Chapter 4 58 Methods Patients TheCatharinaHospital inEindhoven is anational referral centre for patientswith locally advanced rectal cancer and LRRC in The Netherlands. From 1994 to 2015, a total of 334 consecutive patientswith LRRCwithoutmetastases or with resectablemetastaseswere treated with curative intent by a multimodality approach. For this study, only patients operated in the last 10 years (between 2005 and 2015), were selected, leaving a total of 214 patients for analysis. By reviewing theMR images, clinical findings, and endoscopy and pathology reports of all individual patients, the compartment of LRRC was determined. Of the 214 patients, 24 had a recurrence in the perineal region, 89 had a recurrence in the anastomosis or rectal stump, 18 had a recurrence in the anterior compartment, 28 had a recurrence in the mid-presacral area, and 4 patients had a recurrence from a mesorectal lymph node after a previous partial mesorectal excision. The remaining 51 patients had a solitary latLR, with definitely no anastomotic component. This unique patient group will be described further in this study. Subregions in the lateral compartment In order to be able to categorize different types of latLRs, three regions could be determined by meticulously reviewing the MR images. Lower latLRs Defined as located caudal to the piriformis muscle on MR imaging, on the level of the sacrotuberal ligament. Posterior extensionof these distal lateral recurrences meant invasion of the ligament and/or distal sacrum. At this level, the pelvis tapers and the anterior organs are very near to the sacral region; therefore, in latLR in this region, anterior extension is often seen—into the seminal vesicles and bladder in males, and into the vagina/cervix/uterus in females. Middle latLRs On the level of the piriformis muscle on MR imaging, along the internal iliac vessels. Posterior extension of these recurrences was seen in the piriformis muscle, and sometimes in the sacral nerve plexus at levels S2–S4. In the case of large recurrences, invasion of the anterior organs was observed. Upper latLRs Location of the latLR along the common iliac and/or external iliac vessels on MR imaging. Sometimes these vessels were invaded by the recurrence.