DOI:10.2214/AJR.05.1813
AJR 2006; 187:185-190
© American Roentgen Ray Society
Sonography of Inguinal Region Hernias
David A. Jamadar1,
Jon A. Jacobson1,
Yoav Morag1,
Gandikota Girish1,
Farhad Ebrahim1,
Thomas Gest2 and
Michael Franz3
1 Department of Radiology, University of Michigan Hospitals, 1500 E Medical
Center Dr., TC2910, Ann Arbor, MI 48109.
2 Division of Anatomical Sciences, University of Michigan Medical School, Ann
Arbor, MI.
3 Department of Surgery, University of Michigan Hospitals, Ann Arbor, MI.
Received October 14, 2005;
accepted after revision January 6, 2006.
Address correspondence to D. A. Jamadar
(djamadar{at}umich.edu).
CME
This article is available for 1 CME credit. See
www.arrs.org
for more information.
Abstract
OBJECTIVE. The purpose of this article is to describe the anatomy of
the inguinal region in a way that is useful for sonographic diagnosis of
inguinal region hernias, and to illustrate the sonographic appearance of this
anatomy. We show sonographic techniques for evaluating inguinal, femoral, and
spigelian hernias and include surgically proven examples.
CONCLUSION. Understanding healthy inguinal anatomy is essential for
diagnosing inguinal region hernias. Sonography can diagnose and differentiate
between various inguinal region hernias.
Keywords: abdominal imaging • gastrointestinal radiology • inguinal hernia • sonography
Introduction
Ahernia is "the protrusion of a part or structure through the tissues
normally containing it"
[1], either through an opening
in the tissues or via stretching of the tissue wall. External abdominal
hernias are usually found in the inguinal region, where most are direct and
indirect inguinal hernias and femoral hernias
[2,
3]. Hernias may be associated
with significant morbidity and even mortality
[2,
4]. Although traditionally
diagnosed clinically, hernias may be difficult to identify
[4] and even more difficult to
classify. Sonography is used to evaluate and differentiate inguinal hernias
[5]. In this pictorial essay,
we review anatomy, describe sonographic technique, and illustrate the common
inguinal region hernias.
Anatomy
The inguinal region is composed of muscle and fascial layers
(Fig. 1), and structures that
traverse these layers are potential weak points. In the extreme lower
abdominal region, the three lateral muscle layers (external oblique, internal
oblique, and transversus abdominis) form an aponeurosis that extends toward
midline over the rectus abdominis muscle. The lateral margin of the rectus
abdominis muscle is marked by a fascial condensation, the linea semilunaris.
The transversalis fascia is located deep in relation to these structures. The
inguinal canal traverses these muscle and fascial layers, containing vascular
and neural structures, and the spermatic cord (in men) or round ligament (in
women).
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Fig. 1 —Illustration of man's dissected right inguinal region from
anterior view shows reflected external oblique aponeurosis (E), reflected
internal oblique aponeurosis (I), and transversus abdominis muscle (T).
Conjoint tendon (C) is medial to deep ring through which passes vas deferens
and accompanying artery and vein to form spermatic cord (S). Note superficial
ring (straight arrow), inguinal ligament (curved arrow), and
transversalis fascia and extraperitoneal fat (F).
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The inguinal ligament, the folded and thickened lower border of the
external oblique aponeurosis, attaches at the anterior superior iliac spine
and pubic tubercle and medially forms the inferior floor of the inguinal
canal. The posterior opening of the inguinal canal or deep inguinal ring
(Fig. 2) is an anatomic defect
in the transversalis fascia. The anterior opening of the inguinal canal or
superficial inguinal ring is a triangle-shaped anatomic defect in the external
oblique aponeurosis immediately superior and lateral to the pubic tubercle,
where the contents of the inguinal canal can escape. Condensation of the
internal oblique and trans-versus abdominis aponeuroses forms the conjoint
tendon, and a reflection of the inguinal ligament forms the lacunar ligament
(Fig. 2). The inferior
epigastric artery originates from the external iliac artery proximal to the
inguinal ligament, initially passing along the medial boundary of the deep
inguinal ring, and ascends obliquely and medially to the rectus abdominis
muscle.
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Fig. 2 —Illustration of man's right inguinal region as viewed from
within abdomen. Inferior epigastric artery (solid straight arrow),
rectus abdominis muscle (R), and inguinal ligament (curved arrow)
define boundaries of Hesselbach's triangle (H), location of direct hernia.
Indirect inguinal hernia passes through deep ring (open arrow), which
is lateral to inferior epigastric artery and above inguinal ligament. Location
of femoral hernia (asterisk) is usually lateral to lacunar ligament
(L) and inferior in relation to medial inguinal ligament. Note conjoint tendon
(C) and vas deferens (arrowhead).
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When the posterior abdominal wall is viewed from within
(Fig. 2), the inguinal ligament
and the inferior epigastric artery divide the inguinal region into three
primary anatomic areas. One area, called the inguinal or Hesselbach's
triangle, is bounded inferiorly by the inguinal ligament, medially by the
lateral margin of the rectus abdominis, and superiorly by the inferior
epigastric artery. A second area, the femoral region, is inferior in relation
to the medial aspect of the inguinal ligament, and a third area is lateral to
the inferior epigastric artery and just above the inguinal ligament.
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Fig. 3 —57-year-old man with intraoperative laparoscopic view of
right direct inguinal hernia. Open arrows show inferior epigastric artery and
solid arrows show inguinal ligament, which define lateral and inferior
boundaries of Hesselbach's triangle through which direct hernia defect (D) is
distended by gas used during laparoscopy. Deep inguinal ring (curved
arrow) is closed by gas pressure, but medial boundary
(arrowheads) can be seen. Note that extraperitoneal fat obscures vas
deferens, external iliac artery, and other anatomic details.
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Fig. 4 —Illustration of man's right inguinal region from anterior
view shows transducer position to evaluate for spigelian hernia (1), indirect
inguinal hernia (2), direct inguinal hernia (3), and femoral hernia (4). Note
locations of inguinal ligament (curved arrow), rectus abdominis
muscle (R), lateral boundary of Hesselbach's triangle (H) defined by inferior
epigastric artery (open arrow), and spermatic cord
(arrowhead).
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Fig. 5A —25-year-old man with right spigelian hernia. Pre-Valsalva
maneuver sonogram over linea semilunaris in axial plane corresponding to
transducer position 1 in Figure
4 (hernia not visible) showing right rectus abdominis muscle (R),
inferior epigastric artery (curved arrow), peritoneal fat stripe
(straight arrows), and lateral abdominal muscles (M).
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Fig. 5B —25-year-old man with right spigelian hernia. Post-Valsalva
maneuver sonogram in same location showing peritoneal fat stripe distorted by
fat-containing spigelian hernia (arrows) at linea semilunaris. Note
rectus abdominis muscle (R) and lateral abdominal muscles (M).
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Fig. 6A —40-year-old man with healthy right inguinal anatomy. Sonogram
of inguinal region parallel and cranial to inguinal ligament corresponding to
transducer position 2 in Figure
4 shows spermatic cord (C), external iliac artery (A), inferior
epigastric artery (E), femoral vein (V), and superior pubic ramus (curved
arrow).
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Fig. 6B —40-year-old man with healthy right inguinal anatomy. Sonogram
of inguinal region (transducer position not illustrated in
Fig. 4) directly over and
parallel to inferior epigastric artery (E), spermatic cord short axis
(arrows), external iliac artery (A), and rectus abdominis (R).
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Pathology
By viewing the posterior wall of the inguinal region from within (Figs.
2 and
3), one can appreciate several
sites prone to herniation. The first site is the deep inguinal ring, where an
indirect inguinal hernia occurs. Here, herniated structures enter the inguinal
canal lateral to the inferior epigastric artery and superior to the inguinal
ligament, and extend for a variable distance through the inguinal canal. A
second site of herniation is at the inferior aspect of the Hesselbach's
triangle, where a direct inguinal hernia usually occurs. This weakened area is
just lateral to the conjoint tendon and medial to the inferior epigastric
artery, in contrast to the indirect inguinal hernia that originates lateral to
the inferior epigastric artery. A third weakened area is inferior in relation
to the inguinal ligament and lateral to the lacunar ligament, where a femoral
hernia occurs, typically medial and adjacent to the femoral vessels. The
fourth area is at the lateral margin of the rectus abdominis muscle, superior
to the inferior epigastric artery as it crosses the linea semilunaris, where a
spigelian hernia occurs. Indirect inguinal hernias are most common regardless
of sex; femoral hernias are more common in women.
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Fig. 7 —40-year-old man showing healthy right inguinal anatomy.
Sonogram of inguinal region parallel to and directly over inguinal ligament,
distal to origin of inferior epigastric artery (transducer position not
illustrated in Fig. 4). Note
femoral artery (A), femoral vein (V), inguinal ligament (straight
arrows), and superior pubic ramus (curved arrow).
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Fig. 8A —30-year-old man with sonogram of right indirect inguinal
hernia with transducer positioned parallel to and cranial to inguinal ligament
corresponding to transducer position 2 in
Figure 4. Pre-Valsalva maneuver
sonogram (hernia not visible) shows external iliac artery (A), inferior
epigastric artery (E), and superior pubic ramus (curved arrow).
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Fig. 8B —30-year-old man with sonogram of right indirect inguinal
hernia with transducer positioned parallel to and cranial to inguinal ligament
corresponding to transducer position 2 in
Figure 4. Post-Valsalva
maneuver sonogram shows external iliac artery (A), inferior epigastric artery
(E), dilated external iliac vein (V), superior pubic ramus (curved
arrow), and indirect inguinal hernia (H) originating from lateral to
external iliac artery (arrowhead) and traversing inguinal canal from
lateral to medial. (Left = lateral)
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Sonographic Technique and Appearances
Because the inguinal region structures are superficial, a linear transducer
of 10 MHz or greater is effective, although in some patients with a larger
body habitus a transducer of 7 MHz may be needed. In the obese, distortion of
anatomy, the presence of pannus, and the sound-attenuating properties of
adipose tissue may make indentifying the anatomy more difficult. Initially,
examination of the inguinal region is done with the patient supine. It is
essential to ask the patient to increase abdominal pressure (Valsalva
maneuver) at each of the sonographic steps to identify transient hernias.
The Valsalva maneuver is a critical component of the examination, because
in many patients the hernia may be completely reduced at rest. In addition,
the characteristic movement of the herniating tissues often clinches the
diagnosis. This dynamic capability of sonography is an advantage when compared
with other cross-sectional imaging techniques. Reexamination with the patient
standing is also recommended if supine evaluation does not reveal herniation.
Herniated bowel contents may show peristalsis, and herniated fat will appear
hyperechoic. It is also important to evaluate for reducibility and bowel
viability identified by peristalsis or mucosal blood flow.
Spigelian Hernia
The sonography examination for a spigelian hernia should begin at the
lateral margin of the rectus abdominis (the linea semilunaris) in the
transverse plane from the level of the umbilicus
(Fig. 4). As the transducer is
moved inferiorly, the inferior epigastric artery can be identified as it
passes deep in relation to the lateral border of the rectus abdominis muscle.
Just superior to this location, along the linea semilunaris, is the site where
a spigelian hernia may occur (Figs.
5A and
5B). The inferior epigastric
artery is then followed inferiorly to the external iliac artery, defining the
lateral boundary of Hesselbach's triangle
(Fig. 4).
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Fig. 9A —39-year-old man with direct inguinal hernia. Sonogram of
right inguinal region parallel to and cranial to inguinal ligament
corresponding to transducer position 3 in
Figure 4. Pre-Valsalva maneuver
sonogram shows (hernia not visible) peritoneal fat stripe (straight
arrows) medial to inferior epigastric artery (curved arrow).
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Fig. 9B —39-year-old man with direct inguinal hernia. Sonogram of
right inguinal region parallel to and cranial to inguinal ligament
corresponding to transducer position 3 in
Figure 4. Post-Valsalva
maneuver sonogram shows direct inguinal hernia deforming peritoneal reflection
(straight arrows) medial to inferior epigastric artery (curved
arrow). (Left is lateral, right is medial.)
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Fig. 10A —31-year-old woman with femoral hernia. Sonogram of right
inguinal region parallel to and caudad to inguinal ligament corresponding to
transducer position 4 in Figure
4. Pre-Valsalva maneuver sonogram shows (hernia not visible)
femoral artery (A), femoral vein (V), and superior pubic ramus (curved
arrow).
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Fig. 10B —31-year-old woman with femoral hernia. Sonogram of right
inguinal region parallel to and caudad to inguinal ligament corresponding to
transducer position 4 in Figure
4. Post-Valsalva maneuver sonogram shows dilated femoral vein (V)
lateral to femoral hernia (arrows). Superior pubic ramus (curved
arrow) is also seen.
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Indirect Inguinal Hernia
For an indirect inguinal hernia, once the transducer is positioned where
the inferior epigastric artery originates from the external iliac artery, it
is rotated obliquely so that the medial aspect is inferior, along the long
axis of the inguinal ligament (Fig.
4). In men, the healthy spermatic cord can be seen in longitudinal
and transverse planes as a heterogeneous hyperechoic structure with hypoechoic
tubules and vascularity, originating from the internal inguinal ring (Figs.
6A and
6B). This structure should be
differentiated from the inguinal ligament
(Fig. 7), which has a more
compact fibrillar appearance, is taut extending from the ilium to the pubis,
and is just inferior in relation to the internal inguinal ring. With the
transducer positioned longitudinal to the inguinal canal and visualizing the
inferior epigastric artery at its origin, an indirect inguinal hernia can be
seen protruding anteriorly toward the transducer from its origin lateral to
the inferior epigastric artery. The herniated tissue then turns medially
anterior to the inferior epigastric artery and extends inferomedially as it
traverses and often distends the inguinal canal parallel to the skin surface
(Figs. 8A and
8B). An indirect inguinal
hernia may reach the pubic tubercle and exit the superficial ring and may
enter the scrotum in a man.
Direct Inguinal Hernia
Similar to indirect inguinal hernia evaluation, for a direct inguinal
hernia the transducer is placed longitudinal to the inguinal canal and
anterior to the inferior epigastric artery origin
(Fig. 4). However, the
transducer is moved medially because direct inguinal hernias originate medial
to the inferior epigastric artery in Hesselbach's triangle. Imaging superior
to the inguinal canal as well as in the orthogonal plane will ensure complete
evaluation of Hesselbach's triangle. With the Valsalva maneuver, this hernia
will protrude directly anteriorly toward the transducer (Figs.
9A and
9B).
Femoral Hernia
Having evaluated the inguinal region superior to the inguinal ligament, the
transducer is moved inferior to the inguinal ligament
(Fig. 4), and the area medial
to the femoral vein is evaluated for femoral hernia (Figs.
10A and
10B). During the Valsalva
maneuver, the femoral vein will normally dilate and should be differentiated
from a femoral hernia.
Sports Hernia
The sports hernia has been inconsistently described in the literature.
Proposed causes include a weak and dilated deep inguinal ring
[6], a deficiency in the
posterior wall of the inguinal canal
[7], injury of the conjoint
tendon or transversalis fascia
[8], or another abnormality in
the absence of a hernia [9]. It
is possible that a sports hernia could represent several different pathologies
common to a specific subset of patients.
Conclusion
The inferior epigastric artery at its origin is a critical anatomic
landmark in differentiating indirect from direct inguinal hernias; a hernia
originating lateral to the inferior epigastric artery is indirect, whereas one
that is medial is direct. Femoral hernias characteristically occur medially to
the femoral vein and inferiorly in relation to the inguinal ligament.
Spigelian hernias occur at the lateral margin of the rectus abdominis superior
to the inferior epigastric artery where it crosses the linea semilunaris. With
an understanding of inguinal region anatomy and knowledge of the variety of
hernias found in the inguinal region, sonographic diagnosis can assist the
surgeon in managing this common clinical condition.
Acknowledgments
We thank Sarah Abate and Anna Browning for their help with the artwork and
formatting the images.
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Top
Abstract
Introduction
