Ball of wool / Yarn sign (hydatid cyst)

The ball of wool sign, also referred to as the yarn sign or congealed water lily sign, is an ultrasound appearance, representing degeneration of hydatid cysts . The inner side of the cyst detaches from the cyst wall and folds on itself, causing a change from anechoic (fluid) to a solid, hyperechoic appearance without internal septations or daughte Renal hydatid infection

Renal hydatid infection is extremely rare and is seen in less than 5% of patients with hydatid disease1. Infection is caused by a parasitic zoonosis with the Echinococcus tape worm.  The kidneys are the most commonly affected urinary organs, but bladder, prostate, seminal vesicles and testis can also be involved