Rectovaginal endometriosis with nodular smooth muscle metaplasia diagnosed via transrectal ultrasound-guided fine-needle aspiration cytology: An underused minimally invasive diagnostic technique?

Rectovaginal endometriosis is a severe variant of deeply infiltrating endometriosis. Laparoscopic assessment with tissue sampling remains the gold standard for diagnosis of endometriosis. However, transvaginal (TVUS) and transrectal ultrasound (TRUS) have been shown to be especially helpful in the diagnosis of deep endometriosis. We present the case of a 49-year-old female with menorrhagia, dysmenorrhea, and constipation. Upon pelvic examination, an incidental mass was palpated. A computed tomography (CT) scan revealed an anterior rectal wall mass and colonoscopy was non-diagnostic. Further work-up with MRI showed a 3.9 cm mass centered within the upper rectovaginal septum. TRUS guided fine-needle aspiration (TRUS-FNA) revealed cohesive epithelial cell groups without significant cytologic atypia and a second population of bland spindle cells. Cell block slides showed glandular epithelium with associated stroma that exhibited endometrial morphology and immunophenotype. Nodular fragments of spindle cells with smooth muscle immunophenotype and fibrosis were also present. The overall morphologic findings were consistent with rectovaginal endometriosis with nodular smooth muscle metaplasia. Medical management with nonsteroidal aromatase inhibitor with radiologic follow-up was selected. Rectovaginal endometriosis represents a type of deep endometriosis usually associated with severe pelvic symptoms. Metaplastic smooth muscle cells are a frequent component of endometriosis in the rectovaginal pouch with nodular growth and may present diagnostic challenges. TRUS-FNA is a minimally invasive procedure that can provide an accurate diagnosis of endometriosis, even in this variant of deep infiltrating disease.