Pie-in-the-sky sign | Radiology Signs

Answer:

The pie-in-the-sky sign is elevation of the bladder high above the pelvic floor by a large pelvic haematoma, so that the contrast-filled bladder sits abnormally high in the lower abdomen, usually compressed into a teardrop or pear shape by the surrounding blood. It is seen after major pelvic ring fracture and is an alerting sign rather than a diagnosis: it indicates substantial retroperitoneal and prevesical bleeding and raises the question of an associated bladder or posterior urethral injury. In men the classical association is membranous urethral disruption, and the correct sequence is a retrograde urethrogram before any attempt at catheterisation when there is blood at the meatus, inability to void or a high-riding prostate. Bladder integrity is assessed with CT cystography performed by retrograde gravity instillation of about 300 to 350 mL of dilute contrast; a passively clamped drainage catheter or an excretory-phase CT alone is unreliable and misses injuries. The distinction that determines management is between extraperitoneal rupture, in which contrast tracks in the prevesical space in a flame-shaped or molar tooth configuration and is usually treated by catheter drainage, and intraperitoneal rupture, in which contrast outlines bowel loops and pools in the paracolic gutters and requires surgical repair. A teardrop bladder without extravasation may also be produced by bilateral pelvic lipomatosis or lymphadenopathy in the non-traumatic setting.

Why is it called so?

The bladder is displaced so far superiorly that it appears to float high above its normal position, like a pie in the sky.

Pathophysiology

High-energy pelvic ring disruption tears the rich presacral and prevesical venous plexuses and the cancellous fracture surfaces bleed freely into the extraperitoneal space of Retzius, which is loose areolar tissue offering little resistance. The expanding haematoma lifts the bladder off the pelvic floor and compresses it laterally, producing both the elevation and the teardrop shape. The same shearing force transmitted through the puboprostatic ligaments avulses the membranous urethra at the genitourinary diaphragm, and fracture fragments or sudden rises in intravesical pressure rupture the bladder itself, which is why the three injuries are so often found together.

Alternative names: Teardrop bladder; pear-shaped bladder

Other associated named signs: Molar tooth sign of extraperitoneal bladder rupture and the flame-shaped extravasation of prevesical contrast leak

References

1. Morgan DE, Nallamala LK, Kenney PJ, Mayo MS, Rue LW 3rd. CT cystography: radiographic and clinical predictors of bladder rupture. AJR Am J Roentgenol. 2000;174(1):89-95. PMID: 10628460.