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CHRONIC AND INTERVENTIONAL PAIN
BRIEF TECHNICAL REPORT
Ultrasound-Guided Pudendal Nerve Block at the Entrance
of the Pudendal (Alcock) Canal
Description of Anatomy and Clinical Technique
Thomas Fichtner Bendtsen, MD, PhD,* Teresa Parras, MD, PhD,† Bernhard Moriggl, MD, PhD,‡
Vincent Chan, MD,§ Lilli Lundby, MD, PhD,|| Steen Buntzen, MD, PhD,|| Karoline Dalgaard, MD,*
Birgitte Brandsborg, MD, PhD,* and Jens Børglum, MD, PhD#
Background and Objectives: Ultrasound-guided techniques for pudendal nerve block have been described at the level of the ischial spine
and transperineally. Theoretically, however, blockade of the pudendal nerve
inside Alcock canal with a small local anesthetic volume would minimize
the risk of sacral plexus blockade and would anesthetize all 3 branches of
the pudendal nerve before they ramify in the ischioanal fossa. This technical report describes a new ultrasound-guided technique to block the pudendal nerve. The technique indicates an easy and effective roadmap to target
the pudendal nerve inside the Alcock canal by following the margin of the
hip bone sonographically along the greater sciatic notch, the ischial spine,
and the lesser sciatic notch.
Methods: The technique was applied bilaterally in 3 patients with chronic
perineal pain. The technique described was also used to locate the pudendal
nerve within Alcock canal and inject dye bilaterally in 2 cadavers.
Results: Complete pinprick anesthesia was obtained in the pudendal territory of the perineum in all 3 patients. Pain was effectively alleviated or reduced in all patients with no affection of the sacral plexus nerve branches.
In the 2 cadavers, all 4 pudendal nerves were successfully targeted
and colored.
Conclusions: This new technique is based on easily recognizable
sonoanatomical patterns. It probably implies no risk of sacral plexus blockade, and the pudendal nerve is anesthetized before any branches ramify
from the main trunk. This promising new technique must be validated in
future clinical trials.
(Reg Anesth Pain Med 2016;41: 00–00)
A
cute and chronic perineal pain is common after gastroenterologic, urologic, gynecologic, and obstetric surgery. Chronic
anoperineal pain can also result from compression of the pudendal
nerve.1 The most prevalent cause of temporary or chronic pudendal nerve injury, typically unilateral, is vaginal delivery.2 Bilateral
injury is uncommon and mostly due to trauma such as straddling
on blunt objects such as bicycle seats.3 Pudendal neuralgia can
impede daily life functions such as sitting and sexual activity.
From the *Department of Anesthesia and Intensive Care Medicine, Aarhus University Hospital, Aarhus, Denmark; †Department of Anesthesia, St Georges
Hospital, London, England; ‡Division of Clinical and Functional Anatomy,
Medical University of Innsbruck, Austria; §Department of Anesthesia, Toronto
Western Hospital, University of Toronto, Toronto, Ontario, Canada; ||Department of Surgery, Aarhus University Hospital, Aarhus, Denmark; and #Department of Anesthesia and Intensive Care Medicine, Copenhagen University
Hospital Roskilde, Copenhagen, Denmark.
Accepted for publication October 21, 2015.
Address correspondence to: Thomas Fichtner Bendtsen, MD, PhD, Department
of Anesthesia and Intensive Care Medicine, Aarhus University Hospital,
Noerrebrogade 44, DK-8000 Aarhus, Denmark (e‐mail: [email protected]).
The authors declare no conflict of interest.
Funding was received from the A.P. Møller and Chastine Mc-Kinney
Møller Foundation.
Copyright © 2016 by American Society of Regional Anesthesia and Pain
Medicine
ISSN: 1098-7339
DOI: 10.1097/AAP.0000000000000355
Pudendal nerve injury is associated with fecal and urinary incontinence due to motor or sensory deficits of the external anal and
urethral sphincters.4
Compression or entrapment of the pudendal nerve or its
branches is typically between the sacrospinous and sacrotuberous
ligaments, or inside Alcock canal, or across the inner margin of
the falciform process, which is part of the sacrotuberous ligament,
or inside the osteofibrotic canal at the base of the penis.5
Pudendal nerve block is indicated for (1) anesthesia in obstetrics (outlet forceps delivery and episiotomy); (2) analgesia involving the perineum after gynecologic, gastroenterologic (eg, rectal
extirpation), or urologic surgery; and (3) diagnostic and therapeutic intervention for perineal chronic pain.
Fluoroscopy is a well-established imaging technique for pudendal nerve blocks. However, ultrasound (US) can achieve similar success as fluoroscopy with added advantages, which include
no exposure to radiation, ready availability in most anesthesiology
departments, and real-time needle insertion guidance.5
Ultrasound-guided blockade of the pudendal nerve has been
performed at the level of the ischial spine and transperineally.6,7
The proximal approach (ie, at the level of the ischial spine) is associated with a moderate risk of concomitant sacral plexus blockade.5 The distal transperineal approach performed in the lithotomy
position is often more painful. With the classical blind technique,
digital palpation of the ischial spine is required through the vaginal wall in female patients or through the rectum in male patients.
This approach, with or without US guidance, typically anesthetizes the dorsal nerve of the penis/clitoris and the perineal nerve
but probably misses the inferior rectal nerve, which branches off
the pudendal nerve in the proximal end of the Alcock canal. Furthermore, the blind technique carries a high risk of injury to blood
vessels, bowel, and bladder and may also injure the physician's
palpating finger.4
METHODS
This report describes a novel technique of US-guided pudendal nerve block inside Alcock canal for pain relief after perineal surgery and for diagnosis and/or treatment of chronic
anoperineal pain. Included are clinical results of bilateral blocks
in 3 patients using this technique and the dye-injection study results in 2 cadavers.
RESULTS
Anatomic Description
The pudendal nerve is a somatic sensorimotor nerve that
originates from the sacral ventral spinal rami S2–S4 (Figs. 1 and
2A, B). It exits the pelvis through the greater sciatic foramen below the inferior margin of the piriformis muscle together with
the internal pudendal artery and veins just cranial to the ischial
spine (Figs. 1 and 2C). The pudendal nerve, artery, and veins have
Regional Anesthesia and Pain Medicine • Volume 41, Number 2, March-April 2016
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Bendtsen et al
Regional Anesthesia and Pain Medicine • Volume 41, Number 2, March-April 2016
FIGURE 1. This figure shows the relevant anatomy of the posterior
approach to the pudendal nerve. Alcock canal is depicted with
cyan color on the internal surface of the obturator internus (yellow
asterisk), anterior to the sacrotuberous ligament (blue asterisk) in
the ischioanal fossa between the obturator internus laterally, and the
levator ani (magenta asterisk) and iliococcygeus (white asterisk)
muscles medially. The Alcock canal contains the pudendal nerve
(yellow) and the internal pudendal artery and vein (red and blue).
The pudendal nerve and vessels wind around the sacrospinous
ligament (green asterisk) that connects the ischial spine with the
lateral margin of the sacrococcyx. At the level of the sacrospinous
ligament, the pudendal nerve runs in close proximity to the
inferior gluteal artery and vein (green arrow), the sacral plexus and
the sciatic nerve (black asterisk). The figure shows the footprint of
the US transducer (blue frame) across the posterior margin of the
ischial tuberosity visualizing the pudendal nerve near the proximal
end of the Alcock canal.
a very short extrapelvic trajectory, as they wind around the posterior aspect of the ischial spine or the sacrospinous ligament
(Figs. 1 and 2C, D) before they reenter the pelvis through the
lesser sciatic foramen (Fig. 2E). The lesser sciatic foramen is the
opening bounded by the lesser sciatic notch as well as the
sacrospinous and sacrotuberous ligaments (Figs. 1 and 2D, E).
The smooth lesser sciatic notch is covered by the internal obturator muscle that winds around the notch (Figs. 2E, F), where it becomes sandwiched between the superior and inferior gemelli
muscles (Figs. 2D, F).
When the pudendal neurovascular bundle passes through the
lesser sciatic foramen, it enters the ischioanal fossa and dives into
the Alcock canal in the sharp angle between the coccygeus and internal obturator muscles (Figs. 1 and 2E, F). The entrance of the
Alcock canal is immediately below the level of the ischial spine,
the sacrospinous ligament and the superior gemellus muscle
(Figs. 2D, E).
Alcock canal is formed by splitting of the internal obturator
fascia. The canal runs across the internal obturator muscle on
the medial side of the ischial tuberosity. It lies just below the hammock of the pelvic floor (ie, the coccygeus and levator ani muscles) and anterior to the sacrotuberous ligament in the distal part
of the lateral wall of the ischioanal fossa.
2
At the level of the ischial spine, the pudendal nerve consists
of a single (60%), 2 (35%), or 3 (5%) trunks. The nerve or the
nerve trunks descend either on the medial (75%), lateral (10%),
or on both (15%) sides of the internal pudendal artery and the distance between the internal pudendal artery and the pudendal nerve
varies between 17 mm medial and 8 mm lateral to the artery.8 The
location of the internal pudendal artery ranges between 10 mm
medial and 11 mm lateral to the tip of the ischial spine.8
The pudendal nerve has 3 terminal branches: (1) the inferior
rectal nerve, originating near the proximal end of the Alcock canal, traverses the fatty tissue of the ischioanal fossa and innervates
the external anal sphincter, the mucous membrane of the lower
part of the anal canal and the perianal skin; (2) the dorsal nerve
of the penis/clitoris runs anteriorly along the inferior pubic ramus
together with the pudendal artery deep to the perineal membrane
which it pierces just below the pubic symphysis, and innervates
the skin of the penis/clitoris; and (3) the perineal nerve and its
deep muscular branch innervate the perineal muscles (deep and
superficial transverse perineal, external urethral sphincter, bulbospongiosus, and ischiocavernosus muscles). It is important to note
that the pelvic floor muscles—the levator ani and the coccygeus
muscles—are innervated by direct branches of the sacral plexus
and by the coccygeal plexus, respectively. The superficial branch
of the perineal nerve innervates the skin of the posterior part of the
scrotum/labia majora (posterior scrotal/labial nerves) and the mucous membrane of the urethra and vagina.
Description of the Technique
Before the block procedures, standard 3-lead electrocardiogram, pulse oximetry, and noninvasive blood pressure monitors
are applied, and a venous access is established.
The technique is designed to provide an easy roadmap to the
target Alcock canal by tracking the margin of the hip bone
sonographically from the greater sciatic notch via the ischial spine
to the lesser sciatic foramen, which leads directly to the entrance
of the Alcock canal.
With the patient lying lateral decubitus (alternatively prone), hip
and knee slightly flexed and the intervention side uppermost, a lowfrequency curved array transducer (Sonosite X-porte, 5–2 MHz
C60xp transducer; Fujifilm Sonosite, Bothell, Washington, or
Epiq7G, C5-1 transducer; Philips, Best, the Netherlands) is placed
on the medial half of the line connecting the posterior superior iliac spine and the greater trochanter (Fig. 3A) after proper skin
sterilization (2% chlorhexidine in 70% isopropyl alcohol). In this
transducer position, the hip bone (ie, the innominate or coxal
bone) is visualized as a continuous hyperechoic line and the superior gluteal artery is seen pulsating deep to the gluteus medius
muscle (Fig. 4, 1AB). The transducer is parallel shifted inferomedially until the continuous hyperechoic line of the hip bone is
broken—that is, the US beam intersects the greater sciatic notch—
using the so-called Para Sacral Parallel Shift technique (Figs. 3B
and 4, 2A).9 The transducer is parallel shifted further distally along
the lateral margin of the greater sciatic notch to the ischial spine
(Figs. 3B and 4, 2A–4B). Proximal to the ischial spine, the pudendal and inferior gluteal arteries emerge from the lesser pelvis under
the lower margin of the piriformis muscle and the head of the femur
is visible lateral to the body of the ischium (Fig. 4, 3AB). When the
US beam intersects the ischial spine, the sacrospinous and
sacrotuberous ligaments generate strong specular reflections (Fig. 4,
4AB). Also, the superior gemellus muscle presents a very characteristic dark shape on top the ischial spine (Fig. 4, 4AB). The pudendal, inferior gluteal, and sciatic nerves as well as the internal
pudendal and inferior gluteal arteries typically lie close together
at this level around the tip of the ischial spine between the
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Regional Anesthesia and Pain Medicine • Volume 41, Number 2, March-April 2016
Ultrasound-Guided Pudendal Nerve Block
FIGURE 2. The figure presents the topographical anatomy of the pudendal nerve in axial cross sections from the levels as follows:
(A) hip bone just cranial to the upper margin of the greater sciatic notch; (B) just caudal to the superior margin of the greater sciatic notch;
(C) at the inferior margin of the greater sciatic notch; (D) at the tip of the ischial spine; (E) at the lesser sciatic notch where the pudendal nerve,
artery, and veins dive via the lesser sciatic foramen into the Alcock canal inside the ischioanal fossa; and (F) the proximal end of the Alcock
canal. l, Lateral; m, medial. The pudendal nerve is depicted as a yellow profile with a cyan border. Asterisks: Red is hip bone; cyan is sacral bone;
and blue, green, and yellow are gluteus medius, maximus, and minimus muscles. Magenta, white, and black are piriformis, coccygeus, and
levator ani muscles. Arrows: Yellow point at sacral plexus, green and red at superior and inferior gluteal arteries, blue at internal pudendal
artery, cyan at sciatic nerve, and magenta at inferior gluteal nerve. Colored structures: Red are arteries, blue are veins, yellow are nerves, cyan
is sacrospinous ligament, magenta is sacrotuberous ligament, green is superior gemellus muscle, and light brown is internal obturator muscle.
Modified excerpt from VH Dissector with permission from Touch of Life Technologies Inc (www.toltech.net). Built on real anatomy from the
National Library of Medicine’s Visible Human Project.
sacrospinous and sacrotuberous ligaments (Fig. 4, 4AB). When
the transducer is parallel shifted just caudal to the ischial spine,
it reaches the lesser sciatic notch, which is smooth and rounded,
where the internal obturator tendon winds around it (Fig. 4,
5AB). The pudendal nerve, artery, and vein converge at the entry
of the Alcock canal (Fig. 4, 5AB). When the transducer is parallel
shifted slightly more distal along the lesser sciatic notch, the pudendal nerve, artery, and vein are visualized inside the proximal
part of the Alcock canal in the sharp angle between the coccygeus
and internal obturator muscles (Fig. 4, 6AB). In this anatomical
location, the inferior rectal nerve branch has not yet branched
away from the pudendal nerve and the nerve is sonographically
visible lateral to the artery (Fig. 4, 6AB). The pulsation of the internal pudendal artery is visible both with 2-dimensional gray
scale view and with color Doppler software on the internal surface
of the obturator internus muscle inside Alcock canal typically lateral to the visible hyperechoic pudendal nerve (Fig. 4, 6AB).
An 80 to 100 mm (dependent on patient size), 22 G, 30degree short bevel needle (Stimuplex Ultra needle; B. Braun,
Melsungen, Germany) is inserted inplane from the medial end
of the transducer (Fig. 3B) and advanced until the needle tip was
adjacent to the pudendal nerve (Fig. 3B). A medial to lateral
FIGURE 3. A shows the placement and orientation of the curved array transducer in the starting position on the line connecting the greater
trochanter (red dot) and the posterior superior iliac spine (blue dot). B shows the direction of the parallel shift of the transducer (green arrow)
and the in-plane needle insertion from the medial end of the transducer.
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Bendtsen et al
Regional Anesthesia and Pain Medicine • Volume 41, Number 2, March-April 2016
FIGURE 4. The figure shows paired US images in gray-scale and color Doppler. Various structures are indicated on the color Doppler
images. 1A–B, The starting position of the scan on the hip bone. 2A–B, The intersection of the US beam and the superior margin of the
greater sciatic notch. 3A–B, Midway along the margin of the greater sciatic notch between superior margin and the ischial spine. 4A–B,
The level of the ischial spine. The sacrospinous and sacrotuberous ligaments are seen as hyperechoic specular reflectors. The characteristic
dark profile of the superior gemellus muscle is seen on top of the ischial spine. The pudendal and sciatic nerves are sandwiched between the
superior gemellus muscle laterally and the internal pudendal and inferior gluteal arteries medially. 5A–B, just distal to the inferior border of
the sacrospinous ligament, the internal obturator muscle winds around the lesser sciatic notch and the pudendal nerve and vessels dive into
the Alcock canal. 6A–B, In the proximal end of the Alcock canal, the pudendal nerve lies lateral to the internal pudendal artery in the corner
between the coccygeus and internal obturator muscles. Insertion of needle (white) is visualized as an inplane approach from the medial end of
the transducer. Pudendal nerve is yellow with a highlighted border. Arteries and veins are red or blue (color Doppler signal). Arrows: White
point at hip bone, magenta at margin of the greater sciatic notch, cyan at sacral bone, red at ischial spine, green at sacrospinous ligament, blue
at sacrotuberous ligament, and yellow at lesser sciatic notch. Asterisks: Green and blue are gluteus maximus and medius muscles, magenta is
piriformis muscle, and white is head of femur. Colored structures: Red-brown is internal obturator muscle, green is superior gemellus muscle,
magenta with highlighted border is sciatic nerve, cyan is coccygeus muscle, and orange is levator ani muscle. il, inferolateral; Sm, superomedial.
approach is recommended to avoid needle contact with the ischial
tuberosity and to minimize the risk of rectal perforation. Needle
penetration of the sacrotuberous ligament generates a characteristic and marked rubbery resistance. The procedure is performed in
combination with electrical nerve stimulation (ENS) as a safety
measure to avoid intraneural injection, with a level of electrical
stimulation of 0.2 mA, 100 milliseconds, and 2 Hz—typically
without eliciting paresthesia at the visual end point. If this level
of electrical stimulation produces paresthesia in the perineum, the
needle tip is retracted until paresthesia disappears. Ten milliliters
of ropivacaine 0.5 % is injected slowly with intermittent aspiration.
Anesthesia of the entire perineum requires bilateral blockade.
Ultrasound-Guided Pudendal Nerve Block in
3 Patients
The technique was used clinically to perform a diagnostic pudendal nerve block bilaterally with ropivacaine 0.5% 10 mL per
side in 3 patients with chronic bilateral perineal pain with the following features: (a) coccygeal pain exacerbated by sitting in a
4
37-year-old woman with regional enteritis and healed anal fissures; (b) phantom pain from the excised anus in a 76-year-old
man following extralevator abdominoperineal excision of rectal
cancer that is exacerbated by eating and drinking; and (c) bilateral
perineal smarting pain 17 years postdelivery in a 44-year-old
woman; the pain is worst in the perianal and clitoral areas and exacerbated by defecation and micturition.
Patients A and B were positioned prone and patient C was
positioned lateral decubitus. The needle was advanced inplane.
Sonoanatomy of the target pudendal nerve and artery and the
surrounding structures was easily visualized bilaterally in all
3 patients. Pinprick sensation was present in the entire perineum
before the block and complete pinprick anesthesia to the cutaneous surface of the perineum (the posterior part of the scrotum/
labia majora, the skin of the penis/clitoris, and the perianal skin)
was noted 10 minutes after block completion. The cutaneous area
between the coccyx and anus (in patient #2, the anal opening was
extirpated and closed) was not anesthetized in any of the
3 patients. This area is innervated by the coccygeal nerve of the
coccygeal plexus. The motor function of the hamstrings and the
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Ultrasound-Guided Pudendal Nerve Block
dorsiflexor and plantar flexor of the foot were not affected in any
of the 3 patients, indicating that the sacral plexus was not affected.
Pain was verbally assessed using a numerical rating scale (0, no
pain and 10, worst pain imaginable). Pain at rest was rated as 0
for 12 hours in patient A, a reduction from 9 to 3 in patient B
and remained so for 10 hours, and complete relief in patient C
for 12 hours. None of the 3 patients had manifest urinary or fecal
incontinence during the nerve blockades.
Ultrasound-Guided Pudendal Nerve injection of
Dye at the Entrance of Alcock Canal in Cadavers
Ultrasound-guided dye injections were performed bilaterally
in 2 cadavers, which were donated to the Division of Clinical and
Functional Anatomy of the Medical University of Innsbruck for
scientific and educational purposes.10,11 Both cadavers were preserved using an arterial injection of an ethanol–glycerol solution
and immersion in phenolic acid in water for 1 to 3 months.12,13
The bodies were positioned prone and the pudendal nerves were
visualized using a low-frequency 6 to 2 MHz curved array transducer (Esaote MyLabSeven US System, AC2541 convex transducer; Esaote, Genova, Italy). The technique described earlier
was used to locate the pudendal nerve within Alcock canal.
An 80-mm, 22-G, short bevel needle (Stimuplex D Plus; B.
Braun, Melsungen, Germany) was inserted inplane from the lateral end of the transducer (Fig. 5A) and advanced—for the sake
of optimum accuracy—until the needle tip entered the pudendal
nerve. It still stands that the needle should be inserted from medial
to lateral, if there is any risk of rectal perforation or bony impediment to the needle insertion from the ischial tuberosity. Only
0.1 mL of a self-composed dye (colored liquid rubber with
acrylic) was injected using a 1.0-mL syringe with an accordingly
accurate scale (Fig. 5B). Thereafter, the cadaver was carefully dissected under manual fixation of the needle as described previously
(Fig. 5C).14 The injection was defined as correct if the needle tip
was found within the target pudendal nerve and the nerve was colored by the dye (Fig. 5D).
All 4 pudendal nerves were successfully targeted and colored
in the 2 cadavers.
DISCUSSION
Our 3 clinical cases have demonstrated accuracy of our
newly described US-guided pudendal nerve block technique as
confirmed by analgesia in the cutaneous perineal territories innervated by the 3 somatic branches of the pudendal nerve and absence of sacral plexus block. The cadaver study has also
confirmed accuracy of pudendal nerve injection. Many techniques
have been described for blockade of the pudendal nerve at the
level of the ischial spine. They include US,6,15 computed
tomography,1,16–18 fluoroscopy,4 and ENS.19 Computed tomography guidance alone1,18 or in combination with US (real-time image fusion)20 has been used at the level of the Alcock canal.
Ultrasound guidance has been used transperineally.7
Kovacs et al15 demonstrated a US-guided pudendal nerve
block technique at the level of the ischial spine in cadavers in
2001. Ultrasound-guided blockade of the pudendal nerve at the
tip of the ischial spine proximal to Alcock canal was also presented by Rofaeel et al6 in 2008. The authors used a curvilinear array transducer 5 to 2 MHz and placed it in the transverse plane
visualizing the lateral border of the sciatic notch. The transducer
was moved caudal until the straight ischial spine became visible.
The pudendal nerve and artery were visualized with color Doppler
sandwiched between the hyperechoic sacrotuberous and sacrospinous ligaments medial to the ischial spine and deep to the gluteus maximus muscle. The needle was inserted inplane from the
© 2016 American Society of Regional Anesthesia and Pain Medicine
FIGURE 5. A shows the placement of the curved array transducer in
a cadaver positioned prone. B shows injection of dye. C shows
dissection along the needle. D verifies that the target pudendal
nerve is red due to the injected dye.
medial end of the transducer aiming medial to pudendal artery between the sacrotuberous and sacrospinous ligaments and guided
by combined US and ENS. The injection at the ischial spine
carries a risk of anesthetizing the sacral plexus and the sciatic
nerve that are adjacent to the pudendal nerve in this location.
Bellingham et al5 compared the US technique by Rofaeel
with fluoroscopy in a randomized controlled trial in 2012 and
found that both techniques were equally accurate although the
US-guided technique required a longer block performance time.
Fluoroscopy exposes the patient and the anesthesiologist to ionizing radiation that makes US the preferable technique. The success
rate of perineal analgesia to pinprick was 82.6% with combined
US and ENS guidance. The frequency of spread to the sacral
plexus/sciatic nerve was estimated to be 21.7%. The pudendal
nerve was sonographically visible in 57% of the patients.
Parras and Blanco7 have presented a US-guided technique to
block the pudendal nerve with an anterior (urogenital) transperineal approach distal to Alcock canal. With the patient supine
and the hips abducted and bent, the US transducer is placed onto
the perineum along the medial margin of the ischiopubic ramus,
visualizing this bone and the adjacent ischiocavernosus muscle.
The transducer is rotated to the transverse view, visualizing the
deep and superficial transverse perineal muscles. At the posterior
margin of the perineal membrane and the transverse perineal muscles, the pulsating internal pudendal artery is visualized with color
Doppler before it dives deep to the transverse perineal muscle and
runs along the medial margin of the ischiopubic ramus. The pudendal nerve is medial or lateral to the artery at this location.
The branching of the pudendal nerve into the inferior rectal,
5
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Regional Anesthesia and Pain Medicine • Volume 41, Number 2, March-April 2016
Bendtsen et al
perineal, and dorsal branches typically occurs in the Alcock canal
proximal to the transverse perineal muscles. According to Parras
and Blanco, the technique is easy and reliable. However, clinical
data about success rate of analgesia and pain relief in patients have
not been presented yet.
The choice of volume of local anesthetic was arbitrary. It can
be speculated that equally effective nerve blockade could be produced with a smaller volume. However, the idea was to demonstrate how it is possible to anesthetize the pudendal nerve inside
Alcock canal without concomitant anesthesia of the sciatic nerve.
Even with 10 mL of local anesthetic, no lower limb paralysis
was observed.
In conclusion, we present a new technique for US-guided pudendal nerve block inside Alcock canal based on easily recognizable sonoanatomical patterns. Our preliminary data show minimal
to no local anesthetic spread to the sacral plexus, and anesthesia
of the pudendal nerve proximal to the branching point of the inferior rectal nerve.
This promising technique has to be validated and compared to
other techniques of US-guided pudendal nerve block at the level
of the ischial spine and transperineally in future clinical trials.
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