeratosis and parakeratosis. Epidermal thickening and surrounding areas of sun-damaged skin are often seen. The normal ordered maturation of the keratinocytes is disordered to varying degrees: there may be widening of the intracellular spaces, cytologic atypia such as abnormally large nuclei, and a mild chronic inflammatory infiltrate. Specific findings depend on the clinical variant and particular lesion characteristics. The seven major histopathologic variants are all characterized by atypical keratinocytic proliferation beginning in the basal layer and confined to the epidermis; they include: Hypertrophic: Notable for marked hyperkeratosis, often with evident parakeratosis. Keratinocytes in the stratum malphigii may show a loss of polarity, pleomorphism, and anaplasia. Some irregular downward proliferation into the uppermost dermis may be observed, but does not represent frank invasion. Atrophic: With slight hyperkeratosis and overall atrophic changes to the epidermis; the basal layer shows cells with large, hyperchromatic nuclei in close proximity to each other. These cells have been observed to proliferate into the dermis as buds and duct-like structures. Lichenoid: Demonstrate a band-like lymphocytic infiltrate in the papillary dermis, directly beneath the dermal-epidermal junction. Achantholytic: Intercellular clefts or lacunae in the lowermost epidermal layer that result from anaplastic changes; these produce dyskeratotic cells with disrupted intercellular bridges. Bowenoid: This term is controversial and usually refers to full-thickness atypia, microscopically indistinguishable from Bowen's Disease. However most dermatologists and pathologists will use it in reference to tissue samples that are notable for small foci of atypia that involve the full thickness of the epidermis, in the background of a lesion that is otherwise consistent with an AK. Epidermolytic: With granular degeneration. Pigmented: Show pigmentation in the basal layer of the epidermis, similar to a solar lentigo. Dermoscopy Dermoscopy is a noninvasive technique utilizing a handheld magnifying device coupled with a transilluminating lift. It is often used in the evaluation of cutaneous lesions but lacks the definitive diagnostic ability of biopsy-based tissue diagnosis. Histopathologic exam remains the gold standard.