The disorder
Mechanism & anatomy
Two ways a window can give way — a surge from within or a surge from without. The route predicts the trigger, and the trigger is the clue.
Explosive and implosive routes
A window can tear in two ways. A sudden rise in pressure inside the head (from straining or lifting) can push outward and burst it; or a sudden rise in pressure in the middle ear (from a forceful nose-blow or diving) can push inward until it tears.
Goodhill described two routes. The explosive route transmits a CSF pressure surge through the cochlear aqueduct to the perilymph, rupturing the window outward; the implosive route is a middle-ear pressure surge that pushes the window inward.1 Toggle the routes:
The distinction is more than historical: it maps onto the history you take. An explosive mechanism follows a strain, lift or cough; an implosive one follows a forceful Valsalva or barotrauma. Either way the result is the same — a leak that lets perilymph escape and pressure transmit abnormally.2
Where it leaks
The round window is the most frequent site, followed by the oval window (a particular concern after stapes surgery). Microfissures and congenital dehiscences are described too. The anatomy of these windows and the labyrinthine fluids is covered in Anatomy and Physiology. Note the overlap with superior canal dehiscence, which produces pressure/sound sensitivity by a fixed third window rather than a leak.
Why it happens
The commonest clear precipitant is barotrauma (diving, flying); others include head or penetrating trauma, iatrogenic injury after stapes surgery, and congenital malformations such as Mondini dysplasia (which also predisposes to recurrent meningitis). A spontaneous category exists but is the most contested and most likely over-diagnosed.2
Key points
- Explosive route: a CSF surge via the cochlear aqueduct ruptures the window outward.
- Implosive route: a middle-ear pressure surge pushes the window inward.
- The round window is the commonest site; the oval window matters after stapes surgery.
- Barotrauma, trauma, surgery and congenital malformation are the causes; spontaneous fistula is contested.