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Original Research |
1 Department of Radiology, Teikyo University School of Medicine, 2-11-1 Kaga,
Itabashi-ku, Tokyo 173-8605, Japan.
2 Department of Surgery, Teikyo University School of Medicine, Tokyo,
Japan.
3 Department of Radiology, Kohga Public Hospital, Shiga, Japan.
4 Department of Surgery, Asakadai Central General Hospital, Saitama,
Japan.
5 Department of Radiology, Shiga University of Medical Science, Shiga,
Japan.
6 Department of Radiology, Osaka-fu Saiseikai Noe Hospital, Osaka, Japan.
Received January 1, 2007;
accepted after revision March 15, 2007.
Address correspondence to S. Suzuki.
Abstract
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MATERIALS AND METHODS. We reviewed the records of 46 femoral hernias in seven centers (review of femoral hernias) and those of 215 groin hernias (femoral hernias, 11; inguinal hernias, 204) in one center (review of groin hernias). We evaluated the presence of hernia, extent of hernia sac based on the relationship between the hernia sac and the pubic tubercle (localized sac: sac was localized lateral to the pubic tubercle; or extended sac: sac extended medial to the pubic tubercle), and compression of the femoral vein on CT images. The chi-square test was used to assess the relationship between the CT findings and femoral versus inguinal hernias in the review of groin hernias.
RESULTS. In the review of 46 femoral hernias, the lesions were detected on CT in 45. In the 45 lesions, all hernia sacs were localized, and 42 lesions showed venous compression. In the review of 215 groin hernias, all 11 femoral hernias had localized sacs with venous compression on CT. Of the 204 inguinal hernias, 98 lesions were detected on CT, 65 had extended sacs, and only 10 showed venous compression. Localized sacs with venous compression were seen much more often in the femoral hernias (11/11, 100%) than in the inguinal hernias (1/92, 1.1%) (p < 0.0001).
CONCLUSION. CT images are useful to differentiate femoral hernias from inguinal hernias.
Keywords: abdominal imaging • CT • femoral hernia • hernia • inguinal hernia
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Review of Femoral Hernias
We retrospectively reviewed the CT scans and surgical reports of 46
consecutive patients who underwent surgery for femoral hernias in seven
centers (May 1995-July 2006): Teikyo University Hospital (n = 11),
Asakadi Central General Hospital (n =11), Osaka-hu Saiseikai Noe
Hospital (n =8), Kohga Public Hospital (n = 6), Shiga
University of Medical Science Hospital (n = 4), Hoyu Hospital
(n =3), and Toyosato Hospital (n = 3). Of these 46 patients,
nine were men and 37 were women. Their mean age was 73 ± 11 (SD) years
(range, 44-92 years).
Twenty-three patients underwent both unenhanced and contrast-enhanced CT, and the others underwent only unenhanced CT. The slice thickness and slice intervals were 5-10 mm. All patients were symptomatic when CT was performed.
Thirty-three of the 46 femoral hernias were incarcerated lesions, which were determined on the basis of physical examination findings. In all the patients, the hernias were unilateral (right side, 30; left side, 16). The contents of the sac were small bowel (n = 29, including five Richter's hernias), omentum (n = 8), appendix (n = 1), and ascites only (n =8).
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CT was performed with a LightSpeed Plus-R (GE Healthcare) scanner in 114 patients and with a HiSpeed QX/i (GE Healthcare) scanner in 87 patients. Scanning parameters were 4 x 2.5 mm collimation, 120 kVp, 400 mAs, and 15-mm table speed per gantry rotation. Images were reconstructed with a slice thickness of 7.5 mm and slice interval of 10.0 mm. One hundred fifty-four patients underwent both unenhanced and contrast-enhanced CT, and the others underwent only unenhanced CT. For enhanced CT, a total of 85-130 mL of iohexol with an iodine concentration of 350 mg I/mL (Omnipaque, Daiichi Pharmaceutical) was given with a power injector at a rate of 1.0-1.5 mL/s. The delay between the start of contrast material administration and the start of helical scanning was 90 seconds.
CT Findings
In each review, two radiologists with 12 and 8 years of experience in
abdominal CT independently reviewed the CT findings on axial images. Both
reviewers were unaware of the surgical findings. Studies were evaluated for
the presence of hernia, the extent of the hernia sac based on the relationship
between the hernia sac and pubic tubercle, and compression of the femoral vein
(venous compression). Differences in opinions between the two radiologists
regarding the CT findings were settled by a third radiologist with 29 years of
experience in abdominal CT. If a hernia was detected, the extent of the hernia
sac was evaluated visually and categorized as extended sac (the sac extended
medial to the pubic tubercle) or localized sac (the sac was localized lateral
to the pubic tubercle) (Fig.
1A,
1B). The femoral vein was
considered compressed by the hernia sac when the following three conditions
were fulfilled: the femoral vein adjacent to the hernia sac was elliptic, the
hernia sac lay in the direction of the minor diameter of the femoral vein, and
the minor diameter of the femoral vein was less than two thirds the diameter
of the femoral vein on the contralateral side in the symmetric direction
(Fig. 2). In the case of
bilateral lesions, only the femoral vein with a smaller minor diameter was
evaluated. In addition, one radiologist measured the maximum minor diameter of
the sac on axial images when the sac was detected.
Statistical Analyses
In the review of groin hernias, statistical analyses were performed using a
commercially available statistical software program (SPSS for Windows
[Microsoft], release 14.0, SPSS). The chi-square test was used to assess the
relationship between femoral and inguinal hernias, and the CT findings of
presence of hernia, extended sac, venous compression, and localized sac with
venous compression. The number of hernia lesions rather than the number of
patients was used for these analyses because some patients had bilateral
lesions.
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To evaluate interobserver agreement, a kappa value was calculated for the four CT findings. Values of 0-0.20 were considered to represent slight agreement; 0.21-0.40, fair agreement; 0.41-0.60, moderate agreement; 0.61-0.80, good agreement; and 0.81-1.00, almost perfect or perfect agreement [10].
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Review of Groin Hernias
The presence of each CT finding is summarized in
Table 1.
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Entire groin hernias—For all 11 femoral hernias, localized sacs with venous compression were detected on CT (Fig. 3), and the average maximum minor diameter of the 11 sacs was 23 ± 4 mm (range, 17-31 mm). For the 204 inguinal hernias, 98 (48.0%) were detected on CT, and the average maximum minor diameter of the 98 sacs was 31 ± 15 mm (range, 12-100 mm). Sixty-five (66.3%) of the 98 lesions had extended sacs.
Ninety-two of the 98 visible inguinal hernias were evaluated for venous compression (one of the two lesions was excluded from the evaluation in six cases of bilateral lesions). Venous compression was seen in 10.9% (10/92) of the inguinal hernias with localized sac (n = 1) or extended sacs (n = 9) (Figs. 4A, 4B and 5A, 5B). The details of the 10 inguinal hernias with venous compression were as follows: One lesion was an unusual type with a localized sac, and the sac of the indirect inguinal hernia protruded from the inguinal canal to the femoral vein through an anomalous opening of the inguinal canal. One lesion had an extended sac and contained the left ovary and fallopian tube. One lesion was a recurrent hernia after surgery and had a narrow orifice and an extended sac. In one lesion with an extended sac on the right, not only the right femoral vein but also the right external iliac vein had a smaller diameter than the veins on the left. The other six lesions had large extended sacs, with their maximum minor diameters greater than 4 cm on axial CT images.
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Incarcerated lesions—Seven of the 11 femoral hernias and 11 of the 204 inguinal hernias were incarcerated lesions (Table 1). All seven incarcerated femoral hernias had localized sacs, and all incarcerated inguinal hernias had extended sacs. The average maximum minor diameters of the seven femoral hernia sacs and the 11 inguinal hernia sacs were 24 ± 3 mm (range, 21-31 mm) and 48 ± 29 mm (range, 24-100 mm), respectively. Venous compression was seen in 100% (7/7) and 45.5% (5/11) in incarcerated femoral and inguinal hernias, respectively. Localized sacs with venous compression were seen in 100% (7/7) and in 0% (0/11) of the incarcerated femoral and inguinal hernias, respectively.
Nonincarcerated lesions—Four of the 11 femoral hernias and 193 of the 204 inguinal hernias were nonincarcerated lesions (Table 1). The hernias were detected on CT in 100% (4/4) of the nonincarcerated femoral hernias and 45.1% (87/193) of the nonincarcerated inguinal hernias. The average maximum minor diameters of the four femoral hernia sacs and 87 inguinal hernia sacs were 21 ± 3 mm (range, 17-23 mm) and 28 ± 8 mm (range, 12-53 mm), respectively. None of the four nonincarcerated femoral hernias had extended sacs, whereas 62.1% (54/87) of the nonincarcerated inguinal hernias had extended sacs. Eighty-one of the 87 visible inguinal hernias were evaluated for venous compression (because one of the two lesions was excluded for the evaluation in six cases of bilateral lesions). Venous compression was seen in 100% (4/4) and 6.2% (5/81) of the nonincarcerated femoral and inguinal hernias, respectively. Localized sacs with venous compression were seen in 100% (4/4) and 1.2% (1/81) of the nonincarcerated femoral hernias and nonincarcerated inguinal hernias, respectively.
Interobserver Agreement
Results of interobserver analyses for the four CT findings indicated almost
perfect agreement (Table
2).
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The inguinal hernia often reduces when the patient lies down, as mentioned by Richards et al. [11]. In our review of groin hernias, more than half of the inguinal hernias reduced when CT was performed. For inguinal hernias, major complications, such as incarceration, obstruction, or strangulation, are rare [11]. A previous report showed that the lifetime risks of strangulation of the inguinal hernia are 0.272 and 0.034 for an 18-year-old man and 75-year-old man, respectively [11, 14]. As for the appropriate approach to asymptomatic or minimally symptomatic patients with inguinal hernia, surgeons hold two opinions: surgical repair and watchful waiting [15]. In a randomized clinical trial, Fitzgibbons et al. [16] concluded that watchful waiting was an acceptable option for men with asymptomatic or minimally symptomatic inguinal hernias. On the other hand, approximately 40% of femoral hernias present with incarceration or strangulation [13]. The high incidence of incarceration or strangulation is sufficient reason to recommend surgery, which should be performed soon after the diagnosis [2, 13]. Therefore, preoperative differentiation of a femoral hernia from an inguinal hernia is important clinically, especially in a nonincarcerated case.
The preoperative diagnosis of a femoral hernia is not easy in an asymptomatic patient because palpating the sac is difficult [2]. Even in a patient with a bulge in the groin, a femoral hernia may resemble an inguinal hernia [17, 18]. Besides inguinal hernia, the differential diagnosis of a femoral hernia based on clinical findings includes inguinal lymphadenopathy, lipoma, femoral artery aneurysm, psoas abscess, hydrocele, and cutaneous lesions. CT is useful for distinguishing these conditions from a groin hernia [3, 4, 19].
Surgeons differentiate a femoral hernia from an inguinal hernia by ascertaining the relation of the neck of the sac to the medial end of the inguinal ligament and the pubic tubercle [13]. The neck of the hernia sac is below and lateral to the medial end of the inguinal ligament in a femoral hernia and is above and medial to the ligament in an inguinal hernia [13]. Therefore, Wechsler et al. [4] suggested that a femoral hernia might be distinguished from an inguinal hernia on the basis of the relationship between the hernia sac and pubic tubercle on CT images. The present data of incarcerated groin hernias are consistent with that suggestion. The sacs extended medial to the pubic tubercles in all the incarcerated inguinal hernias, whereas the sacs were localized lateral to the pubic tubercles in all incarcerated femoral hernias. However, 37.9% (33/87) of the nonincarcerated inguinal hernias in our investigation had localized sacs. Distinguishing femoral from inguinal hernias only by the relationship between the hernia sac and the pubic tubercle is difficult, especially in nonincarcerated cases.
In our study, compression of the femoral vein was seen in all 11 femoral hernias (review of groin hernias) and in 42 (93.3%) of the 45 visible femoral hernias (review of femoral hernias), compared with only 10 (10.9%) of the 92 visible inguinal hernias (review of groin hernias). Because the femoral canal is narrow, the femoral vein can easily be compressed by the contents of the hernia. On the other hand, the orifice of the inguinal hernia is wide, and the inguinal ligament lies between the hernia sac and femoral vein. Therefore, venous compression is seldom seen in an inguinal hernia.
Some points should be considered when the venous compression sign is used for evaluation of groin hernias. The compression sign was not seen in two of the three cases of Richter's-type femoral hernias. In this type, the compression of the femoral vein does not occur because the volume of the hernia content is small. An inguinal hernia with a large content can compress the femoral vein by mass effect. However, the sac of a large inguinal hernia protruded through the inguinal canal and extended medial to the pubic tubercle, whereas that of a femoral hernia was localized lateral to the pubic tubercle. Therefore, the combination of venous compression sign and the extent of the sac based on the relation between the hernia fundus and pubic tubercle is useful in differentiating a femoral hernia from an inguinal hernia on CT images. These findings can be evaluated with high agreement even on unenhanced CT images of 10-mm thickness.
When interpreting a CT scan in a patient suspected of having a groin hernia, one may use the following algorithm: When the hernia sac extends medial to the pubic tubercle, the diagnosis of inguinal hernia can be made with confidence. If the hernia sac is located lateral to the pubic tubercle, the presence of venous compression suggests the diagnosis of femoral hernia with a high probability. It is expected that the CT diagnosis has high reproducibility and objectivity because almost perfect interobserver agreement was obtained for these CT findings.
As mentioned previously, preoperative differentiation of a femoral hernia from an inguinal hernia is important clinically, especially in a nonincarcerated case, because it can affect the indication for surgery. All 12 visible nonincarcerated femoral hernias had localized sacs with venous compression (review of femoral hernias). On the other hand, only one of the 81 visible nonincarcerated inguinal hernias had a localized sac with venous compression (review of groin hernias). Therefore, these CT findings are useful in differentiating femoral hernias from inguinal hernias in nonincarcerated cases.
Our study has some limitations. First, the selection of the patients in the comparison between femoral and inguinal hernias might have a bias. Among 296 consecutive patients who underwent surgery for groin hernias, 201 underwent abdominal CT and only these 201 were selected for this investigation. Second, no attempt was made to directly identify the type of hernias by identification of the hernia orifice on CT images. The slice thickness and interval affect the difficulty of identifying the hernia orifice. CT images with a thinner slice thickness on MDCT may permit the direct identification of the type of hernia based on its orifice. Coronal and sagittal reconstructions might be helpful in the future in differentiating groin hernias. Third, it is difficult to evaluate venous compression in patients who have preexisting collapsed femoral veins or femoral veins with laterality in diameter or deformity of the pelvic girdle.
In conclusion, the extent of the sac based on the relationship between the hernia sac and pubic tubercle and compression of the femoral vein on CT images are the keys to the differentiation of femoral from inguinal hernias.
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