What could a 4cm density in the pelvis be. it also said on the myelogram that it was an incomplete image and recommended a pelvic ultrasound.

What did the doctor say?

In medical-lese this is how you say the test is non-diagnostic . Follow their advice and let them set you up for the ultrasound. (Super easy test, walk in but on gown have a nice chat with the tech while they scan you. Get dressed walkout feeling none the worse.)