Published in:
01-07-2019 | Classics in Abdominal Radiology
The “hot air balloon” sign
Published in: Abdominal Radiology | Issue 7/2019
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A hot air balloon (Fig. 1) has been used as a metaphor for the imaging appearance of a giant sigmoid diverticulum, a rare complication of colonic diverticular disease. Defined as diverticulum greater than 4 cm in diameter [1], the etiology of a “giant” diverticulum remains unclear, but a commonly proposed mechanism is a ball-valve effect, where gas enters but cannot leave the diverticulum [1, 2]. Plain film radiographs often demonstrate a smooth, gas filled structure recalling the metaphorical sign (Fig. 2) [1]. CT also recalls the sign and provides a more definitive diagnosis, demonstrating the gas filled diverticulum (the “envelope” of the hot air balloon) and the connection to the colonic lumen on the anti-mesenteric side (representing the balloon’s “basket”) (Fig. 3) [1].
Fig. 1
A hot air balloon in flight. https://unsplash.com/search/photos/hot-air-balloons on 1/26/2019
Fig. 2
Scout view prior to abdominopelvic CT demonstrates a smooth, rounded gas filled structure (solid red arrow) within the left pelvis measuring approximately 5.5 cm in diameter, a giant sigmoid diverticulum
Fig. 3
Axial CT scan of the pelvis in the same patient seen in Fig. 2 demonstrates the giant gas filled sigmoid diverticulum (solid red arrow) and the connection to the colonic lumen (dotted red arrow)
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