Published in:
01-10-2019 | Classics in Abdominal Radiology
The “cogwheel” sign of hydrosalpinx
Published in: Abdominal Radiology | Issue 10/2019
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A cogwheel (Fig. 1) has been used to describe the appearance of a hydrosalpinx imaged in cross section, as seen on ultrasound (Fig. 2) [1]. Throughout the fallopian tube, there are longitudinal folds and mucosal rugae, that in concert with cilia, help transport an egg to the uterus and also help clear fluid from the fallopian tube into the peritoneal cavity [2]. If the fallopian tube becomes blocked, usually in the ampullary segment which constitutes half the length of the tube [2], fluid is not cleared and the fallopian tube becomes dilated and fluid-filled producing a hydrosalpinx [1]. When this occurs, the longitudinal folds of the fallopian tube can become thickened, and appear more pronounced at imaging, recalling the pronged teeth of a cogwheel and producing the pathognomonic “cogwheel” sign of hydrosalpinx, when the tube is imaged in cross section (Fig. 3a) [1].
Fig. 1
Cogwheels with their spokes along the outer rim. The inferior cogwheel, with its spokes radiating inward, is more typical of the “cogwheel sign.” Photograph by Lynn Della Grotta
Fig. 2
Ultrasound image showing a left hydrosalpinx in cross section. The fallopian tube is fluid-filled with thickened folds along the periphery producing the “cogs” on the wheel (white arrows)
Fig. 3
a Coronal-enhanced CT image of the pelvis from another patient demonstrates a left hydrosalpinx with central fluid attenuation and thickened folds along the outer rim (blue arrows), producing the “cogwheel” sign. b A sagittal-enhanced CT image shows the elongated nature of the folds in the dilated tube to better advantage (yellow arrows)
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