Diagnosis of Inguinal Region Hernias with Axial CT: The Lateral Crescent Sign and Other Key Findings 1

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1 Note: This copy is for your personal non-commercial use only. To order presentation-ready copies for distribution to your colleagues or clients, contact us at GASTROINTESTINAL IMAGING Diagnosis of Inguinal Region Hernias with Axial CT: The Lateral Crescent Sign and Other Key Findings 1 E1 ONLINE-ONLY CME This article meets the criteria for 1.0 AMA PRA Category 1 Credit TM. See /education /rg_cme.html LEARNING OBJECTIVES After reading this article and taking the test, the reader will be able to: Identify relevant anatomic structures visible at axial CT of the inguinal and femoral region. List key anatomic features that help differentiate direct inguinal hernias, indirect inguinal hernias, and femoral hernias. Discuss how to differentiate the major types of hernias of the inguinal and femoral region at axial CT, including use of the lateral crescent sign of direct inguinal hernias. Joan Hu Burkhardt, MD Yevgeniy Arshanskiy, MD J. Lawrence Munson, MD Francis J. Scholz, MD Available at Differentiation of direct inguinal hernias, indirect inguinal hernias, and femoral hernias is often difficult at clinical examination and presents challenges even at diagnostic imaging. With the advent of higherresolution multidetector computed tomography (CT), the minute anatomic detail of the inguinal region can be better delineated. The authors examine the appearance of these hernias at axial CT, as the axial plane remains the diagnostic mainstay of evaluation of acute abdomen. They review and label key anatomic structures, present cases of direct and indirect inguinal hernias and femoral hernias, and demonstrate their anatomic differences on axial images. Direct inguinal hernias protrude anteromedial and inferior to the course of the inferior epigastric vessels, whereas indirect inguinal hernias protrude posterolateral and superior to the course of those vessels. The proposed lateral crescent sign may be useful in diagnosis of early direct inguinal hernias, as it represents lateral compression and stretching of the inguinal canal fat and contents by the hernia sac. Femoral hernias protrude inferior to the course of the inferior epigastric vessels and medial to the common femoral vein, often have a narrow funnel-shaped neck, and may compress the femoral vein, causing engorgement of distal collateral veins. Familiarity with these anatomic differences at axial CT, along with the lateral crescent sign of direct inguinal hernias, may help the radiologist better assist the clinician in accurate diagnosis of the major types of hernias of the inguinal region. Supplemental material available at /rg /-/dc1. RadioGraphics 2011; 31(2):E1 E12 Published online /rg Content Codes: 1 From the Department of Diagnostic Radiology, Lahey Clinic Medical Center, 41 Mall Road, Burlington, MA Presented as an education exhibit at the 2009 RSNA Annual Meeting. Received May 10, 2010; revision requested June 15 and received November 15; accepted November 15. For this CME activity, the authors (J.H.B., Y.A., J.L.M.), editors, and reviewers have no relevant relationships to disclose. F.J.S. is the owner of FSpoon Co. Address correspondence to J.H.B. ( Joan.H.Burkhardt@lahey.org). RSNA, 2011 radiographics.rsna.org

2 E2 March-April 2011 Introduction The lifetime risk of spontaneous abdominal hernias is substantial in the general population, at approximately 5% (1,2). The vast majority of these hernias are inguinal hernias (80% of cases), while femoral hernias make up 5%; the remaining 15% include umbilical, epigastric, incisional, and other types of hernias. The risk of strangulation is lowest for direct inguinal hernias, which can often be monitored and managed conservatively. Indirect inguinal hernias are at moderate risk of strangulation, whereas approximately 40% of femoral hernias manifest with strangulation (3). Unfortunately, clinical examination is often unreliable for differentiation among hernia types (4,5). Thus, the ability to differentiate among these three types of groin hernias would be extremely helpful in risk stratification and planning care of the patient. Computed tomography (CT) remains the best available imaging tool for evaluation of acute abdomen and abdominal hernias (6 8). With the advent of higher-resolution multidetector CT scanners, fine detailed anatomy not well defined previously is now better visualized. This improved visualization allows definition of the small structures of the inguinal canal and improves diagnosis and differentiation between the hernia types. Axial CT remains the mainstay of diagnostic imaging, since axial images are typically examined first; if disease is suspected, then coronal or sagittal reformatted images are used for problem solving. Without suspicion of disease on axial images, reformatted images of this region may not be studied for fine detail. In this article, we review relevant anatomic structures related to inguinal and femoral hernias and label these structures on axial CT images, then define anatomic differences that are useful for differentiating direct and indirect inguinal hernias and femoral hernias. We suggest use of the lateral crescent sign, which may be helpful in diagnosis of direct inguinal hernias with axial CT. Normal Anatomy of the Inguinal Canal The normal inguinal canal is a narrow diagonal tunnel lined by the aponeuroses of the three radiographics.rsna.org abdominal wall muscles. The anterior wall of the inguinal canal is formed by the aponeuroses of the external and internal oblique muscles; the superior wall is formed by the aponeuroses of the internal oblique and transversus abdominis muscles; the posterior wall is formed by the transversalis fascia and the conjoint tendon, which represents the juncture of the internal oblique and transversalis fascia medially at the pectineal line; and the inferior wall is formed by the inguinal ligament of Poupart, which is the folded-up lower border of the external oblique aponeurosis and extends from the anterior superior iliac spine to the pubic tubercle (9). The conjoint tendon is the layer onto which mesh is laid during the typical Lichtenstein-type tensionfree inguinal hernia repair (10). The inguinal canal runs from the deep inguinal ring to the superficial inguinal ring from superiorly posterolateral to inferiorly anteromedial. The deep or internal inguinal ring is a gap in the transversalis fascia just superior to the inguinal ligament and lateral and posterior to the inferior epigastric vessels. The superficial or external inguinal ring is an opening in the external oblique aponeurosis just superior and lateral to the pubic tubercle. In the female, the inguinal canal transmits the round ligament of the uterus and the ilioinguinal nerve to the labia majora. In the male, the inguinal canal transmits the spermatic cord to the scrotum. The spermatic cord is covered by the fascia from all three abdominal wall muscle aponeuroses and comprises the ductus (vas) deferens, testicular artery and veins (pampiniform plexus), and genital branch of the genitofemoral nerve. The ilioinguinal nerve runs along the front of the spermatic cord (11). In both genders, the canal also contains lymphatic vessels and sympathetic nerve fibers, along with fat and connective tissue. The Hesselbach triangle is anatomically defined medially by the rectus abdominis muscle, superolaterally by the inferior epigastric vessels, and inferiorly by the inguinal ligament. The inferior epigastric artery arises from the external iliac artery immediately above the inguinal ligament, passes obliquely upward along the medial margin of the internal inguinal ring, and eventually anastomoses above the umbilicus with the superior epigastric artery.

3 RG Volume 31 Number 2 Burkhardt et al E3 Figure 1. Entrance of the inguinal canal contents into the internal inguinal ring, just superolateral to the origin of the inferior epigastric vessels. Diagrams (left) and CT images (right) (top image obtained at a higher level than bottom image) show that the deep circumflex vessels originate just opposite the inferior epigastric vessels (vv). art = artery, n = nerve, v = vein. At axial CT, the confluence of the structures that enter the inguinal canal at the internal inguinal ring to form the canal contents is well visualized (Fig 1). The deep circumflex vessels originate from the external iliac vessels almost directly opposite the origin of the inferior epigastric vessels and may be useful to identify the origin of the inferior epigastric vessels at axial imaging. The deep circumflex vessels then proceed toward the anterior superior iliac spine in a course nearly parallel to that of the inguinal ligament, as they lie just deep to the lateral aspect of the ligament and are sometimes helpful in its identification (10). The testicular vessels and vas deferens can be seen entering the internal inguinal ring just lateral to the origin of the inferior epigastric vessels. An understanding of the embryology of the inguinal canal will assist in comprehension of inguinal canal disease. The gubernaculum testis is a cord of muscular and fibrous tissue that attaches superiorly to the lower pole of the fetal gonad and inferiorly to the skin of the fetal groin, which later becomes either the labia majora or the scrotum. In the male, the gubernaculum testis functions in guiding the descent of the testis through the inguinal canal into the scrotum and leaves no remnant in the adult. In the female, the midpoint of the gubernaculum eventually attaches to the uterus and becomes the ovarian ligament and round ligament. The processus vaginalis (or canal of Nuck in females) is an invagination of the peritoneum into the inguinal canal anterior to the gubernaculum; it becomes obliterated in a superior-to-inferior direction around the time of birth. In females, the processus normally leaves no remnant in the adult. In males, normally only the scrotal portion of the processus remains to form the tunica vaginalis testis (12). The femoral triangle is bordered superiorly by the inguinal ligament, medially by the border of the adductor longus muscle and the lacunar ligament, and laterally by the border of the sartorius muscle, with the iliopsoas, pectineal, and adductor longus muscles forming its floor. The lacunar ligament extends from the medial aspect of the inguinal ligament backward to the pectineal line, which is the upper ridge of the superior pubic ramus. The femoral triangle contains the femoral sheath, which is formed by the deep fascia lata of the thigh and enfolds the femoral artery, femoral vein, and femoral canal, from lateral to medial. Just lateral to the femoral artery and femoral sheath is the femoral nerve. The femoral canal is the space within the femoral sheath medial to the femoral vein and contains a lymph node (node of Cloquet). The femoral ring is often described as the widest, most proximal portion of the femoral canal.

4 E4 March-April 2011 radiographics.rsna.org Figure 2. Detailed anatomy of the inguinal and femoral regions. Direct inguinal hernias protrude medial to the inferior epigastric vessels and anteromedial to their course. Indirect inguinal hernias protrude superolateral to the course of the inferior epigastric vessels. Femoral hernias traverse the femoral ring, inferior to the course of the inferior epigastric vessels and medial to the common femoral vein. Figure 3. Fat-containing direct inguinal hernia with a small vessel inside it. Diagrams (left) and CT images (right) (top image obtained at a higher level than bottom image) show a lateral crescent of compressed and stretched inguinal canal contents, including fat, the vas deferens, and testicular vessels. The hernia emerges anteromedial to the inferior epigastric vessels. As one scrolls the axial CT images from superior to inferior, the inferior epigastric vessels can be traced to their origin from anteromedial to inferolateral, the hernia sac protrudes medial to their course, and the inguinal canal contents are seen compressed laterally by the hernia sac. vv = vessels. Types of Inguinal Hernias Direct Inguinal Hernia Direct inguinal hernias by definition protrude through the Hesselbach triangle, above the inguinal ligament and medial to the course of the inferior epigastric vessels (and therefore medial and caudal to the origin of the inguinal canal at the internal inguinal ring) (Fig 2). These hernias are generally acquired and increase in incidence with age, as they result from weakening of the transversalis fascia in the Hesselbach triangle. Direct inguinal hernias occur most commonly in men and are less often associated with strangulation than are indirect inguinal or femoral hernias, possibly because direct inguinal hernias usually do not traverse the entire course of the canal and thus are less vulnerable to constriction (13). A direct inguinal hernia emerges anteromedial to the origin of the inferior epigastric vessels and bulges the anterior abdominal wall lateral to the rectus muscle; the sac is directed inferior to the

5 RG Volume 31 Number 2 Burkhardt et al E5 Figure 4. Right fat-containing direct inguinal hernia. CT image (a) and color-coded image (b) show a direct hernia (light blue) compressing the inguinal canal contents (green dots) and fat (yellow) into a thin lateral crescent. The common femoral artery (red) and vein (blue) are lateral to the hernia sac (see also Movie 1). Figure 5. Lateral fat crescent of a left direct inguinal hernia. CT image (a) and color-coded image (b) show the fat and other inguinal canal contents (small blue and red dots) flattened into a thin lateral crescent (outlined in yellow). Herniated omentum (white) is covered by visceral peritoneum (green). The common femoral vein (large blue dot) and artery (large red dot) are seen coursing just posterolateral to the hernia sac (see also Movie 2). inferior epigastric vessels as it protrudes (Fig 3). Note that the inguinal canal contents (ie, testicular vessels, vas deferens, etc) are compressed and stretched laterally by the hernia, and the normal fat of the inguinal canal is pushed into a semicircle of tissue that resembles a moon crescent. This lateral crescent of fat is a useful diagnostic sign of direct inguinal hernia. As the hernia extends more inferiorly, the inguinal canal contents are further squeezed and stretched into the lateral crescent, and the fat of the crescent disappears (Fig 4; see also Movie 1). A sliver of the inguinal ligament can be seen just inferior to the inguinal canal. Occasionally, edematous omentum can be seen herniating into a fatcontaining direct inguinal hernia, as the inguinal canal contents are compressed and stretched laterally by the hernia into a lateral crescent (Fig 5; see also Movie 2).

6 E6 March-April 2011 radiographics.rsna.org Figure 6. Diagram shows a right direct inguinal hernia in axial projection. The inguinal canal contents (anterior red and blue dots) are compressed laterally by the bulging hernia, which is seen as a rounded defect in the anterior abdominal wall fascia (purple line). The hernia sac emerges medial to the course of the inferior epigastric vessels (posterior red and blue dots) (see also Movie 3). Figure 7. Indirect inguinal hernia. CT images (left) (top image obtained at a higher level than bottom image) and diagrams (right) show a fascial defect at the neck of an indirect hernia. Indirect inguinal hernias protrude superolateral to the course of the inferior epigastric vessels. The round ligament cannot always be clearly identified on axial CT images. vv = vessels. As the inferior epigastric vessels are traced back to their origin from anteromedial to posterolateral, the inguinal canal is compressed laterally along its course by the hernia sac (Movie 3). The neck of the hernia sac can be seen arising medial to the course of the inferior epigastric vessels (Fig 6). This relationship can be subtle and is not always simple to determine at axial CT. Therefore, the lateral crescent sign, which is easily and quickly identified on axial CT images, is useful in the diagnosis of direct inguinal hernias. Indirect Inguinal Hernia By definition, indirect inguinal hernias arise lateral and superior to the course of the inferior epigastric vessels, lateral to the Hesselbach triangle, and protrude through the deep or internal inguinal ring to enter the inguinal canal. In the male, they enter the canal anterior to the spermatic cord and may extend through the external inguinal ring into the scrotum. In the female, indirect hernias follow the round ligament into the labia majora (Fig 7). Juxtafunicular indirect hernias remain within the inguinal canal but emerge outside the spermatic cord into the surrounding soft tissues (14). Indirect inguinal hernias are five times more common than direct hernias. In boys, indirect inguinal hernias are the result of a congenital defect of a patent processus vaginalis. In adults, they are acquired due to weakness and dilatation of the internal inguinal ring (7). On axial CT images, the neck of the hernia arises lateral and superior to the course of the

7 RG Volume 31 Number 2 Burkhardt et al E7 Figure 8. Indirect inguinal hernia containing colon. CT image (a) and color-coded image (b) show an indirect hernia emerging lateral to the course of the inferior epigastric vessels (small blue and red dots), which arise from the external iliac vein and artery (large blue and red dots) (see also Movie 4). Figure 9. Indirect inguinal hernia. CT image (a) and color-coded image (b) show a left indirect hernia. The hernia sac originates lateral to the course of the inferior epigastric artery (red dots), which arises from the external iliac artery (J). Edematous fluid and fat stranding can be seen within the hernia sac. The right side demonstrates a relatively normal-appearing deep inguinal ring arising lateral to the course of the inferior epigastric artery (see also Movie 5). inferior epigastric vessels. Thus, the hernia neck will be superolateral to the course of the inferior epigastric vessels. As the hernia sac protrudes further caudally, it is directed lateral to medial within the inguinal canal. In Figures 8 and 9, note the origin of the hernia sac lateral to the course of the inferior epigastric vessels (see also Movies 4 and 5). The inguinal canal contents are not compressed into a lateral crescent and may be difficult to identify, as the canal contents will appear to make up part of the hernia and may appear to be contained within the hernia sac. Femoral Hernia Femoral hernias exit below the inguinal ligament and protrude through the femoral ring into the femoral canal, medial to the common femoral vein and lateral to the lacunar ligament. These hernias often compress the femoral vein. In one recent retrospective review, a localized hernia sac with femoral venous compression was seen much more often in femoral hernias than in inguinal hernias, especially if the hernia was incarcerated (15).

8 E8 March-April 2011 radiographics.rsna.org Figure 10. Femoral hernia. CT images (left) (top image obtained at a higher level than bottom image) and diagrams (right) show a femoral hernia, the neck of which is just medial to the common femoral vein. The vein demonstrates a subtle concavity anteriorly, which is secondary to compression by the hernia neck and sac. The fat-containing hernia has numerous dilated distal small collateral veins, which are secondary to the femoral vein compression. Note the inguinal canal, which contains edema, just medial to the femoral hernia neck. Figure 11. Femoral hernia with edema. CT image (a) and color-coded image (b) show a femoral hernia sac (magenta) that contains edema (green). The hernia sac protrudes into the fat of the femoral canal (yellow) and slightly flattens the medial aspect of the common femoral vein (blue) (see also Movie 6). Red dot = common femoral artery. Femoral hernias are relatively uncommon, with a prevalence less than one-tenth that of inguinal hernias. Femoral hernias have a female predominance of 4:1, which is thought to be secondary to dilatation of the femoral ring connective tissues due to the hormonal and physical changes of pregnancy (16). For unclear reasons, femoral hernias are twice as common on the right than on the left (16). On axial CT images, the neck of the femoral hernia sac can be seen as a narrow protrusion through the femoral ring just medial to the common femoral vein (Fig 10), which often appears indented and compressed by the hernia sac. Femoral venous compression may then cause engorgement of small distal collateral veins around the hernia sac. Femoral hernias typically have a characteristic funnel-shaped neck. The inguinal canal, which is medial to the sac, may appear edematous, but careful inspection will reveal that the entire extent of the canal and its contents are preserved. Note that the neck of the femoral hernia sac emerges caudal to the origin of the inferior epigastric vessels, as the femoral ring is inferior to their origin. The femoral hernia sac may contain edema, with subtle compression of the femoral vein (Fig 11; see also Movie 6). A pantaloon hernia is any combination of two adjacent hernia sacs of the inguinal or femoral region (Fig 12; see also Movie 7).

9 RG Volume 31 Number 2 Burkhardt et al E9 Figure 12. Pantaloon hernia. CT image (a) and color-coded image (b) show a pantaloon hernia that consists of combined direct inguinal and femoral hernia sacs (green dots). The common femoral vein and artery (large blue and red dots) are just lateral to the femoral hernia sac. The inguinal canal contents (small blue and red dots) are compressed into a lateral fat-containing crescent (yellow) (see also Movie 7). Figure 13. Incarcerated femoral hernia. CT image (a) and color-coded image (b) show an incarcerated femoral hernia that causes small bowel obstruction. Note the flattened anteromedial aspect of the femoral vein (large blue area), a finding indicative of compression, and the resultant engorged distal collateral veins (small blue areas). The hernia neck emerges caudal to the course of the inferior epigastric vessels, and the hernia sac projects laterally into the femoral canal. Just lateral to the vein is the common femoral artery (red) (see also Movie 8). Complications of Inguinal Hernias Inguinal and femoral hernias could contain virtually any organ or tissue found in the lower abdomen. These may include but are not limited to fat, small or large bowel, a portion of the bowel wall (Richter hernia), omentum, incarcerated appendix (Amyand hernia), bladder, Meckel diverticulum (Littré hernia), and gonads; such cases have been well described in the recent literature (11,17). Femoral hernias are the most likely to strangulate, whereas direct inguinal hernias are the most benign. Other complications include intestinal obstruction, incarceration, volvulus, perforation, appendicitis or diverticulitis, and tumors that may be found incidentally in the hernia (18). On axial CT images, a strangulated or incarcerated femoral hernia demonstrates significantly engorged distal collateral veins, a flattened common femoral vein from compression by the hernia sac and neck, and signs of edema and inflammation within the hernia sac and bowel wall (Fig 13; see also Movie 8). The appendix is

10 E10 March-April 2011 radiographics.rsna.org Figure 14. Amyand hernia. CT image (a) and color-coded image (b) show the appendix (yellow) within an Amyand hernia. The indirect hernia originates superolateral to the course of the inferior epigastric artery (red) (see also Movie 9). sometimes found within an incarcerated hernia sac; this is called an Amyand hernia (Fig 14; see also Movie 9). CT Diagnosis of Inguinal Region Hernias A thorough understanding of the detailed anatomic relationships in the inguinal region on axial CT images is critical to the diagnosis and differentiation of the three main types of hernias in this region. The course of the inferior epigastric vessels as well as the common femoral vein are critical landmarks, as their relationship to the hernia neck will determine the type of hernia (Fig 15; see also Movie 10). Direct inguinal hernias exit medial and anterior to the course of the inferior epigastric vessels, then are directed inferior to the inferior epigastric vessels as the hernia sac protrudes. They represent a bulge in the anterior abdominal wall lateral to the rectus muscle. We have described the lateral crescent sign, which represents the laterally displaced and compressed inguinal canal, including its fat and contents. Indirect inguinal hernias exit superolateral to the course of the inferior epigastric vessels, then are directed lateral to medial following the inguinal canal as the hernia sac protrudes toward the scrotum or labia. Indirect inguinal hernias will appear to contain all the usual contents of the inguinal canal, which are not compressed or stretched. Femoral hernias exit inferior to the course of the inferior epigastric vessels, just medial to the common femoral vein; they compress the vein, often causing subtle concavity in its contour. Femoral hernias typically demonstrate a narrow hernia neck and engorged distal collateral veins secondary to femoral venous compression. Evaluation of hernias of the inguinal region with axial CT does have some limitations. For example, the inguinal ligament is often better defined on coronal images. However, the suspicion of an inguinal or femoral hernia must arise from inspection of axial images, as they are and probably will remain the first-pass method of diagnostic interpretation. The differentiation of direct versus indirect inguinal hernias is challenging in any plane. Femoral hernia sacs may well be easily identified within the femoral canal on coronal images, but identifying the neck of the hernia likely also requires confirmation on axial images. There are inherent limitations to CT in detection and grading the severity of these hernias. Image acquisition with the patient supine will lead to reduction of many small reducible hernias, although these may be less clinically relevant. In one study of groin hernias, more than one-half of the inguinal hernias became reduced when supine CT was performed (15). However, prone CT has not proved helpful in improving the diagnosis of inguinal hernias (19). Some authors have stressed the importance of performing the Valsalva maneuver to maximize diagnostic yield (6,20), although the true added

11 RG Volume 31 Number 2 Burkhardt et al E11 Figure 15. March of the inguinal region hernias. Diagrams trace the inferior epigastric vessels back to their origin, from superior to inferior and left to right. Large blue and red dots = common femoral vein and artery. (a) Indirect inguinal hernia originates lateral to the course of the inferior epigastric vessels (small blue and red dots). (b) Direct inguinal hernia demonstrates a lateral fat crescent of the compressed inguinal canal (black crescent) and originates medial to the inferior epigastric vessels (small blue and red dots). (c) Femoral hernia (green) protrudes inferior to the origin of the inferior epigastric vessels and medial to the common femoral vein (blue), which is compressed (see also Movie 10). value of the maneuver has not been tested in a direct comparison study, to our knowledge. In patients suspected to have hernia, Emby and Aoun (20) advocate performing CT with the patient in the lateral decubitus position combined with performance of the Valsalva maneuver during the examination; however, only two anecdotal cases were presented. An expansion of that case study with a larger series of patients and with direct comparison of imaging with and without the Valsalva maneuver, along with validation with surgical findings, might settle the question. Ideally, patients without hernia would be included as well, to evaluate the dynamic appearance of the inguinofemoral region under increased intraabdominal pressure and to determine whether false-positive findings of hernia could increase with such stress maneuvers. Multiple attempts have been made in the literature to define criteria to help differentiate these three types of groin hernias. Using the pubic tubercle, which is the distal insertion site of the inguinal ligament, as a surrogate marker for distinguishing femoral hernias, Wechsler et al (13) proposed that femoral hernias can be identified below and lateral to the pubic tubercle as the sac emerges from the femoral canal, whereas inguinal hernias will lie above and medial to the pubic tubercle. Delabrousse et al (21,22) elaborated on this criterion and proposed that direct inguinal hernias will lie entirely anterolateral to the pubic tubercle, whereas indirect inguinal hernias will traverse the orthogonal line through the pubic tubercle and extend partially anteromedial to the tubercle, owing to their location in the inguinal canal. In a study of 42 patients, Delabrousse et al (21) used the pubic tubercle as a criterion in combination with traditional criteria; they were able to correctly classify each hernia with surgical concordance. In a similar recent study, Cherian and Parnell (23) used this criterion and traditional criteria in all three imaging planes for the diagnosis of groin hernias. They were able to classify hernias accurately in nine of 11 patients; six of seven inguinal hernias and three of four femoral hernias were correctly classified. Although use of the pubic tubercle may be promising in differentiation between groin hernias, one can imagine that a larger hernia sac will likely not be confined to only one quadrant in relation to the pubic tubercle. Therefore, differentiation of groin hernias, especially larger hernias, may be difficult with this criterion. The surgical approach differs significantly for inguinal versus femoral hernias. Inguinal hernias typically require an oblique incision along the inguinal ligament, whereas femoral hernias require a vertical incision. Thus, differentiation between these types of hernias is critical to preoperative planning. With the advent of laparoscopic inguinal hernia repair, it is arguable whether differentiation between direct and indirect inguinal hernias is necessary; however, since direct hernias are less likely to strangulate, correct identification of direct inguinal hernias will allow them to be managed more conservatively. Current surgical

12 E12 March-April 2011 guidance still dictates that indirect inguinal and femoral hernias routinely warrant surgery, as they are at higher risk for complications such as strangulation and obstruction (23). Thus, the ability to differentiate direct inguinal hernias from the higher-risk hernias may indeed prove beneficial to patients and helpful to practitioners in determining management of groin hernias. Conclusions In this article, we propose the lateral crescent sign as an easily detectable sign of an early direct inguinal hernia. This sign may be less useful in cases of extremely large hernias, which may compress the inguinal canal to such a thin sliver that it may not be readily detectable at CT. Spermatic cord lipomas should not be confused with fatcontaining hernias or the lateral crescent sign, as lipomas are typically located lateral or inferior to the spermatic cord and cause no compression of its contents, whereas inguinal hernias protrude anteromedial to the cord (17). Although the lateral crescent sign has yet to be tested with surgical confirmation in a patient study, we believe that it is reasonable in the radiologic and anatomic sense and represents the logical deduction and observation resulting from a large accumulated experience in evaluating hernias on axial CT images. The observation of this sign lays the groundwork for future investigations and hopefully an adequately powered patient study to confirm its utility in the diagnostic differentiation of direct inguinal hernias. Indeed, the lateral crescent sign may become a useful adjunct in diagnosis of direct inguinal hernias with axial CT, so that these hernias can be differentiated from those with a higher risk of complications. Acknowledgments. Many thanks to Vinald Francis for his companion illustrations of the relevant anatomy. References 1. Greenfield LJ. Review for surgery: scientific principles and practice. Philadelphia, Pa: Lippincott Williams & Wilkins, Rubenstein RS, Rand Corporation, US Department of Health and Human Services. Surgical conditions. Santa Monica, Calif: Rand, Bailey H, Love RJM, Russell RCG, Williams NS, Bulstrode CJK. Bailey and Love s short practice of surgery. London, England: Arnold, Naude GP, Ocon S, Bongard F. Femoral hernia: the dire consequences of a missed diagnosis. Am J Emerg Med 1997;15(7): radiographics.rsna.org 5. Ralphs DN, Brain AJ, Grundy DJ, Hobsley M. How accurately can direct and indirect inguinal hernias be distinguished? BMJ 1980;280(6220): Højer AM, Rygaard H, Jess P. CT in the diagnosis of abdominal wall hernias: a preliminary study. Eur Radiol 1997;7(9): Lee GH, Cohen AJ. CT imaging of abdominal hernias. AJR Am J Roentgenol 1993;161(6): Miller PA, Mezwa DG, Feczko PJ, Jafri ZH, Madrazo BL. Imaging of abdominal hernias. RadioGraphics 1995;15(2): Gray H, Standring S, Ellis H, Berkovitz BKB. Gray s anatomy: the anatomical basis of clinical practice. Edinburgh, Scotland: Elsevier Churchill Livingstone, Cherian PT, Parnell AP. Radiologic anatomy of the inguinofemoral region: insights from MDCT. AJR Am J Roentgenol 2007;189(4):W177 W Shadbolt CL, Heinze SB, Dietrich RB. Imaging of groin masses: inguinal anatomy and pathologic conditions revisited. RadioGraphics 2001;21(spec issue):s261 S Kirkpatrick A, Reed CM, Bui-Mansfield LT, Russell MJ, Whitford W. Radiologic-pathologic conference of Brooke Army Medical Center: endometriosis of the canal of Nuck. AJR Am J Roentgenol 2006;186 (1): Wechsler RJ, Kurtz AB, Needleman L, et al. Crosssectional imaging of abdominal wall hernias. AJR Am J Roentgenol 1989;153(3): Ekberg O, Fork FT, Fritzdorf J. Herniography in atypical inguinal hernia. Br J Radiol 1984;57(684): Suzuki S, Furui S, Okinaga K, et al. Differentiation of femoral versus inguinal hernia: CT findings. AJR Am J Roentgenol 2007;189(2):W78 W Zarvan NP, Lee FT Jr, Yandow DR, Unger JS. Abdominal hernias: CT findings. AJR Am J Roentgenol 1995;164(6): Bhosale PR, Patnana M, Viswanathan C, Szklaruk J. The inguinal canal: anatomy and imaging features of common and uncommon masses. RadioGraphics 2008;28(3): Aguirre DA, Santosa AC, Casola G, Sirlin CB. Abdominal wall hernias: imaging features, complications, and diagnostic pitfalls at multi-detector row CT. RadioGraphics 2005;25(6): Markos V, Brown EF. CT herniography in the diagnosis of occult groin hernias. Clin Radiol 2005;60 (2): Emby DJ, Aoun G. CT technique for suspected anterior abdominal wall hernia. AJR Am J Roentgenol 2003;181(2): Delabrousse E, Denue PO, Aubry S, Sarlieve P, Mantion GA, Kastler BA. The pubic tubercle: a CT landmark in groin hernia. Abdom Imaging 2007 Mar 27 [Epub ahead of print] 22. Delabrousse E, Michalakis D, Sarliève P, Paratte B, Rodière E, Kastler B. Value of the pubic tubercle as a CT reference point in groin hernias. J Radiol 2005;86(6 pt 1): Cherian PT, Parnell AP. The diagnosis and classification of inguinal and femoral hernia on multisection spiral CT. Clin Radiol 2008;63(2):

13 Teaching Points March-April Issue 2011 Diagnosis of Inguinal Region Hernias with Axial CT: The Lateral Crescent Sign and Other Key Findings Joan Hu Burkhardt, MD Yevgeniy Arshanskiy, MD J. Lawrence Munson, MD Francis J. Scholz, MD RadioGraphics 2011; 31(2):E1 E12 Published online /rg Content Codes: Page E2 The risk of strangulation is lowest for direct inguinal hernias, which can often be monitored and managed conservatively. Indirect inguinal hernias are at moderate risk of strangulation, whereas approximately 40% of femoral hernias manifest with strangulation (3). Page E2 In the female, the inguinal canal transmits the round ligament of the uterus and the ilioinguinal nerve to the labia majora. In the male, the inguinal canal transmits the spermatic cord to the scrotum. The spermatic cord is covered by the fascia from all three abdominal wall muscle aponeuroses and comprises the ductus (vas) de-ferens, testicular artery and veins (pampiniform plexus), and genital branch of the genitofemoral nerve. Page E10 Direct inguinal hernias exit medial and anterior to the course of the inferior epigastric vessels, then are directed inferior to the inferior epigastric vessels as the hernia sac protrudes. They represent a bulge in the anterior abdominal wall lateral to the rectus muscle. We have described the lateral crescent sign, which represents the laterally displaced and compressed inguinal canal, including its fat and contents. Page E10 Indirect inguinal hernias exit superolateral to the course of the inferior epigastric vessels, then are directed lateral to medial following the inguinal canal as the hernia sac protrudes toward the scrotum or labia. Indirect inguinal hernias will appear to contain all the usual contents of the inguinal canal, which are not compressed or stretched. Page E10 Femoral hernias exit inferior to the course of the inferior epigastric vessels, just medial to the common femoral vein; they compress the vein, often causing subtle concavity in its contour. Femoral hernias typically demonstrate a narrow hernia neck and engorged distal collateral veins secondary to femoral venous compression.