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DOI:10.2214/AJR.05.1251
AJR 2006; 187:1168-1178
© American Roentgen Ray Society

Original Research

Inguinofemoral Hernia: Accuracy of Sonography in Patients with Indeterminate Clinical Features

Philip Robinson1, Elizabeth Hensor2, Mark J. Lansdown3, N. Simon Ambrose3 and Anthony H. Chapman3

1 Department of Radiology, Leeds Teaching Hospitals, St. James University Hospital, Chancellor Wing, Beckett St., Leeds LS9 7TF, United Kingdom.
2 Department Of Epidemiology, University Of Leeds, Leeds, United Kingdom.
3 Department of Surgery, Leeds Teaching Hospitals, Leeds, United Kingdom.

Received July 19, 2005; accepted after revision September 27, 2005.

 
Address correspondence to P. Robinson (p.robinson{at}leedsth.nhs.uk).


Abstract
Top
 Abstract
Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
OBJECTIVE. The objective of our study was to investigate the accuracy of sonography in patients with symptoms suggestive of a hernia and normal or equivocal clinical examination findings.

SUBJECTS AND METHODS. Fifty-nine consecutive patients (47 men, 12 women; median age, 51 years; range, 19-82 years) were enrolled in a prospective study of sonography and herniography for investigation of inguinofemoral pain. All patients were referred with a history suggestive of hernia but with equivocal clinical features by three experienced surgeons. All patients underwent sonography and herniography examinations performed by experienced radiologists blinded to clinical details. The imaging variables recorded for each side were normal (including posterior inguinal wall bulging), hernia (indirect, direct, femoral, and abdominal wall), or nondiagnostic. The percentage of exact agreement, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated for sonography and herniography and were compared with surgery when performed; then all sides for sonography were compared with herniography.

RESULTS. Surgery was performed in 18 patients (31%) on 21 sides and found hernia (n = 20) and patulous posterior inguinal wall (with no hernia) (n = 1). Compared with surgery, the results of sonography versus herniography, respectively, were exact agreement (91% vs 71%), sensitivity (95% vs 70%), specificity (100% vs 100%), PPV (100% vs 100%), and NPV (50% vs 14%). The sensitivity of sonography was significantly higher than that of herniography (McNemar test, p = 0.025). Both techniques had one false-negative in the same patient. Herniography had five additional false-negatives identified as hernias at sonography and surgery. Compared with herniography as the reference, the sonography findings were in exact agreement in 91% (107/118) of the cases; and sensitivity was 90% (19/21); specificity, 91% (88/97); PPV, 68% (19/28); and NPV, 98% (88/90).

CONCLUSION. Sonography is an accurate technique for the detection of inguinofemoral hernias in patients with clinically equivocal findings.

Keywords: abdominal imaging • dynamic sonography • inguinofemoral hernia • sonography


Introduction
Top
 Abstract
 Introduction
Subjects and Methods
 Results
 Discussion
 References
 
Most clinically significant hernias can be diagnosed on clinical examination and managed without the use of diagnostic imaging. However, there are recognized limitations to clinical assessment, and a significant proportion of patients with symptoms suggestive of a hernia are found to have normal or equivocal clinical examination findings [1-5]. In this patient group, the clinician can proceed to surgical exploration if symptoms are severe enough, but surgery is invasive and is associated with potential morbidity.

Herniography has been evaluated in patients with equivocal clinical features and has been shown to be a very sensitive, but potentially nonspecific, technique, for depiction of asymptomatic hernias. Herniography has a low complication rate, but the procedure is still relatively invasive and requires ionizing radiation [6-10].

Sonography has been evaluated in infants for confirming clinically evident inguinal hernias, but a varied accuracy is reported for the assessment of the contralateral inguinal canal [11-14]. Sonography has been shown to be an accurate preoperative technique in adults for confirming hernias evident on clinical examination [1, 15-20]. There have been no studies, to our knowledge, evaluating sonography in a large cohort of adult patients with clinically equivocal features.

The aim of this study was to prospectively evaluate the accuracy of sonography in assessing patients with symptoms suggestive of an inguinofemoral hernia who have normal or equivocal clinical examination findings.


Subjects and Methods
Top
 Abstract
 Introduction
 Subjects and Methods
Results
 Discussion
 References
 


Figure 1
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  		Fig. 1A —52-year-old man who presented with left inguinal pain; normal findings were seen on sonography. Line drawing (A) and longitudinal sonography image (B) of left inguinal canal show inferior epigastric vessels (IE) laterally, hyperechoic fibrillar inguinal ligament (arrowheads), and transversalis fascia (arrows). Canal contents are fat, nerves, and hypoechoic vessels (asterisks).

 


Figure 2
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  		Fig. 1B —52-year-old man who presented with left inguinal pain; normal findings were seen on sonography. Line drawing (A) and longitudinal sonography image (B) of left inguinal canal show inferior epigastric vessels (IE) laterally, hyperechoic fibrillar inguinal ligament (arrowheads), and transversalis fascia (arrows). Canal contents are fat, nerves, and hypoechoic vessels (asterisks).

 


Figure 3
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  		Fig. 1C —52-year-old man who presented with left inguinal pain; normal findings were seen on sonography. Line drawing (C) and short-axis sonography image (D) of inguinal canal show oval-shaped canal (arrows) containing multiple hypoechoic vessels (small asterisks). Inferior and deep in relation to canal is psoas muscle (P) with rectus abdominis muscle (RAb) superiorly. Posterior and slightly superior to canal is echogenic margin (arrowheads) of transversalis fascia with preperitoneal fat (large asterisk), bowel, and peritoneum deep to fascia.

 


Figure 4
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  		Fig. 1D —52-year-old man who presented with left inguinal pain; normal findings were seen on sonography. Line drawing (C) and short-axis sonography image (D) of inguinal canal show oval-shaped canal (arrows) containing multiple hypoechoic vessels (small asterisks). Inferior and deep in relation to canal is psoas muscle (P) with rectus abdominis muscle (RAb) superiorly. Posterior and slightly superior to canal is echogenic margin (arrowheads) of transversalis fascia with preperitoneal fat (large asterisk), bowel, and peritoneum deep to fascia.

 
After obtaining institutional ethics committee approval for the study, 72 consecutive patients were enrolled in a prospective study of sonography and herniography for the investigation of inguinofemoral pain. During the study, 13 patients were excluded for failing to attend herniography or clinical appointments (or both), leaving 59 patients (47 men, 12 women; median age, 51 years; range, 19-82 years) in the study.

Clinical Features
All patients were referred by three surgeons experienced in hernia management who completed an initial examination form with patient demographics, clinical symptoms, and clinical findings. All patients had a history of inguinofemoral pain (> 3 months) suggestive of a hernia in 64 sides (five patients had bilateral symptoms) but on clinical examination, normal (n = 52) or equivocal (n = 12) clinical features were present. Equivocal clinical features included tenderness but not a focal mass or cough impulse. Thirty-six patients had right-sided symptoms and 28, left-sided symptoms, including five patients with bilateral symptoms. Ten patients had previously undergone herniorrhaphy presenting with recurrent pain ipsilateral to the side of the previous surgery.

Sonography Examination
Each patient underwent sonography (Elegra or Antares, Siemens Medical Solutions) performed by an experienced radiologist using a linear transducer (13-5- or 9-5-MHz depending on patient body habitus). The radiologist was blinded to the clinical information but was aware that the patient had been referred with inguinofemoral symptoms suggestive of a hernia.

A longitudinal image of the inguinal canal was obtained, including the inferior epigastric vessels at their origin from the femoral vessels as a landmark for the deep inguinal ring (Figs. 1A and 1B). The inguinal ligament was seen as a linear echogenic structure deep in relation to the subcutaneous fat blending with the deep fascia. Deep in relation to the ligament were multiple hyper- and hypoechoic linear structures, representing vessels, nerves, and cords within the canal. Deep in relation to the canal, the psoas muscle, peritoneum, bowel, and preperitoneal fat were identified. Assessment of the canal with the patient at rest and during straining, coughing, and performing a slow Valsalva maneuver was performed while maintaining light transducer pressure.

The inguinal canal was then assessed in its short axis, which is the anatomic sagittal plane (Figs. 1C and 1D). To obtain this view, the radiologist scanned the femoral vessels longitudinally to view the inferior epigastric vessels as they arise and pass superiorly toward the rectus abdominis muscle. The transducer was then moved medially to show the short axis of the inguinal canal and its hypoechoic tubular contents with peritoneum, fat, and bowel lying posterosuperiorly. Assessment of this area with the patient at rest and during straining, coughing, and performing a slow Valsalva maneuver was performed while maintaining light transducer pressure.

An indirect inguinal hernia was defined as a protrusion of fat, bowel, or both through the internal inguinal ring and extending along the inguinal canal parallel to its long axis (Figs. 2A, 2B, 2C, 2D, and 2E). A direct inguinal hernia was defined as a defect in the posterior inguinal wall within the transversus abdominis fascia allowing protrusion of the hernia into the inguinal canal (Figs. 3A, 3B, 3C, 3D, and 3E). An abdominal wall hernia was defined as protrusion of the hernia through an abdominal wall defect into the subcutaneous fat. Posterior inguinal wall bulging was recorded if there was marked compression of the canal contents on straining by the transversus abdominis fascia but with no fascial defect or hernia present (Figs. 4A, 4B, and 4C). Other features were recorded as normal, including patent processus vaginalis, defined as two opposing echogenic layers of peritoneum sliding over each other on straining.


Figure 5
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  		Fig. 2A —61-year-old woman who presented with left inguinal pain from left indirect inguinal hernia. Herniography image shows left indirect hernia (arrows) with contrast material filling distally.

 

Figure 6
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  		Fig. 2B —61-year-old woman who presented with left inguinal pain from left indirect inguinal hernia. Longitudinal sonography image obtained while patient was at rest shows inferior epigastric vessels (IE), inguinal ligament (arrowheads), and transversalis fascia (arrows).

 

Figure 7
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  		Fig. 2C —61-year-old woman who presented with left inguinal pain from left indirect inguinal hernia. Sonogram obtained while patient strained shows that hypoechoic hernia (asterisk) arises lateral to inferior epigastric vessels (IE) expanding canal (thin arrows) and displacing ligament (arrowheads) and transversalis fascia (thick arrows).

 

Figure 8
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  		Fig. 2D —61-year-old woman who presented with left inguinal pain from left indirect inguinal hernia. Short-axis sonography image while patient was at rest shows inguinal canal (arrows).

 

Figure 9
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  		Fig. 2E —61-year-old woman who presented with left inguinal pain from left indirect inguinal hernia. Sonogram obtained while patient strained shows that canal is expanded (arrows) by extension of indirect hernia along its long axis.

 

Figure 10
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  		Fig. 3A —73-year-old woman with left inguinal pain from left direct inguinal hernia. Herniography image shows left direct inguinal hernia (arrows) and surgical clips from previous surgery.

 

Figure 11
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  		Fig. 3B —73-year-old woman with left inguinal pain from left direct inguinal hernia. Longitudinal sonography image obtained while patient was at rest shows inferior epigastric vessels (IE), inguinal ligament (arrowheads), transversalis fascia (arrows), and contents including prominent vessel (asterisks).

 

Figure 12
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  		Fig. 3C —73-year-old woman with left inguinal pain from left direct inguinal hernia. Sonogram obtained while patient strained shows that hernia (asterisk) extends (small arrows) through posterior wall defect (margin marked by large arrows) medial to inferior epigastric vessels (IE).

 

Figure 13
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  		Fig. 3D —73-year-old woman with left inguinal pain from left direct inguinal hernia. Short-axis sonography image obtained while patient was at rest shows canal (arrowheads), prominent vessel (asterisk), and transversalis fascia (arrows).

 

Figure 14
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  		Fig. 3E —73-year-old woman with left inguinal pain from left direct inguinal hernia. Sonogram obtained while patient strained shows that hernia (asterisk) enters through posterior wall defect (margin marked by thick arrows) compressing (thin arrows) contents of inguinal canal (arrowheads).

 

Figure 15
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  		Fig. 4A —33-year-old man who presented with right inguinal pain from right posterior inguinal wall bulging. Herniography image shows broad-based bulge (arrows) of transversalis fascia.

 

Figure 16
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  		Fig. 4B —33-year-old man who presented with right inguinal pain from right posterior inguinal wall bulging. Short-axis sonography image of inguinal canal obtained while patient was at rest shows inguinal canal (arrowheads) and psoas muscle (P), with transversalis fascia lying superiorly and posteriorly (arrows).

 

Figure 17
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  		Fig. 4C —33-year-old man who presented with right inguinal pain from right posterior inguinal wall bulging. Sonogram obtained while patient strained shows that bowel (two asterisks) and preperitoneal fat (one asterisk) are displacing intact transversalis fascia (arrows), which is markedly compressing inguinal canal (arrowheads).

 
The femoral vessels were then viewed in the transverse plane inferior to the inguinal canal where the femoral canal lies medial to the femoral vein. Assessment of the femoral canal with the patient at rest and during straining (coughing and performing a slow Valsalva maneuver) was performed while maintaining light transducer pressure. A femoral hernia was defined as a protrusion of the hernia into the femoral canal.

Sonography variables recorded for each side were normal (including posterior wall bulging), hernia (indirect, direct, femoral, and abdominal wall), or nondiagnostic. If a hernia was detected, its contents were recorded as fat, bowel, or both (Figs. 5A, 5B, 5C, 5D, and 5E).


Figure 18
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  		Fig. 5A —56-year-old woman with right inguinal pain. Herniography findings were false-negative; right indirect hernia was detected at sonography and confirmed at surgery. Herniography image shows no evidence of inguinal hernia.

 

Figure 19
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  		Fig. 5B —56-year-old woman with right inguinal pain. Herniography findings were false-negative; right indirect hernia was detected at sonography and confirmed at surgery. Longitudinal sonography image obtained while patient was at rest shows inferior epigastric vessels (IE), inguinal ligament (arrowheads), and transversalis fascia (arrows).

 

Figure 20
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  		Fig. 5C —56-year-old woman with right inguinal pain. Herniography findings were false-negative; right indirect hernia was detected at sonography and confirmed at surgery. Sonogram obtained while patient strained shows that hypoechoic hernia (asterisk) consisting of fat arises laterally to inferior epigastric vessels (IE), expanding canal (arrows) and displacing inguinal ligament (arrowheads).

 

Figure 21
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  		Fig. 5D —56-year-old woman with right inguinal pain. Herniography findings were false-negative; right indirect hernia was detected at sonography and confirmed at surgery. Short-axis sonography image of inguinal canal while patient was at rest shows round canal (arrowheads).

 

Figure 22
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  		Fig. 5E —56-year-old woman with right inguinal pain. Herniography findings were false-negative; right indirect hernia was detected at sonography and confirmed at surgery. Sonogram obtained while patient strained shows that canal is expanded by extension of indirect hernia (asterisk) along its long axis, which results in compression of other canal contents (arrowheads).

 
Herniography
All patients underwent herniography on the same day within 4 hours of sonography (range, 1-4 hours). All examinations were performed by an experienced radiologist blinded to clinical features and sonography findings. The examination was performed with the patient supine and with an empty bladder. A puncture site was chosen halfway between the umbilicus and the pubis symphysis, and the skin was infiltrated with local anesthetic. If there was a scar in the vicinity of the proposed puncture site, an alternative site was chosen to the left or right of the midline. A 3.5-inch (8.9-cm) 20-gauge spinal needle was advanced through the abdominal wall, and additional local anesthetic (10 mL) was injected to flush bowel loops away from the needle tip as the peritoneal cavity was entered. Iohexol 300 (Omnipaque, Nycomed) was injected, and the flow into the peritoneal cavity was observed under fluoroscopy with an additional 50 mL of contrast medium then injected into the peritoneal cavity. The needle was removed, and the patient was turned to ensure that the contrast medium flowed over the peritoneal surface.

With the patient straining, the filming sequence used was as follows: erect posteroanterior, right and left posteroanterior oblique, and lateral and prone posteroanterior with the head of the table elevated 30° and with 30° cranial tube angulation relative to the table. The same variables as those recorded for sonography were recorded for each side: normal (including posterior wall bulging), hernia (indirect, direct, femoral, and abdominal wall), or nondiagnostic.

Clinical Outcome
Referring surgeons were not blinded to the imaging results, because doing so was considered unethical. All cases were reviewed with the results of both techniques and the clinicians blinded to the findings of a specific technique—that is, if there was a discrepancy, the clinician did not know which technique had detected the hernia. A management plan was recorded with four possible outcomes: discharge to primary care referrer, discharge to pain management consultant, further review in surgical clinic, or schedule for surgery. The clinical case notes were then reviewed at 3-month intervals with the outcome recorded each time. If surgery was not performed, follow-up was for a minimum of 12 months.

Statistical Analysis
The Stuart-Maxwell test of marginal homogeneity was applied to assess the agreement between surgery and herniography and between surgery and sonography when the outcome was normal, bulge, or hernia.

The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of sonography and herniography were separately compared with surgery, when performed, on the basis of a binary outcome (normal or hernia) with bulges considered "normal." Of these measures, only the differences in sensitivity and specificity were statistically compared, using the McNemar test, with 95% CIs for the difference in sensitivity and specificity calculated [21]. The percentage of exact agreement, sensitivity, specificity, PPV, and NPV of all sonography findings were compared with herniography as the imaging reference.


Results
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
Discussion
 References
 
None of the sonography or herniography examinations was classified as nondiagnostic and no complications were reported. For all sonography examinations, the canal and inferior epigastric vessels were visible. In patients who had undergone previous surgery for hernia, focal acoustic shadowing from scar tissue was present but did not undermine the assessment of the inguinal canal for the presence of a hernia.

Surgery
Eighteen patients (18/59 = 31%) underwent surgery, with 21 sides (21/118 = 18%) operated on. Surgical findings included hernia (n = 20) and patulous posterior inguinal wall (with no hernia) (n = 1). Hernias were classified as direct inguinal hernia (n = 10), indirect inguinal hernia (n = 8), spigelian hernia (n = 1), and incisional hernia (n = 1). Six of these hernias were on the original asymptomatic side: three were repaired as part of bilateral surgery and the other three, although initially on the asymptomatic side, subsequently became symptomatic on follow-up.

Correlation of Sonography and Herniography with Surgery
Sonography and herniography findings are separately compared with surgical findings in Tables 1 and 2, respectively. The sensitivity, specificity, PPV, and NPV for sonography and herniography are compared with surgery in Table 3. The sensitivity of sonography was significantly higher than that of herniography for the patients who underwent surgery (difference in sensitivity, 0.25; 95% CI, 0.02-0.47; McNemar test, p = 0.025). The NPV appeared to be higher for sonography than for herniography, but these values could not be statistically examined beyond comparison of the CIs for sonography NPV and herniography NPV, which were wide and overlapping because of the small sample size. It is therefore unlikely that the results differ significantly. The specificity and PPV did not differ at all.


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  		TABLE 1: Sonography Findings in 21 Sides That Underwent Surgery

 

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  		TABLE 2: Herniography Findings in 21 Sides That Underwent Surgery

 

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  		TABLE 3: Performance Measures for Sonographic Detection of Abnormalities in 118 Sides with Herniography Findings as the Reference Standard

 

Sonography—Classification of the 19 hernias detected on sonography was correct in all cases. In one case, sonography showed normal findings, but an indirect hernia was found at surgery (Tables 1 and 3). For another case, sonography depicted posterior inguinal wall bulging and a patulous posterior inguinal wall was found at surgery. The sonography results did not differ significantly from the surgery findings (Stuart-Maxwell test, p = 0.607).

Herniography—Classification of the 14 hernias detected on herniography was correct in all cases. For another five cases, herniography reported findings of no hernia with four hernias (three direct and one indirect) and one patulous posterior wall detected at surgery (Tables 2 and 3). For one of these cases in which a hernia was found at surgery, sonography findings were also normal, but for the remaining four cases, sonography depicted posterior inguinal wall bulging in one case and a hernia consisting of preperitoneal fat in three cases. In another two cases, herniography showed posterior inguinal wall bulging with two direct hernias found at surgery, and in both of these cases sonography also detected direct hernias. The herniography results differed significantly from the surgery findings (Stuart-Maxwell test, p = 0.040).

Correlation of sonography and herniography—The findings and accuracy of sonography compared with herniography are presented in Tables 4 and 5, respectively. Both techniques showed normal findings in all 118 femoral canals and in 69 inguinal canals (Tables 4, 5, 6).


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  		TABLE 4: Herniography and Sonography Findings for All 118 Sides Evaluated

 

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  		TABLE 5: Performance Measures for Sonography and Herniography in the Detection of an Abnormality in 21 Sides with Surgical Findings as the Reference Standard

 

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  		TABLE 6: Frequency of Hernias and Posterior Wall Bulging Detected in 64 Symptomatic Sides and 54 Asymptomatic Sides on Herniography and Sonography

 

Sonography showed posterior inguinal wall bulging in nine sides for which herniography findings were normal. One of these sides underwent surgery, during which a patulous posterior wall was detected. Herniography depicted posterior inguinal wall bulging in 11 sides; for those sides, findings on sonography were normal in five cases, a bulge in four cases, and direct inguinal hernias in the remaining two cases. Surgery was performed in the latter two cases and confirmed the diagnoses of direct inguinal hernia.

Sonography and herniography both depicted hernias in 20 sides: 14 were confirmed at surgery and six sides did not undergo surgery. In another nine sides, sonography depicted an inguinal hernia, whereas herniography revealed normal appearances in seven sides and bulging in two sides. Surgery was performed in three of these cases and confirmed three inguinal hernias. In two sides with normal findings at sonography, herniography showed inguinal hernias; however, surgery was not performed in either patient.

A comparison of the incidence of hernias and posterior wall bulging on symptomatic and asymptomatic sides for herniography and sonography is shown in Table 6.

The findings of herniography and sonography did not differ significantly; however, there was some evidence that if the sample size had been slightly larger, a difference might have emerged (Stuart-Maxwell test, p = 0.077).

Clinical Outcome
The median follow-up for all patients was 6 months (range, 3-18 months). The clinical outcome for all patients is summarized in Figure 6.


Figure 23
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  		Fig. 6 —Flowchart shows clinical outcome for all patients (n = 59).

 
Of the 18 patients who underwent surgery, three patients developed recurrent pain, including the one patient with posterior wall bulging detected on sonography and at surgery. All three patients underwent repeat sonography; two patients had normal findings (including the previously reported bulging) and one patient had findings suggestive of a small recurrent indirect hernia (thought to be not consistent with the current symptoms). All three patients were referred to the anesthetic pain management service with a clinical diagnosis of ilioinguinal neuralgia.

In the remaining 41 patients who did not undergo surgery, two patients were scheduled for surgery; in one, a hernia was present on both sonography and herniography, and in the other, a hernia was seen on sonography only. Both operations were cancelled because the patients became asymptomatic before surgery. Alternate diagnoses were made in four patients— namely, adhesions, irritable bowel, adductor longus tendinopathy, and varicocele. The latter two cases were diagnosed on the basis of sonography findings, and the patients were pain-free after subsequent injection (adductor longus tendinopathy) and embolization (varicocele).


Discussion
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
References
 
A number of articles have reviewed the accuracy of herniography in patients with clinically equivocal findings [4, 6, 8, 10, 22, 23]. In the series involving the general population (range, 70-146 patients), hernias were detected on the symptomatic side in 27-40% of patients and asymptomatic hernias were detected in 6-18% of patients [4, 6, 8, 23]. In this current study, herniography depicted hernias in 27% of the 64 symptomatic sides (33% on sonography) and 9% of the 54 asymptomatic sides (15% on sonography). In the previous herniography series, all the imaging features could not be verified because a variable number of patients underwent surgery (range, 14-33% of cases) [4, 6, 8, 23]. In addition, not all patients with symptomatic hernias proceeded to surgery because some symptoms resolved spontaneously [8]. In those patients who did undergo surgery, high sensitivities (96-100%) and specificities (98-100%) for herniography are reported.

False-negative herniography findings can potentially occur because of small hernias and loculation of contrast material, which prevents flow into the hernia sac, or hernias predominantly consisting of fat [6, 23]. False-positive herniography findings can occur when the hernia reduces completely at surgery while the patient is under anesthesia. In the current study, 31% of the patients underwent surgery (18 of the cases), and herniography had a significantly lower sensitivity (70%) than sonography (95%). This difference in sensitivity was mainly because five false-negative cases at herniography were identified as fat-containing inguinal hernias at sonography and surgery.

The previous herniography series that have reported higher accuracies than our study had no other imaging techniques to influence management. This may have led to a lower level of surgical intervention in patients with negative herniography findings compared with this study. Our study shows sonography can depict fat-filled hernias, probably because it allows real-time visualization of the hernia contents and does not depend on the secondary sign of contrast movement within the peritoneum.

Studies of CT and MRI have not been performed in patients with equivocal clinical findings of inguinal hernia, to our knowledge. Reviews of abdominal CT series have shown CT to be an effective technique for detecting and classifying abdominal hernias predominantly in patients with diffuse symptoms and a palpable abnormality [19, 24-28]. Although some studies of dynamic MR technique have been presented, those series were performed in patients with clinically evident hernias before surgery [1, 29, 30]. In their 1999 study [1], van den Berg et al. reported a slightly superior accuracy of MRI to sonography, which is discussed later in this article. At present, these MR techniques have not been widely accepted or evaluated in clinical practice.

In a number of sonography studies, researchers have assessed adult patients with clinical findings of inguinal or abdominal wall hernias before surgery [1, 15-20]. In one of the earliest studies, Deitch and Soncrant [16] evaluated 95 patients, with the radiologists not blinded to the heterogeneous clinical features in the cohort. Their cohort included 25 patients with normal sonography findings who did not proceed to surgery, which may imply that the referring clinicians did not have a definite diagnosis of hernia in this subgroup. However, the remaining 70 patients who did undergo surgery had fixed abdominal masses or clinically evident hernias. Most other sonography studies have involved assessment of patients (range, 19-220 patients) before surgery. This study design results in a high surgical correlation, but it also results in bias with no significant number of clinically equivocal cases being evaluated.

In most other studies, researchers have reported a high sensitivity (86-100%) and specificity (82-97%) for sonographic diagnosis of inguinal hernias, with more varied accuracies (45-85%) for hernia classification [1, 15-20]. However, some of these studies used lower-frequency transducers than we used, which may have resulted in poor visualization of the landmarks used to classify hernia type [1, 17]. In our study of clinically equivocal cases, the sensitivity and specificity for sonography were high in cases in which surgical verification was available. Classification of hernia type was correct for both sonography and herniography in all true-positive cases.

Few studies have compared different imaging techniques in the assessment of patients with clinically suspected hernias. One study compared MRI, sonography, and clinical examination in patients with clinically evident hernias before surgery [1]. Those researchers found that clinical examination was less accurate than sonography (sensitivity, 92.7%; specificity, 81.5%) and reported a slightly higher specificity for dynamic MRI than sonography. However, four of the five false-positive sonography findings resulted from bulging of the posterior inguinal wall being recorded as "direct inguinal hernia."

In previous sonography studies, most of the false-negative findings have been attributed to small hernias (not quantified) or technical errors due to operator inexperience [1, 17, 18]. False-positive findings have been attributed to reporting cases of bulging and inguinal lipoma as "direct inguinal hernia" and "indirect inguinal hernia," respectively [1, 16-19]. Bulging of the transversalis fascia, in which the posterior inguinal wall almost occludes the inguinal canal on straining but with no actual herniation, has been proposed as a source of pain or as a "prehernia" condition [1, 9, 23, 31]. Unfortunately, the literature does not show that this feature correlates with pain or is part of the spectrum of direct inguinal hernia [19, 32].

Two articles have reviewed sonography assessment of the transversalis fascia in athletes with chronic groin symptoms and found posterior wall bulging did not correlate with the side or severity of pain [31, 32]. Another study of athletes found posterior wall bulging in seven symptomatic and four asymptomatic sides using herniography, but surgery was not performed in eight of those 11 cases [9]. In our series, herniography showed posterior inguinal wall bulging in 11 sides (seven symptomatic and four asymptomatic), and sonography showed bulging in 13 sides (eight symptomatic and five asymptomatic) (Table 6). We believe that these findings do not represent a hernia and should be cautiously interpreted as a positive feature because these findings may represent a variation of normal. In the one case in which herniography was normal and sonography showed unilateral bulging, the patient underwent surgery, with mesh reinforcement performed. However, this procedure did not relieve the patient's symptoms despite bulging being absent on sonography postoperatively. Limitations of this study include the fact that the clinicians could not ethically be blinded to the imaging findings, which may explain why most of patients with the normal imaging findings did not proceed to surgery. Although this does not allow an accurate evaluation of NPV for both techniques, the proportion of patients who did proceed to surgery compares favorably with herniography studies consisting of similar patient profiles [4, 6, 8, 23]. After imaging and the initial review by the referring surgeon, patients were followed by case note review, not by pain scores, because a scoring system has not been standardized for primary inguinofemoral pain or presented in previous herniography studies.

In conclusion, this prospective study of patients with equivocal clinical features for hernia has shown sonography to be an accurate technique with a higher sensitivity and NPV than herniography in the patients who underwent surgery (p < 0.05). Sonography and herniography had a high level of exact agreement, with the main disagreement occurring in cases of fat-filled hernias detected on sonography that appeared normal on herniography. Although sonography is operator-dependent, we believe that when the expertise is available, sonography should be the first-line imaging investigation of abdominal wall and inguinal hernias in patients with clinically equivocal findings and herniography should be reserved for use in cases in which sonography findings are inconclusive.


References
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 

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Imaging of abdominal wall hernias
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