exactly what i was thinking.
i get black heads regualrly and have had a few tha were several mm in length, if left unchecked both blackheads and spots can grow down a pore and when squeezed have an incredible length. This may be a similar thing?
i've seen them that size several times. you aren't thinking of centimeters are you? 4mm is only about a quarter of an inch. if the sack were already breaking down and the surface opening big enough one could compress that easily into a linear 4mm string.
heck i've extracted comedones that big! (senior citizens that hadn't been groomed very well)
chelly do you think it would be possible to squeeze a cyst out 4 mm long? wouldnt that have to be cut out? cut away from the surrounding tissue? stage did it have a ribbed texture or anything? what made it look like a worm?
if not what buminabum suggested it may have been a simple cyst. somethimes the sack can grow linear and have the look and smell of rotten cottage cheese.
you can look up sebaceous cyst, pilar cyst or epidermal cyst and get quite a bit of images.
hmmm look up SCREW-WORM FLY google images to see if it is similar to what you saw.