Ultrasound imaging for inguinal hernia: a pictorial review.

Inguinal hernia presents as a bulging mass over the groin area and accounts for 75% of abdominal wall hernias [ 1 ]. The reported lifetime risk of inguinal hernia is 27% in men and 3% in women [ 1 ]. The greater susceptibility of the male population is due to the persistent opening of the abdominal wall muscles for the passage of spermatic cords and testicular vessels. Inguinal hernias can be classified into direct and indirect hernias. Direct hernia is derived from protrusion of the intra-abdominal contents through a weak abdominal wall, while indirect hernia results from protrusion toward the inguinal canal. The prevalence of direct inguinal hernia is approximately half that of indirect inguinal hernia in the general population [ 1 ]. Ultrasonography (US) is the first modality of choice to examine palpable lesions at the inguinal area [ 2 ] due to its advantages, such as portability and an absence of radiation. Computed tomography (CT) and magnetic resonance imaging are regarded as problem-solving tools to be used after US. In older male patients, direct inguinal hernia with herniation of peritoneal fat is incidentally seen on abdominal and pelvic CT scans. US has been criticized for being operator-dependent, since a prompt diagnosis relies significantly on the examiner’s skill and experience. This review aims to provide an in-depth review of the use of US for the evaluation of inguinal hernia, with particular emphasis on the regional anatomy, relevant scanning tips, identification of subtypes, postoperative follow-up, and diagnosis of pathologies mimicking inguinal hernia.

Regarding the differential diagnosis, hydrocele should be the top differential diagnosis of inguinal hernia, especially in neonates or infants. Hydrocele is discussed in the previous section ("Ultrasonography of Indirect Inguinal Hernia"), and the discussion is not repeated here. In adult patients, lymphadenopathy ( Fig. 17A ) and tumors such as lipomas ( Fig. 17B ) are common differential diagnoses for palpable inguinal masses. Endometriosis (presence of endometrial tissue outside the uterus) can manifest as a palpable mass in the inguinal region [ 20 ] but is rare. Extra-pelvic endometrial tissues can be found in the cutaneous, subcutaneous, and intramuscular layers. If they involve the inguinal canal and the round ligament, symptoms such as indirect inguinal hernia may ensue. Since the ectopic tissues are firmly attached to the canal wall, they do not migrate during a change in position or during the Valsalva maneuver. Unlike typical indirect inguinal hernias, which are mostly asymptomatic, endometriosis is usually painful and its severity varies according to the menstrual cycle. On US, inguinal endometriosis appears as a hypoechoic nodular mass inside the inguinal canal or next to the inguinal ligament ( Fig. 18 ). A petechial increase in power Doppler activity is commonly observed inside the lesion ( Fig. 19 ). Dynamic mobilization of the transducer reveals firm attachment of the mass to the adjacent tissues. The thickness of the endometrial tissues may vary in different phases of the menstrual cycle. Massive ascites may be seen as bilateral swelling of the inguinal area and sometimes accompany cord or scrotal hydrocele. The causes of ascites are multifaceted, including malignancy, malnutrition, cirrhosis, chronic heart failure, and chronic renal failure. Ascites can be transudative (protein content 25 g/L) [ 21 ]. Transudate usually appears as an anechoic homogenous fluid collection with posterior enhancement on US imaging ( Fig. 20 ). In contrast, exudate contains various amounts of debris and internal septa. US-guided aspiration of ascites is helpful for determining its biochemical profile, as well as for symptomatic relief. Sarcopenia (decreased muscle mass and function) is prevalent in the aging population [ 22 , 23 ]. In a previous study, thinning of the rectus abdominis, external oblique, and internal oblique muscles was observed on US imaging in 103 middle-aged and older healthy women [ 24 ]. Weakness of the abdominal wall muscles can be observed after abdominal surgery. In case of severe involvement, the lower abdominal region protrudes during standing, mimicking bilateral inguinal hernia ( Fig. 21 ).

The present review demonstrates the usefulness of US imaging in the evaluation of inguinal hernia. The inferior epigastric artery is the most important landmark for differentiating between indirect and direct inguinal hernias. Dynamic US imaging combined with postural changes and the Valsalva maneuver is helpful for symptom reproduction. In patients undergoing hernia repair surgery, US imaging is helpful for detecting postoperative complications and recurrence of hernia.