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by the American Institute of Ultrasound in Medicine J Ultrasound Med 29:105-110 • 0278-4297
Sonographic Findings of Inguinal EndometriosisDepartments of Radiology (D.M.Y., H.C.K., J.K.R.) and Pathology (G.Y.K.), Kyung Hee University East-West Neo Medical Center, Seoul, Korea; and Department of Radiology, Kyung Hee University Medical Center, Seoul, Korea (J.W.L.). Address correspondence to Dal Mo Yang, MD, Department of Radiology, Kyung Hee University East-West Neo Medical Center, 149 Sangil-Dong, Gangdong-Gu, Seoul 134-090, Korea. E-mail: dmy2988{at}yahoo.co.kr
Objective. The purpose of this series was to describe the sonographic findings of inguinal endometriosis. Methods. This was a retrospective analysis of 3 cases of inguinal endometriosis. The following gray scale and color Doppler sonographic features were analyzed: size, shape, echogenicity, and blood flow within inguinal endometriosis. Results. The size of inguinal endometriosis ranged from 3.1 to 4.2 cm (mean, 3.7 cm). All 3 cases were cystic lesions. Two of 3 cases were lesions with internal septa. On color Doppler sonography, 1 of the 3 cases showed a few flow signals within the lesion, whereas in 2 of the 3 lesions, no blood flow could be identified within the lesions. Conclusions. Although the sonographic features of inguinal endometriosis may be variable, endometriosis should be included in the differential diagnosis when unilocular and multilocular cystic masses are seen on sonography.
Key Words: color Doppler sonography • endometriosis • inguinal endometriosis • sonography Abbreviations: MRI, magnetic resonance imaging
Endometriosis is a common gynecologic disorder and is characterized by the proliferation of endometrial tissue at ectopic sites. The sites most frequently involved are within the pelvis, including the ovaries, uterine ligaments, fallopian tubes, pouch of Douglas, cervix, and vagina.1 However, endometriosis may affect the gastrointestinal tract, urinary tract, chest, skin, umbilicus, abdominal wall, and inguinal canal.1 Although several cases of inguinal endometriosis have been reported, imaging findings have rarely been described.2–4 In addition, although sonography is the first-line diagnostic examination for the evaluation of inguinal lesions, sonographic descriptions of inguinal endometriosis are scant. To the best of our knowledge, the sonographic findings of inguinal endometriosis have been presented for fewer than 10 cases.5–10 This series describes the sonographic findings of 3 new cases of inguinal endometriosis.
We retrospectively reviewed the case files of 3 patients with inguinal endometriosis. Patient ages ranged from 29 to 49 years (mean, 40 years). The diagnosis of inguinal endometriosis was based on surgical resection. All sonographic examinations were performed with a 5- to 12-MHz transducer and an iU22 unit (Philips Healthcare, Bothell, WA). Color Doppler sonography was performed with optimized color Doppler parameters. The power level, threshold, persistence, and wall filter were individually adjusted to maximize the detection of blood flow through the field of view. Sonographic findings were determined by retrospective analysis of images. Two radiologists interpreted gray scale and color Doppler sonographic images. The radiologists determined the size, shape, echogenicity, and degree of blood flow of inguinal endometriosis.
All patients had painful swelling of the right inguinal region. All were medically well before admission and had not had abdominal surgery before. None of the women had cyclic pain. The time between the onset of symptoms and first presentation ranged from 1 day to 2 months (mean, 21 days).
The sonographic findings in patients with inguinal endometriosis are summarized in Table 1
All patients underwent surgical excision. Gross specimens showed unilocular (n = 1) and mutilocular (n = 2) cysts containing old hemorrhage. No solid portion was found within the masses. An inguinal hernia was not seen in any patient. A microscopic examination revealed endometrial glands surrounded by endometrial stromal cells in a fibrous wall. In the case of the unilocular cyst, the lining of the epithelium was mesothelium (Figure 3C  ).
Table 2
Endometriosis is defined as the presence of endometrial glands and stroma outside the uterine cavity. Endometriosis in the inguinal region was first reported by Cullen11 in 1896, and the incidence of endometriosis was found to be 0.6% in women.12
Direct extension of endometrial tissue along the round ligament is a possible pathogenesis of inguinal endometriosis.2 The canal of Nuck, which is a small evagination of the parietal peritoneum that accompanies the round ligament through the inguinal ring into the inguinal canal, provides the most likely pathway for endometrial tissue to implant in the superficial inguinal soft tissue (Figure 4
The usual symptoms of endometriosis are progressive dysmenorrhea, menstrual irregularities, dyspareunia, infertility, and pelvic pain.1 Common symptoms associated with inguinal endometriosis are inguinal pain and the presence of an inguinal mass, which sometimes becomes enlarged during the menstrual period.2,4 Reported imaging appearances of inguinal endometriosis are rare. On computed tomography, inguinal endometriosis shows the presence of a soft tissue mass with the same density as muscle.2,3 Characteristic magnetic resonance imaging (MRI) findings of pelvic endometriosis are high signal intensity on fat-suppressed T1-weighted images and hypointensity on T2-weighted images.2,4 T2 shortening in endometriosis is thought to be the result of recurrent hemorrhage. However, in half of the reported cases of inguinal endometriosis, MRI features were not specific and included intermediate or high signal intensity on T2-weighted images.3,5 The sonographic appearance of inguinal endometriosis might be expected to be cystic because of intralesional bleeding associated with menstruation. However, the sonographic features of inguinal endometriosis are variable.5–10 The presence of solid masses,5–7 cystic masses,8,10 and combined cystic and solid masses9 has been described. In previous studies, for 3 solid masses, 2 masses were hypoechoic,5,6 and 1 mass was hyperechoic.7 All of the cystic masses had internal septa.8,10 In our series, all 3 lesions were seen as cystic masses without internal echoes in the right inguinal area on sonography, and 2 of the 3 masses had internal septa. These sonographic findings are different from findings for abdominal wall endometriosis that arises near cesarean delivery scars. Most abdominal wall endometriosis shows a solid appearance with an irregular margin on sonography, and internal vascularity has been seen within these masses on color Doppler sonography.15,16 We believe that this difference is due to the different environmental situation between the two types of lesions. Inguinal endometriosis usually develops in the canal of Nuck, which is a cavity filled with fluid. If bleeding occurs within the implanted endometrial tissues, the canal of Nuck may be obliterated, and the structure may be vulnerable to formation of a cystic mass. In 1 of our cases, the cyst wall was lined by mesothelium. This result may suggest cyst formation by obliteration of the canal of Nuck for implanted endometrial tissues. In contrast, cyst formation is difficult for abdominal wall endometriosis because this lesion usually occurs in cesarean delivery scars, which is a limited space rather than the canal of Nuck. Francica et al16 stated that sonography is the sole diagnostic imaging technique for the evaluation of abdominal wall endometriosis. Both computed tomographic and MRI features are nonspecific and do not seem to add any value to a sonographic examination. Sonographically guided fine-needle aspiration is helpful for rapid and accurate diagnosis of inguinal endometriosis and enables a malignancy to be excluded.15 When inguinal endometriosis presents as a solid mass on sonography, the differential diagnosis includes neoplasms such as sarcoma, lymphoma, metastasis, an abscess, and hematoma.1,5 When inguinal endometriosis presents as a cystic mass on sonography, it should be differentiated from a hydrocele of the canal of Nuck and an inguinal hernia. Our study was limited by its retrospective design and a small study population. Therefore, further studies with larger sample sizes are necessary to examine the sonographic findings of inguinal endometriosis. Despite these limitations, familiarity with the sonographic findings of inguinal endometriosis is important for the diagnosis and treatment of patients with painful inguinal swelling. In conclusion, although the sonographic features of inguinal endometriosis may be variable, a cystic appearance is not rare. Endometriosis should be included in the differential diagnosis when a unilocular or multilocular cystic mass in patients with painful inguinal swelling is encountered on sonography.
Received August 20, 2009, from the Departments of Radiology (D.M.Y., H.C.K., J.K.R.) and Pathology (G.Y.K.), Kyung Hee University East-West Neo Medical Center, Seoul, Korea; and Department of Radiology, Kyung Hee University Medical Center, Seoul, Korea (J.W.L.). Revision requested September 8, 2009. Revised manuscript accepted for publication September 10, 2009.
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Abstract
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