English: Low magnification micrograph of the distal right coronary artery with complex atherosclerosis and luminal narrowing. Masson's trichrome.

Arteries have three layers (tunica intima, tunica media and tunica adventitia). These can be seen on the micrograph:

• Adventitia (outermost layer) = green fluffy material (collagen),
• Media (middle (muscular) part) = red (smooth muscle actin),
• Intima (inner part, in contact with the blood) = green (collagen) with some red (smooth muscle actin).

Features of atherosclerosis seen on the micrograph:

• The tunica intima is severely thickened; it measures up to approximately 1/3 of a millimetre. Normally, it is one cell layer thick (approximately 10 micrometres).
• There is fragmentation of the internal elastic lamina (a very thin black wavy layer) between the intima and media.
• There is a partial duplication of the internal elastic lamina.
• There is smooth muscle infiltration of the intima (from the media), i.e. red staining of the intima.
• There is significant luminal narrowing. The section of the artery shown has only 25-35% of the cross-sectional area it once had; the artery's original lumen was approximately where the double layer of elastin is seen (the internal elastic lamina).

Features that may be seen in atherosclerosis but are not evident in the micrograph:

• Calcifications.
• Cholesterol crystals.