Normal Anatomy of the Inguinal Canal
The inguinal canal is an oblique passage in the anterior abdominal wall that acts
as a conduit for the spermatic cord to the scrotum in the males and the round ligament
of the uterus to the labia majora in the females. It also transmits the ilioinguinal
nerve and genital branch of genitofemoral nerve in both the sexes. The inguinal canal
connects the two openings: the deep and superficial inguinal rings. The superficial
inguinal ring is an inverted V-shaped triangular defect in the medial end of the external
oblique aponeurosis, superolateral to the pubic tubercle. The deep inguinal ring is
an oval opening in the fascia transversalis that lies halfway along the inguinal ligament
posteriorly.[2] The normal contents of the inguinal canal are depicted in [Table 1], and in [Figs. 1] and [2].
Table 1
Normal contents of the inguinal canal
|
Male
|
Female
|
|
Spermatic cord
|
Round ligament
|
|
Ductus deferens
|
Ilioinguinal nerve to the labia majora
|
|
Testicular artery and veins
Genital branch of the genitofemoral nerve
Ilioinguinal nerve
|
Genital branch of genitofemoral nerve
|
Fig. 1 Normal contents of the inguinal canal.
Fig. 2 Axial (A) and coronal (B) computed tomographic image showing normal contents of the inguinal canal.
Boundaries of the Inguinal Canal
Following are the boundaries of inguinal canal:
-
Anteriorly: External oblique aponeurosis and internal oblique aponeurosis
-
Posteriorly: Conjoint tendon medially and fascia transversalis laterally
-
Superiorly: Internal oblique and transversus abdominis muscles
-
Inferiorly: Inguinal ligament and lacunar ligament[2]
Inguinal Hernia
The inguinal hernias account for 75% of abdominal wall hernias, with a lifetime risk
of 27% in men and 3% in women.[3] The inguinal hernia is classified into direct and indirect inguinal hernias ([Fig. 3)]. The indirect inguinal hernia is more common, usually congenital due to failure
of embryonic closure of the processus vaginalis and it herniates lateral to the inferior
epigastric artery. A direct inguinal hernia is usually acquired due to a weakness
in the fascial floor of the inguinal canal and it herniates medial to the inferior
epigastric artery.[4]
Fig. 3 Types of inguinal hernia.
Role of Imaging
Imaging plays a significant role in differentiating direct from indirect inguinal
hernia in obese patients and patients with chronic pain. Ultrasound and computed tomography
have been significantly used in our institution in clinically uncertain cases, for
the preoperative evaluation of strangulated hernia and to assess the presence of any
postoperative complications. multidetector computed tomography scan (MDCT) plays an
invaluable role in evaluating irreducible inguinal hernia with an excellent spatial
resolution and helps in differentiating various lesions that can mimic an inguinal
hernia. Early detection of the inguinal region abnormalities can reduce the risk of
morbidity and mortality and facilitate proper treatment. The unusual contents of the
inguinal canal are broadly classified into two categories such as congenital and acquired
pathologies as depicted in [Table 2].
Table 2
Unusual contents of the inguinal canal
|
Congenital
|
Acquired
|
|
Visceral organs
|
Visceral organs
|
|
Testis
Ovary
Uterus
Fallopian tube
|
Appendix
Ureter
Urinary bladder
Sigmoid colon
Stomach
|
|
Malignancy
Malignant/metastatic lymph nodes
Infection
Abscess
|
Herniation of Urinary Bladder
The herniation of the urinary bladder in an inguinal hernia is a rare entity with
an incidence ranging from 0.5 to 3% of reported hernia cases. This condition was first
described by Levine in 1951 as a “scrotal cystocele.”[5] Various factors contribute to the development of urinary bladder hernias, such as
bladder outlet obstruction causing chronic bladder distention and contact of the bladder
wall with the hernial orifices, loss of bladder tone, obesity, pericystitis, perivesical
bladder fat protrusion, and space-occupying pelvic masses.
These patients usually present with urinary retention or complaints of double voiding.
Voiding cystourethrography is the best diagnostic imaging modality for inguinal bladder
hernia. Abdominal CT is indicated in obese males, aged more than or equal to 50 years,
with inguinal swelling and lower urinary tract symptoms. In such a case, the delayed
phase of the contrast-enhanced CT study demonstrated the contrast-opacified urinary
bladder lying within the hernia sac ([Fig. 4]).
Fig. 4 A 51-year-old male with complaints of abdominal distension and lower abdomen pain.
Unenhanced computed tomography (CT) abdomen at the level of the pelvis in axial view
(A) showing herniation of the urinary bladder (arrow) through the right inguinal canal,
which is better visualized in contrast-enhanced scan in delayed phase in axial (B) and reformatted sagittal (C) view as the contrast filled bladder (arrow) is seen within the right inguinal hernia.
A 55-year-old male with abdominal pain, vomiting, and burning micturition. Unenhanced
CT abdomen at the level of the pelvis in axial (D), reformatted coronal (E), and sagittal (F) views showing herniation of the urinary bladder (arrow) into the right scrotal sac.
Urinary bladder hernias have been classified into three types based on their relationships
with the peritoneum: paraperitoneal hernias, the most common type, in which the extraperitoneal
portion of the hernia lies along the medial wall of the sac; intraperitoneal hernias,
in which the herniated bladder is completely covered by peritoneum ([Fig. 4]); and extraperitoneal hernias, in which the bladder herniates without any relation
with the peritoneum.[6]
Anatomically, the inguinal hernias of the urinary bladder may be classified as indirect,
entering through the internal inguinal ring and running laterally to the inferior
epigastric artery, or direct, protruding through Hesselbach's triangle of the posterior
wall of the inguinal canal and running medially to the vessel.[7]
The herniation of the urinary bladder is associated with significant urological complications
such as obstructive uropathy, urinary tract infections, perforation of the bladder,
and bladder infarctions.
Ureteral Hernia
Inguinal herniation of the ureter is a rare condition, usually asymptomatic and diagnosed
incidentally, but some of the patients may present with urinary symptoms such as dysuria,
frequency, and urgency. Ureteral inguinal hernias are more common in the fifth and
sixth decades of life with slight male preponderance.[8] It is important to diagnose this condition preoperatively as there is a high possibility
of iatrogenic injury to the ureter during hernia repair, if the condition is not recognized.
CT urogram is the best method to identify this phenomenon. It is indicated as the
first line of investigation for patients with groin lump and unexplained renal failure
or unilateral hydronephrosis on ultrasound scan.
The ureteral inguinal hernia is classified into paraperitoneal and extraperitoneal
types based on its relation with the peritoneum.[9]
Paraperitoneal inguinal herniation of the ureter is defined by a loop of the ureter
that descends with a peritoneal sac into the hernia ([Fig. 5]). This is an acquired pathology, highly associated with kidney transplants, and
intraoperative transplant risk factors such as excess length of the grafted ureter
and passing the ureter over the spermatic cord.
Fig. 5 A 60-year-old male with swelling in the left groin. Ultrasonogram images (A and B) showing a tubular fluid-filled structure (arrow) seen entering the left inguinal
canal, looping within and passing back into the abdominal cavity, suggestive of a
possible left ureteral inguinal hernia. Unenhanced computed tomography abdomen at
the level of the pelvis in axial (C), reformatted coronal (D), and sagittal (E) views showing the left ureter [arrow] extending into the left inguinal canal and
looping back to insert into the bladder.
Extraperitoneal inguinal herniation of the ureter is rarer than the paraperitoneal
type. It is mostly due to congenital malformation, caused by the failure of the ureter
to separate from the mesonephric duct during development. It is commonly associated
with other genitourinary abnormalities such as crossed renal ectopia and nephroptosis.
Herniation of Female Genital Organs
Inguinal hernias containing the ovaries ([Fig. 6]) and uterus ([Fig. 7]) are rare entities but comparatively more common in female infants than adults.
It is usually associated with congenital genitourinary tract anomalies such as Mayer-Rokitansky-Küster-Hauser
syndrome. A female infant with an inguinal hernia should be thoroughly evaluated to
determine whether the contents include ovaries or not because the ovaries are at increased
risk of incarceration and infarction.[10] Incarceration of the ovary is common and has been reported in up to 43% of cases.[11] Herniation of female genital organs in inguinal hernia is usually due to incomplete
closure of the processus vaginalis of the peritoneum during embryogenesis. Normally
the processus vaginalis along with the round ligament of the uterus passes through
the inguinal canal toward the labia majora. The processus vaginalis usually disappears
by 8 months of gestation. If its patency persists, the patent processus vaginalis
is termed as the canal of Nuck. Ultrasonography with a high-frequency transducer is
the imaging modality of choice for evaluating inguinal hernia in infants.
Fig. 6 A 2-month-old female baby with swelling in the right groin region. Ultrasonogram
images showing right direct inguinal hernia with right ovary (arrow in B) as herniating content through a defect (arrow in A).
Fig. 7 (A–D) A 2-month-old female infant with swelling in the right groin region. Ultrasonogram
images showing herniation of the uterus (arrow) and right ovary (star) into the right
inguinal hernia.
Undescended Testis in Inguinal Canal
Testicular descent is a complex kinetic process. The testes develop in the dorsal
abdominal wall and migrate toward the inguinal canal through the deep inguinal ring
at around 21 weeks of gestation. The gubernaculum connects the testes to the scrotum.
Under testosterone influence, the gubernaculum contracts, then the testes migrate
into the scrotum at around 30 weeks.[12]
About 1 to 3% of full-term infants and approximately 15 to 30% of premature infants
will have undescended testis at birth.[13] The incidence of undescended testis in the inguinal canal ([Fig. 8]) is 70% when compared with other locations of undescended testis.[14] In rare cases of androgen insensitivity syndrome, the phenotypic females despite
of having functional testes and normal male karyotype usually present late with primary
amenorrhea. Delayed diagnosis in such cases increases the chance of gonadal malignancy.
Early diagnosis in such cases with a combined approach of clinical suspicion and imaging
in female infants with an inguinal region swelling can reduce the chance of malignant
transformation.
Fig. 8 A 5-year-old male child with abdomen pain. Unenhanced computed tomography abdomen
at the level of the pelvis in axial (A) and reformatted coronal (B) views showing bilateral testis (arrow) in the inguinal canal.
Herniation of Sigmoid Colon
The visceral content of the inguinal hernia sac is commonly a small bowel loop. Rarely,
the sigmoid colon can herniate as content ([Fig. 9]). Forsaken inguinal hernias may lead to grievous results in certain patients.[15] If a sigmoid colon inguinal herniation is missed, it can lead to devastating complications
such as bowel obstruction, strangulation, and infarction. A thorough preoperative
evaluation is needed to exclude other associated intra-abdominal pathologies.
Fig. 9 (A and B) An 89-year-old male patient's left inguinal swelling. Contrast-enhanced computed
tomographic abdomen in venous phase at the level of the pelvis showing sigmoid colon
[arrow] herniating content in the left inguinal canal.
Herniation of Appendix (Amyand Hernia)
Amyand's hernia is a rare type of inguinal hernia in which the appendix is trapped
within the herniated sac ([Fig. 10]). Though the incidence of Amyand hernia is uncommon, the appendix may become incarcerated
within the hernia and can lead to further complications such as strangulation and
perforation. Amyand's hernia is named after Claudius Amyand, who performed the first
successful appendectomy for an 11-year-old boy who presented with a right inguinal
hernia. The incidence of Amyand's hernia varies from 0.19 to 1.7% of reported hernia
cases.[16] Amyand's hernia is more common in children than in adults, due to the patency of
the processus vaginalis at a young age. Few works of literature state that Amyand
hernia is more common in males and always on the right side.[16]
Fig. 10 A 56-year-old male patient came with abdominal pain and low backache. Unenhanced
computed tomography abdomen at the level of the pelvis in axial (A) and reformatted coronal (B) sections showing blind-ending tubular appendix (arrow) arising from the cecum and
entering the right inguinal canal.
The clinical symptoms can be misleading and more often resemble those of strangulated
inguinal hernia than the classic signs and symptoms of appendicitis. Before the advent
of MDCT, these hernias were usually diagnosed during surgery, but now it can be diagnosed
preoperatively and help the surgeon be prepared for the course of management.
Lymph Nodes in Inguinal Region
Lymph nodes in the inguinal region are often incidentally identified during routine
imaging of the abdomen and pelvis. Distinguishing between reactive lymph nodes ([Fig. 11]) from malignant lymph nodes ([Figs. 12]
[13]
[14]) can be a challenging task. Various imaging methods should be used to characterize
lymph nodes with regard to the size, shape, internal characteristics, and blood flow
patterns. No standard imaging criteria available to rule out malignancy, as the possibility
of lymph node metastasis exists regardless of nodal size, as early microscopic involvement
may not show any gross abnormalities on imaging. Inguinal lymph nodes are the most
common sites of metastasis for malignant lymphoma ([Figs. 13] and [14]), squamous cell carcinoma of the anal canal, vulva and penis ([Fig. 12]), malignant melanoma, and squamous cell carcinoma of skin over lower extremities
or trunk.[17] Metastasis to lymph nodes has a significant impact on staging each pelvic tumor,
treatment, and the prognosis.
Fig. 11 A 59-year-old female patient left inguinal swelling, unenhanced computed tomography
abdomen at the level of the pelvis in axial (A) and reformatted coronal (B) views showing enlarged lymph nodes (arrow) in the bilateral inguinal canal.
Fig. 12 A 63-year-old male patient's k/c/o penile malignancy. Contrast-enhanced computed
tomography abdomen in venous phase at the level of the pelvis in axial (A) and reformatted coronal (D) views showing large lymph nodal mass lesion (arrow) with central areas of necrosis
(star). Increased area of metabolic activity (B, C) in the left inguinal region shown in positron emission tomography-computed tomography.
Fig. 13 A 25-year-old female patient's k/c/o small bowel (ileocolic junction) B cell lymphoma
with abdominal pain. Contrast-enhanced computed tomography abdomen in venous phase
at the level of the pelvis in axial (A) and reformatted coronal (B) views showing multiple large lymph nodal mass lesions (arrow) in the bilateral inguinal
region.
Fig. 14 A 78-year-old male patient's k/c/o retroperitoneal lymphoma. Noncontrast-enhanced
computed tomography abdomen at the level of the pelvis in axial (A) and coronal (B) sections showing multiple large lymph nodal mass lesions (arrow) in the bilateral
inguinal region.
Inguinal Region Abscess
Abscesses involving the inguinal region ([Fig. 15]) are often seen as manifestations of complex soft-tissue infections or intra-abdominal
pathologies. The inguinal region communicates with the peritoneal or retroperitoneal
space and thigh through several paths, such as the psoas sheath, femoral canal, sacrosciatic
notch, pudendal canal, and obturator foramen.[18] It has been reported that inguinal abscesses might extend from peritoneal or retroperitoneal
abscesses. The primary causes of an inguinal abscess may be ruptured appendicitis,
colonic diverticulitis, and pyelonephritis.[19] Hence, the abscess may be of extrapelvic or intrapelvic origin. CT or magnetic resonance
imaging helps assess the extent of the abscess and aids in deciding the treatment
plan.
Fig. 15 A 29-year-old female patient's c/o right inguinal region swelling. Contrast-enhanced
computed tomography abdomen in venous phase at the level of the pelvis in axial (A) and reformatted coronal (B) views showing peripherally enhancing collection (arrow) in the right inguinal region.
