Pathophysiology
Clinical meaning
The ear is divided into three anatomic regions essential for systematic otoscopic and audiometric assessment. The external ear includes the auricle (pinna) and external auditory canal (EAC), a 2.5 cm S-shaped tube lined with skin, ceruminous glands, and hair follicles in its lateral cartilaginous portion, transitioning to a thin bony canal medially. The tympanic membrane (TM) separates the external from middle ear and consists of three layers: an outer squamous epithelial layer, a middle fibrous layer providing structural rigidity, and an inner mucosal layer continuous with the middle ear mucosa. The TM is divided into the pars tensa (larger, taut inferior portion) and pars flaccida (smaller, superior portion where cholesteatomas originate). Normal TM landmarks visible on otoscopy include the handle of the malleus (manubrium), the umbo (tip of malleus at the TM center), the lateral process of the malleus, and the cone of light (light reflex at 5 o'clock position in the right ear, 7 o'clock in the left). The middle ear is an air-filled cavity containing the ossicular chain (malleus, incus, stapes) that conducts sound vibrations from the TM...