Inguinal endometriosis: a differential diagnosis of right groin swelling in women of reproductive age

Abstract

We reported a case of right inguinal endometriosis in a 41-year-old woman with unremarkable surgical and gynaecological history. She presented with right groin swelling for a month since her last menstrual period. Clinically the swelling was first diagnosed as inguinal hernia and later histologically proven to be endometriosis.

Background

Endometriosis has been first described by Allen in 1896 but the pathogenesis remains controversial. Several theories have been described. Metaplasia of coelomic mesothelial cells and the seeding via an open route are two popular theories of inguinal endometriosis.¹

Endometriosis is the growth of endometrial stroma and glands outside uterine cavity. Inguinal endometriosis is usually related to the extraperitoneal portion of round ligament but can also be found in hernia sacs, lymph node or the canal of Nuck. It is a rare presentation with prevalence of 0.3%–0.6%.² Inguinal endometriosis commonly presents at the right side in women of reproductive age.³ Cyclical pain of the mass was reported.³ Four out of nine patients presented with cyclical pain of the groin mass. Cough impulse can be positive if the mass is cystic.⁴ A case of inguinal endometriosis collected from the canal of Nuck has reported, which presented as a reducible right groin swelling. Less than 50% of cases of inguinal endometriosis have been diagnosed preoperatively.^5–7 It is a rare disease and a correct preoperative diagnosis might be challenging.

Case presentation

We report a case of inguinal endometriosis in a 41-year-old healthy woman and no surgical history. She presented with a sudden onset of right groin swelling for a month since her last menstrual period. The size of the mass was stable and it was not tender. She was otherwise asymptomatic. Gynaecological history was unremarkable. She had regular menstrual cycle of 28 days without dysmenorrhoea or menorrhagia. Obstetrics history was unremarkable with two spontaneous normal vaginal deliveries. Physical examination revealed a firm, smooth, immobile and irreducible mass with 3 cm diameter in the medial and superior aspect of the pubic tubercle. Cough impulse was equivocal.

Investigations

White blood cell count was normal and other blood results including liver function test, renal function test and amylase were unremarkable. Imaging has not been performed.

Differential diagnosis

Inguinal hernia and abscess were the main differential diagnoses.

Treatment

The provisional diagnosis was incarcerated inguinal hernia and operation was performed. Well-defined round fibrous wall with brownish thick material was noticed after skin incision. No hernia sac was revealed. Mass was next to the external opening of inguinal canal on top of the external oblique layer with no cephalic communication. The mass was treated as abscess perioperatiprogesterone vely and incision and drainage was performed. The fibrous wall of mass has been mostly excised.

The bacterial culture was negative and pathology report revealed endometriosis. Sections showed fibrous tissue focally infiltrated by a few small, isolated glands lined by a single layer of ciliated cuboidal epithelium, surrounded by fibroblastic storm, areas of haemorrhage, cholesterol clefts with aggregates of foamy histiocytes and focal granulation tissue (figure 1). Immunohistochemical staining showed that the granular epithelium and clusters of stromal cells were positive for estrogen receptor (ER) and progesterone receptor (PR) and negative for calretnin. The stromal cells expressed CD+10 (figure 2). Histology and immunohistochemical stains were consistent with endometriosis.

Figure 1.

H&E section shows small, isolated glands lined by a single layer of ciliated cuboidal epithelium surrounded by fibroblastic stroma and haemorrhage.

Figure 2.

The stromal cells are positive for CD10 on immunohistochemistry.

Outcome and follow-up

Postoperation was uneventful and this woman was referred to gynaecology for assessment.

Discussion

The preoperative diagnosis of inguinal endometriosis is challenging. Ultrasonography (USG) has been reported as imaging tool to differentiate among inguinal hernia, abscess and cystic mass though findings are usually non-specific.^8–10 Non-homogeneous hypoechoic content with ill-defined and blurred margin has been identified but the echoic pattern is largely affected by the haemorrhagic and fibrous components of the lesion.^{9 10} Intralesional vascularisation has also been reported.^{9 10} MRI is particularly useful in delineating the size and depth of the lesion for operative plan. However, the sensitivity of both USG and MRI in diagnosing an inguinal endometriosis is unknown. Inconclusive imaging is common, and diagnosis is usually supported by clinical manifestation.^{11 12}Fine needle aspiration cytology (FNAC) has been used. However, the findings can be inconclusive depending on the amount of sample and the proportion of fibrous tissue. FNAC is controversial with risk of implantation at the puncture sites.¹³ In view of limited value and sensitivity of diagnostic methods of inguinal endometriosis, clinical history and physical examination play a crucial role to reach the preoperative diagnosis.

Medical treatment including contraceptive pill/oral contraceptives and danazol has been reported but the overall successful rate is low.¹⁴ Surgical excision is inevitable and diagnostic. Surgical resection results in cure in more than 95% of cases.¹⁰ However, high recurrence rate of 9.1% has been reported with inadequate resection.^{9 10} No study of the resection margin has been published. Sometimes, mesh repair might be needed in case of large defect after complete resection and the preoperative planning is important. CT and MRI are important in preoperative evaluation of mass.^{9 10}

Malignancy transformation and subfertility are two important clinical implications. Malignancy change in endometriosis is very rare with the prevalence of about 1%. Endometrial adenocarcinoma is predominant.¹⁰ The use and effectiveness of chemotherapy is unknown.¹⁰ Subfertility and pelvic endometriosis has been linked to inguinal endometriosis with no strong evidence but referral to gynaecology was suggested.

Learning points.

• Inguinal endometriosis is a rare but important differential diagnosis in women of reproductive age who present with right groin lump with or without cyclical pain.

• Good preoperative planning of inguinal endometriosis is important in complete resection and reducing recurrence rate.

• Clinical history including gynaecological history is important in making diagnosis of inguinal endometriosis.