The diagnosis of rectal lesions is a challenging task, and the accuracy of the primary staging is important preoperatively. A relatively novel technology makes it possible to measure the tissue stiffness during endorectal ultrasonography.

The purpose of this study is to evaluate the diagnostic value of Shear Wave Elastography (SWE). The hypothesis is that the tissue stiffness is higher in malignant tissue than in benign lesions.

This study will include patients with an endoscopy verified rectal lesion referred to the radiology department for pretreatment evaluation.

During the investigation, patients will undergo magnetic resonance imaging (MRI) and endorectal ultrasonography (ERUS). During the ERUS, the tissue stiffness of the lesion and visible lymph nodes will be measured using the SWE technology.

Hypotheses:

1. Tumour stiffness measurement by SWE gives a statistically significantly higher value in malignant processes than in benign rectal tumors.
2. Tissue stiffness measurement with SWE gives a statistically significantly higher value in lymph node metastases than in reactive enlarged lymph nodes.
3. There is a statistically significant correlation between SWE and MRI apparent diffusion coefficient (ADC)

Histopathology report of surgical specimen will serve as endpoint.

Inclusion Criteria:

• Adults above 18 years of age
• Rectal lesions discovered during endoscopy
• Lesions located no more than 15 cm above the anal verge

Exclusion Criteria:

• Non-eligibility for MRI (e.g. claustrophobia, implants)
• Preoperative radiotherapy and/or chemotherapy