Fibromuscular Dysplasia
Findings: There is a focal short segment stenosis of the right middle segment renal artery. This patient has fibromuscluar dysplasia.
Discussion: The pathologic classification of FMD is as follows:
Intimal fibroplasia
o This accounts for fewer than 10% of all cases of renal FMD.
o Collagen deposition occurs in the intima of the vessels.
o Internal elastic lamina may be disrupted.
o The lumen may be concentrically narrowed in a relatively short region, causing a ringlike stenosis on angiography, or it may be narrowed over a longer region as a smooth tubular stenosis.
Medial fibroplasia (3 subtypes)
o Medial dysplasia
+ This accounts for 80% of renal cases and most carotid cases.
+ Regions of thick, fibrodysplastic, collagenized tunica media alternate with regions of thinned media.
+ The result is the classic string-of-beads appearance on angiography.
o Perimedial fibroplasia
+ This accounts for 10-15% of all renal cases of FMD.
+ Patchy collagen deposition is observed in the outer media without disruption of the external elastic lamina.
+ This subtype can also result in the string-of-beads appearance on angiography, but the beads are not dilated to a larger diameter than that of the original vessel.
o Medial hyperplasia
+ This accounts for 1-2% of all renal cases of FMD.
+ True smooth muscle concentric hyperplasia without fibrotic changes is noted.
+ The result is a smooth stenosis on radiographic study.
Adventitial fibroplasia
o This form results in fewer than 1% of all renal cases of FMD.
o Dense collagen replaces the normally loose connective tissue of the adventitia.
Intimal fibroplasia
o This accounts for fewer than 10% of all cases of renal FMD.
o Collagen deposition occurs in the intima of the vessels.
o Internal elastic lamina may be disrupted.
o The lumen may be concentrically narrowed in a relatively short region, causing a ringlike stenosis on angiography, or it may be narrowed over a longer region as a smooth tubular stenosis.
Medial fibroplasia (3 subtypes)
o Medial dysplasia
+ This accounts for 80% of renal cases and most carotid cases.
+ Regions of thick, fibrodysplastic, collagenized tunica media alternate with regions of thinned media.
+ The result is the classic string-of-beads appearance on angiography.
o Perimedial fibroplasia
+ This accounts for 10-15% of all renal cases of FMD.
+ Patchy collagen deposition is observed in the outer media without disruption of the external elastic lamina.
+ This subtype can also result in the string-of-beads appearance on angiography, but the beads are not dilated to a larger diameter than that of the original vessel.
o Medial hyperplasia
+ This accounts for 1-2% of all renal cases of FMD.
+ True smooth muscle concentric hyperplasia without fibrotic changes is noted.
+ The result is a smooth stenosis on radiographic study.
Adventitial fibroplasia
o This form results in fewer than 1% of all renal cases of FMD.
o Dense collagen replaces the normally loose connective tissue of the adventitia.
Source: Emedicine.com