An ‘double tumor image’ rectal endoscopic ultrasound image

Abstract

A 55-year-old man with decompensated alcoholic cirrhosis, was being evaluated for possible liver transplantation. His sigmoidoscopy showed an 8-mm diameter, sessile polypoid lesion in the rectum. Endoscopic biopsy was suggestive of a carcinoid tumor. A rectal endoscopic ultrasound (EUS) examination was performed with an electronic radial echoendoscope (GF UE 160AL5; Olympus, Japan), coupled with an ultrasound processor (Aloka ProSoundα-5). The image of the rectal lesion (Fig. 1) showed a mirror image artifact or duplication artifact of the lesion in the rectum. The ultrasound transducer produces the ultrasound beam and detects the returning echoes reflected from tissue interfaces. The distance of a reflector from the transducer is calculated by the “time of flight” of the returning echoes. When sound waves are reflected by highly reflective and curved surfaces (a ‘specular reflector’), some signals do not return directly to the transducer, but are reflected by adjacent portions of the reflector (Fig. 2). In this case, some ultrasound waves reflected off the rectal carcinoid tumor did not reach the transducer directly, but first bounced off at the air-water interface. Since these echoes have an increased ‘round trip time’, and are coming from a tangential direction, they are localized by the transducer to the opposite side of the air–water interface. This creates a mirror image artifact or a ‘double tumor image’. Structures immediately adjacent to highly reflective acoustic interfaces may appear to be duplicated because of reverberations of echoes between the transducers, lesion, and specular reflector (Fig. 3). The recording of “off-axis” information results in the Fig. 1 Rectal EUS image of a sessile polypoid lesion seen on sigmoidsoscopy