(61) Labial Endometriosis in a Pre-Menarchal Patient

Background: The prevalence of endometriosis in adolescent populations is difficult to ascertain, with some studies estimating that almost 40% of post-menarchal adolescents with pelvic pain have endometriosis. Reports of endometriosis in pre-menarchal patients are even more limited and highlight a still-evolving understanding of the pathogenesis of the disease. No prior documented case has described labial endometriosis in a pre-menarchal female.

Case: An 11 year old pre-menarchal patient presented to the emergency room (ER) with a tender vulvar mass. The mass had been present for several weeks and was increasingly painful. She was afebrile, had no associated symptoms, and denied recent trauma to the area. On exam, a 6 x 6 cm mass was noted on the right labia minora with mild tenderness to palpation but no surrounding erythema or swelling. The patient was noted to have Tanner Stage 2 breast and pubic hair development. The presumed diagnosis was a hematoma and she was discharged by the ER team with planned follow up with Pediatric and Adolescent Gynecology for consultation.

The patient presented again 2.5 weeks later with increased pain and size of the labial mass. She continued to be afebrile and without associated symptoms. Labial ultrasound demonstrated a 5 x 4.5 x 3 cm multi-septated structure with concentric solid and vascular components. Pelvic MRI also showed a 4.9 x 4.5 x 5 cm multiseptated cystic structure. Presumed diagnosis was a super-infected hair follicle and plan was made for incision and drainage in the operating room. Grossly, the mass was noted to be well-encapsulated, consistent with an encapsulated hematoma with a cystic wall structure and septations. Due to proximity to the clitoral hood, a small amount of capsule was left in situ and a Penrose drain was left in place. The mass was sent to pathology which reported hemosiderin-laden macrophages and CD10 positive stromal cells suggestive of endometriosis.

Comments: This report presents the first case of labial endometriosis in a pre-menarchal patient. Vulvar/perineal endometriosis is generally rare, with other cases in post-menarchal adolescents typically associated with recent vulvar trauma not seen in this case. In general, endometriosis is considered to be a progressive disease associated with menses, which highlights the atypical nature of this case. Though multiple theories exist as to the pathogenesis of the disease, the theory of retrograde menstruation is widely accepted. This case, however, suggests that alternate theories such as coelomic metaplasia or mullerian embryonic rests may also contribute.