A lentigo () (plural lentigines, ) is a small pigmented spot on the skin with a clearly defined edge, surrounded by normal-appearing skin. It is a harmless (benign) hyperplasia of melanocytes which is linear in its spread. This means the hyperplasia of melanocytes is restricted to the cell layer directly above the basement membrane of the epidermis where melanocytes normally reside. This is in contrast to the "nests" of multi-layer melanocytes found in moles (melanocytic nevi). Because of this characteristic feature, the adjective "lentiginous" is used to describe other skin lesions that similarly proliferate linearly within the basal cell layer. Diagnosis
Conditions characterized by lentigines include:
Lentigo simplex
Solar lentigo (Liver spots)
PUVA lentigines
Ink spot lentigo
LEOPARD syndrome
Mucosal lentigines
Multiple lentigines syndrome
Moynahan syndrome
Generalized lentiginosis
Centrofacial lentiginosis
Carney complex
Inherited patterned lentiginosis in black persons
Partial unilateral lentiginosis
Peutz–Jeghers syndrome
Lentigo maligna
Lentigo maligna melanoma
Acral lentiginous melanoma

Differential diagnosis
Lentigines are distinguished from freckles (ephelis) based on the proliferation of melanocytes. Freckles have a relatively normal number of melanocytes but an increased amount of melanin. A lentigo has an increased number of melanocytes. Freckles will increase in number and darkness with sunlight exposure, whereas lentigines will stay stable in their color regardless of sunlight exposure. Treatment
Lentigines by themselves are benign, however one might desire the removal or treatment of some of them for cosmetic purposes. In this case they can be removed surgically, or lightened with the use of topical depigmentation agents.
Major aortopulmonary collateral arteries (or MAPCAs) are arteries that develop to supply blood to the lungs when native pulmonary circulation is underdeveloped. Instead of coming from the pulmonary trunk, supply develops from the aorta and other systemic arteries. Pathogenesis and anatomy
Major aortopulmonary collateral arteries (MAPCAs) develop early in embryonic life but regress as the normal pulmonary arteries (vessels that will supply deoxygenated blood to the lungs) develop. In certain heart conditions the pulmonary arteries do not develop. The collaterals continue to grow, and can become the main supply of blood to the lungs. Though it is usually associated with congenital heart diseases with decreased pulmonary blood flow like tetralogy of Fallot or pulmonary atresia it may be seen sometimes in isolation i.e. not associated with any congenital heart disease in that case it is termed as isolated aortopulmonary collateral artery. In these cases it may be one of the cause of congestive cardiac failure in neonates.Pulmonary arteries come from the right side of the heart, and usually carry deoxygenated blood from the body. These collateral arteries carry blood which has already been oxygenated by the lungs, so are of little use in helping the body to get oxygen. Associated conditions
Pulmonary atresia with ventricular septal defect (or Tetralogy of Fallot with pulmonary atresia) will result in the development of systemic collaterals. Implications of a systemic collateral supply
Major aortopulmonary collateral arteries come from the systemic circulation, because of this they will often have higher pressure than normal found in the lungs, leading to pulmonary hypertension.