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Endoluminal MR Imaging of the Rectum and Anus: Technique, Applications, and Pitfalls

¹ Departments of Radiology (J.S., E.R., A.W.Z., J.S.L.)
² Surgery (W.R.S.), University Hospital Rotterdam Dijkzigt, Erasmus University Rotterdam, the Netherlands
³ Department of Radiology, Academic Medical Center, P.O. Box 22700, 1100 DE Amsterdam, the Netherlands (J.S., J.S.L.)

View larger version (93K): [in a new window]   Figure 1.  Photograph shows endoluminal coils for endorectal (top) and endoanal (bottom) MR imaging.

View larger version (132K): [in a new window]   Figure 2a.  (a) Axial proton-density–weighted GRE (repetition time msec/echo time msec = 23.7/13.8) MR image through the lower part of the anal sphincter shows the external sphincter (ES) as the outer part of the sphincter complex and as relatively hypointense. The internal sphincter (IS) is the inner muscular part of the sphincter complex and is relatively hyperintense. The longitudinal muscle (LM) is within the intersphincteric space (ISS) between the internal and external sphincters. The sphincter complex is surrounded by the ischioanal space (IAS). (b) Axial proton-density–weighted GRE (23.7/13.8) MR image through the upper part of the sphincter complex shows the slinglike puborectal muscle (PRM) as the outer part of the complex. The muscle is relatively hypointense. IAS = ischioanal space, IS = internal sphincter, U = urethra, V = vagina. (c) Coronal T2-weighted turbo spin-echo (2,500/100) MR image through the anal sphincter clearly demonstrates the muscular parts of the anal sphincter and their relation to each other. ES = external sphincter, IAS = ischioanal space, IS = internal sphincter, J = anorectal junction, LAM = levator ani muscle, LM = longitudinal muscle, PRM = puborectal muscle. (d) Midsagittal T2-weighted turbo spin-echo (2,500/100) MR image through the anal sphincter clearly demonstrates the relation between the external sphincter (ES) and the puborectal muscle (PRM), especially posteriorly. IS = internal sphincter, LAM = levator ani muscle.

View larger version (159K): [in a new window]   Figure 2b.  (a) Axial proton-density–weighted GRE (repetition time msec/echo time msec = 23.7/13.8) MR image through the lower part of the anal sphincter shows the external sphincter (ES) as the outer part of the sphincter complex and as relatively hypointense. The internal sphincter (IS) is the inner muscular part of the sphincter complex and is relatively hyperintense. The longitudinal muscle (LM) is within the intersphincteric space (ISS) between the internal and external sphincters. The sphincter complex is surrounded by the ischioanal space (IAS). (b) Axial proton-density–weighted GRE (23.7/13.8) MR image through the upper part of the sphincter complex shows the slinglike puborectal muscle (PRM) as the outer part of the complex. The muscle is relatively hypointense. IAS = ischioanal space, IS = internal sphincter, U = urethra, V = vagina. (c) Coronal T2-weighted turbo spin-echo (2,500/100) MR image through the anal sphincter clearly demonstrates the muscular parts of the anal sphincter and their relation to each other. ES = external sphincter, IAS = ischioanal space, IS = internal sphincter, J = anorectal junction, LAM = levator ani muscle, LM = longitudinal muscle, PRM = puborectal muscle. (d) Midsagittal T2-weighted turbo spin-echo (2,500/100) MR image through the anal sphincter clearly demonstrates the relation between the external sphincter (ES) and the puborectal muscle (PRM), especially posteriorly. IS = internal sphincter, LAM = levator ani muscle.

View larger version (150K): [in a new window]   Figure 2c.  (a) Axial proton-density–weighted GRE (repetition time msec/echo time msec = 23.7/13.8) MR image through the lower part of the anal sphincter shows the external sphincter (ES) as the outer part of the sphincter complex and as relatively hypointense. The internal sphincter (IS) is the inner muscular part of the sphincter complex and is relatively hyperintense. The longitudinal muscle (LM) is within the intersphincteric space (ISS) between the internal and external sphincters. The sphincter complex is surrounded by the ischioanal space (IAS). (b) Axial proton-density–weighted GRE (23.7/13.8) MR image through the upper part of the sphincter complex shows the slinglike puborectal muscle (PRM) as the outer part of the complex. The muscle is relatively hypointense. IAS = ischioanal space, IS = internal sphincter, U = urethra, V = vagina. (c) Coronal T2-weighted turbo spin-echo (2,500/100) MR image through the anal sphincter clearly demonstrates the muscular parts of the anal sphincter and their relation to each other. ES = external sphincter, IAS = ischioanal space, IS = internal sphincter, J = anorectal junction, LAM = levator ani muscle, LM = longitudinal muscle, PRM = puborectal muscle. (d) Midsagittal T2-weighted turbo spin-echo (2,500/100) MR image through the anal sphincter clearly demonstrates the relation between the external sphincter (ES) and the puborectal muscle (PRM), especially posteriorly. IS = internal sphincter, LAM = levator ani muscle.

View larger version (138K): [in a new window]   Figure 2d.  (a) Axial proton-density–weighted GRE (repetition time msec/echo time msec = 23.7/13.8) MR image through the lower part of the anal sphincter shows the external sphincter (ES) as the outer part of the sphincter complex and as relatively hypointense. The internal sphincter (IS) is the inner muscular part of the sphincter complex and is relatively hyperintense. The longitudinal muscle (LM) is within the intersphincteric space (ISS) between the internal and external sphincters. The sphincter complex is surrounded by the ischioanal space (IAS). (b) Axial proton-density–weighted GRE (23.7/13.8) MR image through the upper part of the sphincter complex shows the slinglike puborectal muscle (PRM) as the outer part of the complex. The muscle is relatively hypointense. IAS = ischioanal space, IS = internal sphincter, U = urethra, V = vagina. (c) Coronal T2-weighted turbo spin-echo (2,500/100) MR image through the anal sphincter clearly demonstrates the muscular parts of the anal sphincter and their relation to each other. ES = external sphincter, IAS = ischioanal space, IS = internal sphincter, J = anorectal junction, LAM = levator ani muscle, LM = longitudinal muscle, PRM = puborectal muscle. (d) Midsagittal T2-weighted turbo spin-echo (2,500/100) MR image through the anal sphincter clearly demonstrates the relation between the external sphincter (ES) and the puborectal muscle (PRM), especially posteriorly. IS = internal sphincter, LAM = levator ani muscle.

View larger version (140K): [in a new window]   Figure 3. Figures 3–5. (3) Axial proton-density–weighted GRE (23.7/13.8) MR image shows a large anterior defect (arrows) of the external sphincter (ES), which is somewhat atrophic. A relatively small lesion (arrowhead) is seen in the left anterior aspect of the internal sphincter (IS). LM = longitudinal muscle. (4) Axial proton-density–weighted GRE (23.7/13.8) MR image shows an anterior defect (open arrows) of the internal sphincter (IS). An anterior defect and scar tissue (solid arrow) of the longitudinal muscle (LM) and external sphincter (ES) are also seen. (5a) Axial proton-density–weighted GRE (23.7/13.8) MR image demonstrates a left-sided posterolateral defect and scar tissue (arrows) of the internal sphincter (IS). Compare the normal right lateral aspect of the internal sphincter. The left posterolateral aspect of the external sphincter (ES) is somewhat irregular. (5b) Coronal T2-weighted turbo spin-echo (2,500/100) MR image helps confirm the findings in a. Compare the normal right aspect of the internal sphincter (IS) with the lesion on the left (arrow). The superoinferior extent of the lesion is clearly evident. ES = external sphincter, PRM = puborectal muscle.

View larger version (127K): [in a new window]   Figure 4. Figures 3–5. (3) Axial proton-density–weighted GRE (23.7/13.8) MR image shows a large anterior defect (arrows) of the external sphincter (ES), which is somewhat atrophic. A relatively small lesion (arrowhead) is seen in the left anterior aspect of the internal sphincter (IS). LM = longitudinal muscle. (4) Axial proton-density–weighted GRE (23.7/13.8) MR image shows an anterior defect (open arrows) of the internal sphincter (IS). An anterior defect and scar tissue (solid arrow) of the longitudinal muscle (LM) and external sphincter (ES) are also seen. (5a) Axial proton-density–weighted GRE (23.7/13.8) MR image demonstrates a left-sided posterolateral defect and scar tissue (arrows) of the internal sphincter (IS). Compare the normal right lateral aspect of the internal sphincter. The left posterolateral aspect of the external sphincter (ES) is somewhat irregular. (5b) Coronal T2-weighted turbo spin-echo (2,500/100) MR image helps confirm the findings in a. Compare the normal right aspect of the internal sphincter (IS) with the lesion on the left (arrow). The superoinferior extent of the lesion is clearly evident. ES = external sphincter, PRM = puborectal muscle.

View larger version (120K): [in a new window]   Figure 5a. Figures 3–5. (3) Axial proton-density–weighted GRE (23.7/13.8) MR image shows a large anterior defect (arrows) of the external sphincter (ES), which is somewhat atrophic. A relatively small lesion (arrowhead) is seen in the left anterior aspect of the internal sphincter (IS). LM = longitudinal muscle. (4) Axial proton-density–weighted GRE (23.7/13.8) MR image shows an anterior defect (open arrows) of the internal sphincter (IS). An anterior defect and scar tissue (solid arrow) of the longitudinal muscle (LM) and external sphincter (ES) are also seen. (5a) Axial proton-density–weighted GRE (23.7/13.8) MR image demonstrates a left-sided posterolateral defect and scar tissue (arrows) of the internal sphincter (IS). Compare the normal right lateral aspect of the internal sphincter. The left posterolateral aspect of the external sphincter (ES) is somewhat irregular. (5b) Coronal T2-weighted turbo spin-echo (2,500/100) MR image helps confirm the findings in a. Compare the normal right aspect of the internal sphincter (IS) with the lesion on the left (arrow). The superoinferior extent of the lesion is clearly evident. ES = external sphincter, PRM = puborectal muscle.

View larger version (146K): [in a new window]   Figure 5b. Figures 3–5. (3) Axial proton-density–weighted GRE (23.7/13.8) MR image shows a large anterior defect (arrows) of the external sphincter (ES), which is somewhat atrophic. A relatively small lesion (arrowhead) is seen in the left anterior aspect of the internal sphincter (IS). LM = longitudinal muscle. (4) Axial proton-density–weighted GRE (23.7/13.8) MR image shows an anterior defect (open arrows) of the internal sphincter (IS). An anterior defect and scar tissue (solid arrow) of the longitudinal muscle (LM) and external sphincter (ES) are also seen. (5a) Axial proton-density–weighted GRE (23.7/13.8) MR image demonstrates a left-sided posterolateral defect and scar tissue (arrows) of the internal sphincter (IS). Compare the normal right lateral aspect of the internal sphincter. The left posterolateral aspect of the external sphincter (ES) is somewhat irregular. (5b) Coronal T2-weighted turbo spin-echo (2,500/100) MR image helps confirm the findings in a. Compare the normal right aspect of the internal sphincter (IS) with the lesion on the left (arrow). The superoinferior extent of the lesion is clearly evident. ES = external sphincter, PRM = puborectal muscle.

View larger version (127K): [in a new window]   Figure 6. Figures 6, 7. (6) Axial T2-weighted turbo spin-echo (2,500/100) MR image of the lower part of the anal sphincter reveals scar tissue (arrows) outside the right lateral aspect of the external sphincter (ES). The scar tissue resulted from a right-sided lateral episiotomy. IS = internal sphincter. (7) Axial T2-weighted turbo spin-echo (2,500/100) MR image obtained after surgery for anal atresia reveals an absent internal sphincter and an anteriorly deficient external sphincter (ES) bilaterally.

View larger version (101K): [in a new window]   Figure 7. Figures 6, 7. (6) Axial T2-weighted turbo spin-echo (2,500/100) MR image of the lower part of the anal sphincter reveals scar tissue (arrows) outside the right lateral aspect of the external sphincter (ES). The scar tissue resulted from a right-sided lateral episiotomy. IS = internal sphincter. (7) Axial T2-weighted turbo spin-echo (2,500/100) MR image obtained after surgery for anal atresia reveals an absent internal sphincter and an anteriorly deficient external sphincter (ES) bilaterally.

View larger version (149K): [in a new window]   Figure 8.  Coronal T2-weighted turbo spin-echo (2,500/100) MR image shows an atrophic external sphincter, only some thin portions of which remain (arrows) (cf Fig 2c). The internal sphincter (IS), longitudinal muscle (LM), and puborectal muscle (PRM) are normal.

View larger version (28K): [in a new window]   Figure 9.  Illustration shows Parks classification of perianal fistulas. There is a transsphincteric fistula with extension of the tract through the external sphincter (upper left), an intersphincteric tract confined to the intersphincteric space and internal sphincter (upper right), a fistula passing through the levator ani muscle over the top of the puborectalis muscle into the intersphincteric space (suprasphincteric fistula) (lower right), and an extrasphincteric fistula passing through the ischiorectal fossa and levator ani muscle into the rectum (lower left).

View larger version (105K): [in a new window]   Figure 10a. Figures 10–12. (10a) Axial T2-weighted turbo spin-echo (2,500/100) MR image of the upper part of the anal sphincter demonstrates a fistula (arrow) in the intersphincteric space (ISS) anteriorly. Some veins are also seen anteriorly (arrowheads). IS = internal sphincter, PRM = puborectal muscle. (10b) Sagittal slightly oblique T2-weighted turbo spin-echo (2,500/100) MR image shows a tract (arrows) that is limited to the intersphincteric space between the internal sphincter (IS) and the external sphincter (ES) and is therefore classified as an intersphincteric fistula. The tract approaches the anorectal junction (J) but does not extend into the supralevator space. A cavernous body is seen anteriorly (*). (11a) Axial T2-weighted turbo spin-echo (2,500/100) MR image demonstrates an abscess (arrows) in the intersphincteric space (ISS) posteriorly. ES = external sphincter, IS = internal sphincter, LM = longitudinal muscle. (11b) Sagittal slightly oblique T2-weighted turbo spin-echo (2,500/100) MR image shows the internal opening (open arrow) of the intersphincteric abscess (solid arrows) and the relation of the fistula to the internal sphincter (IS) and external sphincter (ES). (12a) Axial T2-weighted turbo spin-echo (2,500/100) MR image of the upper part of the anal sphincter demonstrates a fistula (arrows) traversing the puborectal muscle (PRM) posteriorly on the right. The tract is classified as a transsphincteric fistula. This fistula has the typical morphology of an active perianal fistula in that the tract is filled with fluid. (12b) On an axial T2-weighted turbo spin-echo (2,500/100) MR image obtained with spectral inversion recovery (fat saturation), the tract is more conspicuous (arrows).

View larger version (142K): [in a new window]   Figure 10b. Figures 10–12. (10a) Axial T2-weighted turbo spin-echo (2,500/100) MR image of the upper part of the anal sphincter demonstrates a fistula (arrow) in the intersphincteric space (ISS) anteriorly. Some veins are also seen anteriorly (arrowheads). IS = internal sphincter, PRM = puborectal muscle. (10b) Sagittal slightly oblique T2-weighted turbo spin-echo (2,500/100) MR image shows a tract (arrows) that is limited to the intersphincteric space between the internal sphincter (IS) and the external sphincter (ES) and is therefore classified as an intersphincteric fistula. The tract approaches the anorectal junction (J) but does not extend into the supralevator space. A cavernous body is seen anteriorly (*). (11a) Axial T2-weighted turbo spin-echo (2,500/100) MR image demonstrates an abscess (arrows) in the intersphincteric space (ISS) posteriorly. ES = external sphincter, IS = internal sphincter, LM = longitudinal muscle. (11b) Sagittal slightly oblique T2-weighted turbo spin-echo (2,500/100) MR image shows the internal opening (open arrow) of the intersphincteric abscess (solid arrows) and the relation of the fistula to the internal sphincter (IS) and external sphincter (ES). (12a) Axial T2-weighted turbo spin-echo (2,500/100) MR image of the upper part of the anal sphincter demonstrates a fistula (arrows) traversing the puborectal muscle (PRM) posteriorly on the right. The tract is classified as a transsphincteric fistula. This fistula has the typical morphology of an active perianal fistula in that the tract is filled with fluid. (12b) On an axial T2-weighted turbo spin-echo (2,500/100) MR image obtained with spectral inversion recovery (fat saturation), the tract is more conspicuous (arrows).

View larger version (140K): [in a new window]   Figure 11a. Figures 10–12. (10a) Axial T2-weighted turbo spin-echo (2,500/100) MR image of the upper part of the anal sphincter demonstrates a fistula (arrow) in the intersphincteric space (ISS) anteriorly. Some veins are also seen anteriorly (arrowheads). IS = internal sphincter, PRM = puborectal muscle. (10b) Sagittal slightly oblique T2-weighted turbo spin-echo (2,500/100) MR image shows a tract (arrows) that is limited to the intersphincteric space between the internal sphincter (IS) and the external sphincter (ES) and is therefore classified as an intersphincteric fistula. The tract approaches the anorectal junction (J) but does not extend into the supralevator space. A cavernous body is seen anteriorly (*). (11a) Axial T2-weighted turbo spin-echo (2,500/100) MR image demonstrates an abscess (arrows) in the intersphincteric space (ISS) posteriorly. ES = external sphincter, IS = internal sphincter, LM = longitudinal muscle. (11b) Sagittal slightly oblique T2-weighted turbo spin-echo (2,500/100) MR image shows the internal opening (open arrow) of the intersphincteric abscess (solid arrows) and the relation of the fistula to the internal sphincter (IS) and external sphincter (ES). (12a) Axial T2-weighted turbo spin-echo (2,500/100) MR image of the upper part of the anal sphincter demonstrates a fistula (arrows) traversing the puborectal muscle (PRM) posteriorly on the right. The tract is classified as a transsphincteric fistula. This fistula has the typical morphology of an active perianal fistula in that the tract is filled with fluid. (12b) On an axial T2-weighted turbo spin-echo (2,500/100) MR image obtained with spectral inversion recovery (fat saturation), the tract is more conspicuous (arrows).

View larger version (145K): [in a new window]   Figure 11b. Figures 10–12. (10a) Axial T2-weighted turbo spin-echo (2,500/100) MR image of the upper part of the anal sphincter demonstrates a fistula (arrow) in the intersphincteric space (ISS) anteriorly. Some veins are also seen anteriorly (arrowheads). IS = internal sphincter, PRM = puborectal muscle. (10b) Sagittal slightly oblique T2-weighted turbo spin-echo (2,500/100) MR image shows a tract (arrows) that is limited to the intersphincteric space between the internal sphincter (IS) and the external sphincter (ES) and is therefore classified as an intersphincteric fistula. The tract approaches the anorectal junction (J) but does not extend into the supralevator space. A cavernous body is seen anteriorly (*). (11a) Axial T2-weighted turbo spin-echo (2,500/100) MR image demonstrates an abscess (arrows) in the intersphincteric space (ISS) posteriorly. ES = external sphincter, IS = internal sphincter, LM = longitudinal muscle. (11b) Sagittal slightly oblique T2-weighted turbo spin-echo (2,500/100) MR image shows the internal opening (open arrow) of the intersphincteric abscess (solid arrows) and the relation of the fistula to the internal sphincter (IS) and external sphincter (ES). (12a) Axial T2-weighted turbo spin-echo (2,500/100) MR image of the upper part of the anal sphincter demonstrates a fistula (arrows) traversing the puborectal muscle (PRM) posteriorly on the right. The tract is classified as a transsphincteric fistula. This fistula has the typical morphology of an active perianal fistula in that the tract is filled with fluid. (12b) On an axial T2-weighted turbo spin-echo (2,500/100) MR image obtained with spectral inversion recovery (fat saturation), the tract is more conspicuous (arrows).

View larger version (127K): [in a new window]   Figure 12a. Figures 10–12. (10a) Axial T2-weighted turbo spin-echo (2,500/100) MR image of the upper part of the anal sphincter demonstrates a fistula (arrow) in the intersphincteric space (ISS) anteriorly. Some veins are also seen anteriorly (arrowheads). IS = internal sphincter, PRM = puborectal muscle. (10b) Sagittal slightly oblique T2-weighted turbo spin-echo (2,500/100) MR image shows a tract (arrows) that is limited to the intersphincteric space between the internal sphincter (IS) and the external sphincter (ES) and is therefore classified as an intersphincteric fistula. The tract approaches the anorectal junction (J) but does not extend into the supralevator space. A cavernous body is seen anteriorly (*). (11a) Axial T2-weighted turbo spin-echo (2,500/100) MR image demonstrates an abscess (arrows) in the intersphincteric space (ISS) posteriorly. ES = external sphincter, IS = internal sphincter, LM = longitudinal muscle. (11b) Sagittal slightly oblique T2-weighted turbo spin-echo (2,500/100) MR image shows the internal opening (open arrow) of the intersphincteric abscess (solid arrows) and the relation of the fistula to the internal sphincter (IS) and external sphincter (ES). (12a) Axial T2-weighted turbo spin-echo (2,500/100) MR image of the upper part of the anal sphincter demonstrates a fistula (arrows) traversing the puborectal muscle (PRM) posteriorly on the right. The tract is classified as a transsphincteric fistula. This fistula has the typical morphology of an active perianal fistula in that the tract is filled with fluid. (12b) On an axial T2-weighted turbo spin-echo (2,500/100) MR image obtained with spectral inversion recovery (fat saturation), the tract is more conspicuous (arrows).

View larger version (104K): [in a new window]   Figure 12b. Figures 10–12. (10a) Axial T2-weighted turbo spin-echo (2,500/100) MR image of the upper part of the anal sphincter demonstrates a fistula (arrow) in the intersphincteric space (ISS) anteriorly. Some veins are also seen anteriorly (arrowheads). IS = internal sphincter, PRM = puborectal muscle. (10b) Sagittal slightly oblique T2-weighted turbo spin-echo (2,500/100) MR image shows a tract (arrows) that is limited to the intersphincteric space between the internal sphincter (IS) and the external sphincter (ES) and is therefore classified as an intersphincteric fistula. The tract approaches the anorectal junction (J) but does not extend into the supralevator space. A cavernous body is seen anteriorly (*). (11a) Axial T2-weighted turbo spin-echo (2,500/100) MR image demonstrates an abscess (arrows) in the intersphincteric space (ISS) posteriorly. ES = external sphincter, IS = internal sphincter, LM = longitudinal muscle. (11b) Sagittal slightly oblique T2-weighted turbo spin-echo (2,500/100) MR image shows the internal opening (open arrow) of the intersphincteric abscess (solid arrows) and the relation of the fistula to the internal sphincter (IS) and external sphincter (ES). (12a) Axial T2-weighted turbo spin-echo (2,500/100) MR image of the upper part of the anal sphincter demonstrates a fistula (arrows) traversing the puborectal muscle (PRM) posteriorly on the right. The tract is classified as a transsphincteric fistula. This fistula has the typical morphology of an active perianal fistula in that the tract is filled with fluid. (12b) On an axial T2-weighted turbo spin-echo (2,500/100) MR image obtained with spectral inversion recovery (fat saturation), the tract is more conspicuous (arrows).

View larger version (128K): [in a new window]   Figure 13. Figures 13–16. (13) Coronal T2-weighted turbo spin-echo (2,500/100) MR image demonstrates a supralevatoric abscess (open arrow) with a tract (arrowheads) and an infralevatoric internal opening (solid arrow). (14) Radial oblique T2-weighted turbo spin-echo (2,500/100) MR image shows an abscess (solid arrows) in the levator ani muscle (LAM) but no extension into the supralevator space (SLS). The internal opening of the abscess (open arrow) is clearly visible. (15) Axial T2-weighted turbo spin-echo (2,500/100) MR image of the upper part of the anal sphincter in a patient suspected of having a complex fistula shows multiple tracts anteriorly (arrows). IS = internal sphincter, PRM = puborectal muscle. (16) Axial T2-weighted turbo spin-echo (2,500/100) MR image through the upper part of the sphincter complex demonstrates a horseshoe-shaped abscess (*) in the puborectal muscle (PRM) and the ischioanal space (IAS).

View larger version (123K): [in a new window]   Figure 14. Figures 13–16. (13) Coronal T2-weighted turbo spin-echo (2,500/100) MR image demonstrates a supralevatoric abscess (open arrow) with a tract (arrowheads) and an infralevatoric internal opening (solid arrow). (14) Radial oblique T2-weighted turbo spin-echo (2,500/100) MR image shows an abscess (solid arrows) in the levator ani muscle (LAM) but no extension into the supralevator space (SLS). The internal opening of the abscess (open arrow) is clearly visible. (15) Axial T2-weighted turbo spin-echo (2,500/100) MR image of the upper part of the anal sphincter in a patient suspected of having a complex fistula shows multiple tracts anteriorly (arrows). IS = internal sphincter, PRM = puborectal muscle. (16) Axial T2-weighted turbo spin-echo (2,500/100) MR image through the upper part of the sphincter complex demonstrates a horseshoe-shaped abscess (*) in the puborectal muscle (PRM) and the ischioanal space (IAS).

View larger version (139K): [in a new window]   Figure 15. Figures 13–16. (13) Coronal T2-weighted turbo spin-echo (2,500/100) MR image demonstrates a supralevatoric abscess (open arrow) with a tract (arrowheads) and an infralevatoric internal opening (solid arrow). (14) Radial oblique T2-weighted turbo spin-echo (2,500/100) MR image shows an abscess (solid arrows) in the levator ani muscle (LAM) but no extension into the supralevator space (SLS). The internal opening of the abscess (open arrow) is clearly visible. (15) Axial T2-weighted turbo spin-echo (2,500/100) MR image of the upper part of the anal sphincter in a patient suspected of having a complex fistula shows multiple tracts anteriorly (arrows). IS = internal sphincter, PRM = puborectal muscle. (16) Axial T2-weighted turbo spin-echo (2,500/100) MR image through the upper part of the sphincter complex demonstrates a horseshoe-shaped abscess (*) in the puborectal muscle (PRM) and the ischioanal space (IAS).

View larger version (133K): [in a new window]   Figure 16. Figures 13–16. (13) Coronal T2-weighted turbo spin-echo (2,500/100) MR image demonstrates a supralevatoric abscess (open arrow) with a tract (arrowheads) and an infralevatoric internal opening (solid arrow). (14) Radial oblique T2-weighted turbo spin-echo (2,500/100) MR image shows an abscess (solid arrows) in the levator ani muscle (LAM) but no extension into the supralevator space (SLS). The internal opening of the abscess (open arrow) is clearly visible. (15) Axial T2-weighted turbo spin-echo (2,500/100) MR image of the upper part of the anal sphincter in a patient suspected of having a complex fistula shows multiple tracts anteriorly (arrows). IS = internal sphincter, PRM = puborectal muscle. (16) Axial T2-weighted turbo spin-echo (2,500/100) MR image through the upper part of the sphincter complex demonstrates a horseshoe-shaped abscess (*) in the puborectal muscle (PRM) and the ischioanal space (IAS).

View larger version (146K): [in a new window]   Figure 17.  Axial T2-weighted turbo spin-echo (2,500/100) MR image in a woman with a clinical history of anovaginal fistula after vaginal delivery shows an anovaginal fistula filled with hyperintense fluid (arrows).

View larger version (171K): [in a new window]   Figure 18. Figures 18, 19. (18) Coronal radial oblique T2-weighted turbo spin-echo (2,500/100) MR image demonstrates a lobulated rectal tumor (T) extending close to the anorectal junction (J). There is no extension through the muscular layer (arrowhead) into the perirectal fat, and no enlarged lymph nodes are seen. SV = seminal vesicles. (19) Axial T2-weighted turbo spin-echo (2,500/100) MR image shows a recurrent rectal adenocarcinoma (T). The tumor has a spiculated border with invasion of the right seminal vesicle (SV). The window setting was optimized for demonstration of the tumor and seminal vesicle, resulting in high signal intensity near the imaging coil.

View larger version (148K): [in a new window]   Figure 19. Figures 18, 19. (18) Coronal radial oblique T2-weighted turbo spin-echo (2,500/100) MR image demonstrates a lobulated rectal tumor (T) extending close to the anorectal junction (J). There is no extension through the muscular layer (arrowhead) into the perirectal fat, and no enlarged lymph nodes are seen. SV = seminal vesicles. (19) Axial T2-weighted turbo spin-echo (2,500/100) MR image shows a recurrent rectal adenocarcinoma (T). The tumor has a spiculated border with invasion of the right seminal vesicle (SV). The window setting was optimized for demonstration of the tumor and seminal vesicle, resulting in high signal intensity near the imaging coil.

View larger version (121K): [in a new window]   Figure 20a. Figures 20, 21. (20a) Axial T2-weighted turbo spin-echo (2,500/100) MR image demonstrates invasion of a rectal tumor (T) through the rectal wall (W) into the perirectal fat (arrows). No invasion of the prostate gland (P) is seen. (20b) Coronal radial oblique T1-weighted turbo spin-echo (500/17) MR image obtained after administration of gadodiamide (Omniscan; Nycomed, Oslo, Norway) shows invasion of the perirectal fat (arrowheads). The tumor is seen displacing but not invading the levator ani muscle (LAM) and is very close to the anorectal junction (J). A fat plane is visible between the tumor and the levator ani muscle. (21a) Axial T2-weighted turbo spin-echo (2,500/100) MR image shows non-Hodgkin lymphoma (T) adjacent to the longitudinal muscle (LM). The exact tumor location is difficult to determine without a complementary longitudinal imaging sequence. P = prostate gland. (21b) Sagittal radial oblique T1-weighted turbo spin-echo (500/17) MR image obtained after administration of gadodiamide reveals that the tumor (T) is located between the puborectal muscle (PM) and the levator ani muscle (LAM).

View larger version (126K): [in a new window]   Figure 20b. Figures 20, 21. (20a) Axial T2-weighted turbo spin-echo (2,500/100) MR image demonstrates invasion of a rectal tumor (T) through the rectal wall (W) into the perirectal fat (arrows). No invasion of the prostate gland (P) is seen. (20b) Coronal radial oblique T1-weighted turbo spin-echo (500/17) MR image obtained after administration of gadodiamide (Omniscan; Nycomed, Oslo, Norway) shows invasion of the perirectal fat (arrowheads). The tumor is seen displacing but not invading the levator ani muscle (LAM) and is very close to the anorectal junction (J). A fat plane is visible between the tumor and the levator ani muscle. (21a) Axial T2-weighted turbo spin-echo (2,500/100) MR image shows non-Hodgkin lymphoma (T) adjacent to the longitudinal muscle (LM). The exact tumor location is difficult to determine without a complementary longitudinal imaging sequence. P = prostate gland. (21b) Sagittal radial oblique T1-weighted turbo spin-echo (500/17) MR image obtained after administration of gadodiamide reveals that the tumor (T) is located between the puborectal muscle (PM) and the levator ani muscle (LAM).

View larger version (153K): [in a new window]   Figure 21a. Figures 20, 21. (20a) Axial T2-weighted turbo spin-echo (2,500/100) MR image demonstrates invasion of a rectal tumor (T) through the rectal wall (W) into the perirectal fat (arrows). No invasion of the prostate gland (P) is seen. (20b) Coronal radial oblique T1-weighted turbo spin-echo (500/17) MR image obtained after administration of gadodiamide (Omniscan; Nycomed, Oslo, Norway) shows invasion of the perirectal fat (arrowheads). The tumor is seen displacing but not invading the levator ani muscle (LAM) and is very close to the anorectal junction (J). A fat plane is visible between the tumor and the levator ani muscle. (21a) Axial T2-weighted turbo spin-echo (2,500/100) MR image shows non-Hodgkin lymphoma (T) adjacent to the longitudinal muscle (LM). The exact tumor location is difficult to determine without a complementary longitudinal imaging sequence. P = prostate gland. (21b) Sagittal radial oblique T1-weighted turbo spin-echo (500/17) MR image obtained after administration of gadodiamide reveals that the tumor (T) is located between the puborectal muscle (PM) and the levator ani muscle (LAM).

View larger version (149K): [in a new window]   Figure 21b. Figures 20, 21. (20a) Axial T2-weighted turbo spin-echo (2,500/100) MR image demonstrates invasion of a rectal tumor (T) through the rectal wall (W) into the perirectal fat (arrows). No invasion of the prostate gland (P) is seen. (20b) Coronal radial oblique T1-weighted turbo spin-echo (500/17) MR image obtained after administration of gadodiamide (Omniscan; Nycomed, Oslo, Norway) shows invasion of the perirectal fat (arrowheads). The tumor is seen displacing but not invading the levator ani muscle (LAM) and is very close to the anorectal junction (J). A fat plane is visible between the tumor and the levator ani muscle. (21a) Axial T2-weighted turbo spin-echo (2,500/100) MR image shows non-Hodgkin lymphoma (T) adjacent to the longitudinal muscle (LM). The exact tumor location is difficult to determine without a complementary longitudinal imaging sequence. P = prostate gland. (21b) Sagittal radial oblique T1-weighted turbo spin-echo (500/17) MR image obtained after administration of gadodiamide reveals that the tumor (T) is located between the puborectal muscle (PM) and the levator ani muscle (LAM).

View larger version (162K): [in a new window]   Figure 22. Figures 22, 23. >(22) On an axial proton-density–weighted GRE (23.7/13.8) MR image obtained 2.5 cm above the lower edge of the external sphincter in a male patient, the morphology of the external sphincter (ES) posteriorly (arrow) may suggest a tear but is actually a normal variant of the external sphincter. External sphincter tissue is also present more anteriorly (arrowhead). (23) Axial proton-density–weighted GRE (23.7/13.8) MR image obtained 1.4 cm superior to the caudal edge of the external sphincter in a female patient does not demonstrate the external sphincter anteriorly (arrows). This finding does not represent a defect but is the normal aspect of the anterior sphincter at this level in a female. The external sphincter is approximately 1.4–1.6 cm high in healthy females. IS = internal sphincter, TPM = transverse perineal muscle.

View larger version (154K): [in a new window]   Figure 23. Figures 22, 23. >(22) On an axial proton-density–weighted GRE (23.7/13.8) MR image obtained 2.5 cm above the lower edge of the external sphincter in a male patient, the morphology of the external sphincter (ES) posteriorly (arrow) may suggest a tear but is actually a normal variant of the external sphincter. External sphincter tissue is also present more anteriorly (arrowhead). (23) Axial proton-density–weighted GRE (23.7/13.8) MR image obtained 1.4 cm superior to the caudal edge of the external sphincter in a female patient does not demonstrate the external sphincter anteriorly (arrows). This finding does not represent a defect but is the normal aspect of the anterior sphincter at this level in a female. The external sphincter is approximately 1.4–1.6 cm high in healthy females. IS = internal sphincter, TPM = transverse perineal muscle.

View larger version (145K): [in a new window]   Figure 24a.  (a) Axial T2-weighted turbo spin-echo (2,500/100) MR image of the central part of the anal sphincter in a patient with a complex fistula at the lower part of the sphincter shows a hyperintense oval structure (arrow) anterior to the internal sphincter (IS). This structure might be interpreted as a fistula or small abscess. The hyperintensity is caused by fat in the intersphincteric space, which also has high signal intensity due to high sensitivity proximal to the imaging coil (near field effect). (b) MR image obtained with spectral inversion recovery (fat saturation) shows the oval structure with low signal intensity (arrow).

View larger version (132K): [in a new window]   Figure 24b.  (a) Axial T2-weighted turbo spin-echo (2,500/100) MR image of the central part of the anal sphincter in a patient with a complex fistula at the lower part of the sphincter shows a hyperintense oval structure (arrow) anterior to the internal sphincter (IS). This structure might be interpreted as a fistula or small abscess. The hyperintensity is caused by fat in the intersphincteric space, which also has high signal intensity due to high sensitivity proximal to the imaging coil (near field effect). (b) MR image obtained with spectral inversion recovery (fat saturation) shows the oval structure with low signal intensity (arrow).

View larger version (144K): [in a new window]   Figure 25a.  (a) Axial T2-weighted turbo spin-echo (2,500/100) MR image shows a hyperintense structure (arrow) in the intersphincteric space that may represent a fistula. (b) On a coronal slightly oblique T2-weighted turbo spin-echo (2,500/100) MR image, the hyperintense structure in the right lateral aspect of the intersphincteric space (arrows) has a very thin wall and a lobulated, serpiginous aspect. This structure is a vein and not a fistula. The vein is continuous with the periprostatic veins. Compare this case with the perianal fistula shown in Figure 10b, which has a straighter course, a thicker wall, and no connection to vascular structures.

View larger version (140K): [in a new window]   Figure 25b.  (a) Axial T2-weighted turbo spin-echo (2,500/100) MR image shows a hyperintense structure (arrow) in the intersphincteric space that may represent a fistula. (b) On a coronal slightly oblique T2-weighted turbo spin-echo (2,500/100) MR image, the hyperintense structure in the right lateral aspect of the intersphincteric space (arrows) has a very thin wall and a lobulated, serpiginous aspect. This structure is a vein and not a fistula. The vein is continuous with the periprostatic veins. Compare this case with the perianal fistula shown in Figure 10b, which has a straighter course, a thicker wall, and no connection to vascular structures.

View larger version (138K): [in a new window]   Figure 26a.  (a) Axial T2-weighted turbo spin-echo (2,500/100) MR image of a patient with a rectal carcinoma demonstrates artifacts in the phase-encoding direction caused by rectal contractions. The MR imaging findings might be interpreted as tumor invasion through the rectal wall (arrows) because no normal muscular layer is visible. (b) Sagittal oblique T2-weighted turbo spin-echo (2,500/100) MR image reveals that there is no invasion in or through the muscular layer of the rectal wall (W). The partial volume effects seen in a are not present. This case demonstrates the importance of longitudinal sequences as part of the imaging protocol.

View larger version (148K): [in a new window]   Figure 26b.  (a) Axial T2-weighted turbo spin-echo (2,500/100) MR image of a patient with a rectal carcinoma demonstrates artifacts in the phase-encoding direction caused by rectal contractions. The MR imaging findings might be interpreted as tumor invasion through the rectal wall (arrows) because no normal muscular layer is visible. (b) Sagittal oblique T2-weighted turbo spin-echo (2,500/100) MR image reveals that there is no invasion in or through the muscular layer of the rectal wall (W). The partial volume effects seen in a are not present. This case demonstrates the importance of longitudinal sequences as part of the imaging protocol.

View larger version (140K): [in a new window]   Figure 27.  Coronal radial oblique T1-weighted turbo spin-echo (500/17) MR image obtained after administration of gadodiamide in a patient with a distal rectal tumor shows the tumor reaching nearly to the anorectal junction (J). However, high-signal-intensity inflammatory tissue (arrow) is visible between the overhanging lower part of the tumor (T) and the rectal wall (W). The tumor base is located 2 cm above the anorectal junction. Consequently, sphincter-saving surgery was performed. At surgery, the cauliflower-like tumor was seen to overhang the distal rectal wall. There was sufficient normal rectum distally to allow anastomosis.