Ultrasound of the Groin: A Pictorial Review

Abstract

The groin is a complex and clinically important area involving numerous fascia, muscles and neurovascular structures. Physical findings can be confusing and accurate diagnosis of groin pathology often relies on imaging. Ultrasound is considered by many as the modality of choice for evaluating groin pain or mass. This review aims to illustrate the sonographic anatomy of this region, the techniques in imaging hernia orifices, characteristic features of various types of hernias and groin masses.

Keywords

ultrasound groin hernia

Introduction

Groin pain or groin mass is a common clinical presentation. However, identifying the cause for the symptoms is often difficult as clinical signs are frequently non-specific. Ultrasound is an important diagnostic tool in the assessment of the groin region, because it has excellent soft tissue contrast, does not involve ionizing radiation and is readily available.¹ Not only can it detect and characterize groin hernias with high sensitivity and specificity, it can also identify other causes of groin masses or pain.^{2, 3} In this article, the sonographic features of normal and commonly encountered pathology in the groin region are demonstrated.

Clinical anatomy

From a practical point of view, the groin composes of the inguinal canal and femoral triangle. The inguinal canal is an oblique passage in the lower abdomen and has two openings: internal/deep and external/superficial rings. The internal ring is situated 1 cm superior to the inguinal ligament and lateral to the inferior epigastric artery (IEA). The external ring is located within the Hesselbach's triangle, inferior and medial to the IEA and superior to the inguinal ligament. In men, the inguinal canal contains the spermatic cord and in women the round ligament. In both sexes, it also transmits the genital branch of the genitofemoral nerve. The spermatic cord/round ligament enters the inguinal canal from the abdominal cavity from the internal ring and exits through the external ring.^{4, 5}

The femoral triangle is inferior to the inguinal ligament and bound laterally by sartorius and medially by adductor longus. It contains the femoral sheath which wraps round the femoral neurovascular bundle. It is divided into three compartments: lateral, intermediate and medial. The lateral compartment houses the femoral artery, the intermediate compartment the femoral vein. The medial compartment (the femoral canal) contains only the lymphatics and the widest and most proximal part of the medial compartment is known as the femoral ring (Figure 1).^6-9

Figure 1

Surface anatomy of the groin region. The inguinal ligament (blue line) stretches from the anterior superior iliac spine to the pubic tubercle. The inferior epigastric artery (IEA) arises from the external iliac artery just superior to the inguinal ligament. Lateral to the IEA and superior to the inguinal ligament is the location of the internal ring (I). The external ring (E) is medial to the IEA and superior to the inguinal ligament within the Hesselbach triangle (green triangle). The femoral ring (F) is medial to the femoral vein and Inferior to the inguinal ligament

Sonographic techniques

Accurate diagnosis of groin hernia using ultrasound requires a systematic approach. In our institute, the patient is first examined lying supine with the groin adequately exposed while keeping patient's dignity. As the structures of the inguinal region are superficial, a linear high frequency probe (e.g. 7 MHz or greater) is usually more suitable, but it is not uncommon to use a curvilinear, low-frequency probe in obese patients (e.g. 3.5 MHz).

During the examination, all the groin hernia orifices (i.e. the femoral, internal and external rings) are examined in two planes (longitudinal and transverse) (Figure 2), at rest and during raised intra-abdominal pressure. Raised intra-abdominal pressure is usually achieved by employing the Valsalva manoeuver. This is crucial because hernias may be transient and not demonstrated at rest (Figure 3).

Figure 2

The groin should be examined in two planes, with the probe longitudinal (red line) and transverse (green line) to the inguinal canal (yellow line). An indirect inguinal hernia originates from the internal ring (I), lateral to the inferior epigastric artery (IEA), whereas a direct inguinal hernia originates from the external ring (E), medial to the IEA. A femoral hernia originates form the femoral ring (F), inferior to the inguinal liagment

Figure 3

This femoral hernia (red arrow) is only visible during a Valsalva manoeuver. The hernia sac can be seen protruding through the femoral ring, medial to the femoral vein

A hernia is identified when peritoneal contents can be seen protruding through the hernia orifices. Bowel loops may show peristalsis, while herniated fat may appear hypoechoic. If a hernia is identified, its reducibility, the size of its neck and viability of its contents must be assessed. Presence of free fluid, absence of colour Doppler signals and irreducibility should raise the suspicion of a strangulated or incarcerated hernia (Table 1).^{2, 10, 11} If no hernia is demonstrated with the patient lying supine, the examination should be repeated while the patient is standing erect.

Table 1

Definition of commonly encountered terms relating to hernias

Hernia	‘Protrusion of an organ or tissue out of the body cavity in which it normally lies’
True hernia	A protrusion of organ or tissue that has a hernia sac surrounding the contents
Hernia sac	A protruding pouch of peritoneum that contains a herniated organ or tissue
Hernia neck	The narrowest part of the hernia, where it protrudes through the abdominal wall weakness or defect (Figure 8)
Reducible hernia	A hernia where the hernia sac can be returned back into the abdominal cavity either spontaneously or by gentle pressure
Irreducible/incarcerated hernia	A hernia where the hernia sac cannot be returned to the abdominal cavity
Strangulated hernia	An irreducible hernia, where the blood supply to the hernia contents have been compromised. This is a surgical emergency and patients usually present with pain and may be systemically unwell

When locating the internal ring, the inguinal ligament and the IEA can be used as landmarks. The inguinal ligament runs between the anterior superior iliac spine and the pubic tubercle and it appears as an echogenic band on ultrasound (Figure 4).^{4, 12} The IEA arises from the external iliac artery with its base just superior to the midpoint of the inguinal ligament. In our experience, colour or pulsed wave Doppler can be very helpful in identifying the IEA as it ascends medially to lie deep in the rectus abdominus muscle (Figure 5). The external ring can be found superior to the inguinal ligament, medial to the IEA and superolateral to the pubic tubercle. As inguinal hernias can descend into the scrotum, examination of the scrotum is essential.

Figure 4

Normal sonographic appearance of the inguinal region. The inguinal ligament appears as an echogenic linear structure (blue arrows) when the probe is longitudinal to it. IEA denotes the inferior epigastric artery

Figure 5

Visualization of the inferior epigastric artery (IEA) by power Doppler. Identifying the IEA allows accurate differentiation of different types of inguinal hernia

The femoral ring can be assessed by placing the transducer inferior to the inguinal ligament and medial to the femoral vein. A femoral hernia will appear inferiomedial to the pubic tubercle. During Valsalva manoeuver, the femoral vein usually dilates and obliterates the potential space in the femoral ring (Figure 6). Thus, if the femoral vein fails to dilate, a femoral hernia should be suspected.^{10, 11}

Figure 6

The femoral vein usually dilates and obliterates the potential space in the femoral ring (blue arrows) during Valsalva manoeuver. Failure to do so raises the possibility of a femoral hernia. FA denotes the femoral artery

Common groin hernias

There are three potential weaknesses in the groin where hernias can occur: the internal ring, external ring and femoral ring (Figure 1).¹⁰ A true hernia must be contained within a hernia sac, which is a peritoneum pouch enclosing the hernia. The majority of groin hernia sacs contain either fat or small bowel, but other unusual contents such as colon (7%), the ovaries (3%), bladder (<1%) and the appendix (<1%) have also been described in the literature.¹³

Inguinal hernias originate from either the internal or external ring. They are classified into direct and indirect hernias, depending on their relationship with the IEA.

Indirect inguinal hernia

In an indirect inguinal hernia, the hernia enters the deep ring and passes through the inguinal canal to the external ring. If the hernia sac extends into the scrotum, it is considered as a complete indirect inguinal hernia (Figure 7), whereas if the hernia sac is limited within the inguinal canal, it is an incomplete indirect inguinal hernia (Figure 8).¹⁴ In children, an indirect inguinal hernia occurs because of the failure of closure of the processus vaginalis, an embryonic out-pouching that descends into the scrotum with the testis during development (Figure 9). In adults, the pathophysiology is different and is due to an acquired weakness and dilation of the internal ring.

Figure 7

In a complete indirect inguinal hernia, the hernia sac extends down into the scrotum. Bowel loops (red arrow) can be seen at the same level of the contralateral testis in this transverse ultrasound image

Figure 8

In an indirect inguinal hernia, the hernia sac (red arrows) enters the internal ring (blue arrow), which is located lateral to the inferior epigastric artery (yellow arrow) and limited to within the inguinal canal

Figure 9

Patent processus vaginalis. Longitudinal ultrasound image showing a cystic tubular structure (blue arrows) extending from the internal ring to the scrotum

Direct inguinal hernia

As for direct inguinal hernias, they protrude directly out of the external ring. These hernias are all acquired hernias and are due to a weakness of the transversalis fascia below the conjoined tendon (Figure 10).¹⁵

Figure 10

A direct inguinal hernia (red arrow) exits the external ring (blue arrow) directly, medial to the inferior epigastric artery (yellow arrow). PT denotes the pubic tubercle, an important landmark when locating the external ring

Femoral hernia

Femoral hernias occur when the abdominal viscera are forced under pressure into the femoral canal and protrude through the potential space in the femoral ring (Figure 3). They have a predisposition to the right and can again be classified as complete or incomplete, depending whether the hernia extends beyond the saphenous hiatus. Femoral hernias are more likely to strangulate than inguinal hernias, as the boundaries of the femoral ring are largely uncompressible (except for the femoral vein).^{11, 12}

These three types of hernia account for around 70–75% of all abdominal hernias.¹⁶ The majority of hernias occur in men, with around 50% of them indirect inguinal hernias, 40% direct inguinal hernias and the remaining 10% femoral hernias. Women are 20 times less likely to suffer from groin hernias, with the majority (70%) being indirect inguinal hernias. Around 30% of them are femoral hernias and it is rare to have direct inguinal hernias in women.^{11, 17}

Rarer groin hernias

There is also a group of less common groin hernias, accounting for 1–2% of all anterior abdominal hernias, that can present with similar symptoms.¹⁷

Obturator hernia

An obturator hernia can present as a groin mass as its contents protrude through the obturator canal. It classically occurs in elderly, malnourished women, due to loss of supporting connective tissue and the wider female pelvis. Patients can also present with small bowel obstruction and incarceration.¹⁸ Ultrasound may sometimes identify an obturator hernia during examination of the femoral ring, as the obturator canal lies in a similar plane, deep to the femoral canal. However, CT is the gold standard for diagnosis (Figure 11).^{11, 19}

Figure 11

An obturator hernia (blue arrow) can sometimes be seen on ultrasound deep to the femoral vessels (yellow arrows). Computed tomography remains the gold standard for diagnosing this type of hernia

Spigelian hernia

A spigelian hernia may also present as a groin mass. Usually below the level of the umbilicus, the hernia protrudes through the spigelian fasia, the aponeurotic layer between the rectus abdominus muscle medially and the linea semilunaris. It most commonly occurs where the semicircular line crosses the linea semiluaris at the level of the arcuate line.²⁰ When looking for a spigelian hernia, the examination should begin at the level of the umbilicus and along the linea semilunaris and following the IE A until reaching the Hasselbach triangle.¹⁰ It also has a high incidence of incarceration. Ultrasound often shows a divarication of the linea semilunaris with hernia sac protruding on Valsalva manoeuver. CT is again superior in identifying and characterizing the hernia (Figure 12).^{10, 11}

Figure 12

Ultrasound (a) and axial computed tomography (b) Images of a spigelian hernia (red arrows), which occur through a defect in the lateral border of the rectus sheath

Incisional hernia

As the name suggests, an incisional hernias occurs at the site of previous surgery, an iatrogenic potential weakness of the anterior abdominal wall (Figure 13).¹¹ Examination of an incision hernia is similar to all other hernias with the transducer directly above the incision site in two planes, while the patient is lying supine, during Valsalva manoeuver and when standing up.

Figure 13

The appearance of an incisional hernia is the same as other hernias (red arrows). This hernia contains only fat and the patient presented with pain at the surgical site after undergoing abdominal surgery

Sportsman hernia

Sportsman hernia is a complex clinical entity that encompasses a syndrome of chronic groin pain. The proposed pathophysiology is a small bulge in the posterior wall of the inguinal canal. Up to 90% of cases occur in men, usually during sports activities (hence the name!) and are probably related to excessive or high repetitive shear forces through the pelvic attachments of poorly balanced hip adductor and abdominal muscle activation, resulting in posterior wall weakening.²¹ On ultrasound, a mild posterior inguinal wall protrusion on Valsalva manoeuver may be seen. An accompanying conjoint tendon abnormality is usually present. However, the presence of a small bulge in the internal ring is often seen in asymptomatic patients. Therefore a Sportsman hernia cannot be diagnosed on imaging alone and clinical symptoms must be present.²

Hernia mimics

Spermatic cord lipoma

There are also many causes of groin pain and mass other than hernias. The most common mimic, with an estimated prevalence of 22.5%, is a spermatic cord lipoma. The term cord lipoma is a misnomer because it is not a true benign tumour, but rather herniation of retroperitoneal fat into the inguinal canal via the internal ring. It often coexists with an inguinal hernia.^{23, 24} Sonographic appearance of a cord lipoma is a lesion of medium to low echogenicity (due to variable fat contents), lateral or inferior to the spermatic cord and discrete from other scrotal structures (Figure 14).^{6, 25}

Figure 14

Cord lipoma, (a) On ultrasound, a cord lipoma (red arrows) has a hypoechogenic appearance due to its fat content and can be separated from other structures such as the testis (T) and the epididymal head. (b) On magnetic resonance imaging, it again exhibits signal characteristics of fat

Collections

Haematoma (Figure 15) or focal fluid collections (Figure 16) may also present as a groin mass. They can be the result of anticoagulation therapy, trauma, surgery or venous or arterial catheter insertion. They can be differentiated from an inguinal hernia by their location (they tend to be superficial, although haematoma can also be intramuscular) and there is no movement during Valsalva manoeuver. On ultrasound, there may be surrounding soft tissue and fat inflammatory changes and the collection may be septated and/or have a heterogeneous appearance, with or without gas locules. If the patient is clinically unwell, an abscess should be considered.²⁶

Figure 15

A haematoma can be the result of trauma, surgery or anticoagulation therapy. This patient presented with a large haematoma after a recent hernia repair. Ultrasound showed a multiseptated fluid collection with no colour Doppler flow demonstrated. The patient was managed conservatively

Figure 16

This patient developed a seroma/fluid collection (red arrows) a few days after groin surgery. There is significant surrounding subcutaneous oedema and the incision can still be visualized (yellow arrows)

Varicocele

Varicocele is another important differential for groin mass. It is due to abnormal dilation of the pampiniform Plexus in the spermatic cord. Patients often present with groin pain, soft mass and infertility. On ultrasound, it appears as a compressible tubular structure and colour Doppler can be helpful in identifying the presence of blood flow. Varicocele can be primary (incompetent internal spermatic vein, usually on the left side) or secondary (raised pressure on testicular vein). If varicocele is identified, it is obligatory to examine the testicles and the kidneys (Figure 17).^{26, 27}

Figure 17

Varicocele is due to dilation and tortuosity of the pampiniform plexus. This can either be primary or secondary. Examination of the kidneys is mandatory if varicocele is found

Saphenous varix

Saphenous varix can be confused with a femoral hernia clinically, particularly if it is thrombosed. Focal dilation of the saphenous vein proximal to its passage through the cribriform fascia in the groin may be differentiated from a femoral hernia on sonography.²⁸

Malignancy

Many tumours and metastases have been described as hernia mimics. Although rare, liposarcoma is the most common malignant primary lesion of the cord. It often presents as a slow-growing painless soft tissue mass (Figure 18). Direct invasion or metastatic spread from melanoma, testicular and prostate cancers can also present as groin masses, although they are all rare. Imaging features of these lesions are often non-specific and the role of ultrasound is to differentiate these lesions from a hernia and occasionally to provide image-guided biopsy or fine needle aspiration in order to obtain histological samples. Further imaging, including computed tomography and magnetic resonance imaging, are often necessary. Nevertheless, lymphadenopathy is often found in the inguinal region and may indicate infection or malignancy (Figure 19).^{6, 26}

Figure 18

Sarcoma of the groin. (a) On ultrasound, it has an irregular outline and heterogeneous texture. (b) Magnetic resonance imaging allows the lesion (red arrow) to be further characterized and its anatomy delineated

Figure 19

An enlarged lymph node can often present as a groin mass (red arrow). It can often be palpable because it is superficial. Infection and disseminated malignancy should be considered if lymphadenopathy is present

Conclusion

A good knowledge of groin anatomy and clear understanding of a variety of hernia pathophysiology are essential in order to diagnose groin hernias accurately. The inguinal ligament is an important landmark in separating inguinal from femoral hernias, whereas the location of the hernia neck in relation to the IEA is crucial in differentiating direct from indirect inguinal hernias. There are also rarer hernias and lesions (both benign and malignant) that cause pain or present as a groin mass. Ultrasound is useful in the assessment of the groin and a systematic approach is required for accurate diagnosis.

Declarations

Competing interest:

Funding: None.

Ethical approval: N/A.

Guarantors: KC, GA, PP, AR, DT.

Contributorship: KC, AR and DT were involved in study conception and design. KC and PP were involved in literature search and manuscript preparation. KC, GA, PP, AR and DT were involved in editing manuscript.

Footnotes

Acknowledgements

We would like to thank Mr. Robert Spry for modeling for the surface anatomy and providing normal sonographic appearances of the groin.

References

Bradley

, Morgan

, Pentlow

, Roe

. The groin hernia – an ultrasound diagnosis? Ann R Coll Surg Engl 2003; 85: 178–80.

Lassandro

, Iasiello

, Pizza

. Abdominal hernias: Radiological features. World J Gastrointest Endosc 2011; 3: 110–7.

van den Berg

, de Valois

, Go

, Rosenbusch

. Detection of groin hernia with physical examination, ultrasound, and MRI compared with laparoscopic findings. Invest Radiol 1999; 34: 739–43.

Moore

, Dalley

. Anterolateral Abdominal Wall. Clinically Oriented Anatomy. 4th edn. London: Lippincott Williams & Wilkins, 1999: 178–208

Moore

, Dalley

. Organization of Thigh Muscles. Clinically Oriented Anatomy. 4th edn. London: Lippincott Williams & Wilkins, 1999: 531–48

Bhosale

, Patnana

, Viswanathan

, Szklaruk

. The inguinal canal: anatomy and imaging features of common and uncommon masses. Radiographics 2008; 28: 819–35.

van den Berg

, de Valois

, Go

, Rosenbusch

. Radiological anatomy of the groin region. Eur Radiol 2000; 10: 661–70.

Shadbolt

, Heinze

, Dietrich

. Imaging of groin masses: inguinal anatomy and pathologic conditions revisited. Radiographics 2001; 21: S261–71

Cherian

, Parnell

. Radiologic anatomy of the inguinofemoral region: insights from MDCT. Am J Roentgenol 2007; 189: W177–83

10.

Jamadar

, Jacobson

, Morag

. Sonography of inguinal region hernias. Am J Roentgenol 2006; 187: 185–90.

11.

Ryan

. Groin hernias: mechanical anatomy and ultrasound evaluation. Soundeffects 2003: 24–8

12.

Abdeen

, Shabana

. Review of inguinal region hernias on MDCT: a vascular roadmap. Appl Radiol 2011; 40: 16–21.

13.

Gurer

, Ozdogan

, Ozlem

, Yildirim

, Kulacoglu

, Aydin

. Uncommon content in groin hernia sac. Hernia 2006; 10: 152–5.

14.

van den Berg

, Rutten

, de Valois

, Jansen

, Rosenbusch

. Masses and pain in the groin: a review of imaging findings. Eur Radiol 1998; 8: 911–21.

15.

Zarvan

, Lee

Jr , Yandow

, Unger

. Abdominal hernias: CT findings. Am J Roentgenol 1995; 164: 1391–5.

16.

Kingsnorth

, LeBlanc

. Hernias: inguinal and incisional. Lancet 2003; 362: 1561–71.

17.

Dabbas

, Adams

, Pearson

, Royle

. Frequency of abdominal wall hernias: is classical teaching out of date? JRSM Short Rep 2011; 2: 5

18.

Aguirre

, Casola

, Sirlin

. Abdominal wall hernias: MDCT findings. Am J Roentgenol 2004; 183: 681–90.

19.

Stamatiou

, Skandalakis

, Zoras

, Mirilas

. Obturator hernia revisited: surgical anatomy, embryology, diagnosis, and technique of repair. Am Surg 2011; 77: 1147–57.

20.

Larson

, Farley

. Spigelian hernias: repair and outcome for 81 patients. World J Surg 2002; 26: 1277–81.

21.

Caudill

, Nyland

, Smith

, Yerasimides

, Lach

. Sports hernias: a systematic literature review. Br J Sports Med 2008; 42: 954–64.

22.

Garvey

, Read

, Turner

. Sportsman hernia: what can we do? Hernia 2010; 14: 17–25.

23.

Lilly

, Arregui

. Lipomas of the cord and round ligament. Ann Surg 2002; 235: 586–90.

24.

Nasr

, Tormey

, Walsh

. Lipoma of the cord and round ligament: an overlooked diagnosis? Hernia 2005; 9: 245–7.

25.

Gooding

. Sonography of the spermatic cord. Am J Roentgenol 1988; 151: 721–4.

26.

Jamadar

, Jacobson

, Morag

. Characteristic locations of inguinal region and anterior abdominal wall hernias: sonographic appearances and identification of clinical pitfalls. Am J Roentgenol 2007; 188: 1356–64.

27.

Robson

, Wolstenhulme

, Knapp

. Is there a co-association between renal or retroperitoneal tumours and scrotal varicoceles? A systematic review. Ultrasound 2012; 20: 182–91.

28.

Wales

, Azose

. Saphenous varix: ultrasonic diagnosis. J Ultrasound Med 1985; 4: 143–5.