Best in Practice Protocols: Rectal MRI

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Best in Practice Protocols: Rectal MRI

Mukesh Harisinghani, MD

Overview

• Pertinent anatomy and staging information

• MR Imaging– Protocol– Imaging pointers for surgical resection and

staging

– What to include in the report

Evaluation of Rectal Cancer Colo-Rectal Cancer

• Rectal cancer as a entity is inseparable from colorectal group

• Third most common cancer worldwide

• 2010– New cases: 39,670 (rectal cancers only)– Deaths (colon and rectal cancers

combined): 51,370

MRI Local Staging

EndoSonogr

(ERUS) Stagi

Rectal Ultra aphy

Local ng

PET CT Metastatic Work

up

Why MRI

• Excellent depiction of anatomy• MRI superior to ERUS in determining

the depth of transmural invasion (T stage) and local extension

• MRI comparable to ERUS for detecting lymph node metastases (N stage)

World J Gastroenterol 2008; 14(22): 3504

Rectal Anatomy

Upper Rectal Tumor: 12 -16 cm

Middle Rectal Tumor: 6-12 cm

Lower Rectal Tumor: < 6 cm

16 cm

1

2

3

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T2 W

Mucosa and Submucosa

Muscularis PropriaT2 W

MR Rectal Wall

HyHpyopinetreinseensDearRkinRging

T2 W

Pelvic Floor

Terms We Need to be Familiar With

• Mesorectal fascia

• Total Mesorectal Excision (TME)• Circumferential Resection Margin

(CRM)Mesorectal

Fascia

Total Mesorectal Excision(TME)

Circumferential Resection Margin (CRM)

• The shortest distance from the tumor or lymph nodes to the mesorectal fat is called the circumferential resection margin (CRM).


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MRI Rectal Protocol

Torso Phased ArrayMulti Channel Coil

> T2 –SAG

> Hi Res Oblique T2:Axial and Coronal

> Wide FOV Ax T2

Diffusion Weighted Images

Multiphasic Gd-Enhanced Series

1.5T or 3T

MR Pointers: Oblique Plane

MR Pointers

• Optimal TE on T– ~ 60 msec

2w

MRI Pointers

• Motion Correction– BLADE / PROPELLER

MRI Pointers: Time Saver

T2 SPACE/CUBE


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Role of MR Imaging

• Stratify patients into the following categories to guide presurgical therapy and surgical resection

– Early

– Local spread

– Distant Spread

What Matters and We Should Evaluate on MRI

• T stage

• CRM status

• Nodal stage

• Position of tumor

• T stage

• CRM status

• N stage


T1

T2

T3

Luminal Length Not as Important as Lateral Spread

T3T2

T4


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Beware of Desmoplastic Reaction

T3 T2

• T stage

• CRM status

• N stage


• When is CRM threatened– Primary tumor, tumor deposit or positive

lymph node in close proximity to mesorectal fascia

– <1 mm of CRM

– Bad prognosis; high recurrence rate

– Negative when distance > 6 mm

• T stage

• CRM status

• N stage


Good T3Bad T3Bad T3Bad T3

• T stage

• CRM status

• N stage


Most positive nodes are 5 – 7 mm in size

• T stage

• CRM status

• N stage



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• T stage

• CRM status

• N stage


Irregular Margins Heterogenous Signal

MR Accuracy

• T Staging : 65-91 %

• N Staging : 43-85 %

• CRM : 95 %

MRI is more accurate in predicting free resection margin than T stage !!!

Beets-Tan RG et al. Lancet 2001 Brown G et al. BJS 2003 & RSNA 2004 Nagtegaal I et al. Am J Surg Path 2002

Report• Location of the tumor in low, mid or high

rectum

• Length of the tumor for surgicalplanning

• Circumferential or not;

• T-stage; T3• Circumferential resection margin in mm

on anterior, posterior and lateral side.

• N-stage

Conclusion

• MRI useful for T staging and CRMstatus determination

• Used to stratifying patients prior totherapy

• Attention to proper technique is critical

• Role of DWI still emerging


Documents

Best in Practice Protocols: Rectal MRI