Disorders of the Groin and Hip: Groin Pain

Introduction

Commoner causes of groin discomfort in the general population include inguinal hernias and muscle strains in the lower abdominal wall and upper thigh. Muscular strains in this group of patients often do not present to a primary care physician and certainly further management in the form of imaging is not necessary. The majority of symptomatic inguinal hernias can also be diagnosed clinically but there is a role for imaging in equivocal cases as there are well-recognized limitations to clinical assessment. The clinical role of ultrasound in the assessment of patients with groin pain has greatly increased in the last 10 years and this technique is now commonly used for the diagnosis of clinically indeterminate hernias and for the assessment of postoperative patients with groin pain.

The situation in the professional athlete is more controversial, with a number of aetiologies for chronic groin pain described. Especially in the case of osteitis pubis, adductor dysfunction and prehernia complex (or sportsman's hernia), research has been relatively anecdotal, describing a number of differing pathologies and treatments. Although there are a large number of pathologies that can cause groin pain, including infection, neuralgia or tumour, this section will concentrate on inguinofemoral hernias and muscular strain, highlighting the strengths and limitations of ultrasound.

Normal Anatomy

Anatomically the groin contains the soft tissues of the inguinofemoral region between the anterior superior iliac spine and the symphysis pubis involving the upper thigh and inferior abdominal wall. Soft tissue structures include the skin, superficial fat and fascia, musculature (abdominal and upper thigh), extraperitoneal (preperitoneal) fat and peritoneum.

The inguinal canal allows the passage of vessels, nerves, lymphatics and the spermatic cord (round ligament in females) from within the abdomen to the external genitalia. The posterior wall of the canal is formed by the muscle, aponeurosis and fascia of transversus abdominis and also part of the internal oblique. The anterior canal wall is formed from the fascia of the external oblique muscle ( Fig. 17.1 ). The deep (internal) inguinal ring is a defect within the transversus abdominis fascia that allows the contents of the inguinal canal to leave the abdomen and enter the canal proper. The canal then extends obliquely, medially and inferiorly towards the pubic crest where the superficial (external) inguinal ring, a defect in the external oblique fascia, allows the contents to leave the canal ( Fig. 17.2 ). Superficial to the canal is subcutaneous fat and skin, whereas the iliopsoas muscle lies deep to it on its medial aspect and the external iliac vessels pass on the lateral aspect as they enter the thigh. The peritoneum and small bowel lie posterosuperiorly ( Figs 17.1 and 17.2 ).

Key Point

Important landmarks include the inferior epigastric vessels (IEVs), which arise from the external iliac vessels and course superiorly deep to rectus abdominis ( Figs 17.3 to 17.5 ). Just after their origin from the external iliac vessels they lie immediately medial to the deep inguinal ring. Therefore if a hernia arises lateral to these vessels, it is indirect (passing through the internal ring), but if it arises medial to the vessels it is a direct hernia (bulging through the posterior wall).

Figure 17.3, Normal IEVs, transverse sonogram, lower abdomen. Normal appearances of rectus abdominis with its thick investing fascia (arrowheads). The inferior epigastric artery (large arrow) and veins (arrowheads) can be seen deep to the muscle but still within the investing fascia.

Figure 17.4, Normal right inguinal canal, transverse sonograms. ( A ) At rest, femoral and IEVs (arrowheads) at the medial aspect of the canal. Multiple tubular structures are traversing the canal deep to the inguinal ligament (short arrows). Note the anteroposterior dimension of the canal (long arrows). ( B, C ) On straining, there is marked distension of the vessels (arrowheads) at the medial aspect of the canal, narrowing of the canal anteroposteriorly (long arrows) but no alteration in the contents of the canal itself.

Figure 17.5, Normal left inguinal canal, sagittal sonograms. ( A, B ) Image obtained at the level of the inferior epigastric vein (*) as it arises from the femoral vein (FV). The inguinal canal is seen as an oval shaped soft tissue area containing multiple tubular structures (arrows) with rectus abdominis (RA) lying superiorly. ( C ) Medial to position in (A). ( D, E ) Medial to (C) at the level of the superficial ring as the contents (arrows) descend over the pubis (Pu) and adductor origin (Add).

Figure 17.1, Sagittal section through the lower oblique muscles and inguinal canal. The oblique muscles with external oblique (1) anteriorly and transversus abdominis (2) posteriorly lie superior to the canal and spermatic cord. The subcutaneous fat (3) and deep fascia (4) lie anterior and blend with the external oblique fascia which inferiorly forms the inguinal ligament (5). The psoas muscle and femoral vessels run deep to the canal with the transversus abdominis fascia and peritoneum lying posteriorly and superiorly.

Figure 17.2, Normal right inguinal canal, transverse sonogram. The IEVs lie medial to the internal ring. The thick echogenic inguinal ligament (large arrows) lies anteriorly, deep to the subcutaneous fat (*). Multiple tubular structures are seen (small arrows) passing medially towards the symphysis pubis (SP) and passing through the external ring where a defect (arrowheads) in the inguinal ligament can be visualized.

Examination Technique and Normal Ultrasound Appearances

It is important to identify the deep inguinal ring when assessing for inguinal hernias. The canal can be initially identified in the long or short axis. Both methods are outlined below and whichever you choose is a personal preference as merely rotating the probe through 90° will obtain the other view.

Long Axis View

There are two main methods for visualizing the epigastric vessels, the landmark for assessing the deep ring on dynamic examination. The first method is to scan the rectus abdominis muscle transversely and identify the inferior epigastric vessels (IEVs) within the rectus sheath on its deep aspect ( Fig. 17.3 ). By continuous scanning in the transverse plane the vessels can be followed inferiorly as they sweep to join the external iliac vessels. However, in obese patients with lax musculature, although it is relatively easy to identify the vessels deep to rectus abdominis, it is difficult to continuously follow them because of the patient's body habitus. Therefore, another technique is to begin with the femoral vessels in the transverse plane and move cranially until the epigastric vessels are seen at their origin and are beginning to pass medially. However, at this point, because the actual course of the inguinal canal is in the transverse oblique plane, the transducer should also be oblique by rotating the medial aspect of the transducer inferiorly.

In this position a longitudinal image of the canal is obtained, which includes the epigastric vessels, femoral vessels and proximal inguinal canal. The inguinal ligament is seen as an echogenic line deep to the subcutaneous fat blending with the deep fascia ( Figs 17.2 and 17.4 ). Deep to the ligament are multiple hyperechoic and hypoechoic linear structures (representing vessels, nerves and cords) within the canal. Their prominence is variable and they pass medially to exit the canal through the external ring (seen as a defect of the inguinal ligament) ( Figs 17.2 and 17.4 ). Depending on body habitus the amount of fat within the canal will also vary. Deep to the canal lies the psoas muscle, but echogenic peritoneum and hypoechoic bowel (and a varying amount of preperitoneal fat) lie posterosuperiorly ( Figs 17.1 and 17.5 ).

Assessment of this area with the patient at rest and straining (performing a slow Valsalva manoeuvre) is now performed.

Key Point

With Valsalva manoeuvre, there is normally bulging of the posterior wall and peritoneum but it should not completely occlude the canal ( Fig. 17.4 ).

Occasionally the venous structures within the canal can also distend but again this is quite variable.

Practice Tip

It is important to instruct the patient to perform the Valsalva manoeuvre slowly (i.e. not cough) and to ensure that transducer pressure is not applied too firmly otherwise any potential hernia will be maintained in reduction.

If the patient finds this difficult then blowing hard with the fist against their lips will produce the same effect.

Short Axis View

The canal should then be assessed in its short axis, which is the anatomical sagittal plane ( Fig. 17.1 ). To primarily obtain this view a sagittal image of the hip is obtained. The probe is then moved medially to the external iliac/femoral vessels and longitudinally to view the IEVs as they arise and begin to pass superiorly towards rectus abdominis ( Fig. 17.5A ). At this point the transducer should be moved slightly more medially to come off the epigastric vessels. The short axis of the inguinal canal with its hypoechoic tubular contents can now be visualized with peritoneum and bowel posterosuperiorly ( Fig. 17.5 ). On straining in a normal subject, there may be slight dilatation of the vessels within the canal and the bowel should move towards the canal but should not completely efface or enter the canal ( Fig. 17.6 ).

Figure 17.6, Normal inguinal canal, sagittal sonograms medial to the IEVs. ( A ) At rest, oval shaped inguinal canal (large arrows) with posterosuperiorly echogenic peritoneum (small arrow). ( B, C ) On straining, the echogenic peritoneum (small arrow) and hypoechoic bowel push inferiorly and anteriorly, compressing the inguinal canal.

Ultrasound Appearance of Inguinal Hernias

Indirect hernias protrude through the internal inguinal ring and extend along the inguinal canal parallel to its long axis. The hernia usually consists of peritoneum, fat and bowel. Occasionally the hernia can be congenital due to a persistent processus vaginalis; however, this can be an incidental finding with the condition persisting in 29% of adults.

Direct inguinal hernias occur due to a defect in the posterior inguinal wall, within the transversus abdominis fascia, allowing protrusion of peritoneum and bowel through the wall into the inguinal canal. Because of this the hernia rarely continues distally along the inguinal canal itself and is more localized in comparison to indirect hernias.

On ultrasound the appearance of the normal inguinal contents can be variable and, unless there is a large irreducible hernia present, it is difficult to determine a small hernia within the canal on static imaging.

Key Point

It is during the dynamic component of the examination that the hernia sac and its contents can be observed moving into the canal and reducing (partially or completely) on rest with transducer pressure.

Practice Tip

In the transverse plane an indirect hernia arises lateral to the epigastric vessels and extends through the long axis of the canal ( Figs 17.7 and 17.8 ).

When scanning sagittally (short axis of the canal) the indirect hernia can be seen distending the canal and effacing its contents ( Figs 17.7 and 17.8 ).

Practice Tip

In the transverse plane a direct hernia will protrude through the posterior canal wall medial to the epigastric vessels ( Fig. 17.9A ).

In the sagittal plane (short axis of the canal) the direct hernia will push into the canal from the posterior and superior aspect and efface its contents ( Fig. 17.9B ).

Figure 17.7, Right indirect inguinal hernia. ( A, B ) Transverse sonogram during straining shows the IEVs on the medial aspect of the canal marking the internal inguinal ring. There is marked distension of the canal by hypoechoic bowel and echogenic peritoneum (arrows) arising lateral to the IEVs and pushing along the canal. ( C, D ) Corresponding sagittal sonogram shows psoas (Ps) and marked distension of the canal with obliteration of the normal contents by bowel (arrows).

Figure 17.8, Incarcerated right indirect inguinal hernia. ( A ) Transverse sonogram at rest shows the IEVs, hernia of bowel and fat (arrows) entering through the deep ring (*). ( B ) Corresponding sagittal sonogram shows marked distension of the canal with obliteration of the normal contents by bowel (arrows).

Figure 17.9, Right direct hernia. ( A, B ) Transverse sonogram during straining shows the IEVs and adjacent transversus fascia (arrows) lateral to a hernia of bowel and fat (*) entering through posterior wall defect. ( C, D ) Corresponding sagittal sonogram shows hypoechoic loop of bowel (small arrows) pushing through the posterior wall (large arrows).

The contents of any hernia have a similar appearance on ultrasound, with a relatively hyperechoic margin of the peritoneum and hypoechoic bowel contents (predominantly fluid and gas) ( Figs 17.7 to 17.9 ). If the hernia is a persistent processus vaginalis it will appear similar to peritoneum, with two opposing echogenic layers seen sliding over each other on straining. Occasionally preperitoneal fat will also herniate into the canal, appearing more homogeneous and hyperechoic compared to the bowel and sometimes moving with the bowel and peritoneum ( Fig. 17.10 ). Careful note should also be made on scanning in either plane for other less common inguinal abnormalities, e.g. lipoma, haematoma, lymph node, varicocele, cyst of Nuck or undescended testicle ( Figs 17.11 to 17.13 ).