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Radiologic-Pathologic Conference of Brooke Army Medical Center |
1 Department of Radiology, Brooke Army Medical Center, 3851 Roger Brooke Dr.,
Fort Sam Houston, TX 78234.
2 Department of Radiology, Wake Forest University, Winston-Salem, NC
27157-1088.
3 Department of Pathology, Brooke Army Medical Center, Fort Sam Houston, TX
78234.
Received May 1, 2005; accepted after revision July 9, 2005.
The opinions and assertions contained herein are those of the authors and
should not be construed as official or as representing the opinions of the
Department of the Army or the Department of Defense.
Keywords: canal of Nuck • endometriosis • genitourinary tract imaging • MRI • PET
A41-year-old woman undergoing clinical and imaging evaluation for adrenocorticotropic hormone (ACTH)-independent Cushing's syndrome was found to have a lipid-poor left adrenal adenoma on abdominal CT. Further evaluation with PET/CT supported a diagnosis of lipid-poor adrenal adenoma but also revealed a spiculated 3-cm soft-tissue mass in the right inguinal region that exhibited intense (standardized uptake value, 4.0) 18F-FDG activity (Fig. 1A). MRI showed the lesion to have intermediate T1 (Fig. 1B) and markedly low T2 (Fig. 1C) signal characteristics, extending through the right inguinal canal into the right lateral mons pubis (Fig. 1C). Sonography-guided core biopsy was performed, and histologic findings were consistent with endometriosis (Fig. 1D).
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Although PET/CT is a valuable technique in evaluating for neoplasms, this case illustrates the importance of correlating increased 18F-FDG activity with cross-sectional imaging examinations. Infection, inflammation, physiologic muscular activity, brown fat, and metabolically active lesions (i.e., endometriosis) all can show markedly increased 18F-FDG uptake.
Endometriosis is a common gynecologic disease affecting 1-2% of all women. Classically, it is characterized by implantation of endometrial tissue outside the uterine cavity, resulting in bleeding, cyclical pain, and scarring. Typically, endometriosis occurs within the ovaries and peritoneum [1]. However, rarer cases have been reported in the vagina, rectum, lung (potentially leading to catamenial pneumothorax), subcutaneous tissues, and inguinal canal [2, 3]. The prevailing theory to explain the mechanism of endometriosis is retrograde menstruation (implantation theory), which proposes that viable endometrial tissue is refluxed through the fallopian tube during menstruation and deposited on the peritoneal surface or pelvic organs [1].
The gubernaculum testis, which is embryologically a cord of fibrous and muscular tissue, attaches inferiorly to the skin of the fetal groin that forms the labium majus and continues superiorly through the inguinal canal to become attached at its midpoint to the uterus. This fibrous band forms the round and ovarian ligaments. The processus vaginalis peritonei, through which the testes descend in males, is a tubular fold of peritoneum that, in the female inguinal canal, invaginates anterior to the round ligament and is called the canal of Nuck. In the adult, this canal is normally obliterated [4]. Occasionally the canal of Nuck will remain patent, creating a communication between the peritoneal cavity and the female inguinal canal [4]. In such cases, the canal of Nuck provides the most likely pathway for endometrial tissue to implant in the superficial inguinal soft tissues.
First described by Cullen in 1896, extraperitoneal inguinal endometriosis has an incidence of 0.4% [3]. The most consistent finding is an inguinal mass (96%), predominately found on the right side (87%). Pain is the next most common symptom (78%). However, only slightly more than half of the patients (57%) report symptoms related to menses. It has been proposed that extrapelvic endometriosis farther away from the uterus tends to lose its hormonal receptors and response, hence the lack of cyclical symptoms [5].
Surgical excision is the treatment of choice because it provides both diagnostic and therapeutic benefits.
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  D. M. Yang, H. C. Kim, W. Jin, C. W. Ryu, J. K. Ryu, D. H. Nam, S. I. Choi, and S. J. Lim Inguinal Endometriosis Presenting as a Multicystic Mass on Sonography J. Ultrasound Med., October 1, 2007; 26(10): 1449 - 1451. [Full Text] [PDF]
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