Non-pigmented AKs: linear or wavy vascular patterning, or a "strawberry pattern," described as unfocused vessels between hair follicles, with white-haloed follicular openings. Pigmented AKs: gray to brown dots or globules surrounding follicular openings, and annular-granular rhomboidal structures; often difficult to differentiate from lentigo maligna. Prevention
Ultraviolet radiation is believed to contribute to the development of actinic keratoses by inducing mutations in epidermal keratinocytes, leading to proliferation of atypical cells. Therefore, preventive measures for AKs are targeted at limiting exposure to solar radiation, including:

Limiting extent of sun exposure
Avoid sun exposure during noontime hours between 10:00 AM and 2:00 PM when UV light is most powerful
Minimize all time in the sun, since UV exposure occurs even in the winter and on cloudy days
Using sun protection
Applying sunscreens with SPF ratings 30 or greater that also block both UVA and UVB light, at least every 2 hours and after swimming or sweating
Applying sunscreen at least 15 minutes before going outside, as this allows time for the sunscreen to be absorbed appropriately by the skin
Wearing sun protective clothing such as hats, sunglasses, long-sleeved shirts, long skirts, or trousersRecent research implicating human papillomavirus (HPV) in the development of AKs suggests that HPV prevention might in turn help prevent development of AKs, as UV-induced mutations and oncogenic transformation are likely facilitated in cases of active HPV infection.
It is the most common cause of primary mitral regurgitation in the United States, causing about 50% of cases. Myxomatous degeneration of the mitral valve is more common in women as well as with advancing age, which causes a stretching of the leaflets of the valve and the chordae tendineae. Such elongation prevents the valve leaflets from fully coming together when the valve closes, causing the valve leaflets to prolapse into the left atrium, thereby causing MR.Ischemic heart disease causes MR by the combination of ischemic dysfunction of the papillary muscles, and the dilatation of the left ventricle. This can lead to the subsequent displacement of the papillary muscles and the dilatation of the mitral valve annulus.Rheumatic fever (RF), Marfans syndrome and the Ehlers–Danlos syndromes are other typical causes. Mitral valve stenosis (MVS) can sometimes be a cause of mitral regurgitation (MR) in the sense that a stenotic valve (calcified and with restricted range of movement) allows backflow (regurgitation) if it is too stiff and misshapen to close completely. Most MVS is caused by RF, so one can say that MVS is sometimes the proximal cause of MI/MR (that is, stenotic MI/MR) and that RF is often the distal cause of MVS, MI/MR, or both. MR and mitral valve prolapse are also common in Ehlers–Danlos syndromes.Secondary mitral regurgitation is due to the dilatation of the left ventricle that causes stretching of the mitral valve annulus and displacement of the papillary muscles.