Fibromuscular dysplasia (FMD) of the renal artery is a non-inflammatory, non-atherosclerotic arterial disease causing renovascular hypertension in young women. The most common histological type of FMD shows a characteristic angiographic appearance called 'string of beads'. Which arterial layer is predominantly affected in the most common type?

• A Tunica intima (intimal fibroplasia)
• B Tunica adventitia (periarterial fibroplasia)
• C Internal elastic lamina (elastin fibroplasia)
• D Tunica media (medial fibroplasia) ✓

Explanation

The most common type of FMD is medial fibroplasia (comprising ~75–80% of all FMD cases), which affects the tunica media with alternating areas of fibromuscular thickening and thinning/microaneurysm formation, producing the classic 'string of beads' appearance on angiography where bead diameter exceeds the normal artery diameter. This pattern differs from intimal fibroplasia (smooth focal stenosis, seen in children) and perimedial fibroplasia (beads smaller than artery, outer media). FMD affects renal arteries (causing hypertension) and carotid/vertebral arteries (causing stroke or pulsatile tinnitus).

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.