To present a rare clinical case of a prolapsed Müllerian cyst in a postpartum woman, initially misdiagnosed as anterior vaginal wall compartment prolapse versus Gartner's duct cyst, and to underscore the diagnostic challenges and surgical considerations in distinguishing vaginal cysts within urogynecology practice.

A 30-year-old woman (P1) presented to Urogynecology clinic with a two-months history of a progressively enlarging mass protruding from the introitus, first noticed during pregnancy. The patient reported postpartum dyspareunia and local pressure symptoms without urinary or fecal incontinence.

On physical examination, a 6 × 4 cm cystic, non-tender, reducible mass was identified on the anterior vaginal wall, clinically mimicking a cystocele. Pelvic magnetic resonance imaging (MRI) revealed a well-circumscribed, thin-walled 3.6 cm cyst arising from the upper anterior vaginal wall, provisionally diagnosed as a Gartner’s duct cyst, imaging underestimated the cyst size compared to clinical findings.

Given the symptomatic presentation and inconclusive imaging, surgical excision was indicated. 
Under general anesthesia, diagnostic cystoscopy with methylene blue dye was injected into the cyst to excluded communication with the urinary tract, urethral diverticulum, and vesicovaginal fistula. A vertical incision was made over the anterior vaginal wall, allowing access to the encapsulated cyst. Complete enucleation of the cyst was performed, followed by symmetric trimming of redundant vaginal mucosa. Hemostasis was achieved, and the defect was closed in layers using absorbable sutures.

Intraoperative findings confirmed a well-encapsulated cyst, with no urethral or bladder involvement. 
The patient had an uneventful postoperative recovery and was discharged on the same day. 
Histopathology confirmed a benign Müllerian cyst lined by columnar epithelium with no evidence of Atypia or malignancy. 
At four weeks follow-up, the patient reported complete resolution of her symptoms with satisfactory wound healing and no residual tissue.

Müllerian cysts, though uncommon, account for 30–40% of vaginal cysts, with an overall estimated prevalence of 0.5% among women. They arise from remnants of the paramesonephric duct due to incomplete embryological regression. Typically asymptomatic and benign, these midline vaginal wall lesions are often discovered incidentally during routine examinations. However, in rare cases, they may prolapse and clinically mimic anterior vaginal wall prolapse—particularly in postpartum patients.

This case highlights the diagnostic complexity arising from the overlap between symptomatic Müllerian cysts and anterior compartment prolapse. This challenge is compounded by physiological changes in the postpartum period, including hormonal shifts, increased intraabdominal pressure, and pelvic floor remodeling.These factors can amplify the clinical visibility of Müllerian cysts, necessitating meticulous evaluation.

While preoperative imaging is a valuable diagnostic tool, it may underestimate lesion size, extent, or nature, leading to clinical ambiguity. In this case, a high index of suspicion prompted further evaluation. Diagnostic cystoscopy, combined with intraoperative dye instillation, was instrumental in excluding urinary tract communication. 
Histopathological analysis ultimately confirmed the diagnosis and remains the gold standard for such cases.

These findings underscore the importance of correlating physical examination with targeted imaging and timely surgical assessment. A comprehensive diagnostic approach is essential in managing rare and atypical presentations like prolapsed Müllerian cysts, ensuring both accurate diagnosis and optimal patient outcomes. 
Experienced urogynecologists should maintain Müllerian cysts in the differential diagnosis of anterior vaginal wall masses, particularly when cystocele or urethral diverticulum is suspected. Accurate diagnosis and complete excision are essential to ensure symptomatic relief, exclude urinary tract involvement, and rule out malignancy. This case emphasizes the critical role of surgical judgment and histopathology in managing complex pelvic floor cases.