What are these LCD defects if not dead pixels?

Over the past weeks, a line of black/turquoise pixels has appeared on the left of the LCD screen of my 2-year old Lenovo laptop, and has slowly spread into the stain photographed below.

However, it does not seem to be "dead" pixels, since images are still visible underneath. The zone does not appear on screenshots.

What could cause this, and why is it spreading ? Is there any way to fix it ?

You probably have a leak or fracture in the liquid crystal layer of your monitor causing it to loose fine control of the light blocking ability of the liquid crystals.

Your display has many layers. One of those layers is a liquid crystal layer that can be controlled in order to block or allow light to pass through to the actual coloured pixel layer. If you can see some kind of image then the light emitting layer is okay as is the actual pixel colours. As you have some image it is quite likely that there is some crystals moving to allow a tiny amount of light through, but not enough to make a reliable image.

_{from http://www.electroschematics.com/5666/liquid-crystal-display/}

_{from http://www.maxi-pedia.com/TFT+LCD+display+monitor+panel}