The round window membrane in the middle ear has how many layers, and what is its significance in intratympanic drug delivery?

• A Three layers — outer epithelium, intermediate connective tissue layer, and inner epithelium — functions as a semi-permeable membrane allowing intratympanic corticosteroid/gentamicin diffusion into the scala tympani perilymph ✓
• B Single layer of epithelium — too thin for sustained drug delivery
• C Two layers — outer epithelium and inner connective tissue
• D Four layers including a basement membrane that completely blocks drug penetration

Explanation

The round window membrane (RWM) consists of three layers: an outer epithelial layer continuous with middle ear mucosa, an intermediate fibrous connective tissue layer, and an inner epithelial layer continuous with the cochlear endothelium. Its semi-permeable nature allows trans-membrane diffusion of drugs placed in the round window niche — the basis for intratympanic drug delivery (corticosteroids for sudden SNHL, gentamicin for Meniere's disease). Drug concentration in perilymph via this route significantly exceeds what is achievable by systemic administration, allowing targeted inner ear pharmacotherapy with minimal systemic side effects.

Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.