Download groin hernias: mechanical anatomy and ultrasound evaluation

groin hernias: mechanical
anatomy and ultrasound evaluation
BY FRANK RYAN, MIR, DMU, MMS, AMS
Frank Ryan continues with a second article following on from ‘Embryology and Anatomy of the Inguinal Canal’ published in soundeffects,
issue 2, 2003. The University of South Australia ASA Student Award was presented to Frank for this work towards his Masters in Medical
Sonography.
Hernia is defined by Anderson [1998,
p.755] as a
‘protrusion of an organ through an
abnormal opening in the muscle wall
of the cavity that surrounds it’. The
emphasis of this review will be the
variable anatomy, mechanics and
distribution of groin hernias with an
explanation of the subsequent
ultrasound techniques.
The main hernia types within the inguinal
and femoral canal regions which are
assessable sonographically are:
a. Inguinal , both direct and indirect;
b. Femoral;
Figure 1. Common sites of inguinal and groin
hernias. (Adapted from Agur, 1991, p. 84).
c. Sports, a form of direct inguinal hernia
(although not a true hernia) and
sometimes referred to as Gilmore’s
groin;
d. Spigelian;
e. Obturator; and
f.
Iatrogenic/Incisional
Figure 2. A posterior view of
the anterior abdominal wall.
(Adapted from Pick, 1977,
p. 1048).
Of these the inguinal, femoral, Spigelian
and incisional hernias are routinely
assessed whereas the sports and
obturator hernia evaluation by ultrasound
techniques are “studies in progress”. Figure
1, demonstrates diagrammatically the
potential sites for groin hernias and their
relationship with the bony and ligamentous
anatomy of the region.
The more common hernia sites, the inguinal
and femoral, are closely related, as shown
in figure 1, and their related anatomical
structures, namely the inguinal canal and
the saphenous opening in the superficial
fascial layers determine the course of the
herniating material.
24 issue 3, 2003
Inguinal Hernias
Inguinal hernias are those exiting the
abdomen through the abdominal wall at the
inguinal region. There are two main types,
classified by the point of exit from the
abdomen:
•
Indirect - alternatively known as oblique,
external or congenital inguinal hernia.
soundeffects
groin hernias: mechanical anatomy and ultrasound evaluation
•
Direct - alternatively known as an
internal inguinal hernia.
Of particular interest when reviewing
inguinal hernias are the fossae formed by
the urachal, hypogastric and epigastric
folds; the internal (or supravesical), the
middle and the lateral (external) inguinal
fossae, the lateral fossa being lateral to the
epigastric vessels with the internal/deep
inguinal ring at its most medial aspect. The
folds and fossae are well demonstrated in
figure 2. The deep inguinal ring is clearly
visible lying lateral to the epigastric vessels
with the vas deferens passing medial to the
femoral vessels, over the inguinal
(Poupart’s ligament) and the epigastric
vessels.
Figure 3. A view of the
inner anterior abdominal
wall in the region of
Hesselbach’s triangle.
(Adapted from Warwick,
1973, p.672).
Indirect Inguinal Hernia
The indirect inguinal hernia, commonly
known as an oblique, external, (Pick, 1977,
p.1049) or congenital inguinal hernia
(Moore, 1992, p.147) involves the passage
of bowel or fatty material through the
inguinal canal. The material enters at the
deep ring pushing a pouch of peritoneum
before it and passes through the superficial
ring. The degree of herniation varies and
an indirect hernia may be either complete,
that is passing completely through the
canal, or incomplete, being retained within
the canal where it is referred to as a
bubonocele (Pick, 1977, p. 1051).
An indirect inguinal hernia occurs where
the stalk of the processus vaginalis, which
normally obliterates in both sexes, remains
as a potential passageway, hence the term
congenital. Generally the hernia does not
appear until adulthood and may not occur at
all unless circumstances are right, hence if
the processus is present the potential for a
hernia is there also. An indirect hernia may
also be acquired, projecting through this
area of potential weakness in the abdominal
wall when it is overstressed (Moore, 1992,
p. 147).
Under normal circumstances the processus
vaginalis closes at birth, or soon after. This
closure is thought to progress from two
points, namely the internal abdominal ring
and the top of the epididymis. The portion
below the epididymis remains, enveloping
the testis as the tunica vaginalis (Pick,
1977, p.1051). A similar situation may occur
in females where the gubernaculum passes
through the inguinal canal and terminates in
the labia majora. Persistence of the
processus vaginalis appears as the canal
of Nuck (Moore, 1992, p.147). A defect in
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Figure 4. Hesselbach’s
triangle as viewed from the
front. The limits of the
triangle are clearly shown.
(Adapted from Warwick,
1973, p. 525).
closure may occur at any point and this
determines the type of indirect hernia that
may form.
The mechanics of the indirect or oblique
hernia and the tissue planes involved is
varied and, generally the differences not
appreciated by ultrasound examination. Of
note is the point of passage through the
abdominal wall, that is, through the deep
ring.
Direct Inguinal Hernia
A direct inguinal hernia is a protrusion of
bowel or omentum (or viscera) through a
weakness in the lower abdominal wall
medial to the epigastric vessels in an area
defined as the inguinal or Hesselbach’s
triangle. This triangle is formed by the lower
lateral margin of the rectus muscle, the
medial half of the inguinal ligament and
conjoint tendon and the epigastric vessels.
Hesselbach’s triangle is clearly outlined in
figure 3 - the anterior abdominal wall as
seen from behind. The arching transversus
abdominis is seen lying lateral to the deep
inguinal opening where it blends with the
internal oblique to form the inguinal ligament.
Figure 4, below, demonstrates the same
area from the anterior aspect and gives an
appreciation of the limited size of the area
involved. The triangle lies posterolateral to
the superficial inguinal ring and includes the
area of the canal wall that is formed only by
the transversalis fascia, hence it is a weak
area in the anterior abdominal wall (Moore,
1992, p.148).
Direct inguinal hernias are always acquired
(Warwick, 1973, p. 1298) and differ from
the indirect type in that they do not pass
through the inguinal canal but medial to its
external (superficial) opening. There are
two types, the appearances depending on
issue 3, 2003 25
groin hernias: mechanical anatomy and ultrasound evaluation
the point of exit through the abdominal wall.
opening (Pick, 1977, p. 1062).
From figure 2, above, it can be seen that the
obliterated hypogastric vessels form a cord
which separates Hesselbach’s triangle into
two fossae, the medial (or supravesical)
and the middle inguinal fossae (Pick, 1977,
p.1052). A third fossa, the lateral (or
external) inguinal fossa lies lateral to the
epigastric vessels.
A portion of the lumen of the gut may
protrude into the femoral canal and become
trapped and strangulated. In this instance
the bowel is not obstructed but the
entrapped portion may become gangrenous.
This type of hernia is known as a Richter’s
hernia (Bailley, 1948, p.476).
The first type of direct inguinal hernia is one
where the herniating material passes
through the abdominal wall in the area of
the middle inguinal fossa, lateral to the
conjoint tendon and medial to the epigastric
vessels. It pushes both peritoneum and
transversalis fascia before it and enters the
inguinal canal, exiting at the superficial. It
differs from an indirect hernia in that it does
not enter the deep ring and is invested by all
layers of the cord except the internal
spermatic fascia ring (Warwick, 1973,
p.1298). Sonographically this hernia
appears very similar to an indirect inguinal
hernia and must be distinguished from this.
The relationship to the epigastric vessels
and the lack of activity lateral to them will
provide the clue.
In the second form of direct inguinal hernia,
the most frequent herniation (Warwick,
1977, p.1298) is through the conjoint tendon
itself. Here the contents push a sac of
peritoneum before them as they exit the
abdomen. Alternatively the conjoint tendon
may bulge forming a sac to accommodate
the herniation (Pick, 1977, p. 1053). This
form of direct hernia does not enter the
inguinal canal or the spermatic cord, hence
the layers of tissue covering it are distinct
to the other forms of inguinal hernia.
Femoral Hernia
A femoral hernia occurs when the
abdominal viscera is forced under pressure
into the femoral canal. The herniating
material is invested with a layer of
peritoneum which forms the hernial sac
(Pick, 1977, p. 1061). The extent of a
femoral hernia may be quite dramatic. The
passage of the hernia is downwards,
through the femoral ring to the saphenous
opening, forward through this opening to
the boundaries formed by the fascia lata
and then upwards into the loose areolar
tissue of the groin anterior to the inguinal
ligament (Pick, 1977, p.1061). Femoral
hernias may be classified as complete or
incomplete. An incomplete hernia extends
to the level of the saphenous opening but
not beyond and a complete hernia extends
beyond the bounds of the saphenous
26 issue 3, 2003
Table 1 demonstrates the relative incidence
of the three main groin hernia types in men,
women and children.
Table 1. Relative Incidence of Groin
Hernias (Adapted from Friedland,2002,
internet search)
Direct
Indirect Femoral
Men
40%
50%
10%
Women
Rare
70%
30%
Children
Rare
100%
Rare
Sportsman’s Hernia
The syndrome where chronic groin pain
persists, particularly in athletes, has been
described by Gilmore, and subsequently
labelled “Gilmore’s Groin” (Brukner, 2002, p.
392; Brannigan, 2000, p.329) or simply
“Sportsman’s/Sports hernia” (Kemp, 1998,
p. 2). The term hernia is a misnomer as the
condition rarely exists with a true hernia
present (Brannigan, 2000, p.329). Kemp
[1998, p.1] describes the surgical features
of the condition as:
the rectus. They are rare (Bailley, 1948,
p.482) and from my own experience in
ultrasound usually present not as a hernia
but as a divarication of the linea semilunaris
with the abdominal contents projecting
forward on straining. True herniations do
occur and are often better demonstrated by
CT scanning where the overall perspective
is better addressed. Fatty protrusion may
occur under stress near the neurovascular
bundle containing the inferior epigastric
vessels and the branches of the intercostal
nerves (Warwick, 1973, p. 1049) causing
pain.
Obturator Hernia
Obturator hernias occur through the
obturator canal which lies in a plane similar
to the femoral canal but deep to it (figures 1
and 3). The obturator canal courses deep to
the pubic ramus whereas the femoral canal
lie anterior to the ramus. An obturator hernia
may be appreciated sonographically by
increasing the field of view when scanning
the femoral canal. Movement deep to the
femoral canal may indicate an obturator
herniation.
Iatrogenic/Incisional Hernias
•
A torn external oblique aponeurosis
causing dilatation of the superficial
inguinal ring;
•
•
A torn conjoint tendon; and
As the name suggests, these hernias occur
at the site of previous surgery, which could
include appendicectomy or caesarean
section. The intervention may leave an
area of potential weakness in the abdominal
wall, which may lead to a hernia or
divarication. Synonyms for this condition
include abdominal or ventral hernias
(Anderson, 1998, pp.3 and 1702).
Dehiscence between the conjoint
tendon and the inguinal ligament.
Ultrasound Examination
The pain is localised to an area adjacent
and lateral to the pubic tubercle in the area
of the conjoint tendon and may be confused
with osteitis pubis. Scanning of this region
in a longitudinal plane across the short axis
of the spermatic cord often shows a
straightening of the posterior canal wall
(compared to the normally curved, concave
arrangement) and a reduction in the
diameter of the spermatic cord (Orchard,
1998, p.134). As stated above, the condition
is not true hernia and static images do not
demonstrate the condition well. It is best
assessed dynamically (Orchard, 1998, p.
137).
Spigelian Hernia
This is a hernia through the linea semilunaris
(linea Spigelii), the aponeurosis between the
muscles of the lateral abdominal wall and
Patient Preparation
•
•
Dietary preparation is not required.
•
•
Informed consent should be obtained.
•
Appropriate cover should be provided
to preserve modesty and dignity.
•
A comfortable examination room and
warm gel are recommended.
The procedure technique and the
degree of the patients’ participation
should be explained.
The patient should undress to the
degree required to provide adequate
access to the groin, lower abdomen
and upper thigh.
Imaging Technique
Imaging of the groin encompasses
soundeffects
groin hernias: mechanical anatomy and ultrasound evaluation
examination of both sides as bilateral
hernias are common (Bailley, 1948, p.465;
Bax, 2002, [internet search]) and occur in
up to 30% of cases. Examination should
include the following areas:
•
•
Conjoint tendon area and pubic tubercle.
•
•
•
•
Superficial inguinal ring.
Femoral canal - include a deeper field of
view to assess the obturator canal.
Deep inguinal ring.
Lower linea alba and rectus muscles.
Lower linea semilunaris.
All areas should be examined in two planes,
both transverse/oblique and longitudinal
both at rest and with the patient using some
technique to increase intraabdominal
pressure. This may include:
•
•
Method
Valsalva technique.
Blowing into the back of the hand,
blowing out the cheeks.
•
Raising the head and/or feet from the
examination couch.
•
Coughing. Here the violence of the
action may preclude satisfactory
viewing of the areas.
In a normal study each area is imaged in the
transverse/oblique plane only, however an
abnormal study should include both
transverse images and the longitudinal or
oblique planes which best demonstrate the
abnormality.
A routine examination of the inguinal/groin
region encompasses:
•
•
•
•
•
•
•
Figure 5A (left) and 5B (above). The Femoral Canal
Conjoint tendon area, including straining.
Femoral canal - at rest.
Femoral canal - straining.
Superficial ring - at rest.
Superficial ring - straining.
Deep ring - at rest.
Deep ring - straining.
Further images of each area are taken as
determined by the condition at hand The
transverse/oblique plane parallels the
inguinal ligament, which runs obliquely from
the ASIS to pubic tubercle, and the inguinal
canal giving a longitudinal image of the
canal. Scanning in the longitudinal plane
using the epigastric vessels as a reference
point will give a cross sectional view of the
cord at a slightly oblique angle. Angulation
of the transducer to best visualise in two
planes is necessary and will vary from
patient to patient.
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Conjoint tendon area
The transducer should be placed at the
lateral aspect of the pubic tubercle and
angled upwards and obliquely towards the
ASIS. The inguinal ligament will appear as
an echogenic band. The posterior wall of
the canal and conjoint tendon will lie below
the ligament. Scan at rest and with the
patient straining in both long and short axis
planes along the ligament. Note any
excessive movement or herniation. A
herniation or bulging of the wall will be
toward the transducer.
Femoral canal
Scan transversely at the level of the pubic
tubercle with the transducer aligned
vertically. The femoral vessels and canal
will lie with the pubic ramus arcing medially.
Scan both at rest and with straining and
observe any abnormal movement within the
canal medial to the dilating femoral vein.
Scan longitudinally just medial to the femoral
vein at rest and straining, as above. Adjust
the depth of the field of view to assess for
a possible obturator hernia. This may
appear as movement deep to the femoral
vessels.
Superficial ring
Scan the femoral vessels transversely and
find the level of the epigastric vessels. The
inguinal canal lies anterior and medial to
these vessels. To obtain a view in the long
axis of the canal, angle cranially and align
the transducer with the inguinal ligament.
The canal and spermatic cord may be seen
behind the ligament and may measure up to
1cm in diameter. Assess both at rest and
straining and look for excessive dilatation of
the canal and movement of tissues through
it. Be aware of a dilated fat or bowel filled
canal which exceeds 1cm at rest.
Herniation may appear as a bulging of the
canal wall medially or a lateral to medial
movement arising from the medial aspect of
the epigastric vessels
Deep ring
As with the superficial ring locate the
epigastric vessels and align the transducer
as above. The deep ring lies lateral to these
vessels. Again scan with the patient at rest
and straining and look for movement of
tissues lateral to medial crossing the
vessels. A herniation in the region will
appear to originate deep to the transducer
and course towards the superficial ring,
possibly entering the scrotum or labia
majora.
Rectus and Symphysis Pubis
Scan the distal rectus muscles and
symphysis area in two planes. Inflammatory
processes or haematoma may appear as a
hypoechoic focus or organising clot.
Linea Alba and Semilunaris
Scan transversely along the line of the linea
alba and linea semilunaris with the patient
both at rest and straining. Assess for
herniation through or between the layers of
the aponeurosis or divarication of the
muscle junction.
Figures 5A and B show the femoral canal at
rest and with the patient straining. In B the
femoral vein is clearly seen dilated to the
right, or medial to the femoral artery. A
femoral hernia will appear in the canal
medial to the vein. The pubic ramus and
pectineus muscle lie deep to the vessels.
issue 3, 2003 27
groin hernias: mechanical anatomy and ultrasound evaluation
Medical, Nursing and Allied Health
Dictionary. 5th edition. St.Louis:Mosby
3. Bailley, Hamilton and Love, R.J. McNeill,
7th Ed, (1948). “A Short Practice of
Surgery”. H.K. Lewis & Co:London
4. Bax, Tim, Sheppard, Brett C. and Crass,
Richard A., (1999). “Surgical Options in
the Management of Groin Hernias”.
Viewed October 2002, <http://
www.aafp.org/afp/990101ap/143.html>
5. Brannigan, A.E., Kerin, M.J. and
McEntee G.P. (200). “Gilmore’s Groin
Repair In Athletes”. Journal of
Orthopaedic & Sports Physical Therapy.
Vol. 30, No 6.
Figure 6A (left). The Superficial Inguinal Ring.
Figure 6B (above). The Deep Inguinal Ring.
Figures 6A and B clearly show the
landmarks of the superficial and deep rings.
The femoral artery and vein as well as the
epigastric vessels are well seen. In A the
long arrow points to the superficial ring. A
direct hernia may appear to move from left
to right mimicking an indirect hernia passing
through the canal. Generally a direct hernia
will be seen to move towards the
transducer, passing through the
transversalis fascia. Figure 6B shows the
vessels indicating the site of the deep ring.
An indirect or congenital hernia will arise
deep to the transducer and move across
and in front of the femoral vessels. The
epigastric vessels indicate the site of the
deep ring.
It is important that both sides are examined
concurrently and the information provided
used to determine the type of hernia
present. Be aware that a direct hernia
originating in the middle inguinal fossa may
enter the inguinal canal and simulate an
indirect hernia and it is important to
distinguish between the two. A complete
examination of the area should include the
lower rectus muscles, linea alba and linea
semilunaris. They should be examined both
at rest and when straining. It is also
important to assess scrotal involvement
with a direct or indirect hernia in males.
Hopefully this article will be of some
assistance to Sonographers who are
struggling with this area as I have in the
past.
Conclusion
It is important in an ultrasound examination
for hernia of the groin and inguinal area, to
understand the anatomy of the area and the
physiology and mechanics of hernia
formation. An understanding of the
embryology of the inguinal canal is helpful.
28 issue 3, 2003
References
1. Agur, Anne, Editor, 9th Ed (1991).
“Grants Atlas of Anatomy”. Williams &
Wilkins: Baltimore.
2. Anderson, K.N.; Anderson, L.E. and
Glanze, W.D., Editors (1998) Mosby’s
6. Clemente, Carmine D, 1997, 4th Ed. “A
Regional Atlas of The Human Body”.
Williams & Wilkins: Baltimore.
7. Friedland, Tom, (date unknown). “XVI.
ICMC-Abdominal Wall, including
Hernias”. Viewed August 2002, <http://
www.medicine.mcgill.ca/mss/NTCs/
Med>
8. Hamilton, W.J. and Mossman. H.W. 4th
Ed (1972). “Human Embryology”. W.
Heffer & Sons Ltd:Cambridge.
9. Kemp, Simon & Batt, Mark E. (1998).
“The Sports Hernia: A Common Cause
of Groin Pain”. The Physician And
Sports medicine. Vol.26 No1.
10. Orchard, J.W, Read, J.W.,Neophyton, J.
and Garlick, D. (1998). “Groin pain
associated with ultrasound finding of
inguinal canal posterior wall deficiency
in Australian Rules Footballers”. British
Journal of Sports Medicine. Vol 32.
11. Pick, T. Pickering and Howden, Robert,
Editors, (1977). “The Classic
Collectors Edition- Gray’s Anatomy”.
Bounty Books:New York.
12. Warwick, Roger and Williams, Peter,
Editors 35th ED(1973). “Gray’s
Anatomy”.
Longman:Norwich.
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