1. Role of MRI in Primary Rectal Cancer Staging and Management
Gerard Smith
Austin Radiology

2. Overview Basic Epidemiology Basic Rectal Anatomy
Key Anatomical Concepts
The Role of MRI in Clinical Staging and its relevance to Treatment decisions

3. Rectal Cancer Statistics
Jemal A, Siegal R, Ward E, et al. Cancer statistics, CA Cancer J Clin. 2009;50:

4. Rectal Cancer Statistics
Australia in 2005
13,076 new cases of colorectal carcinoma
13% of all cancer cases
4165 deaths
Lifetime risk of 1 in 12
Rectal Cancer accounts for approx 1/3 of all colorectal cases
TROG Cancer Research: trog.com.au

5. Anatomy of the Rectum Approximately 15 cm long
Divided into lower, mid & upper thirds
Lower: up to 5 cm from anal verge
Lies below the peritoneal reflection
Middle: 5 to 10 cm from anal verge
Peritoneal reflection extends over the anterior surface
Upper: 10 to 15 cm from anal verge
Peritoneum covers the anterior and lateral aspects of rectum
The mid to lower rectum is enveloped by the mesorectal fascia (MRF)

6. Mesorectal Fascia (MRF)
Exists below the peritoneal reflection, extends to the pelvic floor and is an encircling fascia that contains:
Rectum
Perirectal fat
Perirectal LN
Perirectal vessels
Variable in its definition
Tapers distally
Posteriorly it lays anterior to the presacral fascia

7. Total Mesorectal Excision (TME), and the Circumferential Resection Margin
Surgical standard for rectal excision
The rectum and the perirectal tissues en-bloc are excised
The plane of the dissection is along the outer aspect of the MRF
The Circumferential Resection Margin (CRM) is therefore in effect the MRF
TME surgery has reduced local recurrence rates significantly (from 38% to 8%)
Recurrence rates ? Dropped from approx 30% to ?8%

8. Total Mesorectal Excision

9. The Role of MRI To assist in clinical staging
The treatment for rectal cancer is surgery (TME) with stage appropriate neoadjuvant therapy
Intent of clinical staging is to identify patients suitable for
upfront surgical resection
neoadjuvant therapy followed by surgery
Need accurate preoperative assessment
Tumor (T) and Nodal (N) Stage
Depth of tumor invasion beyond the muscle wall
Relationship of the tumor to the MRF/CRM

10. Neoadjuvant Therapy Most commonly Chemoradiotherapy
Short and Long course Radiotherapy
Its addition in the treatment of locally advanced rectal carcinoma prior to TME has further reduced local recurrence rates from 8% to approximately 2%
CRT is more effective, better tolerated, associated with better compliance and less toxicity when given as neoadjuvant therapy compared with post operatively
?low rectal site an indication for CRT

11. Anatomy of the Rectal Wall
CIS T1 T2
Mucosa: thin hypointense line
Submucosa: thicker band of high signal
Muscularis propria: outer low signal intensity line T3

12. Staging of Rectal Carcinoma: TNM
T Staging
T1: Confined to the submucosa
T2: Confined to the muscularis propria
T3: Beyond the muscularis propria
T4: Extension to involve
Visceral peritoneum (T4a)
Pelvic organs (T4b) such as prostate, seminal vesicles, cervix/uterus, bladder, pelvic side wall or pelvic floor.

13. T Staging of Rectal Carcinoma
T1: Confined to Submucosa
T2: Confined to Muscularis Propria

14. T Staging of Rectal Carcinoma
T3: Beyond Muscularis Propria

15. T Staging of Rectal Carcinoma
T4a: Involvement of Peritoneum

16. T Staging of Rectal Carcinoma
T4b: Involvement of Pelvic Organs

17. T Staging of Rectal Carcinoma
Difficult to depict T1 from early T2 on MRI
Endorectal US plays a role
MRI may overcall T2 tumors as early T3
Due to desmoplastic response in perirectal fat
Perirectal extension should be called when the tumor margin within the perirectal fat is nodular and irregular and not low intensity linear spicules

18. T3 Staging of Rectal Carcinoma
Majority (80%) of rectal cancers present as T3 tumors
The degree of extension beyond the muscularis propria is important prognostically and potentially to the Rx chosen
T3a <1mm
T3b 1-5mm
T3c >5-15mm
T3d >15mm
Early stage T3 (<5mm) 85% 5yr cancer specific survival
Advanced stage T3 (>5mm) 54% 5yr cancer specific survival
(Merkel et al. Int J Colorectal Dis 2001; 16: )

19. MRI and histopathology were equivalent to within 0.5mm
Prospectively assessed 295 patients who underwent primary TME surgery and compared the extramural depth of invasion on MRI to histopathology
MRI and histopathology were equivalent to within 0.5mm
Note was achieved by using standardized imaging techniques, pre study imaging and pathology workshops, and standardized imaging and pathology interpretation criteria
Radiology 2007; 243:

20. Nodal staging N1 1-3 nodes N2 4 + nodes Regional LN are:
perirectal, superior, middle and inferior rectal, sigmoid and inferior mesenteric, lateral sacral, sacral promontory, and internal iliac
External Iliac and retroperitoneal LN are not regional but represent metastatic disease

21. Nodal staging Nodal staging on MRI is difficult
Nodal size criteria of limited value
Nodal morphology improves accuracy
Irregular node contour
Variable signal intensity
Other techniques studied to improve accuracy include
USPIO-enhanced MRI
(Lahaye MJ, et al. Radiology 2008)
Gadofosveset-enhanced MRI
(Lambregts DM, et al. Abdominal Imaging 2012)

22. 437 LN identified on pathology
42 TME specimens transversely sectioned and directly compared with MRI slices
437 LN identified on pathology
102 not seen on MRI because too small (<3mm) but only 2 of these contained metastases
51 above the area imaged and 7 of these contained metastases
Size of benign and malignant LN similar
Radiology 2003; 227(2):

23. Compared with using a 5mm cut-off
When an irregular border or mixed signal intensity used for diagnosis
Sensitivity 85% (95%CI 74% - 92%)
Specificity 97% (95%CI 95% - 99%)
Compared with using a 5mm cut-off
Sensitivity 68%
Specificity 78%
Systematic Review and Meta-analysis ( )
Lymph Node involvement
Sensitivity 77% (95%CI 69%-84%)
Specificity 71% (95%CI 59%-81%)
Radiology 2003; 227(2):
Ann Surg Oncol 2012; 19:

24. Mesorectal Fascial Involvement
MRI is accurate in predicting an at risk CRM
Tumor within 1 mm of the MRF is predictive of a positive CRM
Advancing tumor margin
Metastatic lymph node
Malignant deposit
Extramural Vascular Invasion (EMVI)
Low rectal tumors are at greater risk of MRF involvement
Identification of tumor involvement of the MRF modifies surgical approach

25. Extramural Vascular Invasion (EMVI)
EMVI is the presence of tumor cells within blood vessels beyond the muscularis propria
Present in 30-40% of specimens
Associated with synchronous metastatic disease
EMVI independently predicts local and distant recurrence and poorer overall survival

26. Retrospective study of 94 patients Sensitivity 62% Specificity 88%
Relapse Free Survival at 3yrs
35% MRI-EVMI +ve
74% MRI-EVMI –ve
British Journal of Surgery 2008; 95:

27. Summary
Understanding of the key anatomical concepts of the MRF, CRM and TME surgery
Understanding of the clinical staging of rectal cancer and the triage of patients to surgery alone or neoadjuvant CRT followed by surgery
The limitations of Nodal staging and the importance of morphology over size
Importance of assessing the tumor with respect to the MRF

28. Thank you