Teaching Case

A 40-year-old female presented with a firm, painful enlarging mass overlying the right superior pubic ramus.

A 40-year-old nulliparous female presented with a six-month history of a firm, enlarging painful mass anterior to the right superior pubic ramus. Her surgical history included a total abdominal hysterectomy seven years previously for endometriosis and fibroids.   A CT Pelvis (Fig. 1) was initially obtained which demonstrated non-specific, mass-like enlargement of the inferior aspect of the right rectus muscle, adjacent to the superior pubic ramus. No underlying erosive changes or periostitis was identified. Mild associated subcutaneous fat stranding was present. The differential included an avulsion injury; however, as there was no history of trauma, an underlying neoplastic process was a consideration and an MRI was performed.   The MRI demonstrated a 2.3 by 3.3 centimetre mass arising from the right adductor tubercle. On the gradient sequences (Fig. 2), susceptibility artifact was seen, consistent with hemorrhage. This was substantiated by the presence of T1 hypertintense foci through the lesion. Enhancement was noted within the surrounding soft tissues (Fig. 3), including the right rectus and pectineus muscles. Underlying T2 prolongation was seen within the right adductor tubercle.   To rule out the presence of a low-grade sarcoma, an ultrasound guided percutaneous biopsy was performed. The histology demonstrated characteristic endometrial glands and associated stromal cells, consistent with endometriosis. The patient subsequently underwent wide surgical excision for definitive treatment.

Endometriosis, first described by Rokitansky in 1860, is a common gynaecological condition in menstruating women and while the overall prevalence is not known, it is estimated to be 5-10% (1). Endometriosis is defined as growth of functioning endometrial glands and stroma outside of the uterine cavity (2). An endometrioma is the formation of a discrete mass of endometriosis. The development of endometriosis can either be intra- or extra-pelvic. Intra-pelvic locations are the most common and include the ovaries, uterosacral ligaments, rectovaginal septum, peritoneum, urinary bladder and pouch of Douglas (3). Extra-pelvic sites are more unusual with case reports describing implants in numerous locations, including the lungs, appendix, brain, skin, liver, the inguinal canal and anterior abdominal wall. Involvement of the rectus muscle is rare (3). While there are scattered reports of spontaneous occurrence of endometriosis in the anterior abdominal wall, endometriosis associated with a chronic surgical scar is a well-documented entity. The highest frequency is with Caesarean section scars, estimated at 0.2% (4). Other procedures that have been implicated include laparotomies, laparoscopies, amniocentesis, abdominoplasty and placement of ventriculo-peritoneal shunts. Several pathophysiology models have been proposed for endometriosis, discussed by Woodward et al (1): (1) Metastatic theory due to spread of endometrial cells via retrograde menstrual implantation, hematologic or lymphatic spread or intraoperative implantation. (2) Metaplastic theory defined by differentiation of serosal surfaces or müllerian remnant tissue. (3) Induction theory in which ectopic endometrial tissue releases substances that promote differentiation of multipotential mesenchymal cells. While the metastatic theory is widely accepted, a multifactorial etiology utilizing all of the aforementioned concepts is likely the most probable explanation (1). A painful, palpable mass in the anterior abdominal wall is a non specific finding for which there is a broad differential including: abscess, incisional or ventral hernia, hematoma, granuloma, sebaceous cyst as well as benign (e.g. lipoma) or malignant (e.g. sarcoma or lymphoma) neoplastic disease. A prospective diagnosis of endometrioma requires a high index of suspicion. The imaging characteristics of abdominal wall endometriosis on ultrasound, CT and MR imaging are non-specific. Sonographic examination can reveal a well-defined, vascular hypoechoic mass; however, cystic and complex cystic/solid lesions have been reported. A hyperechoic rim may be seen, representing inflammatory and reactive changes to the ectopic endometrial tissue (1). CT imaging usually demonstrates a poorly marginated, possibly enhancing solid mass, which is usually isodense to the adjacent musculature. Associated fat stranding may be seen (5,6). On MRI, T1 and T2 sequences will demonstrate a heterogenous mass with hyperintense foci while gradient sequences will show susceptibility artifact. These findings are due to the presence of blood products (5). Enhancement will be seen on post gadolinium T1 fat-saturated sequences. MRI and CT, although non-specific, are useful for delineating extent of disease while excluding potential alternate diagnoses. While pharmacological therapy is possible, definitive diagnosis and therapeutic management is obtained with wide local excision (6).