Isolated Round Ligament Dermoid Cyst Mimicking an Inguinal Hernia through a False-positive Cough Impulse: A Case Report

Abstract

Background: Persistent canal of Nuck or round ligament lesions are rare causes of female inguinal swellings that can clinically mimic inguinal hernias, making preoperative diagnosis challenging. Aim: To report an isolated round ligament dermoid cyst in an elderly female presenting clinically as an inguinal hernia, and to highlight the diagnostic challenges associated with atypical cystic groin lesions. Presentation of Case: A 76-year-old woman presented with a progressively enlarging left inguinal swelling of one-year duration. Examination revealed a soft, mobile, non-tender mass extending toward the labia majora. Although non-reducible, the swelling demonstrated a cough impulse, initially favoring the diagnosis of an inguinal hernia. Contrast-enhanced computed tomography showed a well-circumscribed cystic lesion along the course of the round ligament, radiologically suggestive of a Canal of Nuck cyst. Due to persistent diagnostic uncertainty, surgical exploration was performed. Intraoperatively, a thick-walled cyst containing sebaceous material and keratinous debris was identified without evidence of a true hernial sac or peritoneal communication. Complete excision of the lesion was carried out, followed by posterior wall reinforcement using modified Bassini repair with Prolene darning. Histopathological examination confirmed a benign dermoid cyst. The postoperative recovery was uneventful. Discussion: Dermoid cysts involving the inguinal canal are exceedingly uncommon, particularly as isolated extra-gonadal lesions of the round ligament in elderly women. In this case, the cough impulse was likely secondary to transmitted intra-abdominal pressure through a weakened inguinal floor, creating a false-positive clinical impression of hernia. In addition, preoperative imaging favored an alternative cystic pathology, emphasizing the difficulty in accurately characterizing rare inguinal lesions preoperatively. Conclusion: Isolated dermoid cysts should be considered in the differential diagnosis of atypical inguinal swellings, particularly when clinical and radiological findings are incongruent. This case highlights the importance of careful intraoperative assessment and histopathological confirmation in establishing the definitive diagnosis.