Transcript Role of MRI in Primary Rectal Cancer Management

Role of MRI in Primary Rectal
Cancer Staging and Management
Gerard Smith
Austin Radiology
Overview
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Basic Epidemiology
Basic Rectal Anatomy
Key Anatomical Concepts
The Role of MRI in Clinical Staging and its
relevance to Treatment decisions
Rectal Cancer Statistics
Jemal A, Siegal R, Ward E, et al. Cancer statistics, 2009. CA Cancer J Clin. 2009;50:225-249
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
Anatomy of the Rectum
• Approximately 15 cm long
• Divided into lower, mid & upper
thirds
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Lower: up to 5 cm from anal verge
– Lies below the peritoneal
reflection
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Middle: 5 to 10 cm from anal verge
– Peritoneal reflection extends
over the anterior surface
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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)
Mesorectal Fascia (MRF)
• Exists below the peritoneal
reflection, extends to the
pelvic floor and is an encircling
fascia that contains:
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Rectum
Perirectal fat
Perirectal LN
Perirectal vessels
• Variable in its definition
• Tapers distally
• Posteriorly it lays anterior to
the presacral fascia
Total Mesorectal Excision (TME), and the
Circumferential Resection Margin
• Total Mesorectal Excision (TME)
– 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%)
Total Mesorectal Excision
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
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
Anatomy of the Rectal Wall
CIS
T1
T2
• Mucosa: thin hypointense line
T3
• Submucosa: thicker band of high signal
• Muscularis propria: outer low signal intensity line
Staging of Rectal Carcinoma: TNM
• T Staging
– T1:
– T2:
– T3:
– T4:
Confined to the submucosa
Confined to the muscularis propria
Beyond the muscularis propria
Extension to involve
• Visceral peritoneum (T4a)
• Pelvic organs (T4b) such as prostate, seminal vesicles,
cervix/uterus, bladder, pelvic side wall or pelvic floor.
T Staging of Rectal Carcinoma
T1: Confined to Submucosa
T2: Confined to Muscularis
Propria
T Staging of Rectal Carcinoma
• T3: Beyond Muscularis Propria
T Staging of Rectal Carcinoma
• T4a: Involvement of Peritoneum
T Staging of Rectal Carcinoma
• T4b: Involvement of Pelvic Organs
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
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
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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: 298-304.)
• 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: 132-139
Nodal staging
• N1
• N2
1-3 nodes
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
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)
• 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): 371-377
• When an irregular border or mixed signal intensity
used for diagnosis
– Sensitivity 85% (95%CI 74% - 92%)
– Specificity 97% (95%CI 95% - 99%)
Radiology 2003; 227(2): 371-377
• Compared with using a 5mm cut-off
– Sensitivity 68%
– Specificity 78%
• Systematic Review and Meta-analysis (2000-2011)
– Lymph Node involvement
– Sensitivity 77% (95%CI 69%-84%)
– Specificity 71% (95%CI 59%-81%)
Ann Surg Oncol 2012; 19:2212-2223
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
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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
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
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: 229-236
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
Thank you