Prostate MRI anatomy UNIVERSITY OF MICHIGAN

1. Atlas of
T2 MRI Prostate Anatomy
with CT Correlation
Patrick McLaughlin, MD, Sara Troyer, BS, Sally Berri, MS, George Hixson,
Amichay Meirovitz, MD, Peter Roberson, PhD, Vrinda Narayana, PhD

2. Table of Contents:
• Introduction ………3
• Zonal Anatomy………5
• Part 1: Overview of T2 MRI scans……... 9
patient 1………10
patient 2………27
patient 3………42
patient 4………62
• Part 2: Variations in Prostate Anatomy………78
Section 1: Variations in TZ size………79
Section 2: Base/Bladder Interface Variations………83
Section 3: Prostate Apex/GUD variations………106
• Part 3: Post-prostate implant distortion of anatomy 141
Mild Distortion ………142
Moderate Distortion………151
Severe Distortion ………160
• Part 4: Contouring the prostate on MRI and CT ……… 172
Pre implant Scans ………173
Post implant Scans ………212

3. Introduction
The following prostate atlas will serve several purposes. First, it is a review of
pelvic MRI anatomy. T2 pelvic scans disclose details of prostate anatomy as well
as anatomy of adjacent critical structures with much greater detail than CT
scans. It is likely that MRI-based planning will ultimately replace CT scanning
due to this clarity and a review of the details of prostate associated anatomy will
be useful.
A second goal is to improve CT contouring of the prostate. We have noted that
with increased experience with MRI scans CT defined prostate volumes begin to
approach MRI defined volumes. There are also a number of clues on registered
images that allow improved interpretation when CT alone is available. The CT
scans in the atlas were obtained on a CT simulator without contrast. They would
not be considered diagnostic level CT scans in the current era. In some respects,
the lack of clarity serves the atlas well. In spite of the limited detail, it is possible
to contour the prostate on the basis of adjacent anatomy defined on CT.
The atlas was created from multiple patients registered with MRI and CT data
sets. The atlas includes both post implant scans and non-implant scans.

4. For the registration portion, CT scans were obtained on a helical scanner in 2 or 3
mm intervals. MRIs were obtained in axial, sagittal, and coronal planes. These
three MRI data sets were then fused by mutual information. A composite prostate
was generated. The composite is not a sum total of areas of agreement of coronal,
sagittal, and axial. Instead, the scan that clarified an individual region was
weighed more heavily than the scans in which a region was not well defined. For
example, at the apex, the coronal scan unambiguously defines the apex due to the
clear interface of the GUD and prostate apex. Therefore, disagreements at the
apex were settled in favor of the coronal defined apex. At the base, the sagittal
view can be extremely useful in distinguishing the prostate from bladder and
seminal vesicle. At mid-gland, there was excellent agreement between the three
MRI data sets. When the MRI is projected on the CT scan to instruct in
contouring of the CT images, the projected contour is from the composite prostate
rather than the axial. It has been projected, in many cases, on the axial MRI for
reference.
The second half of the teaching module following MRI anatomy, MRI-CT
correlation, is an interactive test module. In this “Prost-A-Doodle” module a CT
image is presented, a contour can be entered, followed by review of the registered
MRI image. The MRI contour can then be projected on the CT to allow a back
and forth interactive experience. This module includes both non-implant and
implant patients as well.

5. Zonal Anatomy
• Zonal anatomy refers to radiographically or histologically distinct
regions within the prostate. The initial description and definition
was by McLean and based on ultrasound defined regions.
• 4 major zones are visible in young men
- Peripheral zone (PZ)
- Central zone - peri-ejaculatory duct zone(CZ)
- Transition zone (TZ)
- Anterior fibromuscular stroma (AFS)
• In the following figure the left image depicts the zonal anatomy
of a younger male. With age hypertrophy of the TZ may occur ,
compressing the CZ. This change is depicted in the right figure.

6. Zonal Anatomy of the Prostate

7. Zonal Anatomy of the prostate can be confusing due to different uses of
the word “central zone”. One use of “central zone” is in reference to the
region immediately around the ejaculatory ducts posterior to the urethra
(McLean). This is visible on ultrasound in young men, but TZ
hypertrophy (BPH) compresses the central zone and it is not visible as a
distinct zone in older men. Ironically the central, peri-ejaculatory duct
zone merges with the peripheral zone (PZ) after TZ hypertrophy.
A second use of the term “central” is in reference to TZ hypertrophy. This
informal use may appear in ultrasound or radiology reports but creates
confusion. Two solutions to the ambiguous nomenclature are available.
One solution is to abandon the term central completely, because the
central zone is not visible in most prostate cancer patients. TZ is used to
refer to the zone of hypertrophy. A second solution divides the prostate
into inner, outer, and anterior fibromuscular zones, the schema outlined by
Matthew Rifkin in Ultrasound of the Prostate (Lippincott-Raven) . The
inner zone includes the TZ and periurethral stroma. The outer zone
includes the PZ and the central or peri-ejaculatory duct zone.
Zonal Anatomy

8. In this atlas the term central will be avoided, and TZ, PZ, and AFS will be
used to define the prostate zones.
Zonal anatomy has replaced lobar anatomy with one exception. The term
median lobe hypertrophy refers to a distinct form of hypertrophy noted on
digital exam as a third lobe palpable between the two lateral lobes . On
cystoscopy and radiographically median lobe hypertrophy extends into the
bladder lumen . In some the median lobe hypertrophy is comparable in
size to the entire remaining prostate. It may cause obstruction by a ball
valve mechanism in which the hypertrophied tissue folds over the urethral
opening.
Unlike TZ hypertrophy and BPH, there is no zonal anatomy correlate for
the median lobe. The actual origin of the median lobe may be posterior
TZ or peri-urethral stroma. Histologically it is not distinct from TZ. In
the prior schematic it is presented as originating from the peri-urethral
stroma (right figure), but its actual origin is uncertain.
Zonal Anatomy

9. Part 1: Overview of T2 MRI
scans on pre-prostate implant
patients

10. Axial T2 MRI Images
Patient 1:

11. Image 1 Image 2
Patient 1, Axial T2 MRI
Crura of Corpus Cavernosa
Penile Bulb
Urethra
Rectum
Level: Penile Bulb

12. Image 3 Image 4
Patient 1, Axial T2 MRI
Rectum
Note the penile bulb ends and the GU Diaphragm (GUD) begins.
Urethra
Level: Penile Bulb/ GUD transition

13. Image 5 Image 6
Patient 1, Axial T2 MRI
Rectum
GUD
Urethra Urethra
Pudendal
Canal
External
Sphincter
External
Sphincter
Level: GUD
Note the thickness of the External Sphincter muscle. The circular shape of the
GUD suggests prostate but this is still 1 cm below the prostate. Also note
the Pudendal Canal is clear near the GUD level.

14. Image 7 Image 8
Patient 1, Axial T2 MRI
Rectum
GUD
Note the convex shape of the Levator Ani at the upper GUD (Image 7).
On image 8 the concave shape of the Levator Ani marks the transition
to the prostate apex.
External
Sphincter
External
Sphincter
Level : GUD
Levator Ani
muscle

15. Image 9 Image 10
Patient 1, Axial T2 MRI
Rectum
Prostate apex
Note the external sphincter commonly extends into the prostate apex.
prostate
External
Sphincter
Level: Prostate Apex
Levator Ani
muscle

16. Image 11 Image 12
Patient 1, Axial T2 MRI
Rectum
prostate
Obturator Internus
Obturator Internus
Level: Mid-Prostate
Levator Ani
muscle
AFS

17. Image 13 Image 14
Patient 1, Axial T2 MRI
Rectum
PZ
Note the TZ is visible in images 13 and 14 (also on image 12).
TZ
Bladder muscle /
Bladder neck
Level: Prostate Base

18. Image 15 Image 16
Patient 1, Axial T2 MRI
Rectum
prostate
Bladder
Muscle
Bladder
Muscle
Seminal
vesicles
Note in image 16 the prostate base merges with the root
of the seminal vesicles.
Level: Prostate Base

19. Image 17
Patient 1, Axial T2 MRI
Rectum
Bladder
Muscle
Level: Prostate Base / Seminal Vesicle transition
Seminal
vesicles
Image 18

20. Coronal T2 MRI Images
Patient 1:

21. Image 2
Image 1
Patient 1, Coronal T2 MRI
Crura of Corpus
Cavernosa
Pudendal
Canal
prostate
Seminal
vesicles
GUD
Penile Bulb
Levator Ani
muscle
External
Sphincter
Prostate
apex
The distance between the prostate apex and the penile bulb is visible on the
coronal images. Also note, the external sphincter extends through the GUD
and into the prostate.
Level: Mid-Prostate

22. Image 3 Image 4
Patient 1, Coronal T2 MRI
Crura of Corpus
Cavernosa
prostate
Lower
Sphincter
Penile Bulb
Urethra
Levator Ani
muscle
Level: Mid / Anterior Prostate

23. Image 5
Patient 1, Coronal T2 MRI
prostate
Crura of Corpus
Cavernosa
Penile Bulb/
Corpus Spongiosum
Level: Anterior Prostate

24. Sagittal T2 MRI Images
Patient 1:

25. Image 1 Image 2
Patient 1, Sagittal T2 MRI
Seminal
vesicles
prostate
Seminal
vesicles
Level: Lateral Prostate
Levator
Ani Muscle
Pubic
Symphysis

26. Image 3 Image 4
Patient 1, Sagittal T2 MRI
Seminal
vesicles
prostate
Urethra
Penile Bulb
Rectum
Rectum
Penile Bulb
Seminal
vesicles
Note the urethra is visible through the center of the prostate in image 4. Also, the
definition of the apex is less distinct on sagittal than on coronal. Sagittal views
often clarify the prostate base/ seminal vesicle region.
Level: Mid-Prostate
AFS

27. Axial T2 MRI Images
Patient 2:

28. Image 1 Image 2
Patient 2, Axial T2 MRI
Rectum
Penile Bulb
Crura of Corpus
Cavernosa
Urethra
Level: Penile Bulb

29. Image 3 Image 4
Patient 2, Axial T2 MRI
Urethra
In image 3, the penile bulb ends and the GUD begins .
In image 4, the pudendal canals become clear.
Rectum
GUD
External
Sphincter
Pudendal
Canal
Level: Inferior GUD

30. Image 5 Image 6
Patient 2, Axial T2 MRI
External
Sphincter
GUD
Rectum
Pudendal
Canal
Rectum
Level: GUD

31. Image 7 Image 8
Patient 2, Axial T2 MRI
Rectum
Prostate
Note the TZ becomes clear near the center of the prostate- image 8
Obturator internus
Level: Apex to Mid-Prostate
TZ
AFS

32. Image 9 Image 10
Patient 2, Axial T2 MRI
Prostate
Bladder
Muscle
Rectum
Obturator internus
Note the clarity of the rectal muscle/ rectal wall.
Level: Mid-Prostate
AFS

33. Image 11 Image 12
Patient 2, Axial T2 MRI
Prostate
Rectum
Bladder
Muscle
Level: Prostate Base

34. Image 13 Image 14
Patient 2, Axial T2 MRI
Prostate
Rectum
Bladder
Muscle
Notice the prostate base in images 12-14.
Level: Prostate Base

35. Image 15
Patient 2, Axial T2 MRI
Seminal
vesicles transition
Rectum
Level: Prostate Base / Seminal Vesicle Transition
Seminal
vesicles
Image 16

36. Coronal T2 MRI Images
Patient 2:

37. Image 1 Image 2
Patient 2, Coronal T2 MRI
Prostate
Penile Bulb
Urethra
Crura of Corpus
Cavernosa
External
Sphincter
GUD
Pudendal
Canal
Prostate
apex
Seminal
vesicles
Levator
Ani muscle
Note the distance between the prostate apex and the penile bulb
on coronal MRI.
Level: Mid-Prostate
Pubis

38. Image 3 Image 4
Patient 2, Coronal T2 MRI
Prostate
Penile
Bulb
Crura of Corpus
Cavernosa
External
Sphincter
GUD
Crura of Corpus
Cavernosa
Level: Anterior Prostate

39. Sagittal T2 MRI Images
Patient 2:

40. Image 1 Image 2
Patient 2, Sagittal T2 MRI
Penile Bulb
Rectum
Urethra
External
Sphincter
Seminal
vesicles
Seminal
vesicles
Rectum
Sagittal image 2 cuts though the center of the prostate showing the urethra. Note
the significant base extension posterior to the bladder. Also note that the anterior
fibromuscular stroma is contiguous with the bladder muscle and external sphincter.
Level: Mid-Prostate
AFS
Pubic
symphysis

41. Image 3 Image 4
Patient 2, Sagittal T2 MRI
Prostate
Rectum
Seminal
vesicles
Rectum
Seminal
vesicles
Level: Lateral Prostate

42. Axial T2 MRI Images
Patient 3:

43. Image 1 Image 2
Patient 3, Axial T2 MRI
Penile Bulb
Rectum
Urethra
Level: Penile Bulb

44. Image 3 Image 4
Patient 3, Axial T2 MRI
Rectum
Urethra
External
Sphincter
GUD
Pudendal
Canal
Note the pudendal canals in image 4.
Level: Inferior GUD

45. Image 5 Image 6
Patient 3, Axial T2 MRI
Rectum
External
Sphincter
GUD
Pudendal
Canal
Rectum
Level: GUD

46. Image 7 Image 8
Patient 3, Axial T2 MRI
Prostate
Rectum
Pudendal
Canal
Level: Prostate Apex

47. Image 9 Image 10
Patient 3, Axial T2 MRI
Prostate
Rectum
The TZ is visible in image 9.
Obturator internus
Level: Mid-Prostate
TZ TZ

48. Image 11 Image 12
Patient 3, Axial T2 MRI
Prostate
Rectum
Level: Mid-Prostate
TZ

49. Image 13 Image 14
Patient 3, Axial T2 MRI
Prostate
Rectum
Level: Prostate Base
Note the hypertrophy extends into the bladder lumen. Such hypertrophy has a
distinct shape referred to as a “median lobe”.
Median Lobe Median Lobe

50. Image 15 Image 16
Patient 3, Axial T2 MRI
Prostate
Rectum
Seminal
vesicles
Seminal
vesicles
The defining feature of a median lobe is a “dolphin nose” projection into the
bladder, see coronal view image 6 and sagittal view image 4.
Level: Prostate Base
Median Lobe Median Lobe

51. Image 17 Image 18
Patient 3, Axial T2 MRI
Prostate
Rectum
Seminal
vesicles
Level: Prostate Base
Median Lobe
Median Lobe

52. Image 19 Image 20
Patient 3, Axial T2 MRI
Prostate
Rectum
Seminal
vesicles
Level: Prostate Base/ Seminal Vesicles
Median Lobe
Median Lobe

53. Coronal T2 MRI Images
Patient 3:

54. Image 1 Image 2
Patient 3, Coronal T2 MRI
Prostate
Penile Bulb
Crura of Corpus
Cavernosa
External
Sphincter
GUD
Levator Ani
muscle
Level: Mid-Prostate

55. Image 3 Image 4
Patient 3, Coronal T2 MRI
Prostate
Penile Bulb
Urethra
Crura of Corpus
Cavernosa
External
Sphincter
GUD
Prostate
apex
Levator Ani
muscle
Notice the median lobe as it pushes into the bladder in coronal
images 4-7.
Obturator
internus
Level: Mid-Prostate

56. Image 5 Image 6
Patient 3, Coronal T2 MRI
Prostate
Penile Bulb
Urethra
Crura of Corpus
Cavernosa
Level: Anterior Prostate
Median Lobe

57. Image 7
Patient 3, Coronal T2 MRI
Prostate
Penile Bulb
Crura of Corpus
Cavernosa
Level: Anterior Prostate
Median Lobe

58. Sagittal T2 MRI Images
Patient 3:

59. Image 1 Image 2
Patient 3, Sagittal T2 MRI
Prostate
Penile Bulb
Rectum
Seminal
vesicles
Seminal
vesicles
Rectum
Notice the median lobe in Sagittal images 2-5.
Level: Lateral Prostate
Median Lobe

60. Image 3 Image 4
Patient 3, Sagittal T2 MRI
Prostate
Penile Bulb
Rectum
Urethra
External
Sphincter
Seminal
vesicles
Penile Bulb
Rectum
Seminal
vesicles
Notice the urethra in image 4 is not visible through the center of the prostate,
however, it is visible below the prostate.
Level: Mid-Prostate
Median Lobe
Median Lobe

61. Image 5
Patient 3, Sagittal T2 MRI
Prostate
Rectum
Seminal
vesicles
Level: Lateral Prostate
Median Lobe

62. Axial T2 MRI Images
Patient 4:

63. Image 1 Image 2
Patient 4, Axial T2 MRI
Penile Bulb
Rectum
Urethra
Level: Penile Bulb

64. Image 4
Image 3
Patient 4, Axial T2 MRI
Rectum
Urethra
External
Sphincter
GUD
Level: GUD

65. Image 6
Image 5
Patient 4, Axial T2 MRI
Prostate
Rectum
External
Sphincter
Pudendal
Canal
Prostate apex
The prostate apex begins in image 5.
Level: Prostate Apex

66. Image 8
Image 7
Patient 4, Axial T2 MRI
Prostate
Rectum
Pudendal
Canal
Note the TZ and PZ are visible in image 8.
Obturator internus
Level: Mid-Prostate
TZ PZ

67. Image 10
Image 9
Patient 4, Axial T2 MRI
Prostate
Rectum
Bladder
Muscle
Bladder
Muscle
Level: Mid-Prostate
TZ

68. Patient 4, Axial T2 MRI
Image 12
Image 11
Prostate
Rectum
Bladder
Muscle
Seminal
vesicles
Note the hypertrophy causes the prostate to protrude into the bladder creating a
median lobe. This is seen in images 11-14.
Level: Prostate Base
Median Lobe
Median Lobe

69. Image 14
Image 13
Patient 4, Axial T2 MRI
Prostate
Rectum
Bladder
Muscle
Seminal
vesicles
Bladder
Muscle
Seminal
vesicles
Level: Prostate Base / Seminal Vesicle Interface
Median Lobe

70. Coronal T2 MRI Images
Patient 4:

71. Image 1 Image 2
Patient 4, Coronal T2 MRI
Prostate
Penile Bulb
External
Sphincter
GUD
Pudendal
Canal
Note the pudendal canals on Coronal MRI image 2.
Obturator internus
Level: Mid-Prostate

72. Image 3 Image 4
Patient 4, Coronal T2 MRI
Prostate
Penile Bulb Crura of Corpus
Cavernosa
External
Sphincter
GUD
Prostate
apex
Levator Ani
muscle
Note the TZ is clearly visible in Coronal MRI image 3. Also notice the
short distance between the prostate apex and penile bulb.
Level: Mid-Prostate
TZ

73. Image 5 Image 6
Patient 4, Coronal T2 MRI
Prostate
Penile Bulb
Urethra
Crura of Corpus
Cavernosa
GUD
Images 5-7 show the median lobe pushing into the bladder.
Level: Anterior Prostate
Median Lobe
Median Lobe

74. Image 7
Patient 4, Coronal T2 MRI
Prostate
Penile Bulb
Urethra
Crura of Corpus
Cavernosa
Level: Anterior Prostate
Median Lobe

75. Sagittal T2 MRI Images
Patient 4:

76. Image 1 Image 2
Patient 4, sagittal T2 MRI
Prostate
Penile Bulb
Rectum
Urethra
Seminal
vesicles
Rectum
Penile Bulb
Seminal
vesicles
In Image 1 the urethra is visible through the center of the prostate.
The median lobe can also be seen in sagittal images 1-2.
Level: Mid-Prostate
Median Lobe Median Lobe

77. Image 3 Image 4
Patient 4, sagittal T2 MRI
Prostate
Penile Bulb
Rectum
Seminal
vesicles
Seminal
vesicles
Rectum
Note the visible TZ on sagittal MRI in images 3-4.
Level: Lateral Prostate
TZ

78. Part 2: Variations in
Prostate Anatomy
T2 MRI Axial, Coronal, and Sagittal Pre-Implant scans

79. Variations in TZ Size
Pre-prostate implant T2 MRI scans
Part 2, Section 1

80. Patient 5-medium sized TZ
prostate
rectum
Axial Prone Image Axial Prone Image
TZ

81. Patient 6-large TZ
Axial Supine Image Coronal Image
prostate
rectum
TZ

82. Patient 7
Notice the large TZ accounts for most of the prostate volume.
prostate
rectum
Axial Supine Image Axial Supine Image
TZ

83. Base/ Bladder Interface
Variations
Part 2, Section 2

84. Distinct Bladder neck
Mid-Sagittal MRI
Prior to prostate hypertrophy the bladder neck muscle is visibly distinct. Often in
patients with small glands, little BPH, a distinct bladder neck muscle can be seen
connecting the bladder and the prostate. This muscle often extending into the
prostate as seen above. The internal sphincter is a direct extension of bladder neck
muscle into the prostate.

85. Partially obliterated bladder neck
As the prostate begins to hypertrophy the bladder neck muscle becomes less
distinct. Often, in this stage, muscle can be seen between the prostate and
bladder but it does not extend into the prostate.
Mid-Sagittal MRI

86. Obliterated bladder neck
As hypertrophy continues the bladder neck muscle becomes ‘obliterated’ by the
expanding prostate. Muscle can no longer be clearly seen between the prostate
and bladder.
Mid-Sagittal MRI

87. Median Lobe Hypertrophy
A distinct form of hypertrophy, median lobe hypertrophy, results in a ‘dolphin-
nose’ projection, originating from the posterior, projecting into the bladder lumen.
It should be noted that there is no direct progression from BPH to median lobe
hypertrophy.
Mid-Sagittal MRI

88. Visible Bladder Neck 1
Bladder Neck
AFS
Mid-Sagittal
This prostate has minimal hypertrophy and a visible bladder neck. The AFS can
be seen merging with the bladder muscle. Axial MRI’s through the base are
shown in the following slides.

89. Bladder Neck
Bladder Neck
Note the bladder neck takes on a circular shape as it attaches to the prostate.
Image 1 Image 2
Image 3
Visible Bladder Neck 1

90. Bladder Neck
merging with AFS
The bladder neck merges with the AFS in images 4 and 5.
Image 4 Image 5
Visible Bladder Neck 1

91. Bladder Neck
Mid-Sagittal
Visible Bladder Neck 2
This prostate also has a distinct bladder neck visible on sagittal MRI. Notice
the appearance of this in the following axial scans.

92. Bladder Muscle
Bladder Neck
Bladder Neck
Bladder Muscle
Note the circular shape of the bladder neck as it attaches to the prostate.
Also note the large amount of bladder muscle visible on the scans.
Image 1 Image 2
Image 3
Visible Bladder Neck 2

93. Bladder Neck
Image 4 Image 5
Visible Bladder Neck 2

94. Bladder Neck
AFS
Mid-Sagittal
Visible Bladder Neck 3
This prostate also has a distinct bladder neck muscle.

95. Visible Bladder Neck 3
Bladder Neck
Image 1 Image 2
Note the circular shape of attachment of muscle and prostate.

96. AFS
Image 4
Bladder Neck
merging with AFS
Image 3
Visible Bladder Neck 3
Note the bladder neck muscle merges with the AFS.

97. Mid-Sagittal
Obliterated bladder neck 1
Notice the displacement of the bladder neck muscle after prostate hypertrophy.

98. Obliterated bladder neck 1
Image 1
Image 3
Image 2

99. Image 4 Image 5
Obliterated bladder neck 1

100. Mid-Sagittal
Obliterated bladder neck 2
Notice the prostate protruding into the bladder obliterating and displacing the
bladder neck.

101. Obliterated bladder neck 2
Image 1 Image 2
Image 3

102. Image 5
Image 6
Obliterated bladder neck 2
Image 4

103. The median lobe
enters the bladder
from the posterior
Mid-Sagittal
Median lobe 1
The presence of a median lobe, while a distinct form of hypertrophy, also
obliterates and displaces the bladder neck muscle.

104. Median lobe 1
Image 1
Image 3
Image 2

105. Image 4 Image 5
Median lobe 1

106. Prostate Apex / GUD
Variations
Pre-prostate implant T2 MRI scans
Part 2, Section 3

107. Apex Definition
 Axial MRI
apex /GUD transition
 Ultrasound
apex/GUD transition
 Penile Bulb (1.5 cm above penile bulb)
rule condemned
 Coronal MRI
apex/GUD transition

108. Note the transition from concave levator ani
at the apex versus convex just below the apex.
MRI Apex to GUD Transition
Concave
levator ani
Convex
levator ani

109. Ultrasound Apex / GUD Transition
Apex GUD
Bulbourethral Gland
Prostate
The apex / GUD transition
on ultrasound is clearly
defined in this example.
However in less clear
examples the external
sphincter may be contoured
as prostate. Recognition of
the light H-shaped GUD or
Bulbourethral gland
indicates GUD.
external sphincter

110. MRI GUD Ultrasound GUD
GUD on Ultrasound and MRI
Note the similar shape of the GUD on MRI and ultrasound.

111. Penile Bulb Rule Condemned
The distance between the prostate apex and penile bulb is highly
variable. When measured on MRI with a sample size of 25 the
distance is 1.33 (.32) cm with a range of 0.6 cm to 1.97 cm. Using
the penile bulb rule ( the prostate apex is 1.5 cm above the penile
bulb ) often results in underestimation of the prostate. Also the
penile bulb / GUD interface may be obliterated post implant. (see
part 3 of atlas)
Coronal: Mid-Prostate
Coronal: Mid-Prostate
Coronal: Posterior Prostate

112. Summary of GUD Shape
Note the change in shape of the GUD: just above the penile bulb it is triangular
in shape, near the mid-diaphragm it is circular, then hourglass shaped. These
shapes are often visible in subtle form on CT.
Image 1.
just above
penile bulb
Image 2
Image 3 Image 4. apex

113. Axial Prone Image Coronal Image
External
sphincter
rectum prostate
Penile
bulb
Pudendal
canal
GUD
Coronal cross
section
Crura of corpus
cavernosa
Patient 8
Notice the circular shape of the GUD in the Axial image. The green line
( ) depicts the plane of the coronal image.

114. Patient 9
Axial Prone Image Coronal Image
rectum
Coronal cross
section
External
sphincter
GUD
prostate
Penile
bulb
Crura of corpus
cavernosa
Notice the separation between the prostate and penile bulb
on the Coronal MRI.

115. Patient 10
Axial Prone Image
Coronal Image
rectum
Coronal cross
section
External
sphincter
GUD
prostate
Penile
bulb
Pudendal
canal

116. Patient 11
Axial Supine Image Coronal Image
Coronal cross
section
External
sphincter
GUD
prostate
Penile
bulb
Pudendal
canal
Note the thickness of the external sphincter on coronal.

117. Patient 12
Axial Supine Image Coronal Image
rectum
Coronal cross
section
GUD
prostate
Penile
bulb
Pudendal
canal
Crura of corpus
cavernosa
Note the thin GUD and the minimal separation between the
prostate and penile bulb.

118. Overview of CT and US
contouring errors at the apex

119. Clarity, Obscuration, Clarity
Problem: On CT as contouring proceeds inferior, the prostate is clear
above the apex, unclear at the apex, and mistaken for elliptical or circular
GUD elements below the apex
GUD
CT Mid-Prostate CT Prostate Apex Level CT GUD Level

120. A 3-dimensional view shows when prostate contours have
included too much GUD. A lateral BEV can also be used
to visualized this projection.
3 D View- contouring GUD as prostate -
“pros-teat”
rectum
The same figure with the
MRI prostate shown in light
blue.
3D view of Prostate contoured on
CT to include round GUD and
external sphincter often mistaken for
prostate.
rectum
GUD contoured as
prostate

121. 3 D View- contouring prostate with rectum as
reference - “love handle”
A 3-dimensional view shows the prostate has been contoured in
reference to the clearly visualized rectum, on the assumption the
prostate is adjacent to the rectum . A lateral BEV can be used to
visualize this overestimation. The posterior edge of the prostate is
convex. When aligned to the rectum it appears concave .
3D view of Prostate contoured to the
edge of the rectum on CT
The same figure with the
MRI prostate shown in light
blue
rectum
rectum
Prostate contoured to
the edge of rectum

122. Patient 13: Visible GUD on CT-pre implant
Axial CT 1 AxialT2 MRI 1
Axial CT 2
AxialT2 MRI 2
Penile Bulb
Note directly superior to the penile bulb the CT is unclear.

123. Patient 13-pre implant:
Axial CT 3 AxialT2 MRI 3
Axial CT 4 AxialT2 MRI 4
Note the GUD hourglass shape is visible on CT image 4.

124. Axial CT 5 AxialT2 MRI 5
Axial CT 6
AxialT2 MRI 6
Patient 13-pre implant:

125. Axial CT 7 AxialT2 MRI 7
Axial CT 8 AxialT2 MRI 8
Prostate Apex
Patient 13-pre implant:

126. Patient 14: Example of round GUD on CT-pre implant
Axial CT 1
AxialT2 MRI 1
Axial CT 2
AxialT2 MRI 2
Penile Bulb

127. Axial CT 3 AxialT2 MRI 3
Axial CT 4 AxialT2 MRI 4
Patient 14-pre implant:
Note the GUD appears round on the CT and can be
mistaken for prostate.

128. Axial CT 5 AxialT2 MRI 5
Axial CT 6 AxialT2 MRI 6
The round diaphragm shape continues into the prostate
apex making the GUD/ apex distinction difficult on CT.
Patient 14-pre implant:

129. Axial CT 7 AxialT2 MRI 7
Axial CT 8 AxialT2 MRI 8
Patient 14-pre implant:

130. Patient 15: Unclear GUD- pre implant
Axial CT 1
AxialT2 MRI 1
Axial CT 2
AxialT2 MRI 2

131. Patient 15-pre implant:
Axial CT 3 AxialT2 MRI 3
Axial CT 4 AxialT2 MRI 4
Note that the GUD is not clear on the CT scan making it difficult to determine
prostate apex location. On axial CT 4 the elements are barely visible (external
sphincter and posterior extension of GUD [white on MRI] ).

132. Axial CT 5
AxialT2 MRI 5
Axial CT 6
AxialT2 MRI 6
At the apex, the CT image is still not clear.
Patient 15-pre implant:

133. Axial CT 7
AxialT2 MRI 7
Axial CT 8
AxialT2 MRI 8
Patient 15-pre implant:

134. Patient 16: Example of clear GUD on CT-post implant
Axial CT 1
AxialT2 MRI 1
Axial CT 2
AxialT2 MRI 2

135. Axial CT 3 AxialT2 MRI 3
Axial CT 4 AxialT2 MRI 4
Patient 16-post implant:
Notice the shape of the GUD and external sphincter is
visible on the post implant CT scan as a bull’s eye target
(Axial CT3)

136. Axial CT 5 AxialT2 MRI 5
Axial CT 6 AxialT2 MRI 6
Patient 16-post implant:

137. Patient 17: Unclear GUD- post implant
Axial CT 1
AxialT2 MRI 1
Axial CT 2
AxialT2 MRI 2

138. Patient 17-post implant:
Axial CT 3
AxialT2 MRI 3
Axial CT 4
AxialT2 MRI 4
Note that the GUD is not clear on the CT scan.

139. Axial CT 5
AxialT2 MRI 5
Axial CT 6
AxialT2 MRI 6
The lack of GUD/ prostate apex clarity on CT often results
in overestimation of the prostate at the apex.
Patient 17-post implant:

140. Axial CT 7
AxialT2 MRI 7
Axial CT 8
AxialT2 MRI 8
Patient 17-post implant:

141. Post-prostate implant T2 MRI scans
Part 3: Post Prostate Implant
‘Distortion’ of Anatomy

142. Patient 18:
mild post-implant distortion

143. Patient 18- mild distortion
Pre-implant Coronal T2 MRI Scan Post-implant Coronal T2 MRI Scan
PRE POST
This patient exhibits only mild-post implant ‘distortion’ of surrounding anatomy.
Note the reduced clarity of the prostate border between pre and post scans.
However, the GUD and external sphincter remain fairly clear.

144. PRE POST
Pre-implant sagittal T2 MRI Scan Pre-implant sagittal T2 MRI Scan
Note there is little visible distortion between pre
and post sagittal scans of the same patient.
Patient 18- mild distortion

145. Axial image 1 Axial image 2
Patient 18: Post-Implant, mild distortion

146. Axial image 3 Axial image 4
Patient 18: Post-Implant, mild distortion

147. Axial image 5 Axial image 6
Patient 18: Post-Implant, mild distortion

148. Axial image 7 Axial image 8
Note the inner (TZ) and outer (PZ) prostate zones are distinct.
Patient 18: Post-Implant, mild distortion

149. Axial image 9 Axial image 10
Patient 18: Post-Implant, mild distortion

150. Axial image 11
Patient 18: Post-Implant, mild distortion

151. Patient 19:
moderate post-implant distortion

152. Patient 19- moderate distortion
PRE POST
Pre-implant Coronal T2 MRI Scan Post-implant Coronal T2 MRI Scan
This patient exhibits moderate post-implant ‘distortion’. Note visible distortion
of GUD and external sphincter. Also note the reduced clarity of the
prostate border between pre and post scans.

153. Axial image 1 Axial image 2
Patient 19: Post-Implant, moderate distortion

154. Axial image 3 Axial image 4
Patient 19: Post-Implant, moderate distortion

155. Axial image 5 Axial image 6
Note that the mid-prostate margin remains distinct, however, the inner (TZ) and
outer (PZ) zones are not distinct.
Patient 19: Post-Implant, moderate distortion

156. Axial image 7 Axial image 8
Patient 19: Post-Implant, moderate distortion

157. Axial image 9 Axial image 10
Patient 19: Post-Implant, moderate distortion

158. Axial image 11 Axial image 12
Patient 19: Post-Implant, moderate distortion

159. Axial image 13
Patient 19: Post-Implant, moderate distortion

160. Patient 20:
severe post-implant distortion

161. Patient 20-severe distortion
PRE POST
Pre-implant Coronal T2 MRI Scan Post-implant Coronal T2 MRI Scan
This patient exhibits severe post-implant ‘distortion’. Note the distortion
of both the obturator internus and levator ani muscles post-implant.
Possible hemorrhage
with superior
displacement of
prostate

162. PRE POST
Pre-implant Coronal T2 MRI Scan Post-implant Coronal T2 MRI Scan
Note the reduced clarity of the prostate border, as well as the
obturator internus and levator ani muscles. Also note the TZ
is difficult to define post-implant.
Patient 20-severe distortion

163. PRE POST
Pre-implant Coronal T2 MRI Scan Post-implant Coronal T2 MRI Scan
Note the ‘disappearance’ of the prostate apex and the GUD post-implant. Also
note the difference in levator ani and obturator internus muscles pre vs post.
Patient 20-severe distortion

164. PRE POST
Pre-implant Coronal T2 MRI Scan Post-implant Coronal T2 MRI Scan
Note the swelling and distortion below the prostate.
Patient 20-severe distortion

165. Pre Implant Day of Implant 2 Week Post
Implant
Pre-implant Coronal
T2 MRI Scan
Day of implant Coronal
T2 MRI Scan
Post-implant Coronal
T2 MRI Scan
Note the penile bulb in the Day of Implant MRI compared to the pre
and 2 week post MRIs.
Patient 20- Day of MRI

166. Patient 20: Post-Implant, severe distortion
Axial image 1 Axial image 2

167. Axial image 1 Axial image 2
Patient 20: Post-Implant, severe distortion

168. Axial image 3 Axial image 4
Patient 20: Post-Implant, severe distortion

169. Axial image 5 Axial image 6
Patient 20: Post-Implant, severe distortion

170. Axial image 7 Axial image 8
Patient 20: Post-Implant, severe distortion

171. Axial image 9
Patient 20: Post-Implant, severe distortion

172. Part 4: Contouring the Prostate
on MRI and CT

173. Pre-Implant
Scans

174. Patient 21

175. Patient 21
Axial CT
without Contour
Axial MRI
without Contour
Penile Bulb Level: inferior to the prostate

176. Axial CT
without Contour
Axial MRI
without Contour
Penile Bulb Level: inferior to the prostate
Patient 21

177. Patient 21
Axial CT
without Contour
Axial MRI
without Contour
Penile Bulb Level: inferior to the prostate

178. Patient 21
Axial CT
without Contour
Axial MRI
without Contour
GUD Level: inferior to the prostate - note outline of the GU
diaphragm is often visible on CT.

179. Patient 21
Axial CT
without Contour
Axial MRI
without Contour
GUD Level: inferior to the prostate - again note the outline of the rectangular
GUD is often visible on CT. In this patient the “target” of the external sphincter
and urethra is visible as well. At the apex level these distinctions are no longer
visible (see following images)

180. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 21
Note lack of boundaries
at apex vs. GUD

181. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 21

182. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 21

183. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 21

184. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 21

185. Axial CT
without Contour
Axial MRI
without Contour
Patient 21
Seminal Vesicle Level: superior to the prostate

186. Patient 21
Axial CT
without Contour
Axial MRI
without Contour
Seminal Vesicle Level: superior to the prostate

187. Patient 22

188. Axial CT
without Contour
Axial MRI
without Contour
Patient 22
Penile Bulb Level: inferior to the prostate

189. Axial CT
without Contour
Axial MRI
without Contour
Patient 22
GUD Level: inferior to the prostate

190. Axial CT
without Contour
Axial MRI
without Contour
Patient 22
GUD Level: inferior to the prostate- in this patient the GUD and external sphincter
are not defined on CT.

191. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 22

192. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 22

193. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 22

194. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 22

195. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 22

196. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 22

197. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 22
Note the anterior extent of the prostate

198. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 22

199. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 22

200. Axial CT
without Contour
Axial MRI
without Contour
Patient 22

201. Patient 23

202. Axial CT
without Contour
Axial MRI
without Contour
Patient 23
Penile Bulb Level: inferior to the prostate

203. Axial CT
without Contour
Axial MRI
without Contour
Patient 23
GUD Level: inferior to the prostate

204. Axial CT
without Contour
Axial MRI
without Contour
Patient 23
GUD Level: inferior to the prostate

205. Axial CT
without Contour
Axial MRI
without Contour
Patient 23
GUD Level: inferior to the prostate

206. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 23

207. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 23

208. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 23

209. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 23

210. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 23

211. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 23
Prostate Base/
Seminal Vesicle
Interface

212. Post Implant Scans

213. Patient 24

214. Axial CT
without Contour
Axial MRI
without Contour
Patient 24
Penile Bulb Level: inferior to the prostate

215. Axial CT
without Contour
Axial MRI
without Contour
Patient 24
GUD Level: inferior to the prostate

216. Axial CT
without Contour
Axial MRI
without Contour
Patient 24
GUD Level: inferior to the prostate

217. Axial CT
without Contour
Axial MRI
without Contour
Patient 24
GUD Level: inferior to the prostate

218. Axial CT
without Contour
Axial MRI
without Contour
Patient 24
GUD Level: inferior to the prostate

219. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 24

220. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 24

221. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 24

222. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 24

223. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 24

224. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 24

225. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 24

226. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 24

227. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 24
Prostate Base/
Seminal Vesicle
Interface

228. Axial CT
without Contour
Axial MRI
without Contour
Patient 24

229. Patient 25

230. Axial CT
without Contour
Axial MRI
without Contour
Patient 25
Penile Bulb Level: inferior to the prostate

231. Axial CT
without Contour
Axial MRI
without Contour
Patient 25
Penile Bulb Level: inferior to the prostate- less distinct post implant on CT

232. Axial CT
without Contour
Axial MRI
without Contour
Patient 25
GUD Level: inferior to the prostate

233. Axial CT
without Contour
Axial MRI
without Contour
Patient 25
GUD Level: inferior to the prostate

234. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 25 The levator ani is often contoured as
prostate due to “circling the seeds”
Prostate Apex/ GUD
Interface

235. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 25

236. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 25

237. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 25

238. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 25

239. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 25

240. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 25

241. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 25

242. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 25

243. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 25

244. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 25

245. Patient 26

246. Axial CT
without Contour
Axial MRI
without Contour
Patient 26
Penile Bulb Level: inferior to the prostate

247. Axial CT
without Contour
Axial MRI
without Contour
Patient 26
GUD Level: inferior to the prostate

248. Axial CT
without Contour
Axial MRI
without Contour
Patient 26
GUD Level: inferior to the prostate

249. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 26

250. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 26

251. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 26

252. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 26

253. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 26

254. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 26

255. Axial CT
without Contour
Axial CT
with Contour
Axial MRI
without Contour
Axial MRI
with Contour
Patient 26

256. Axial CT
without Contour
Axial MRI
without Contour
Patient 26

257. NEUROVASCULAR BUNDLE
and CAVERNOSAL NERVES

258. Neurovascular Bundle
The neurovascular bundle was so named by Dr. Walsh
because the nerves are not grossly visible, but track with
the prostatic capsular arteries and veins. These vessels
serve as a surgical landmark for the nerves in nerve sparing
prostatectomy. The vessels are not visible on time-of-flight
angio (see internal pudendal artery section). They are
visible on Color Doppler ultrasound but are not visible on
CT or MRI. The NVB location can be approximated by a
number of methods (1,2). In the superior prostate/ seminal
vesicle region they pass from the lateral seminal vesicle to
the junction of the prostate and rectum. In the inferior
prostate they course within the triangle formed by the
rectum, prostate and levator ani.

259. Lateral Pelvic Fascia
Levator Fascia
Prostate Fascia
Denonvillieres’ Fascia
Prostate Capsule
Rectum
Prostate
Neurovascular Bundle (Schematic) : The neurovascular bundle is
located between the two layers of the lateral pelvic fascia (levator
fascia and prostate fascia) near the junction with Denonvillieres’ fascia.
Neurovascular Bundle (NVB)
NVB

260. Cavernosal Nerves
The terminal branches of the NVB are the cavernosal
nerves. The greater cavernosal nerve was defined in Gray’s
anatomy as a terminal branch of the NVB which coursed
anterior along the GU diaphragm and through the fault in
the anterior GUD through which the dorsal venous
complex passes. Though described as greater due to its
clarity relative to the lesser cavernosal nerve, there are no
references to the greater cavernosal nerve in the modern
surgical / anatomic literature.
The lesser cavernosal nerve passes through the GUD in a
fixed relationship to the external sphincter. In the supine
position: At the apex the nerves are located in the 7 and 5
o’clock position. In mid GUD they are located at 9 and 3
o’clock. In the inferior GUD, just above the Corpus
Cavernosa, they are positioned at 11 and 1 o’clock.

261. Patient 1: Axial T2 MRI

262. Patient 1, Axial T2 MRI
NVB
NVB
Prostate
Bladder

263. Patient 1, Axial T2 MRI
NVB
NVB
Prostate
Bladder

264. Patient 1, Axial T2 MRI
NVB
NVB
Prostate
Bladder

265. Patient 1, Axial T2 MRI
NVB
NVB
Prostate
Rectum

266. Patient 1, Axial T2 MRI
NVB
NVB
Prostate
Rectum

267. Patient 1, Axial T2 MRI
NVB
NVB
Prostate
Rectum

268. Patient 1, Axial T2 MRI
NVB
NVB
Prostate
Rectum

269. Patient 1, Axial T2 MRI
NVB
NVB
Prostate

270. Patient 1, Axial T2 MRI
Neurovascular
bundle (NVB)
Neurovascular
bundle (NVB)
area alongside
Prostate that
would contain
the Greater
Cavernosal
Nerves
area alongside
Prostate that
would contain
the Greater
Cavernosal
Nerves

271. Patient 1, Axial T2 MRI
Level : Prostate Apex
The lesser cavernosal nerves are not visible radiographically.
At the prostate apex they are located nerves at the 7 and 5’o’clock position.
Lesser
Cavernosal
Nerve
Lesser
Cavernosal
Nerve
External
Sphincter
Prostate
Apex

272. Patient 1, Axial T2 MRI
Level : GUD
Lesser
Cavernosal
Nerve
Lesser
Cavernosal
Nerve
External
Sphincter
GUD

273. Patient 1, Axial T2 MRI
Level : mid-GUD
At the mid GUD they are located at the 9 and 3 o’clock position
Lesser
Cavernosal
Nerve
Lesser
Cavernosal
Nerve
External
Sphincter
GUD

274. Patient 1, Axial T2 MRI
Lesser
Cavernosal
Nerve
Lesser
Cavernosal
Nerve
External
Sphincter

275. Patient 1, Axial T2 MRI
At the mid-to-inferior GUD they transition towards
the 11 and 1’o’clock positions.
Lesser
Cavernosal
Nerve
Lesser
Cavernosal
Nerve
Rectum

276. Patient 1, Axial T2 MRI
Level : 1 cut above penile bulb
At the inferior GUD they appear at the 11 and 1’o’clock position.
Lesser
Cavernosal
Nerve
Lesser
Cavernosal
Nerve

277. Patient 2, Axial T2 MRI
Patient Prone

278. Image 7 Image 8
Rectum
Neurovascular
bundle (NVB)
Patient 2, Axial T2 MRI
Neurovascular
bundle (NVB)
Prostate
beg. of
Bladder

279. Patient 2, Axial T2 MRI
NVB
NVB
Prostate
Rectum

280. Patient 2, Axial T2 MRI
NVB
NVB
Prostate
Rectum

281. Patient 2, Axial T2 MRI
NVB
NVB
Prostate
Rectum

282. Patient 2, Axial T2 MRI
Neurovascular
bundle (NVB)
Neurovascular
bundle (NVB)
Prostate

283. Neurovascular
bundle (NVB)
Neurovascular
bundle (NVB)
Patient 2, Axial T2 MRI
area alongside
Prostate that
would contain
the Greater
Cavernosal
Nerves
area alongside
Prostate that
would contain
the Greater
Cavernosal
Nerves

284. Patient 2, Axial T2 MRI
The lesser cavernosal nerves appear at the apex. Note that they seem localized at the
11 and 1’o’clock relative to the prostate because the patient is prone. If supine, it
would be noted at the 5 and 7 o’clock position.
Lesser
Cavernosal
Nerve
Lesser
Cavernosal
Nerve
External
Sphincter
Prostate
Apex
Level: Apex

285. Patient 2, Axial T2 MRI
Here they appear at the 9 and 3’o’clock positions.
Lesser
Cavernosal
Nerve
Lesser
Cavernosal
Nerve
Rectum
External
Sphincter
Level: mid-GUD

286. Image 7 Image 8
Rectum
External
Sphincter Lesser
cavernosal
nerve
Patient 2, Axial T2 MRI

287. Image 7 Image 8
GUD
Rectum
External
Sphincter
Lesser
Cavernosal
Nerve
Patient 2, Axial T2 MRI
Lesser
Cavernosal
Nerve

288. Patient 2, Axial T2 MRI
Lesser
Cavernosal
Nerves
At the inferior GUD the nerves are at 5 and 7 o’clok in the prone patient

289. Patient 3, Axial T2 MRI
Patient Supine

290. Patient 3, Axial T2 MRI
NVB
NVB
Prostate
Rectum

291. Patient 3, Axial T2 MRI
NVB
NVB
Prostate
Rectum

292. Patient 3, Axial T2 MRI
NVB
NVB
Prostate
Rectum

293. Patient 3, Axial T2 MRI
NVB
NVB
Prostate
Rectum

294. Patient 3, Axial T2 MRI
NVB
NVB
Prostate
Rectum

295. Patient 3, Axial T2 MRI
NVB
NVB
Prostate
Rectum

296. Patient 3, Axial T2 MRI
Neurovascular
bundle (NVB)
Neurovascular
bundle (NVB)
area alongside
Prostate that
would contain
the Greater
Cavernosal
Nerves
area alongside
Prostate that
would contain
the Greater
Cavernosal
Nerves

297. Patient 3, Axial T2 MRI
Transition from NVB to cavernosal nerves just above the prostate apex
NVB/Lesser
Cavernosal
Nerve
NVB/Lesser
Cavernosal
Nerve

298. Patient 3, Axial T2 MRI
Level : mid-GUD
At mid GUD they appear at the 9 and 3’o’clock positions.
Lesser
Cavernosal
Nerve
Lesser
Cavernosal
Nerve
External
Sphincter
GUD

299. Patient 3, Axial T2 MRI
At the inferior GUD they appear at the 11 and 1’o’clock position.
Level : GUD
Lesser
Cavernosal
Nerve
Lesser
Cavernosal
Nerve
External
Sphincter
GUD

300. References
• G.S. Merrick, W.M. Butler et al., A comparison of
radiation dose to the neurovascular bundles in men with
and without prostate brachytherapy-induced erectile
dysfunction. Int J Radiat Oncol Biol Phys 48 (2000),
pp.1069-1074.
2. S.J. DiBiase, K. Wallner et al., Brachytherapy radiation
doses to the neurovascular bundles. Int J Radiat Oncol
Biol Phys 46 (2000), pp. 1301-1307.

301. PUDENDAL CANAL and
INTERNAL PUDENDAL
ARTERY

302. The internal pudendal artery is a branch of the
internal iliac artery. It passes along the lateral
pelvic wall and through the pudendal canal. The
pudendal canal is a connective tissue sheath on the
medial surface of the Obturator internus. It then
passes through the inferior fascia of the
genitourinary diaphragm (GUD). Its terminal
branches are within the GUD and supply penile
bulb and corpus cavernosa.
Internal Pudendal Artery

303. Patient 1: Axial T2 MRI

304. Patient 1, Axial MRI
Note the two circled structures as they make their way around the
ischium and up towards the crura in the following images.
IPA
IPA
Prostate
Bladder
Obturator
internus
Obturator
internus
Ischium
Bone Ischium
Bone

305. Patient 1, Axial MRI
IPA
IPA
Bladder

306. Patient 1, Axial MRI
IPA
IPA
Obturator
internus
Rectum

307. Patient 1, Axial MRI
IPA
IPA
Ischioanal/
Ischiorectal
Fossa (IF)

308. Patient 1, Axial MRI
IPA
IPA
Obturator
internus

309. Patient 1, Axial MRI
IPA
IPA

310. Patient 1, Axial MRI
IPA
IPA

311. Patient 1, Axial MRI
IPA IPA

312. Patient 1, Axial MRI
IPA IPA

313. Patient 1, Axial MRI
IPA
IPA

314. Patient 1, Axial MRI
IPA
IPA
External
Sphincter
Prostate
Apex

315. Patient 1, Axial MRI
IPA
IPA
Prostate
Apex
External
Sphincter
Rectum

316. Patient 1, Axial MRI
IPA
IPA
External
Sphincter
GUD
Rectum

317. Patient 1, Axial MRI
IPA
IPA
GUD
External
Sphincter
IF
Levator
ani

318. Patient 1, Axial MRI
IPA
IPA

319. IPA
IPA
Penile
Bulb
Patient 1, Axial MRI
After entering the GUD the IPA into branches to supply the penile
bulb and corpus cavernosum

320. Patient 2: Axial T2 MRI

321. Patient 2, Axial MRI
IPA
Ischium
Prostate
Rectum
Bladder

322. Patient 2, Axial MRI
IPA
Prostate Obturator
internus

323. Patient 2, Axial MRI
IPA
IPA

324. Patient 2, Axial MRI
IPA
IPA

325. Patient 2, Axial MRI
IPA
IPA

326. Patient 2, Axial MRI
IPA
IPA

327. Patient 2, Axial MRI
IPA
IPA

328. Patient 2, Axial MRI
IPA
IPA
External
Sphincter
Prostate
Apex

329. Patient 2, Axial MRI
IPA
IPA
Prostate
Apex

330. Patient 2, Axial MRI
IPA
IPA
External
Sphincter
Rectum

331. Patient 2, Axial MRI
IPA
IPA

332. Patient 2, Axial MRI
IPA
IPA
Rectum
Crura of Corpus
Cavernosa

333. Patient 3: Axial T2 MRI

334. Patient 3, Axial T2 MRI
IPA
IPA
Prostate
Rectum
Obturator
internus

335. Patient 3, Axial T2 MRI
IPA
IPA

336. Patient 3, Axial T2 MRI
IPA
IPA
Prostate
Apex

337. Patient 3, Axial T2 MRI
IPA
IPA
IF
GUD
External
Sphincter

338. Patient 3, Axial T2 MRI
IPA
IPA

339. Patient 3, Axial T2 MRI
The Ischioanal/Ischiorectal Fossa (IF) are the wedge-shaped areas
lateral to the anal canal. The pudendal canal is found on the lateral
wall of the IF.
Ischioanal Fossa
(IAF)
Rectum
IPA
IPA

340. Patient 3, Axial T2 MRI
IPA
IPA

341. Patient 3, Axial T2 MRI
IPA
IPA
Corpus
Cavernosa

342. Patient 3, Axial T2 MRI
IPA
IPA
Corpus
Cavernosum
Corpus
Cavernosum
Penile
Bulb

343. Patient 4: Axial CT and T2 MRI
The following images are a side by side comparison of a
patient CT and correlating Axial T2 MRI. In a subset of
patients it is possible to localize the IPA on CT but it is
more obvious on MRI.

344. Patient 4, CT vs. Axial T2 MRI
Post Implant
IPA
IPA
IPA
IPA

345. Patient 4, CT vs. Axial T2 MRI
Patient 4, CT vs Axial T2 MRI
IPA
IPA
IPA
IPA

346. Patient 4, CT vs. Axial T2 MRI
IPA
IPA
IPA
IPA

347. Locating Pudendal Arteries on
Coronal MRI
The terminal branches of the IPA within the GUD are
poorly visualized on Axial MRI. They can be identified on
Coronal MRI as a cluster of vessels above the corpus
cavernosa. These vessels can be traced posterior to the
pudendal canal which is well visualized on coronal view.

348. Patient 5: Coronal T2 MRI

349. Patient 5, Coronal T2 MRI
IPA
IPA in the
pudendal canal
IF

350. Patient 5, Coronal T2 MRI
IPA
IPA

351. Patient 5, Coronal T2 MRI
IPA
IPA

352. Patient 5, Coronal T2 MRI
IPA
IPA
Levator
ani
Levator
ani

353. Patient 5, Coronal T2 MRI
IPA IPA
Obturator
internus

354. Patient 5, Coronal T2 MRI
IPA IPA
Obturator
internus

355. Patient 5, Coronal T2 MRI
Terminal branches
of IPA =
Terminal IPA
Crura of Corpus
Cavernosum
Terminal branches of
IPA

356. Patient 5, Coronal T2 MRI
Terminal IPA
Terminal IPA
Penile
Bulb
Prostate
Crura of Corpus
Cavernosum

357. Patient 6: Coronal T2 MRI

358. Patient 6, Coronal T2 MRI
IPA
IPA
Rectum

359. Patient 6, Coronal T2 MRI
IPA
IPA

360. Patient 6, Coronal T2 MRI
IPA
IPA

361. Patient 6, Coronal T2 MRI
IPA
IPA

362. Patient 6, Coronal T2 MRI
IPA
IPA

363. Patient 6, Coronal T2 MRI
IPA
IPA

364. Patient 6, Coronal T2 MRI
IPA
IPA

365. Patient 6, Coronal T2 MRI
IPA
IPA
Bladder

366. Patient 6, Coronal T2 MRI
IPA
IPA

367. Patient 6, Coronal T2 MRI
IPA
IPA

368. Patient 6, Coronal T2 MRI
IPA
IPA in pudendal canal
Levator
Ani
Obturator
internus

369. Patient 6, Coronal T2 MRI
IPA
IPA
Prostate
beginning
of crura

370. Patient 7, Coronal T2 MRI

371. Patient 7, Coronal T2 MRI
IPA IPA

372. Patient 7, Coronal T2 MRI
IPA
IPA

373. Patient 7, Coronal T2 MRI
IPA
Bladder
IPA

374. Patient 7, Coronal T2 MRI
Terminal IPA
Terminal IPA
Bladder

375. Patient 7, Coronal T2 MRI
Terminal IPA
Terminal IPA
Bladder

376. Patient 7, Coronal T2 MRI
Terminal IPA
Terminal IPA
Prostate
Bladder
Penile
Bulb

377. Patient 7, Coronal T2 MRI
Terminal IPA
Terminal IPA
Bladder
Penile
Bulb

378. Patient 7, Coronal T2 MRI
Terminal IPA
Terminal IPA
Bladder
Corpus
cavernosum

379. Patient 7, Coronal T2 MRI
Terminal branches
of IPA
Terminal branches
of IPA
Bladder
Penile
Bulb
Corpus
Cavernosum
External
Sphincter

380. Angio vs. Axial MRI
This image shows the fusion of the Angio MRI to its correlating
Axial T2 MRI. Note the IPA is visible on both scans.
IPA
IPA
Prostate

381. Pudendal Arteries on Angiogram
The following angiograms were obtained by a time
of flight MRI sequence, a non contrast study
completed in less than 10 minutes. There is great
variation in the quality of an IPA time of flight
angiogram. The range from poor to excellent
visualization may be due to differences in body
habitus, technical factors and vessel patency. The
following images clearly display the course of the
IPA.

382. Patient 8: IPAAngiogram

383. Patient 8, Angio MRI
IPA
IPA

384. Patient 8, Angio MRI
IPA IPA
Prostate
Obturator
internus

385. Patient 8, Angio MRI
IPA
IPA

386. Patient 8, Angio MRI
IPA
IPA
Prostate

387. Patient 8, Angio MRI
IPA
IPA

388. Patient 8, Angio MRI
IPA
IPA

389. Patient 8, Angio MRI
IPA IPA
IF

390. Patient 8, Angio MRI
IPA
IPA

391. Patient 8, Angio MRI
IPA
IPA

392. Patient 8, Angio MRI
IPA
IPA

393. Patient 8, Angio MRI
IPA
IPA

394. Patient 8, Angio MRI
IPA
IPA

395. Patient 8, Angio MRI
IPA
IPA

396. Patient 8, Angio MRI
Rectum
IPA
IPA

397. Patient 9: IPAAngiogram
(Patient Prone)

398. Patient 9, Angio MRI
IPA
Prostate
IPA
Rectum
Pubic Symphysis
Femoral Head

399. Patient 9, Angio MRI
IPA
IPA
Prostate

400. Patient 9, Angio MRI
IPA
IPA
Rectum
Prostate

401. Patient 9, Angio MRI
IPA IPA

402. Patient 9, Angio MRI
IPA
IPA
IF
IF
Rectum
Prostate

403. Patient 9, Angio MRI
IPA
IPA

404. Patient 9, Angio MRI
IPA IPA

405. Patient 9, Angio MRI
IPA
IPA

406. Patient 9, Angio MRI
IPA
IPA

407. Patient 9, Angio MRI
IPA
IPA

408. Patient 9, Angio MRI
IPA
IPA

409. Patient 9, Angio MRI
IPA
IPA

410. Patient 9, Angio MRI
IPA
IPA

411. Patient 9, Angio MRI
IPA
IPA

412. Patient 9, Angio MRI
IPA
IPA

413. Patient 9, Angio MRI
IPA
IPA

414. Patient 9, Angio MRI
IPA
IPA

415. Patient 9, Angio MRI
IPA
IPA

416. Patient 9, Angio MRI
IPA
IPA

417. Patient 9, Angio MRI
IPA
IPA

418. Patient 9, Angio MRI
IPA
IPA

419. Patient 9, Angio MRI
IPA
IPA
Penile
Bulb

420. Angio MRI vs. CT
The following images are side by side comparisons
of IPA visible on Angio MRI and the equivalent CT.
Since it is difficult to locate the IPA on CT, the
contours shown on CT are cut from the correlated
Angio MRI images.

421. Patient 10, Angio MRI
IPA
IPA
Prostate
Rectum
Rectum

422. Patient 10, Angio MRI
IPA
IPA

423. Patient 10, Angio MRI
IPA
IPA

424. Patient 10, Angio MRI
IPA
IPA

425. Patient 10, Angio MRI
IPA
IPA
Note that the IPA is slightly visible on CT.
Its location is relative to the IPA identified in
the Angio.

426. Angio MRI vs. CT
The following images on CT show the
visible and estimated position of the the
IPA based on its relationship to adjacent
structures. They have not been contoured
but rather encircled broadly to allow review
of the vessel appearance and location on
CT. Calcification of the vessels may
improve visualization on CT.

427. Patient 10, Angio MRI
IPA IPA

428. Patient 10, Angio MRI
IPA IPA

429. Patient 10, Angio MRI
IPA IPA

430. Patient 10, Angio MRI
IPA IPA

431. Patient 10, Angio MRI
IPA IPA

432. A 3D Image of Prostate and critical
adjacent structures