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Thin section MRI in multidisciplinary pre-operative decision making for patients with rectal cancer

Department of Radiology, The Royal Marsden NHS Foundation Trust, Downs Road, Sutton SM2 5PT, UK

View larger version (140K): [in a new window]   Figure 1. CT and MRI images of a primary rectal tumour in the same patient. The primary tumour cannot be clearly delineated and there is insufficient contrast resolution between the primary tumour and the anal sphincter complex on the CT examination. The MR images, however, show tumour clearly in the axial and coronal planes (arrows). The coronal images enable a clear depiction of tumour in relation to the sphincter complex (arrow).

View larger version (200K): [in a new window]   Figure 2. The sagittal T2 weighted scans are used to plan thin-section axial oblique scans. It is important to ensure the scans are obtained in a plane orthogonal to the tumour to prevent over-estimation of tumour spread.

View larger version (188K): [in a new window]   Figure 3. For tumours arising below the origin of the levator muscle, scans are obtained in a coronal or paracoronal plane as shown.

View larger version (211K): [in a new window]   Figure 4. Scan planes used for assessing mesorectal lymph nodes. The mesorectum can be assessed for lymph nodes by planning a block of coronal slices that run parallel to the sacrum.

View larger version (113K): [in a new window]   Figure 5. (a) The peritoneal reflection (arrow) is demonstrated on the sagittal MR image as a low-signal intensity structure, here shown running from the posterior surface of the uterus to the anterior rectal wall. (b) On axial section, the apex of the peritoneal attachment forms a v-shaped configuration, as shown (arrows).

View larger version (92K): [in a new window]   Figure 6. (a) The inferior hypogastric plexus can be seen both on sagittal and coronal imaging. This is demonstrated on these paracoronal images as strands (arrows), measuring between 2 mm and 4 mm in diameter and best seen at the level of the seminal vesicles. (b) On the sagittal images, the inferior hypogastric plexus forms a densely fenestrated meshwork of nerves, of high-signal intensity close to the pelvic sidewall (arrow).

View larger version (80K): [in a new window]   Figure 7. The mesorectal fascia is demonstrated as a low-signal intensity layer surrounding the fatty envelope of the mesorectum (arrows); the corresponding structure can be seen on total mesorectal excision (TME) specimens as the dissection is performed lateral to the mesorectal fascia.

View larger version (211K): [in a new window]   Figure 8. Denonvilliers' fascia is demonstrated on sagittal axial images as low-signal intensity bands, slightly thicker than the mesorectal fascia and is seen over the anterior aspect of the mesorectum behind the seminal vesicles and the prostate (arrowheads).

View larger version (218K): [in a new window]   Figure 9. Axial T2 weighted MR image of the anal sphincter complex. The external sphincter (black arrow) is demonstrated as an almost complete ring of low-signal intensity. The intersphincteric plane is of relatively high signal (arrowhead). The internal sphincter (white arrow) lies more medially and is also demonstrated as a low-signal intensity structure but is continuous with the muscularis propria of the rectum.

View larger version (218K): [in a new window]   Figure 10. Coronal T2 weighted MRI showing the levator muscle (black arrow) running obliquely towards the anorectal junction (arrowheads). The mesorectum is at its most tapered at this point and thus tumours that extend through the muscularis propria are at high risk of circumferential involvement.

View larger version (148K): [in a new window]   Figure 11. Sagittal MR image demonstrating the presacral fascia (black arrow). This lies directly behind the mesorectal fascia (arrowhead).

View larger version (64K): [in a new window]   Figure 12. Axial T2 weighted image and corresponding histopathology section. Tumour extends to within 1 mm of the mesorectal fascia (arrow). This corresponds to positive surgical circumferential margin on the corresponding histological section (arrow).

View larger version (111K): [in a new window]   Figure 13. Histopathological preparation of the specimen. The specimen is sliced after Formalin fixation and the axial tissue slices can either be sampled or embedded whole into large cassettes. Extent of tumour spread (arrowheads) as well as distance to the closest non-peritonealized circumferential resection margin (double arrow) can then be assessed by the pathologist on the haematoxylin and eosin section.

View larger version (154K): [in a new window]   Figure 14. Whole mount histopathology section showing 1 mm graticule overlay, which enables precise measurement of distance to the circumferential margin to be made.

View larger version (78K): [in a new window]   Figure 15. Axial T2 weighted MRI examination and corresponding histopathology section. Multiple tumour deposits are demonstrated (arrow), which lie within 5 mm of the mesorectal fascia, but not within 1 mm of the fascia. Although this tumour distribution indicates a poor prognosis, the circumferential resection margins are predicted as being clear of tumour. The corresponding histopathology section demonstrates clear surgical circumferential resection margins (arrowheads).

View larger version (94K): [in a new window]   Figure 16. Axial thin section T2 weighted image and corresponding histopathology section demonstrating a mixed signal intensity lymph node (arrow), which also has an irregular border. The presence of either one of these features is a good predictor for malignant node involvement shown on the corresponding histopathology slide (arrow).

View larger version (48K): [in a new window]   Figure 17. Identification of benign and malignant nodes using ultra small iron oxide particles (USPIO). Axial T2* weighted images, before and after administration of USPIO, demonstrates three lymph nodes, that are of high-signal intensity before administration of USPIO. Following administration of USPIO normal lymph nodes darken (white arrows) and malignant lymph nodes which do not take up USPIO remain high signal (black arrow) corresponding to histopathology haematoxylin and eosin stained sections demonstrating fully replaced malignant node.

View larger version (154K): [in a new window]   Figure 18. Malignant lymph node (arrow) demonstrated outside the mesorectal envelope. This represents metastatic disease.

View larger version (100K): [in a new window]   Figure 19. Sagittal and axial images of the low rectal tumour. (a) The axial images show apparent tumour spread through the rectal wall into the levator muscle (arrows). However this is artefactual and due to the obliquity of the scan plane. (b) The sagittal image confirmed that the tumour is confined to the rectal wall. The case illustrates the importance of reviewing both the coronal and sagittal images of low rectal tumours.

View larger version (78K): [in a new window]   Figure 20. MRI and corresponding histopathological section showing the primary mid-rectal tumour with nodular extension of tumour into an extramural vein laterally on the left (arrow). When this feature is demonstrated on pre-operative imaging, there is a high positive prediction for extramural venous invasion on histopathology, which in turn is a poor prognostic feature.