Table 1.

Stages of progression. Comparison between MAC and intimal calcifications.

Medial Arterial Calcification		Intimal Calcification
I	Calcification of the internal elastic membrane with or without extension into the media (A and G).	Microcalcification (includes micro and punctate) is identified by calcium particles ranging from >0.5 μm and <1mm in diameter (M and S).	Micro and punctate calcification
II	Calcifications coalescence and becomes confluent (varying in size from 1 to 3 mm), forming fragments of calcification (B and H).	Small calcification is often accompanied by inflammation, areas of microcalcification coalescence forming fragments of calcification that are >1 mm but <3mm in diameter (N and T).	Fragment calcification
III	Calcification length > 3 mm and/or extends to involve >90° of the circumference (C and I).	Calcification of the intima >3mm or >90° (O and U). Calcification can extend and become circumferential (P and V).	Sheet Calcification
IV	Calcifications of the media, spanning the entire circumference (D and J).
Nodular calcification	Nodular calcification is rarely seen in medial wall which is composed of nodules of calcification often accompanied by fibrin (E and K).	Nodular calcification is composed of nodules of calcification often accompanied by fibrin with a fibrous cap (Q and W).	Nodular calcification
Bone formation	Bone formation may be observed in fragmented and areas of sheet calcification (F and L). Bone formation and rarely cartilaginous metaplasia may be seen in late-stage most frequently in stages III and IV, but rarely also in stage II.	Bone formation can be observed within the regions of calcification (R and X).	Bone formation

Modified and reproduced with permission from doi: 10.1016/j.jcmg.2018.08.039; doi: 10.1016/j.ejvs.2020.08.037.