Floating balls sign

The floating balls sign refers to the appearance of multiple mobile globules/spherules of solid, usually fatty, tissue within an adnexal cyst. It is pathognomonic for ovarian mature cystic teratoma .

Terminology

Alternative names include the meatballs or truffle sign .

When a single large ball is floating at a fat-fluid interface, the name Pokemon (Poké) ball sign has been used .

The term sack of marbles sign has also been applied to this appearance but it is more commonly used to describe dermoid cysts of the head and neck .

Epidemiology

Though thought to be uncommon, the sensitivity is up to 25% in some case series .

Pathology

The balls represent spherules of sebaceous or keratinoid debris . They are different from Rokitansky nodules, which are nonfloating mural protuberances . The balls float due to their lower specific gravity compared to cyst fluid .

Radiographic features

The balls are discrete spherical structures located within a cystic mass. They range in size, even within the same cyst, from 5 mm to 4 cm diameter . They also range in number, sometimes in excess of 100 within one cyst .

Two-thirds contain fat demonstrable by CT or MRI .

Ultrasound

The balls are echogenic on a background of anechoic/hypoechoic fluid . No color Doppler signal is present within.

CT

The balls vary in density, from fat density to soft tissue density (-70 to +35 HU) . Sometimes the balls have a fluid or soft tissue density core surrounded by a fat density rim .

MRI

The signal characteristics of the balls usually reflect the sebaceous composition .

• T1: hyperintense rim compared to surrounding fluid, relatively hypointense center
• T2: hypointense rim compared to the surrounding fluid, relatively hyperintense center compared to the outer portion

Fat-saturated sequences or an out-of-phase T1-weighted gradient-echo sequence may demonstrate signal drop, but this is not always present .