Three-dimensional ultrasound in the preoperative staging of rectal cancer: State of the art

Imaging modalities such as endorectal ultrasonography (ERUS), pelvic magnetic resonance (MRI) and computed tomography play a fundamental role in evaluating recatl cancer preoperatively, planning surgical procedures, and selecting patients for neoadjuvant therapy. Based on the best available evidence, ERUS is recommended to accurately discriminate between T1 and T2 lesions, for low rectal cancer, defined as 0-5cm from the anal verge, if local excision (with transanal excision of transanal endoscopic microsurgery) is being considered. MRI is the best modality to detect mesorectal fascia invasion and to predict circumferential resection margin involvement. Both modalities have similar limitations in distinguishing metastatic from bening lumph node in the mesorectum. Due to higher panoramicity and multiplanar reconstruction, three-dimensional ERUS allows to visualize the spatial relationship of the rectal tumour in the context of the surrounding structures, improving the accuracy of ultra-sonographic staging. Technological advances and perspectives of ERUS under investigations are represented by real-time colour elastography, Doppler US and contrast-enhanced US.